Aess guide

CISC
Guide for Specifying
Architecturally Exposed
Structural Steel
by Terri Meyer Boake

CISC
Structural Steel

Copyright © 2012
Canadian InsƟtute of Steel ConstrucƟon
All rights reserved.
This book or any part thereof must not be reproduced
without wriƩen permission from the publisher.
Second EdiƟon
First PrinƟng March 2012
ISBN 978-0-88811-160-9
Front cover images courtesy Terri Meyer Boake

CISC
Structural Steel
Terri Meyer Boake, B.E.S., B.Arch., M.Arch., LEED AP
School of Architecture
University of Waterloo
Waterloo, Ontario
Canadian Institute of Steel Construction
CISC AESS Guide – 3

CISC AESS Guide – Table of Contents - 4
Table of Contents
TABLE OF CONTENTS
Foreword 6
1 The Challenge 7
What Is AESS? 7
Purpose of the Guide 7
EvoluƟon of Architecturally Exposed Structural Steel 7
Development of the New CISC AESS Documents 8
Primary Factors of InŇuence That DeĮne AESS 8
Form, Fit and Finish 9
The Matrix 10
2 Categories 12
The Categories Approach 12
Standard Structural Steel 12
AESS 1 - Basic Elements 13
AESS 2 - Feature Elements (view distance > 6 metres) 14
AESS 3 - Feature Elements (view distance ч 6 metres) 15
AESS 4 - Showcase Elements 16
AESS C - Custom Elements 17
Mixed Categories 17
3 CharacterisƟcs 18
CharacterisƟcs of the Matrix 18
AESS 1 - CharacterisƟcs 1.1 to 1.5 18
AESS C 22
Working Outside of Canada 23
Acknowledgements
This publicaƟon would not have been possible without the input of many dedicated
people in the steel industry. The CISC AESS CommiƩee members from across Canada
put many long hours into sharing their knowledge in order to help create a useful tool
for designing, specifying or creaƟng Architecturally Exposed Structural Steel.
ParƟcular thanks go to Sylvie Boulanger for her assistance in working through the
details of this publicaƟon, and to Walter Koppelaar for his encouragement and sharing
his knowledge of the industry and its inner workings.
It is sincerely hoped that this guide will assist in leveraging the posiƟon and ease of use
of Architecturally Exposed Structural Steel in the Canadian construcƟon industry.
1

7 ErecƟon ConsideraƟons 38
Handling the Steel 38
TransportaƟon Issues 38
Sequencing of LiŌs 38
Site Constraints 38
Care in Handling 38
ErecƟon Issues 39
Combining Steel with Timber 39
Combining Steel with Glass 40
8 Special Acknowledgments 42
9 References and Image Credits 43
Appendices
Appendix 1 - CISC Code of Standard PracƟce 44
Appendix 2 - Sample AESS SpeciĮcaƟon 46
CISC AESS Guide – Table of Contents - 5
4 CoaƟngs and Finishes 24
General Issues 24
Details 25
Surface PreparaƟon 25
Paint Systems 25
Shop Versus Site PainƟng 26
Primers 26
Intumescent CoaƟngs 26
CemenƟƟous/Fibrous Fire ProtecƟon 27
Galvanizing 27
Metalizing 28
Weathering Steel 29
Stainless Steel 30
5 ConnecƟons 30
Detailing Requirements for AESS ConnecƟons 30
General Issues 30
ConnecƟon Mock-Ups 31
Which Type of ConnecƟon Should I Choose? 31
Bolted ConnecƟons 32
Welded ConnecƟons 32
Tubular Steel 33
Cast ConnecƟons 34
6 Curves and Cuts 35
Designing for Complex Curves and Cuts 35
Bending 35
EllipƟcal Tubes 36
Specialized Equipment 36
Shearing 36
CNC Cuƫng 36
Plasma Cuƫng 36
Torch or Flame Cuƫng 37
Hole Punching and Drilling 37
Disclaimer:
It is not the intenƟon of the CISC AESS CommiƩee that the projects and details included in this
Guide should be replicated or necessarily represent “best pracƟces”. They are included only to
allow for a beƩer understanding of the visual intenƟons of the pracƟces and procedures outlined
in the Guide and related speciĮcaƟon documents, with the understanding that “a picture might
be worth a thousand words”.
Image credits:
Unless otherwise noted, all images in this book were taken by Terri Meyer Boake. Images are not
to be reproduced without wriƩen authorizaƟon of the author. All images are credited at the end
of the document using the numbered photo scheme.

Foreword
The Canadian InsƟtute of Steel ConstrucƟon is a naƟonal industry organizaƟon represenƟng the
structural steel, open-web steel joist and steel plate fabricaƟng industries in Canada. Formed
in 1930 and granted a Federal charter in 1942, the CISC funcƟons as a nonproĮt organizaƟon
promoƟng the eĸcient and economic use of fabricated steel in construcƟon.
As a member of the Canadian Steel ConstrucƟon Council, the InsƟtute has a general interest in
all uses of steel in construcƟon. CISC works in close cooperaƟon with the Steel Structures Educa-
Ɵon FoundaƟon (SSEF) to develop educaƟonal courses and programmes related to the design
and construcƟon of steel structures. The CISC supports and acƟvely parƟcipates in the work of
the Standards Council of Canada, the Canadian Standards AssociaƟon, the Canadian Commission
on Building and Fire Codes and numerous other organizaƟons, in Canada and other countries,
involved in research work and the preparaƟon of codes and standards.
PreparaƟon of engineering plans is not a funcƟon of the CISC. The InsƟtute does provide techni-
cal informaƟon through its professional engineering staī, through the preparaƟon and dissemi-
naƟon of publicaƟons, and through the medium of seminars, courses, meeƟngs, video tapes,
and computer programs. Architects, engineers and others interested in steel construcƟon are
encouraged to make use of CISC informaƟon services.
This publicaƟon has been prepared and published by the Canadian InsƟtute of Steel Construc-
Ɵon. It is an important part of a conƟnuing eīort to provide current, pracƟcal informaƟon to
assist educators, designers, fabricators, and others interested in the use of steel in construcƟon.
Although no eīort has been spared in an aƩempt to ensure that all data in this book is factual
and that the numerical values are accurate to a degree consistent with current structural design
pracƟce, the Canadian InsƟtute of Steel ConstrucƟon and the author do not assume responsibil-
ity for errors or oversights resulƟng from the use of the informaƟon contained herein. Anyone
making use of the contents of this book assumes all liability arising from such use. All suggesƟons
for improvement of this publicaƟon will receive full consideraƟon for future prinƟngs.
CISC is located at:
3760 14th Avenue, Suite 200, Markham, Ontario, L3R 3T7
and may also be contacted via one or more of the following:
Telephone: 905-946-0864
Fax: 905-946-8574
Email: info@cisc-icca.ca
Website: www.cisc-icca.ca
CISC AESS Guide – Foreword - 6

CISC AESS Guide – 1 The Challenge - 7
Purpose of the Guide
The factors of inŇuence were worked into the Categories (described in SecƟon 2) and Charac-
terisƟcs (SecƟon 3) as deĮned in the new AESS documents. It was felt that, in order for users of
the new speciĮcaƟon documents to understand more fully the Categories and CharacterisƟcs, an
illustrated document was required. This Guide has been wriƩen to explain in detail the suite of
CISC documents for the speciĮcaƟon of AESS material. It provides visual references to help beƩer
understand the terms of reference. The buildings and connecƟons included in this document
are meant to be representaƟve and to provide clear visual references supporƟng the key facts
explained in the Guide. It is also hoped that the range of projects illustrated will inspire you by
highlighƟng the wide range of possibiliƟes available when designing with Architecturally Exposed
Structural Steel.
It is not the intenƟon of the CommiƩee that the details included herein should be replicated or
necessarily represent “best pracƟces”. They are presented to allow a beƩer understanding of
the visual intenƟons of pracƟces and procedures outlined in the Guide and related speciĮca-
Ɵon documents, with the understanding that “a picture might be worth a thousand words”. In
addiƟon, the projects and details are intended to help architects select appropriate Categories of
AESS which range from AESS1 through AESS4 (see SecƟon 2).
EvoluƟon of Architecturally Exposed Structural Steel
The basic understanding of steel construcƟon lies in its roots as an assembled, largely prefabri-
cated methodology. Steel construcƟon is “elemental” in nature and its arƟstry reliant not only on
the appropriate choice of members (shapes versus tubes), but also on the method of aƩach-
ment. AESS steel design requires detailing that can approach industrial design standards when
creaƟng joints between members. The structural requirements of shear and moment resistance
must be accommodated, along with Ɵghter dimensional tolerances and other consideraƟons
such as balance, form, symmetry and economy. If the creaƟon of connecƟons requires an exces-
sive degree of unique fabricaƟon details, the designer can price the project out of existence. The
method of preparing and Įnishing the connecƟons can also radically increase costs. Specialized
welds and unnecessary ground and Įlled Įnishes increase fabricaƟon and erecƟon expenses.
2 543
1 The Challenge
What Is AESS?
Architecturally Exposed Structural Steel (AESS) is steel that is designed for structural suĸciency
to meet the primary needs of the building, canopies or ancillary structures, while at the same
Ɵme remaining exposed to view. It is therefore a signiĮcant part of the architectural language of
the building. The design, detailing and Įnish requirements of AESS will typically exceed that of
standard structural steel normally concealed by other Įnishes.
Why a Guide for AESS?
This Guide was developed to facilitate beƩer communicaƟon among architects, engineers and
fabricators. It was felt that visual references would help all parƟes understand the intent of the
new AESS documents as applied to the design of structures.
The Guide serves as a companion to two other AESS documents: the Sample AESS SecƟon in
the Structural Steel SpeciĮcaƟon and the CISC Code of Standard PracƟce including the Category
Matrix.
For Whom Is It Intended?
This Guide was created primarily for architects but is also intended for all design professionals in-
terested in AESS applicaƟons. In terms of the relaƟonship between the new AESS documents and
speciĮc areas of pracƟce, engineers have the SpeciĮcaƟon, fabricators have the Code, architects
have the Guide, and all are linked by the Matrix of Categories and CharacterisƟcs. The Matrix sits
at the centre of the suite and provides the connecƟon that links all of the documents.

1 The Challenge
Much of the architectural enjoyment as well as the challenge of designing with AESS lies in the
creaƟon of key details and connecƟons that give the structure its disƟncƟve character. AŌer the
primary choice of member type and system (shape vs. tube), the challenge consists in determin-
ing the method of connecƟon – welding vs. bolƟng, and ulƟmately designing the joint itself.
Whereas designers tend not to be involved in connecƟon issues for concealed structural systems,
exposed systems become the architectural trademark of the building, hence requiring much
involvement. ComposiƟonal issues usually necessitate the addiƟon of extra steel at the joints to
create a beauƟful connecƟon. Unfortunately not all designers are adequately informed regarding
either the choice of appropriate methods of aƩachment or the cost implicaƟons of their choices.
The surge in the use of AESS has created a paradigm shiŌ in the sequenƟal communicaƟon that
usually takes place in a more convenƟonal building where the steel structure is hidden. The ar-
chitect now wants direct access to the fabricator’s shop to verify and comment on the edges and
surfaces of the imagined product, and the engineer is dealing with aestheƟc aspects that impact
the structural integrity of the frame. That leaves the fabricator and the erector somewhere in the
middle between aestheƟc and technical requirements.
The paradigm shiŌ centers on the simple fact that a “nice-looking connecƟon” or a “smooth
surface” has very diīerent meanings whether you are talking to an architect, an engineer or a
fabricator. Such a situaƟon creates a misalignment of expectaƟons in terms of what can be ac-
complished within speciĮc budget limitaƟons. Welds that are contoured and blended are not the
same price as ASTM A325 hexagonal bolts, for example.
Development of the New CISC AESS Documents
It was felt that the normal speciĮcaƟon used for structural steel was incomplete when it came
to serving the special needs of AESS. Therefore, CISC formed a naƟonal Ad Hoc CommiƩee on
AESS (see Special Acknowledgments at the end of the document) and focused on diīerenƟaƟng
Categories because it became clear that not all AESS need be created equal(ly expensive). For
example, viewing distances, coaƟng thicknesses and connecƟon types should maƩer, as they all
impact the nature of the Įnish and detail required in exposed steel. The CommiƩee established
a set of Categories to deĮne the nature of Įnish and tolerance in the steel. The Categories are
further deĮned by a set of technical CharacterisƟcs. To facilitate communicaƟon among archi-
tects, engineers and fabricators, Categories and their associated CharacterisƟcs are presented
in a Matrix to provide an easy graphic reference. In total, three AESS documents reference the
Matrix: a Sample SpeciĮcaƟon, an addiƟon to the CISC Code of Standard PracƟce and this Guide.
Primary Factors of InŇuence That DeĮne AESS
The Canada-wide discussion groups held by the CISC Ad Hoc CommiƩee on AESS determined
that there were primary factors giving rise to the diīerenƟated Categories of AESS:
• ConnecƟons mostly bolted or welded
(diīerent aestheƟcs requiring diīering levels of Įnish)
• Tolerances required at fabricaƟon and erecƟon
(diīerent as a funcƟon of scope and complexity)
• Access to detail to perform required Įnish
(greater concern for workmanship may mean altering the detail or its locaƟon to allow ac-
cess for diīerent types of tools)
BACKGROUND
By 2003, AISC had produced its AESS Guide. During the same period, concerns about
AESS were also emerging in several regions of Canada. Regional CISC iniƟaƟves eventu-
ally culminated in the naƟonal CISC Ad Hoc CommiƩee on AESS in 2005. The idea was
to create a dynamic industry dialogue including architects and engineers, in the hope of
providing a series of documents that would assist in re-visioning the design, speciĮca-
Ɵon, and construcƟon process for AESS.
In the following two years, CISC adapted components of what AISC had developed and
also introduced an underlining Category approach and reduced its scope. The commit-
tee elaborated a Sample SpeciĮcaƟon (for engineers), an addiƟon to the CISC Code of
Standard PracƟce (for fabricators) and a Guide (for architects). Common to all these
documents was a unique Matrix of Categories and CharacterisƟcs used by all.
In parallel, several roundtables were held in Montreal, Toronto and Vancouver, which
typically involved architects, engineers and fabricators. Those sessions helped shape the
orientaƟon and direcƟon of the CommiƩee’s work on the documents.
The Sainsbury Centre for the Performing Arts was designed
and constructed by Norman Foster in 1977. The BriƟsh High
Tech movement brought exposed structural steel to the
forefront of design, and with it an array of issues that had
not been part of architectural discourse for more than a
century. The project used round HSS members and a struc-
ture that was expressed on both the exterior and interior of
the building.
In its arƟcle on Architecturally Exposed Structural Steel
ConstrucƟon in Modern Steel ConstrucƟon (May 2003),
AISC cited the roots of the current trend of exposed steel
and transparency in design to the Chicago O’Hare United
Airlines Terminal designed by Helmut Jahn between 1985
and 1988. Indeed, airport architecture has succeeded in
pushing the use of exposed steel to incredible heights.
6
7

• Degree of expression
(complexity of structure and connecƟons)
• Size and shape of structural elements
(W secƟons and HSS have diīerent detailing requirements and their use infers a diīerent
approach to detailing and Įnish)
• Interior or exterior seƫng
(weathering issues, need to Įre protect, potenƟal for impact damage)
• Paint Įnish, corrosion resistance, Įre protecƟon
(depending on the relaƟve thickness of the Įnish material, more or less care may be re-
quired when preparing the surface, edges and welding of the steel)
Form, Fit and Finish
The primary factors of inŇuence can be further summarized as Form, Fit and Finish. Unlike stan-
dard structural steel that is hidden from view, Architecturally Exposed Structural Steel is a key
element of the expression of the Architectural Design. A large amount of emphasis is placed on
the Form of the steel in the design. The overall Form may vary greatly from regular framing and
might oŌen include curves, unusual angles or three-dimensional elements. Members and con-
necƟons are designed with more aƩenƟon to the way in which their details support the aestheƟc
intenƟons of the design. Bolted or welded connecƟons may be chosen less for their structural
capabiliƟes or ease of erecƟon than for their appearance within the overall intenƟon and form
of the design. This does not mean that their structural integrity is not a key consideraƟon in the
success of the design.
Highly arƟculated steel structures are by their nature more diĸcult to Fit. There is signiĮcantly
less play in the connecƟons, and accumulated errors can result in overall misalignment. This
need to ensure accuracy, ease of fabricaƟon, as well as boƩom line constructability, puts greater
pressure on the details and requires narrower tolerances throughout the enƟre project. Tighter
tolerances will carry through when the exposed steel framing must coordinate with other trades,
in parƟcular areas of signiĮcant glazing and curtain wall. The use of stainless steel spider con-
necƟons for structural glass systems puts addiƟonal pressure on allowable tolerances. If exposed
steel is used with heavy Ɵmber or glulam systems, then the Įt must also take into account the
diīerenƟal movements and erecƟon idiosyncrasies of these other materials.
While the Finish might be the last phase of construcƟon, the selecƟon of the Finish must take
place at the beginning of the AESS design process. Finishes will vary in exposed steel both as a
funcƟon of the design intenƟon and issues relaƟng to weathering, interior or exterior exposure
and Įre protecƟon. A high-gloss Įnish will reveal every imperfecƟon and so will require more
fasƟdious fabricaƟon. A thicker intumescent coaƟng will conceal many surface imperfecƟons.
Galvanizing itself has issues with consistency of Įnish, and its selecƟon may accompany a less
polished selecƟon of details. The boƩom line for the contract is that both Ɵme and money will
be wasted if the level of fabricaƟon care greatly exceeds the nature of the Finish.
ExcepƟons
Form, Fit and Finish consideraƟons will diīer on projects whose intenƟons might fall outside
of tradiƟonal Architecturally Exposed Structural Steel. Steel is oŌen selected as the material of
choice for large art installaƟons. Here there needs to be a customized variaƟon of the consider-
aƟons presented in this Guide which form the basis of dialogue for the team. Where some arƟsts
might be looking for a very plasƟc appearance, others may wish to let the rough nature of the
steel reveal itself.
Reused steel also requires a diīerent set of consideraƟons. Many projects seek to incorporate
reused or salvaged steel for its sustainable qualiƟes. In some instances the steel may be cleaned,
but in others leŌ with its original Įnish so that it can express its reuse. This type of applicaƟon
also demands a variaƟon of the general intenƟons presented in this Guide.
Two diīerent steel trees: one created using W shapes to create a very textured appearance; the other us-
ing mechanical pipe and specialty casƟng and striving for a seamless appearance using a high gloss Įnish.
AESS speciĮcaƟons must be tailored to the overall design intenƟons of each individual project as they are
all somewhat unique.
Specialty glazing systems require Ɵghter toler-
ances and a higher level of Fit on a project.
Composite structural systems require higher levels
of coordinaƟon. The tolerances and construcƟon
pracƟces of the other material must be taken into
account.
8 9 10 11

THE CISC CATEGORY MATRIX FOR SPECIFYING ARCHITECTURALLY EXPOSED STRUCTURAL STEEL (AESS)
AESS 1
AESS 4
AESS 3
AESS 2
12
13
14
Table 1 - AESS Category Matrix
Category AESS C AESS 4 AESS 3
Custom Elements Showcase Elements Feature Elements
Id
Characteris cs
Viewed at a Distance 6
m
1.1 Surface prepara on to SSPC-SP 6
1.2 Sharp edges ground smooth
1.3 Con nuous weld appearance
1.4 Standard structural bolts
1.5 Weld spa ers removed
2.1 Visual Samples op onal op onal
2.2 One-half standard fabrica on tolerances
2.3 Fabrica on marks not apparent
2.4 Welds uniform and smooth
3.1 Mill marks removed
3.2 Bu and plug welds ground smooth and lled
3.3 HSS weld seam oriented for reduced visibility
3.4 Cross sec onal abu ng surface aligned
3.5 Joint gap tolerances minimized
3.6 All welded connec ons op onal op onal
4.1 HSS seam not apparent
4.2 Welds contoured and blended
4.3 Surfaces lled and sanded
4.4 Weld show-through minimized
C.1
C.2
C.3
C.4
C.5
Sample Use:
Elements with special
requirements
Showcase or dominant
elements
Airports, shopping
centres, hospitals,
lobbies
Es mated Cost Premium: Low to High High Moderate
(20-250%) (100-250%) (60-150%)
15
Viewed at a Distance ч 6 m

The CISC Category Matrix encompasses 4 Cat-
egories (AESS 1 through AESS 4). Each category
represents a set of characterisƟcs, which clari-
Įes what type of work will be performed on the
steel, the tolerances to be met, and if a visual
sample is needed. For AESS 1, the associated
characterisƟcs are 1.1 through 1.4; for AESS
2, they are 1.1 through 2.4, and so on. The
categories are selected by the architect. They
are speciĮed at bid Ɵme as an AESS subdivision
of the Structural Steel division in the engineer’s
documents. The categories appear on architec-
ture, engineering, detailing and erecƟon docu-
ments. In general, it is expected that AESS 2
(for elements viewed at a distance) and AESS 3
(for elements viewed at close range) will be the
categories most commonly speciĮed. For more
informaƟon, see: www.cisc-icca.ca/aess.
NOTES
1.1 Prior to blast cleaning, any deposits of
grease or oil are to be removed by solvent
cleaning, SSPC-SP 1.
1.2 Rough surfaces are to be deburred and
ground smooth. Sharp edges resulƟng from
Ňame cuƫng, grinding and especially shearing
are to be soŌened.
1.3 IntermiƩent welds are made conƟnuous,
either with addiƟonal welding, caulking or body
Įller. For corrosive environments, all joints
should be seal welded. Seams of hollow struc-
tural secƟons shall be acceptable as produced.
1.4 All bolt heads in connecƟons shall be on the
same side, as speciĮed, and consistent from
one connecƟon to another.
1.5 Weld spaƩer, slivers and surface disconƟ-
nuiƟes are to be removed. Weld projecƟon up
to 2 mm is acceptable for buƩ and plug-welded
joints.
2.1 Visual samples are either a 3-D rendering, a
physical sample, a Įrst-oī inspecƟon, a scaled
mock-up or a full-scale mock-up, as speciĮed in
Contract Documents.
2.2 These tolerances are required to be one-
half of those of standard structural steel as
speciĮed in CSA S16.
2.3 Members marked with speciĮc numbers
during the fabricaƟon and erecƟon processes
are not to be visible.
2.4 The welds should be uniform and smooth,
indicaƟng a higher level of quality control in
the welding process.
3.1 All mill marks are not to be visible in the
Įnished product.
3.2 Caulking or body Įller is acceptable.
3.3 Seams shall be oriented away from view or
as indicated in the Contract Documents.
3.4 The matching of abuƫng cross-secƟons
shall be required.
3.5 This characterisƟc is similar to 2.2 above. A
clear distance between abuƫng members of 3
mm is required.
3.6 Hidden bolts may be considered.
4.1 HSS seams shall be treated so they are not
apparent.
4.2 In addiƟon to a contoured and blended
appearance, welded transiƟons between
members are also required to be contoured
and blended.
4.3 Steel surface imperfecƟons should be Įlled
and sanded.
4.4 The back face of the welded element
caused by the welding process can be mini-
mized by hand grinding the backside of the
weld. The degree of weld-through is a funcƟon
of weld size and material.
C. AddiƟonal characterisƟcs may be added for
custom elements.
AESS 2 AESS 1 SSS
Feature Elements Basic
Elements
Standard Structural
Steel
Viewed at a Distance > 6
m
CSA S16
op onal
Retail and architectural
buildings viewed at a
distance
Roof trusses for arenas,
retail warehouses,
canopies
Low to Moderate Low None
(40-100%) (20-60%) 0%
Viewed at a Distance > 6 m

CISC AESS Guide – 2 Categories - 12
2 Categories
THE CATEGORIES APPROACH
In the new AESS set of SpeciĮcaƟon documents, Įve Categories have been created that charac-
terize Įve unique levels of Įnish related to AESS. These Categories reŇect the primary factors
of inŇuence, form, Įt and Įnish, and for the purpose of the Matrix, have been reduced to three
main areas of concern:
• the viewing distance (greater or less than 6 metres)
• the type or funcƟon of the building (as this infers potenƟal design requirements for Įnish)
• a range of percentage of potenƟal cost increase over standard structural steel.
Viewing Distance: Six metres was chosen as a base dimension, as it began to diīerenƟate
whether an occupant would be able to scruƟnize the Įnish from a close range and even touch
the product. Six metres represents a normal height of a high ceiling. The ability to see the struc-
ture from a close range can impact the required level of workmanship of the Įnished product. It
makes liƩle sense to grind welds, for instance, on a structure many metres out of eyeshot. When
designing atrium spaces, it is also important to use this measurement in the horizontal direc-
Ɵon, as the view across a space is as criƟcal as the view upward. In certain instances, this might
also include the view down onto the structure. Where steel is viewed from above, care must
be taken to detail the steel to avoid the buildup of grime and trash. Viewing distance can also
impact the requirements of the surface Įnish on the steel members, as some natural blemishes
in the steel from manufacturing, fabricaƟon or mill processes will not be able to be seen at a
distance. There are cost savings if such is recognized prior to specifying the steel.
Type or FuncƟon of the Building: The exposed steel over an ice rink and the exposed steel
in an airport are likely to have diīerent aestheƟc and Įnish requirements. There are a range of
degrees of Įnish between these two building types that are recognized in this document. It is
also suggested that the program of the building and the range of spaces within a project be ex-
amined to assess whether there are in fact a number of types of AESS that need to be speciĮed.
The exposed roof trusses may be AESS 1, and the columns or base details may be AESS 3. If this is
clearly marked on the contract drawings, then the fabricator can adjust the bid according to the
appropriate level of Įnish.
Range of PotenƟal Cost Increase: The percentage values noted on the matrix suggest a range
of increase in the cost to fabricate and erect the AESS Categories over the cost to fabricate and
erect standard structural steel. AddiƟonal Ɵme is involved in the fabricaƟon processes associated
with the speciĮc characterisƟcs of the higher levels of AESS. The erecƟon costs will also increase
as a funcƟon of the complexity of the steel, the degree to which this complex steel can be fab-
ricated in the shop, transportaƟon, access and staging area concerns, and increased tolerance
requirements to Įt the steel. The more complex the AESS and the higher the nature of the Įnish
requirements, the Ɵghter the tolerances become. This increases the Ɵme to erect the steel. For
these reasons the range of increase is fairly wide. It is strongly suggested that, once the type of
AESS has been selected and the Matrix completed, these documents be used as a point of com-
municaƟon and negoƟaƟon among the design and construcƟon team.
Baselines have been established that characterize each of the Įve AESS Categories. A set of
CharacterisƟcs has been developed that is associated with each Category. These are explained in
detail under SecƟon 3 CharacterisƟcs. Higher-level Categories include all of the CharacterisƟcs of
the preceding Categories, plus a more stringent set of addiƟonal requirements. Each Category as
illustrated within this Guide will be shown to be able to reference recognizable building types as
a point of visual orientaƟon.
It is recognized that a wide range of AESS buildings is already in existence. The examples chosen
to illustrate the points in this Guide are not meant to be either deĮniƟve or exhausƟve, but to
create a visual reference to assist in understanding both the intent of the AESS Categories as well
as the nature of the Įnish and workmanship inferred by the CharacterisƟcs listed in the next
secƟon.
MulƟple Types of AESS, Same Project: Diīerent types of AESS can be in use on the same project.
The choice of AESS category will vary according to the use of the space, viewing distance and
types of members. The type of AESS will simply need to be marked clearly on the contract docu-
ments.
Standard Structural Steel (SSS)
The iniƟal point of technical reference is Standard
Structural Steel (SSS) as deĮned in CSA S16, as it
is already established and well understood as a
baseline in construcƟon SpeciĮcaƟons.
Understanding the Categories of Architecturally
Exposed Structural Steel begins by diīerenƟaƟng
structural steel in terms of its degree of expo-
sure. It is assumed that regular structural steel is
either normally concealed for reasons of Įnish
preference or for reasons of Įre protecƟon. The
structural integrity of Standard Structural Steel is
clearly the overriding concern of this material. In
normal circumstances, because it will be either
clad and/or Įre protected, there is liƩle or no
architectural concern over the design of the
details, connecƟons and even necessarily the type
of members chosen. Although some applicaƟons
will be more complicated than others, and hence
priced accordingly, this steel is not subject to the
same consideraƟons as an exposed product.
Architecturally Exposed Structural Steel will follow
all of the same structural requirements as set
out within CSA S16, and be subject to addiƟonal
This structural steel will be hidden behind a
suspended ceiling, so its strength consideraƟons
take priority over its appearance.
This structural steel has spray ĮreprooĮng ap-
plied and will also be hidden from view by ceiling
and wall Įnishes.
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17

requirements as deĮned by the assigned AESS Category (1, 2, 3, 4 or Custom) and the speciĮc set
of CharacterisƟcs associated with each AESS Category. In Architecturally Exposed Structural Steel,
the steel, its materiality and method of connecƟons are “expressed” and form a key part of the
architectural design of the building or project.
AESS 1 – Basic Elements is the
Įrst step above Standard Structural Steel.
This type of applicaƟon would be suit-
able for “basic” elements, which require
enhanced workmanship. This type of
exposed structure could be found in roof
trusses for arenas, warehouses, big box
stores and canopies and should only
require a low cost premium in the range
of 20% to 60% due to its relaƟvely large
viewing distance as well as the lower
proĮle nature of the architectural spaces
in which it is used.
AESS 1 applicaƟons will see the use of
fairly straighƞorward secƟon types such
as W, HSS, and oŌen OWSJ and exposed
proĮled decking. Generally this type of
framing might appear similar to basic
structural steel applicaƟons, other than
the fact that it is leŌ exposed to view.
And because it is leŌ exposed to view,
more care is required to ensure that
the standard structural members are
aligned in a uniform way, that spacing is
kept consistent, and that the surfaces of
the members are properly prepared to
accept uniform Įnishes and coaƟngs. A
greater level of consistency in the use of connecƟons, bolts, and welds is also required.
These types of applicaƟons may or may not require special Įre protecƟon design. This is deter-
mined as a funcƟon of the use of the space. In some situaƟons the steel may be leŌ completely
unprotected or sprinklered, and so it will need to receive only a paint Įnish. Intumescent coat-
ings could be found where the raƟng would be one hour or greater; however, this might not be a
common choice due to the cost of the coaƟng system. The detailing on AESS 1 elements should
not be greatly impacted by the relaƟve thickness or Įnish of the intumescent coaƟng, as much of
this type of steel will be located well above eye level and out of range of touch.
As it is anƟcipated that many AESS projects will specify more than one Category of steel, it will
be common to specify AESS 1 for the ceiling elements of a design, where the distance to view is
in the 6 m or greater range, and use a diīerent class of AESS for those elements, like columns,
that are located at a closer proximity.
Semiahmoo Library, Surrey, B.C.: The project uses a very
simple exposed structure comprised of W secƟons and
OWSJ with a painted Įnish. Some extra care is necessary, in
keeping with the library use of the facility, in the prepara-
Ɵon and installaƟon of the structure. The W secƟons are
exposed to view and touch, but overall the ceiling elements
are viewed at a distance. Had this project used custom
trusses instead of OWSJ members, it would likely have
fallen into AESS 2 Category Steel. In the case of the library,
the steel has been leŌ exposed to save on the use of Įnish
material, which has helped in achieving credits towards
a LEED Silver RaƟng. (lower cost premium with standard
joists)
AlternaƟvely, some specialty custom-
designed steel may be speciĮed but
would be located at a distant view, so
that the fabricaƟon, Įnish of the steel
and workmanship would not come under
close scruƟny. Some of these specialty
fabricaƟons will be similar to those used
in AESS 2, with the distance factor being
the major point of separaƟon.
Another factor that will impact the deci-
sion to ask for AESS 1 versus AESS 2 steel
for an exposed ceiling will be the nature
of the lighƟng. In the case of Semiahmoo
Library, the light level on the ceiling is
high, and the ceiling height at the low
range for this category. In the Ricoh Cen-
tre, the steel is more arƟculated using
curved shapes and HSS members, but the
ceiling is extremely high, and the lighƟng
levels in the low range and addiƟonally
using a type of lighƟng that tends to con-
ceal detail. If the curved steel trusses of
the Ricoh Centre were to be brightly uplit
with a more blue-white type of light that
could accentuate the detail, this structure might need to fall into a higher Category.
Also important to consider when specifying AESS 1 for the ceiling will be the nature of the other
elements and systems that will be incorporated into the ceiling plane. Is it “busy” with mechani-
cal services? Do these need to run parallel or perpendicular to the main structural lines of the
trusses or joists? Are the services to be painted out or accentuated? Typically you will see sprin-
kler runs and HVAC equipment integrat-
ed into most AESS 1 type ceilings. In the
case of retail (big box) stores, you might
also see a high level of signage that will
serve to take the focus away from the
steel systems and therefore allow for a
lower level of Įnish and detailing.
Depending on the environment
(moisture level in the case of rinks and
chemicals in the case of swimming pools,
industrial plants, etc.) this type of steel
may need special coaƟng treatment to
prevent corrosion. This will impact the
overall cost of the installaƟon.
Ricoh Centre, Toronto, ON: This renovaƟon project uses
curved trusses adjacent to the entry area of the arena to
reŇect the curved window of the adjacent historic facade.
The trusses are fabricated from HSS material. Although
there is more fabricaƟon eīort involved than if using oī-
the-shelf components, the trusses are sƟll well above 6 m
from the viewer, so close scruƟny of the Įnishes and con-
necƟons is not possible. (higher cost premium for custom
fabricaƟon)
Ricoh Centre, Toronto, ON: Although the trusses that span
the arena proper in the Ricoh Centre are somewhat closer
to view, they fall into AESS 1 given their more roughly
detailed design style as well as the less reĮned nature of the
space. (low cost premium through the use of standard sec-
Ɵons and connecƟons that are removed from view)
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19
18

Works Yard Oĸce. There are some specialty details added to the repertoire, centred around the
support of the PV skylights and the wood structure.
Edmonton City Hall uses square HSS members to create a very complex high-level truss system to
support a pyramidal skylight. The viewing distance has permiƩed a less fasƟdious level of Įll and
Įnish on the members, as these are not in close range of view or touch. The structure appears
to use all-welded connecƟons. For the straight-run truss elements, the square HSS secƟons align
fairly cleanly. This becomes more diĸcult at the angled junctures of the roof. But given the pyra-
AESS 2 – Feature Elements includes structure that is intended to be viewed at a dis-
tance > 6 m. It is suitable for “feature” elements that will be viewed at a distance greater than
six metres. The process requires basically good fabricaƟon pracƟces with enhanced treatment of
welds, connecƟon and fabricaƟon details, tolerances for gaps, and copes. This type of AESS might
be found in retail and architectural applicaƟons where a low to moderate cost premium in the
range of 40% to 100% over the cost of Standard Structural Steel would be expected.
AESS 2 will generally be found in buildings where the expressed structure forms an important, in-
tegral part of the architectural design intent. The deĮning parameter of viewing distance greater
than 6 metres will infer that you might
Įnd this sort of steel in high-level roof or
ceiling applicaƟons. For this reason you
might be specifying AESS 2 steel for the
distant components of the structure and
a higher grade of AESS for the low-level
elements of the structure. These should
be clearly marked on the drawing sets
so that the treatments can be diīerenƟ-
ated and the respecƟve cost premiums
separated out.
It will be more common to see W or HSS
members speciĮed for this category,
rather than more industrial members
such as OWSJ. This type of applicaƟon
may use a combinaƟon of bolted or
welded connecƟons. As the viewing
distance is great, there is normally less
concern about concealing the connecƟon
aspects of larger pieces to each other –
hence no hidden connecƟons.
In the case of the NaƟonal Works Yard,
the use of exposed steel has reduced
Įnishes and helped in achieving a LEEDTM
Gold raƟng. The predominant secƟon
choice is a W-shape, and the detail-
ing has been kept fairly standard. The
specialty details that support the roof
structure and the Parallam wood beams
remove the details from close scruƟny.
The primary connecƟon choice to join
major secƟons is bolƟng; however, the
elements themselves have been shop-
welded prior to shipping. Although the
steel can be viewed more closely from
the upper Ňoor level, a decision was
made to maintain the tectonic of the
W-secƟons and bolted connecƟons con-
sistent, given the use of the building as a
NaƟonal Trade Centre, Toronto, ON: The project makes
use of relaƟvely standard steel secƟons, but the design and
fabricaƟon employ a higher standard in terms of arrange-
ment and detailing. There is some secƟon bending required
which increases fabricaƟon costs and can impact detailing.
Much of the structure is sƟll located in excess of 6 metres
above view.
NaƟonal Works, Vancouver B.C.: The project uses a more
arƟculated steel design, predominantly with W-secƟons.
Much of the structure is located at ceiling height, so at a
distance for viewing and therefore allowing for a lower
level of detailing and Įne Įnish. This structure interacts
with wood, which will change aspects of its detailing and
coordinaƟon during erecƟon.
Pierre EllioƩ Trudeau Airport, Montreal: The trusses supporƟng this skylight are quite characterisƟc of
AESS 2 type steel. The viewing distance is over 6 metres but the design needs something more than a
standard joist or truss. The detailing is simple, and the viewer is not close enough to see the texture of the
connecƟon, only the form of the truss.
Edmonton City Hall: The trusses that support the pyramidal glass roof are created using square HSS sec-
Ɵons. The viewing distance varies but is typically greater than 6 metres, even from the upper levels. An up-
close inspecƟon reveals many inconsistencies that are reasonable to leave “as is” due to the view distance.
The extra expense to Įll, grind and carefully align the members would be lost on users of the building.
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25 27
21
23 24
26

or characterisƟcs of the steel are not
thoughƞully considered, the AESS for
the project can easily be priced higher.
The cost premium to be found in
AESS 3 steel will depend greatly
upon the types of members chosen,
the nature of the connecƟons, and
the desire of the designer to either
conceal or express the materiality of
the steel itself. As can be seen later in
this document under CharacterisƟcs, it
is assumed that eīort will be put into
further surface preparaƟon to increase
its smoothness and ensure that some of the natural Įn-
ish on the steel and mill marks do not show through the
paint.
There may be more
welded connec-
Ɵons in AESS 3 steel.
Where welds cannot
be done in the shop,
where condiƟons
are more controlled
and jigs can be used
to ensure precise
alignment of the
components, it must
be realized that large amounts of site welding of complex
elements will result in cost premiums. Some site welds
may not be of the same quality as can be expected of shop
welds. It would be expected that the welds will be of a
higher quality than those for AESS 2 structures where the
welds would be out of view and touch due to their height.
AESS 3 welds will be expected to have a very uniform ap-
pearance. Although some touch-up grinding of the welds
may be required to ensure uniformity, complete grinding of
all welds would not be included in this category of steel. It
is assumed that good quality, uniform welds would be leŌ
exposed.
midal shape, round HSS members were not deemed appropriate so a detailing compromise was
required at the junctures, and the viewing distance made this workable.
The cost premium for AESS 2 ranges from 40 to 100%. There may be lower costs associated
with the clean use of standard structural shapes with bolted or simple welded connecƟons, and
higher costs associated with the use of HSS shapes, complex geometries and a predominance
of welded connecƟons. As one of the common applicaƟons of AESS 2 will be for roof, skylight or
ceiling support systems, the Įre-protecƟon method must be known from the outset of the proj-
ect. If intumescent coaƟngs are used, these can help to conceal any inconsistencies in surface
condiƟons.
AESS 3 – Feature Elements includes structures that will be viewed at a distance ч 6m.
The Category would be suitable for “feature” elements where the designer is comfortable allow-
ing the viewer to see the art of metalworking. The welds should be generally smooth but visible
and some grind marks would be acceptable. Tolerances must be Ɵghter than normal standards.
As this structure is normally viewed closer than
six metres, it might also frequently be subject
to touch by the public, therefore warranƟng a
smoother and more uniform Įnish and appear-
ance. This type of structure could be found in
airports, shopping centres, hospitals or lobbies
and could be expected to incur a moderate
cost premium ranging from 60% to 150% over
standard structural steel as a funcƟon of the
complexity and level of Įnal Įnish desired.
When AESS structural elements are brought into close
range for view and potenƟally for touch, it is necessary
for the team to come to a clear understanding about the
level of Įnish that is both required and expected of the
steel. The natural look of welds that would be out of view
in AESS 2 steel will now be visible to the occupant in the
space. Simple bolted connecƟons may need to be de-
signed to look more arƞul if they are to become part of the
architectural language. ConnecƟons will come under closer
scruƟny, so their design, tolerances and uniform appear-
ance will become more important, and the workmanship
required to improve these beyond both Standard Structural
Steel and AESS 1 and 2 could have a signiĮcant impact on
the cost of the overall structure. If the required aƩributes
O’Hare InternaƟonal Airport in Chicago was the Įrst
airport to use AESS. Much of the steel is well within
range of view and touch. A variety of steel shapes
and connecƟon types have been used. The complex
nature of the secƟons and connecƟons called for a
Ɵghter sizing tolerance and even Įnish applicaƟon.
The Palais des Congrès in Mon-
treal uses specialty W secƟons with
trimmed cutouts. Although the steel
is all painted grey, and intumescent
coaƟngs are used, the coloured light
through the curtain wall gives ad-
diƟonal texture to this expression of
steel.
The Canadian War Museum in OƩawa uses AESS to create
a highly arƟculated and rugged expression of the steel in
RegeneraƟon Hall. In this instance a combinaƟon of welded
connecƟons and exposed plate-to-plate moment connec-
Ɵons at the connecƟon points between square HSS secƟons is
the feature of the appearance. Due to the irregularity of the
structure, Ɵght tolerances are required. The proĮled decking
is also leŌ exposed to view.
In the Canadian War Museum there are
exposed welded and bolted connecƟons.
Square plates have been welded to the
HSS members that provide surface for
bolts on all sides of the connecƟon to
ensure a uniform appearance. Flat plates
have been used for the lap-type hinge
connecƟons on the diagonal members,
creaƟng a degree of uniformity within
the scheme.
OƩawa InternaƟonal Airport: The
steel trusses and sloped column sup-
ports are within view and touch by
the passengers. The geometry of the
steel is complex, and the tolerances
and Įnish requirements are character-
isƟc of AESS 3 Feature Element type
steel.
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31
29 32
28

Where bolted connecƟons are employed, more care will be taken to ensure that there is an
aestheƟcally based uniformity in the connecƟons which will likely require more fabricaƟon Ɵme
and potenƟally more material. Simple approaches such as ensuring all bolt heads are located on
uniform sides of the connecƟons can greatly enhance the details with liƩle extra cost. If bolted
connecƟons are required for erecƟon ease but are visually unacceptable, concealed connecƟons
can be employed to give the appearance of a seamless or welded connecƟon without the associ-
ated price tag. For these types of connecƟons the aƩaching plates are kept within the general
line of the members, so that cover plates can be aƩached over the bolted elements. If this is to
be an exterior applicaƟon, concealed connecƟons must be made corrosion-resistant to prevent
hidden rust.
Underlying AESS 3 steel is the idea that it is possible to change the appearance of the Įnal
product to make it smoother to the eye, but it is not always necessary to use more expensive
fabricaƟon techniques to arrive at this point. As will be seen under CharacterisƟcs, it is possible
to use simpler methods to surface Įll or provide the appearance of a conƟnuous weld without
actually welding.
AESS 4 – Showcase Elements or “dominant” elements is used where the designer
intends that the form be the only feature showing in an element. All welds are ground, and Įlled
edges are ground square and true. All surfaces are sanded and Įlled. Tolerances of these fabri-
cated forms are more stringent, generally to half of standard tolerance for standard structural
steel. All of the surfaces would be “glove” smooth. The cost premium of these elements would be
high and could range from 100% to 250% over the cost of standard structural steel – completely
as a funcƟon of the nature of the details, complexity of construcƟon and selected Įnishes.
AESS 4 Showcase Elements represents the highest standard quality expectaƟons of AESS
products. The architectural applicaƟons of this category of steel included in the guide are very
representaƟve of the diverse
nature of these projects. As can
be seen, there is a wide variety of
member types employed, each for
their speciĮc purpose within the
structure or connecƟon. Many of
the column or spanning members
have been custom-fabricated. In
some cases this may be due to
the very large size and structural
capacity required of the member.
In other cases it is due to the par-
Ɵcular architectural style desired
in the exposed structure. Many of
the members tend to employ steel
plate that has been custom-cut to
odd geometries. Such geometries,
when not based on a combinaƟon
of simple circular holes and straight
cuts, will increase the fabricaƟon
costs of the project.
On many of these projects the
edges of the steel have been Įn-
ished to be very sharp and precise.
The straightness of the line of these
members is a criƟcal aspect of their
fabricaƟon that is a requirement of
their architectural use.
AESS 4 makes extensive use of
welding for its connecƟons. In most
cases the weld is ground smooth
and any member-to-member
transiƟons are Įlled and made
extremely seamless in appearance.
This type of Įnish will result in
signiĮcant increases in fabricaƟon
cost, and so they are appropriate
for use in this sort of high-expo-
sure, upscale applicaƟon.
Such special members oŌen require
addiƟonal care in transportaƟon
and handling, as the maximum amount of work is normally carried out in the fabricaƟon shop to
maintain the highest quality of work performed in controlled condiƟons and with more access to
liŌing equipment to posiƟon the elements for Įnishing operaƟons. This type of AESS is oŌen also
painted in the fabricaƟon shop, again to achieve the best quality Įnish. ProtecƟon of these mem-
bers during transportaƟon and erecƟon is criƟcal in order to prevent undue damage to the Įnish.
It is common in some showcase
applicaƟons to see the use of stain-
less steel glazing support systems in
conjuncƟon with the use of AESS 4
regular carbon steel. Stainless steel
is being used frequently to connect
and support large glazing walls,
oŌen with quite innovaƟve custom
systems used to aƩach the spider
connecƟons to the steel. Such sys-
tems require even Įner tolerances
in order to achieve the proper Įt
between the structural members,
glazing systems and AESS. Extra
care in paint applicaƟon is required
to prevent overspill onto the adja-
cent stainless surfaces.
BCE Place in Toronto by Spanish Architect SanƟago Calatrava
uses AESS 4 quality fabricaƟon and Įnish on the lower porƟon of
the tree supports in the Galleria space. All of the members use
welded connecƟons with a hand-smooth Įnish and no apparent
blemishes. Given the arƟculaƟon and complicated geometry, tol-
erances for this structure were even less than one-half standard
fabricaƟon. The “canoes” that form the support for the skylight
are well above view level and use a combinaƟon of welding and
bolƟng.
Pearson InternaƟonal Airport in Toronto uses a combinaƟon
of AESS 4 for the columns and supports that are visible in the
pedestrian areas, and Custom for the “wishbones” that form the
supports for the roof trusses. The supports make use of more
standardized shapes where the “wishbones” require signiĮcantly
more eīort on the part of the fabricator in the creaƟon of spe-
cialty secƟons from plate steel.
The Newseum in Washington, D.C. by Polshek Partnership uses
a combinaƟon of AESS 4 quality steel with some custom specialty
elements in this invenƟve support system which forms the sup-
port and wind bracing for a large mullionless glazed wall at the
front of the building. Stainless steel brackets hook on to parallel
tension supports that are braced on either side of the façade by
these verƟcal trusses fabricated from parallel secƟons of plate
steel.
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35
34

more sculptural in nature. In some
instances the nature of the steel is
intended to be a highlight of the
Įnished project, and in other cases,
the nature of the steel is to be
concealed and the Įnal product to
look more “plasƟc” in nature. The
former may require less care and
the laƩer a higher degree of Įnish
and workmanship than would be
required even for structures in the
AESS 4 range.
The use of stainless structural steel
will also be addressed in this cat-
egory, as this material has diīerent
speciĮcaƟons and parƟcular issues
that must be included to ensure a
high quality of installaƟon.
Mixed Categories are to be expected on almost all projects. Generally no more than two
categories would be expected. It will be very common to specify, based on the viewing distance,
lower-level categories for roof/ceiling framing elements and higher-level categories for columns
and secƟons that are nearer to view and touch.
This will require that the Architect put a “cloud”
note around secƟons or members on their
contract drawings and clearly indicate the AESS
Category.
It is also possible to mix categories on individual
elements. This may be done for secƟons with
a side exposed to view/touch and a side that is
buried or otherwise hidden from view. In this
case a high-level of Įnish may be required on
the exposed AESS face, and a Įnish as low as
Standard Structural Steel on the hidden face.
This is of great Įnancial beneĮt when Įnishing
extremely large members. Again there should
be a “cloud” drawn around the member and the
speciĮc combinaƟon of categories noted. When
using the Categories to this level of detail, it is
also advantageous to be sure that this is clearly
and personally communicated to the fabricator
prior to bidding the job. The fabricator may have
some useful cost-saving suggesƟons which can
posiƟvely impact the overall project.
Heathrow Terminal 5 in London, England by Sir Richard Rogers
Architect uses a range of AESS Category types throughout the ter-
minal. These specialty connecƟons use a combinaƟon of custom
work for the central hinge, casƟngs to connect the ends of the
large HSS supports and truss members to the hinge, and show-
case level of fabricaƟon and Įnish for the legs/column supports.
You need to be Ňying BriƟsh Airways to come across this steel!
University of Guelph Science Building Courtyard uses special
casƟngs to cleanly join mechanical pipe and a structural tree
that stands in the centre of the courtyard. The requirement for a
seamless transiƟon from the pipe to the casƟng required unusual
welding and Įlling of the connecƟon, as well as grinding of the
surface of the casƟng so that its normal textured Įnish would
match the surface condiƟon of the adjacent pipe.
The Bow Encana, Calgary uses an AESS 4 Įnish on
the front two faces of this very large trianglular sec-
Ɵon in order to achieve a very straight edge along
the length of the member. As the rear face of the
member will be hidden from view, it is Įnished as
structural steel to save on fabricaƟon costs. These
members are shipped singly to prevent damage.
AESS C – Custom
Elements was created to allow
for a custom selecƟon of any of the
CharacterisƟcs or aƩributes used
to deĮne the other Categories. It
will allow Ňexibility in the design of
the steel but will therefore require
a high level of communicaƟon
among the architect, engineer and
fabricator. The premium for this
type of AESS could range from 20%
to 250% over regular steel. A wide
range may seem odd for “custom”
elements, but the lower bound
of this Category also includes
specialty reused steel for sustain-
able purposes, and steel that might
be purposefully less reĮned in its
CharacterisƟcs.
The Custom Elements checklist in
the Matrix will also allow design
teams, which may have become familiar with the new AESS speciĮcaƟon suite, to create their
own checklist for a project so as to beƩer reŇect the nature of the project’s aestheƟcs or func-
Ɵon. The Custom checklist also allows for the addiƟon of extra fabricaƟon criteria that must
be agreed upon among team members and used to achieve parƟcular or unusual Įnishes. This
category will be suitable where specialty casƟngs are used, as these require diīerent handling
and Įnishing than do standard steel secƟons due to their inherently diīerent surface Įnish as a
direct result of the casƟng process.
With increases in the reuse of steel
for sustainably-minded projects,
a unique set of criteria will come
into play. Requirements will center
around the presence of exisƟng
Įnishes, corrosion, inconsistencies
between members, and whether
the project needs to showcase the
reuse or blend the material with
new material. As some historic
steel is fastened with rivets, dif-
ferent treatment may be required
where new connecƟons are mixed
with old in order to create visual
coherence.
The Custom Category will also
provide the ability to create a
checklist for members that may be
Angus Technopole, Montreal is a unique reuse applicaƟon of
a former locomoƟve shop as oĸces and commercial space.
The riveted steel was leŌ “as is”, with minimal cleaning and no
repainƟng, to preserve the original look and feel of the building.
Where new steel is required in this project, a custom speciĮcaƟon
is required in order to make it Įt into the aestheƟcs of the old
building.
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CHARACTERISTICS OF THE MATRIX
A set of CharacterisƟcs is associated with each Category. Higher-level Categories include all of the
CharacterisƟcs of the preceding Categories, plus a more stringent set of addiƟonal requirements.
The CharacterisƟcs listed below form the basis for diīerenƟaƟon of the AESS Categories and are
listed in this order in the Matrix. It is suggested that, when using the suite of AESS documents, all
of the CharacterisƟcs associated with each of the Categories be included in the contractual ar-
rangements. For clarity, visual references in the form of steel samples (courtesy of the American
InsƟtute of Steel ConstrucƟon) have been included in the ensuing descripƟons. This Guide also
includes visual references in the built context to assist in clarifying the intenƟon of each bulleted
point.
AESS 1 – Basic Elements would be the Įrst step above Standard Structural Steel. AESS 1 fabri-
caƟon and erecƟon speciĮcaƟons would include CharacterisƟcs 1.1 to 1.5.
1.1 The surface preparaƟon of the steel must meet SSPC SP-6. Prior to blast cleaning, any
deposits of grease or oil are to be removed by solvent cleaning, SSPC SP-1.
Commercial blast cleaning is intended to remove all visible oil, grease, dust, mill scale, rust,
paint, oxides, corrosion products and other foreign maƩer, except for spots and discoloraƟons
that are part of the natural steel material. By using this as a starƟng point, there should not be
issues with the applicaƟon of the range of Įnishes that would be required for AESS 1 through 4
type applicaƟons, as these are normally out of immediate eye range due to their typically high
locaƟons.
CISC AESS Guide – 3 CharacterisƟcs - 18
3 CharacterisƟcs
It should be noted that one of the alternate surface preparaƟon standards, SP-3, commonly
used for structural steel elements, only provides for power tool type cleaning, and should not be
relied upon to provide adequate cleaning for consistent-looking Įnishes in AESS applicaƟons.
1.2 All of the sharp edges are to be ground smooth. Rough
surfaces are to be de-burred and ground smooth. Sharp edges
resulƟng from Ňame cuƫng, grinding and especially shearing are
to be soŌened.
Sharp edges, characterisƟc of standard structural steel, are
considered unacceptable in any AESS applicaƟon. Even if located
out of close viewing range, as in AESS 1 type applicaƟons, this
type of Įnish condiƟon is not adequate in the Įnal fabricaƟon
and installaƟon.
1.3 There should be a conƟnuous weld appearance for all
welds. The emphasis here is on the word “appearance”. Intermit-
tent welds can be made to look conƟnuous, either with addiƟon-
al welding, caulking or body Įller. For corrosive environments,
all joints should be seal welded. The seams of hollow structural
secƟons would be acceptable as produced.
In many projects fabricators are oŌen
asked to create conƟnuous welds when
they are structurally unnecessary. This
adds extra cost to the project and takes
addiƟonal Ɵme and may create distor-
Ɵons. If not structurally required, the
welds themselves need not be conƟnu-
ous. Prior to the applicaƟon of the Įnal
Įnish, appropriate caulking or Įller can
be applied between the intermiƩent
welds to complete the appearance.
Filling between the intermiƩent welds
also helps in the cleaner applicaƟon of
Fig. 1.1B As can be seen from the images above, shot blast cleaning can take what may appear to be rusted
steel, and transform it into a product that is smooth in Įnish and ready to receive subsequent treatments
and coaƟngs.
Fig. 1.2 Sharp Edges ground
smooth. (Courtesy of AISC)
Fig. 1.1A Sample sheet showing the Įnish appearance for steel surface preparaƟon standards. AESS starts
assuming SP-6 Įnish. (Image courtesy of Dry-Tec)
Fig. 1.3 Filling between the intermiƩent welds to give a
conƟnuous weld appearance
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Įnishes and prevents the buildup of dirt in the joints which can be problemaƟc to clean. Care
should be taken in the applicaƟon of Įll materials so that the surfaces beneath are clean, adher-
ence is ensured, and compounds are compaƟble with the type of Įnish applicaƟon.
1.4 It is assumed that bolted connecƟons will use standard structural bolts. When bolƟng,
the heads should all be located on one side of the connecƟon, but they need not be fasƟdiously
aligned. There should also be consistency from connecƟon to connecƟon.
This characterisƟc requires that some addiƟonal care be given when erecƟng the structure. It
is reasonable to expect that all of the bolt heads will be posiƟoned on the same side of a given
connecƟon and all such connecƟons will be treated in a similar manner, so that the look of the
overall structure is consistent. It is not reasonable to expect bolts to be Ɵghtened with the heads
idenƟcally aligned. The structural Ɵghtening of the bolts must take priority.
1.5 Weld splaƩers, slivers, surface disconƟnuiƟes are to be removed as these will mar the
surface, and it is likely that they will show through the Įnal coaƟng. Weld projecƟon up to 2 mm
is acceptable for buƩ and plug-welded joints.
This expectaƟon would hold for both procedures carried out in
the fabricaƟon shop prior to erecƟon as well as weld splaƩer and
surface conƟnuiƟes that might happen during or as a result of erec-
Ɵon. Such a case would follow the removal of temporary steel sup-
ports or shoring elements used to facilitate the erecƟon process.
When these elements are removed, the marred surfaces should be
properly repaired, and any oxidized surfaces repaired prior to Įnal
Įnish applicaƟons.
It was decided to include all weld splaƩer removal so as to avoid
potenƟal conŇict in deciding on the minimum diameter or intensity
of splaƩer to be removed.
AESS 2 – Feature Elements includes structures intended to be viewed at a distance > 6m.
AESS 2 includes CharacterisƟcs for AESS 1, and also CharacterisƟcs 2.1 to 2.4.
2.1 Visual Samples – This CharacterisƟc is noted as an opƟonal requirement for this and all
subsequent Categories due to issues of suitability, cost and scope.
Visual samples that might be used to validate the intenƟon of the Įnal installed product for
AESS can take a variety of forms. Visual samples could be a 3D rendering, a physical sample, a
Įrst-oī inspecƟon, a scaled mock-up or a full-scale mock-up, as speciĮed in contract documents.
Visual samples could range from small pieces of fabricaƟon which might include connecƟons or
Įnishes, to full-scale
components.
Not all projects would
beneĮt from the
construcƟon of large-
scale mock-ups, hence
making this Character-
isƟc opƟonal. In some
cases it is suggested
that an agreement to
incorporate full-scale
mock-ups in the Įnal
project would make
pracƟcal and eco-
nomic sense. Again this
decision would depend
on the parƟcular job
requirements. It is very
important to bear in mind the potenƟal for delay and addiƟonal costs when requiring physical
visual samples in the Ɵmeline of the project. If a fabricator is expected to create a large element,
this will delay the fabricaƟon of similar elements unƟl the approval is reached. There are costs
associated with the creaƟon of large physical mock-ups that must be integrated into the contract
price. For projects with very complex details that are essenƟal to deĮning the style and reading
of the architectural intenƟon, mock-ups can be essenƟal to the AESS project.
Fig. 1.4A Standard structur-
al bolt components include
the TC bolt.
Fig. 1.4C Standard structural bolts
are carefully aligned with nuts all
facing the same direcƟon.
Fig. 1.4B Standard struc-
tural bolt alignment will
vary for Ɵghtening.
Fig. 1.5 Natural splaƩer due
to the weld process is to be
removed.
Fig. 2.1A A digital mock-up was done for this connecƟon. It allowed the client
to understand how the detail would look. It was an eĸcient method that
did not slow down the process. The image above is part of the fabricator’s
detailing package. Fully rendered 3D models can also be used as a point of
clear communicaƟon between the parƟes, to speak more to the Įnal Įnish
appearance, including colour.
Fig. 2.1A A special physical mock-up was made for Pearson InternaƟonal Airport. Although minor modiĮ-
caƟons were made to the detailing for subsequent elements, it was incorporated into the project without
any issue.
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UlƟmately this would indicate that more of the
welds might be carried out in the fabricaƟon shop to
reduce site welding where the condiƟons may not
be opƟmum. This can impact the design of joints as
well as the transportaƟon of potenƟally larger pre-
assemblies and the erecƟon on site. This does not
infer that high quality site welding is not possible,
only that it might incur a cost premium over shop
welding.
AESS 3 – Feature Elements includes structures
that would be viewed at a distance ч 6m. This
increased proximity in viewing distance begins to
place the evidence of certain fabricaƟon processes
into close viewing range. Where some of the natural
evidence of the materiality and connecƟon methods
of steel might be acceptable at a greater viewing distance, the same might not be acceptable “up
close” where the Įnal product can be both viewed and touched. In many cases these markings
will need to be carefully posiƟoned so that they cannot be seen, removed, or concealed.
3.1 Mill marks are to be removed so as not to be visible in the Įnished product. Removal of
these marks would typically be accomplished by grinding.
3.2 BuƩ and plug welds are to be ground smooth and Įlled
to create a smooth surface Įnish. Caulking or body Įller is ac-
ceptable.
These kinds of welds can result in the presence of addiƟonal
material or slight depressions in the members. These imper-
fecƟons will be visible aŌer Įnishing. If addiƟonal material is
present, it should be ground smooth. If there are depressions,
the voids can be Įlled with body Įller and the surface ground
smooth prior to Įnish applicaƟons.
3.3 The normal weld seam
that is the product of creaƟng
HSS shapes is to be oriented
for reduced visibility. In general
the seams are to be oriented
away from view in a consistent manner from member to mem-
ber, or as indicated in the contract documents.
Welded seams are a natural Įnish appearance which is part of
the manufacturing process of HSS members. When choosing
HSS, this is important to bear in mind. A seamless Įnish is not
possible without signiĮcant added expense and Ɵme. There are
other opƟons to grinding the seams. The seams can be consis-
tently located to give a uniform appearance. If HSS seams can be
oriented away from direct view, this is an acceptable soluƟon.
2.2 One-half standard fabricaƟon tolerances,
as compared to the requirements for standard
structural steel in CSA S16, will be required for
this Category. This is to recognize the increased
importance of Įt when assembling these more
complex components.
Large tolerances can lead to a sloppier appear-
ance and lack of uniformity in the connecƟons
and, potenƟally, problems in the erecƟon of
complex geometries. This has a direct impact
on the erecƟon process and the potenƟal cost
implicaƟons of making site modiĮcaƟons to
members that do not Įt. This level of Įt is essen-
Ɵal for all structural members, plates, angles and
components comprising the project. In highly arƟculated projects there is no play in the erecƟon
of the connecƟons. CumulaƟve dimensional errors can be disastrous in the Įƫng of the Įnal ele-
ments of each erecƟon sequence.
2.3 FabricaƟon marks (number markings put on the members
during the fabricaƟon and erecƟon process) should not be
apparent, as the Įnal Įnish appearance is more criƟcal on these
feature elements.
There are diīerent ways of making these markings not appar-
ent. In some instances the marks could be leŌ “as is” but located
away from view. In other cases they may be lightly ground out.
They could also be Įlled prior to Įnishing. The treatment of
these might vary throughout the project as appropriate by mem-
ber and locaƟon.
2.4 The welds should be uniform and smooth, indicat-
ing a higher level of quality control in the welding pro-
cess. The quality of the weld appearance is more criƟcal
in AESS 2, as the viewing proximity is closer.
Quality welding is more stringent in AESS 2 categories
and higher. This is a key characterisƟc, and ensuring good
quality welds can save substanƟal cost in a project. If
welds are uniform and consistent in appearance, there
may be less need for grinding the weld. Too many welded
connecƟons are subjected to needless grinding, which
can add substanƟal increases to a project budget. Weld-
ing is a natural condiƟon of steel connecƟons and, if
neatly done, should be able to remain as part of the Įnal
product.
Fig. 2.2 One-half standard fabricaƟon tolerances
are required for all elements to be incorporated
into AESS 2 and higher.
Fig. 2.3 FabricaƟon marks not
apparent. (Courtesy of AISC)
Fig 2.4B Welds are plainly visible but of good,
uniform quality so complimentary to the
structure.
Fig. 2.4A The grinding of these welds
incurs a cost premium but is necessary
for the seamless look of the connecƟon.
This is not universally necessary, espe-
cially considering the viewing distance
of AESS 2 elements. This treatment
should be saved for AESS 4 Character-
isƟc 4.3 Surfaces Įlled and sanded,
where the elements are in close viewing
range and someƟmes can be touched.
Fig. 3.1 Mill marks removed.
(Courtesy of AISC)
Fig. 3.2 BuƩ and plug welds
ground smooth. Right side
shows groove weld ground
smooth. (Courtesy of AISC)
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3.6 AESS 3 Feature Elements may require all-welded connecƟons. This is noted as opƟonal;
acknowledging that a parƟcular aestheƟc might purposefully call for bolted connecƟons.
This will be addressed in greater detail in SecƟon 5, ConnecƟons, but much of the overall aes-
theƟc intenƟon of a project is held in the decision to use an all-welded structure over one that
either uses some or all bolted connecƟons. Welded connecƟons are easier to fabricate in the
shop. The erecƟon condiƟon on the site might require temporary shoring to hold the geometry
in place while welding is completed. There may be addiƟonal work to repair surfaces that have
been damaged due to the removal of temporary steel such as backing bars.
In some situaƟons, whether due to access constraints or issues of Ɵme, welded connecƟons
might not be possible. AlternaƟvely, if an enƟrely welded appearance is desired, hidden bolts
may be considered as an acceptable soluƟon (see Fig. 3.6A, where a bolted connecƟon is con-
cealed behind the cover plate). If this connecƟon is used in an exterior environment, care must
be taken to seal the joint to prevent water from becoming trapped.
If the seams are located in members whose viewing angles
are mulƟple, then greater care must be taken in detailing the
members to achieve a consistent look. If two HSS members
are joined (see Fig 3.3A), then ensure that the weld seams are
aligned.
3.4 Cross-secƟonal abuƫng surfaces are to be aligned. The
matching of abuƫng cross-secƟons shall be required. Oīsets
in alignment are considered to be unsightly in these sorts of
feature elements at a close range of view.
Part of this characterisƟc may be enhanced by ensuring
that the steel conforms to CharacterisƟc 2.2, half standard
tolerances, but this will not guarantee completely precise
alignment of abuƫng members - parƟcularly when using
“oī-the-shelf” structural secƟons that will have had liƩle
specialty fabricaƟon work done to them (see Fig. 3.4). There
may also be a need to shape or grind the surfaces at the point
of connecƟon to ensure that the surfaces are aligned. In some
lighƟng condiƟons, shadow casƟng may be more problemaƟc
than others. Where the inconsistencies are small, be sure to
incorporate advanced knowledge of the Įnal Įnish coat as it
may either help to conceal or exacerbate these slight misalign-
ments.
3.5 Joint gap tolerances are to be minimized. This Character-
isƟc is similar to 2.2 above. A clear distance of 3 mm between
abuƫng members required.
The use of bolted connecƟons is quite common in many AESS
applicaƟons. Bolted connecƟons may be advantageous for
erecƟon purposes or constructability, and might also suit the
aestheƟc of the project. In keeping with Ɵghter tolerances on
the members themselves, the reducƟon of joint gaps in bolted
connecƟons aids in ensuring consistency and Ɵghter design.
Fig. 3.4 This column splice is within touching range,
but the column Ňanges do not line up and the con-
necƟon plate seems too short.
Fig. 3.3A The natural weld seams
on these connecƟng HSS secƟons
may have been beƩer detailed if
they had been aligned.
Fig. 3.5A Joint gap minimized. The gaps on the leŌ
are standard structural steel, and on the right sized
for AESS. (Courtesy of AISC)
Fig. 3.5B This exposed bolted connecƟon is Ɵghtly
designed and demonstrates uniformity in the
joint gaps.
Fig. 3.3C Given the complexity of the structure
and the lighƟng condiƟons, the seams of the
round HSS secƟons are not apparent to view.
Fig. 3.6A Pictured is a cover plate over a hidden
bolted connecƟon. The appearance of a complete-
ly welded structure is kept, but erecƟon simpliĮed.
Fig. 3.3B The seams on the square
HSS secƟons have been aligned
and, even on the outside face of
the connecƟon, seem in keeping
with the overall design intenƟon.
Fig. 3.6B This design used all-welded connecƟons,
even for this anchoring detail of the truss to the
base plate. Bolted connecƟons were not desired.
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allow for shop fabricaƟon and minimizing site work. This brings in transportaƟon issues and site
access if the resultant members are very large. Also such pieces must be carefully handled and
stored on the site to prevent damage.
4.3 Steel surfaces are to be Įlled and sanded. Filling and sanding is intended to remove or
cover any steel surface imperfecƟons, again due to the close range of view of the members. This
parƟcular point can incur a high cost premium and is a parƟcular case in point that all AESS need
not be created equal. Procedures such as this are not required where the members cannot be
seen.
Great care must be taken to ensure that the Įlled and sanded surface is consistent with the
Įnished surface of the adjacent steel, or variaƟons will be revealed aŌer the Įnished coaƟng is
applied. Steel casƟngs for instance have a diīerent surface than adjacent HSS secƟons, so any
joining surface treatment must mediate the two Įnishes.
4.4 Weld show-through must be minimized. The markings on the back face of the welded ele-
ment caused by the welding process can be minimized by hand-grinding the backside of the weld.
The degree of weld-through is a funcƟon of weld size and material thickness.
AESS C – Custom Elements was
created to allow for a completely
custom selecƟon of any of the
characterisƟcs or aƩributes that
were used to deĮne the other
categories. It would allow complete
Ňexibility in the design of the steel,
but would therefore require a high
level of communicaƟon among the
architect, engineer and fabrica-
tor. The premium for this type of
AESS could range from 20% to
250% over standard steel. A wide
range may seem odd for custom
elements, but the lower bound of
AESS 4 – Showcase or Dominant Elements would be used where the designer intends the
form to be the only feature showing in an element. The technical nature of the steel is to be hid-
den or downplayed. All welds are ground and Įlled edges are ground square and true. All surfaces
are sanded and Įlled. Tolerances of these fabricated forms are more stringent, generally to half of
standard tolerances for structural steel. All of the surfaces would be “glove” smooth.
4.1 The normal weld seam in an HSS member should not be apparent. This may require grind-
ing of the weld seam.
If it is not possible to orient the natural weld seam in the HSS secƟons away from primary view,
or if the viewing angles to the structure are from all sides and it is criƟcal that the HSS appear
more plasƟc, then the seams may need to be ground and Įlled. In some instances where there
are numerous weld seams to conceal, it might be pracƟcal to choose mechanical pipe over round
HSS. Mechanical pipe has the advantage of normally being seamless but has a surface texture
more like an orange peel. It also has diīerent
physical properƟes and may require alternate
approaches when fabricaƟng details. In any case
a change in secƟons must be approved by the
structural engineer.
4.2 Welds are to be contoured and blended. In
addiƟon to a contoured and blended appear-
ance, welded transiƟons between members are
also required to be contoured and blended.
This type of detailing should be reserved for the
most parƟcular applicaƟons, those in very close
proximity for view and touch and those whose
form, Įt and Įnish require this type of seamless
appearance. Grinding and contouring welds is
Ɵme-consuming and thereby very expensive. It
is more easily done in the fabricaƟon shop, in a controlled environment and where the pieces
can be manipulated (by crane if necessary) so that the ironworkers can properly access the
details. In situ high quality welding might require the erecƟon of addiƟonal secure plaƞorms to
access the welded connecƟons, which adds expense to the project. Therefore part of the nego-
ƟaƟon for this type of detailing must begin by looking at maximizing the sizes of the pieces to
Fig. 4.4 Weld show through is minimized. The leŌ-hand images
show weld show-through from a connecƟon on the far side of the
plate. The right-hand image shows how it has been concealed.
(Courtesy of AISC)
Fig. 4.2A Welds contoured and blended. The
leŌ-hand sample shows typical structural welds.
The right-hand sample shows how they have been
welded and contoured. (Courtesy of AISC)
Fig. 4.2B It is easy to see that this detail relies on
a high level of Įnishing – including grinding and
contouring of the welds to achieve its form, Įt
and Įnish.
Fig. 4.3B Surfaces Įlled and sanded. These three examples show very diīerent applicaƟons of AESS 4
whose details require extra care and high-level consistency such that any and all imperfecƟons are Įlled
(typically with body Įller) and sanded prior to the applicaƟon of the Įnish coaƟng. It is parƟcularly impor-
tant in the leŌ and right images where a glossy Įnish is to be applied.
Fig. 4.1. This project uses mechanical pipe instead
of HSS, as the three-dimensional nature of the
structure made posiƟoning seams out of view dif-
Įcult, and a seamless appearance was important.
Grinding of the seams would have been prohibi-
Ɵvely expensive as well as Ɵme-consuming.
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this category also includes specialty reused steel for sustainable
purposes, and steel that might be purposefully less reĮned in its
characterisƟcs.
It is strongly recommended that the team sit down with the Matrix
and speciĮcaƟon documents in hand and manually go through
the list of characterisƟcs. As is illustrated by the range of projects
pictured, the complexity, size, level of Įnish and types of members
used can greatly vary in custom projects, leading to a wide varia-
Ɵon in the cost premium to be expected for this type of project.
The unusual areas of concern for AESS custom projects might
include:
• oversized members
• extraordinary geometries
• curved members
• accessibility issues
• unusual Įnish requirements
• high levels of grinding and Įlling for connecƟons
• transportaƟon problems associated with member size
• diĸcult handling or extra care needed to protect pre-painted
components
Working Outside of Canada
Projects located outside of Canada will bring their
own unique issues to the table. An even higher level
of communicaƟon and agreement will be required
when working with team members that may include
fabricators, erectors and ironworkers who may be
unfamiliar with the level of expectaƟon of AESS
projects in Canada.
There is a high level of similarity and communicaƟon
between Canadian and American systems, as well as
a large number of Canadian fabricators and erectors
accustomed to supplying steel to U.S. locaƟons.
Some countries that have made AESS a part of their
architectural tradiƟon for the past decades boast
highly skilled fabricators, erectors and ironworkers.
Others clearly do not. When working in distant loca-
Ɵons, cauƟon is urged. Request to see sample proj-
ects as a demonstraƟon of quality of workmanship.
Ensure that local or site personnel are quite familiar
with Canadian speciĮcaƟons and expectaƟons. In
many cases a cerƟĮcaƟon may be needed.
Seamless curved structures have their own
fabricaƟon and erecƟon concerns.
Very precise details require special fabricaƟon,
erecƟon and handling.
In this project the arƟst very
much wanted the rough
nature of the steel to show
through, so many aspects that
would normally be removed in
an AESS project were purpose-
fully retained to enhance the
understanding of the material-
ity of steel.
Complex geometry, odd angles and extremely
heavy elements add a cost premium to this proj-
ect. The level of form, Įt and Įnish on this project
is excepƟonally high. In the UK a high level of
tradiƟon of AESS has been established which has
resulted in a highly skilled labour force.
The scale and complexity of this welded project
meant high cost premiums and addiƟonal fabrica-
Ɵon and erecƟon Ɵme. The project was addiƟon-
ally complicated as a result of fabricaƟon and
erecƟon in China. There is far less AESS work that
is rouƟnely made a part of Chinese construcƟon,
so skilled labour can be an issue. The secƟons
were created using plates and, given varied light-
ing condiƟons, many of the welds were visible.
The overall aestheƟc of the project could accom-
modate this level of texture.
The Chinese NaƟonal Theatre uses large plate
steel members to create its trusses. These in turn
are braced by solid rods that use a half-sphere to
manipulate the curve of the connecƟon. The form,
Įt and Įnish on the project are very high. This was
undoubtedly the result of signiĮcant coordinaƟon
and close supervision of the work.
The quality of the ironwork, welding and Įnish on
this museum in inner China was extremely low.
The welds were sloppy. The intumescent coaƟng
appeared to have been applied when the project
was sƟll open to the weather, resulƟng in dirt
streaks down all of the members. In spite of the
overall creaƟve energy of the design of the build-
ing, the lack of care in workmanship due in part
to problems in communicaƟon, supervision and
understanding of the role of AESS undermined this
installaƟon.
83
81
80
79
78
75
76
77
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makes liƩle sense if these are to be coated with
a heavy material. Conversely, if an extremely
glossy Įnish is desired, this might lead to design
decisions that favour welded condiƟons over
bolted ones given the inference of clean lines.
Welded Versus Bolted Structures. Diīerent
coaƟngs, Įnishes, and types of texture of the
coaƟngs and Įnishes may be more or less ap-
propriate as a funcƟon of the tectonic expres-
sion of the structure. Much of the tectonic
character will be deĮned simply by the choice
to use welded or bolted connecƟons as the
main method of aƩachment for the structure.
Shop Versus Site PainƟng. It may be much
more expedient and desirable to pre-Įnish AESS
structures in the fabricaƟon shop. Controlled
condiƟons can lead to a beƩer Įnal product.
This is even more the case if the geometries are
highly complex or if there will be accessibility
issues in painƟng the structure on site. There
are situaƟons where the erecƟon of scaīolding
is prohibiƟvely expensive or strategically impos-
sible. If it is the intenƟon to pre-Įnish members,
then extra care will be required to transport
the elements to the site as well as during the
erecƟon process. Even with extraordinary care,
touch ups can be expected.
Cleaning and Maintenance. AESS installaƟons
might never look as good as on the day on
which the building was opened. Seldom consid-
ered in many projects are issues related to the
maintenance and cleaning of the structures.
White is a fashionable colour for AESS, yet
where it is installed in areas of high urban pol-
luƟon, it can age quickly. Certain steel shapes
can be more easily cleaned by high pressure
washing than others. Flat surfaces and ledges
can provide areas to collect debris. Both the
details and the durability of the coaƟngs must
take into account the urban menace presented
by pigeons. Their droppings are corrosive as
well as a nuisance.
GENERAL ISSUES
The Matrix and AESS SpeciĮcaƟons were intenƟonally designed to exclude coaƟngs as a param-
eter or characterisƟc. The issue of coaƟngs and Įnishes is a highly complex area of concern and
one that may override the decision-making process regardless of the AESS Category.
The selecƟon of coaƟngs and Įnishes for AESS work needs to be known at the outset of the proj-
ect. In many cases, the nature of the Įnish will begin to dictate the level of surface preparaƟon
required for the various elements of the structure as well as much of the fabricaƟon detailing.
The properƟes of diīerent coaƟngs can even begin to skew the decision-making process outlined
within each of the disƟnct categories of the Matrix.
Generally speaking, coaƟngs can be divided into two general categories:
• those that reveal or exacerbate the surface condiƟons and potenƟal imperfecƟons in the
steel (thin coat or glossy Įnishes), and
• those that conceal such surface condiƟons and potenƟally hide aspects of intended details
(thick coats and maƩe or moƩled Įnishes).
CoaƟngs will also be inŇuenced by interior or exterior locaƟons. This will include issues of
weathering, exposure to ice, snow and rain, as well as atmospheric polluƟon. Details will have to
be designed to drain, shed water, and coaƟngs chosen to prevent corrosion on both the exterior
and interior of members. If similar members are being used on the interior and exterior of the
project, consideraƟon must be given to a coaƟng selecƟon that will work with the details in both
places.
The selecƟon of the Įnish may be governed by Įre protecƟon concerns rather than aestheƟcs.
This would be the case with the choice to use intumescent coaƟngs over a regular painted Įn-
ish. Where some intumescent coaƟngs are fairly thin and allow details to show through, others
are by their nature quite thick. Spending project dollars on highly complex arƟculated details
CISC AESS Guide – 4 CoaƟngs and Finishes - 24
4 CoaƟngs and Finishes
The white painted Įnish on this exposed steel
exterior stair was not a good choice. Salt applied to
the treads has resulted in rust stains on both the
supporƟng steel and the concrete below.
The painted white structure at the TGV StaƟon at
Charles de Gaulle Airport in Paris has proven dif-
Įcult to keep clean. Access is not possible over the
full width of the staƟon, leading to severe buildup
of grime over part of the structure. The structure
is easily viewed from above, making the surface
condiƟon even more obvious.
Extreme care and highly specialized detailing was required to join the branches of this tree to the casƟng
nodes. Mechanical pipe was selected for its seamless appearance and structural properƟes. The surface
had to be perfect given the applicaƟon of a glossy painted Įnish and focus lighƟng.
84 85
87
86
Ledges provide an excellent roosƟng place for pi-
geons. Remember to install pigeon-deterring fences
and surfaces to prevent roosƟng and the associated
soiling of the structure and spaces below.
88

General Notes About PainƟng
Steel exposed to view is generally painted for appearance. A one-coat paint system, such as
performance speciĮcaƟon CISC/CPMA 1-73a, is suĸcient for standard warehouse structures
that will not be top coated (Standard Structural Steel and AESS 1). Since the building environ-
ment is controlled, no corrosion occurs once the building is enclosed. These buildings perform
adequately throughout the country. One-coat systems are referenced in Clause 28.7.3.3 of CSA
Standard S16-09.
Steel buildings require no paint when the steel is hidden behind drywall and suspended ceil-
ings. The humidity in such buildings is below the threshold limit for steel corrosion to occur
(Clause 6.6.2 of CSA Standard S16-09). Buildings that have excepƟonally high humidity, such as
swimming pools and water treatment plants, are excepƟons and should be treated as exterior
exposed steel.
Steel exposed to view that will be top-coated for
appearance (AESS 2 and above) requires a prime
coat for adhesion. A fast-dry primer, such as CISC/
CPMA 2-75, is suĸcient to provide the necessary
base. To ensure that this system will perform for
longer periods, a greater degree of cleanliness is
required by the speciĮcaƟon. Hence AESS requires
surface preparaƟon to a minimum SP-6. Consul-
tants must ensure that the Įnish coats are com-
paƟble with the primer. Each paint system oŌen
has its own primer. Alkyd primers are acceptable
but epoxy primers are not. Once the building is
enclosed, no corrosion occurs.
Structural steel that is exposed to view and the
elements on the exterior of buildings require
more thorough cleaning and Įnishing to ensure
long-term performance. Higher degrees of cleanliness along with beƩer quality mulƟ-coat paints
should be considered under these circumstances. Epoxy systems over compaƟble primers are
usually most suitable. Urethanes should be used when wear is a consideraƟon.
Tender documents should include the following informaƟon to ensure good quality coaƟng
systems:
• idenƟĮcaƟon of members to be painted
• a speciĮcaƟon for the degree of cleanliness required to ensure performance such as SSPC
Surface PreparaƟon Standards
• compaƟble primer, intermediate and Įnish paints and if applicable:
- the manufacturer’s product idenƟĮcaƟon
- the average dry Įlm thickness per coat
It is recommended to review the painƟng with a local fabricator or supplier to ensure that the
most suitable system is chosen for a speciĮc applicaƟon.
DETAILS
Surface PreparaƟon
Surface preparaƟon will be done in accordance with the chosen AESS category (1 through 4 or
Custom). Where there are diīerent AESS Categories used in the project, there may also be dif-
ferent surface preparaƟons and diīerent Įnishes required. In AESS applicaƟons, it is essenƟal to
apply the proper surface preparaƟon. If the surface is not adequately cleaned prior to the ap-
plicaƟon of the coaƟng system, the coaƟng system may fail or the surface deĮciencies will show
through.
Finishes for exterior steel structures will require special aƩenƟon to prevent corrosion. Paint will
not make up for design deĮciencies. Even the most sophisƟcated epoxy and vinyl paint coat-
ings cannot compensate for details that create opportuniƟes for corrosion to occur. The basic
selecƟon of member type and connecƟon detailing for exterior structures should ensure that
there are no places where water and debris can collect or puddle. With some care and aƩenƟon,
orientaƟon problems can be overcome. Beams and channels should be orientated with the webs
verƟcal so that water cannot collect and stand for any period of Ɵme. Exposed steel on which
moisture can collect should be detailed with a slope to ensure drainage. Drain holes can be
added if the secƟon cannot be orientated or sloped to drain.
When using hollow secƟons or composite members that create voids on exterior applicaƟons, it
is also necessary to prevent corrosion of the interior surfaces. Seal welds are oŌen speciĮed to
prevent the entrance of moisture or oxygen-laden air into the cavity. For architecturally exposed
steel that is to be painted, seal welds may be speciĮed to prevent unsightly rust bleeding.
Seal welds may be speciĮed on parts to be galvanized to prohibit pickling acids and/or liquid zinc
from entering into a speciĮc region during the galvanizing process; however, a closed volume
should never be galvanized as it will cause an explosion. Aired access should be provided for the
molten zinc to reach all surfaces and therefore avoid explosions. For HSS, it is beƩer simply to
provide drainage at the boƩom of the element to ensure that gasses do not get trapped. Proper
communicaƟon is important when deciding on the method of prevenƟon of moisture entry on
sealed joints. Seal welds can alter load paths and are prohibited in some structural situaƟons. It
might be beƩer to provide a vent space and also galvanize the interior of hollow secƟons. This
will increase costs but will potenƟally provide a
more durable exterior coaƟng.
Paint Systems
The selecƟon of the paint or coaƟng system
should be done at the outset of the project, as
both the colour and Įnish will impact detailing de-
cisions and, therefore, cost. If a high-gloss Įnish is
desired, it will reveal every minute imperfecƟon in
the steel. Flat Įnishes are more accommodaƟng.
Light-coloured paints will quickly reveal corrosion
and dirt. Thin Įnishes will reveal surface imperfec-
Ɵons. Thicker coaƟngs, such as intumescent Įre
protecƟon, can cover or conceal imperfecƟons as
well as Įne details.
This AESS structure is located in a parking struc-
ture in a dusty urban environment. The top of
the HSS tubes is covered with grime, and there
is evidence of dirt dripping to the underside of
the tubes.
90
This AESS structure has been sandblasted prior
to painƟng to arrive at this uniform textured
surface. The treatment helps to conceal potenƟal
fabricaƟon inconsistencies in this high-proĮle
structure.
89

The required thickness of the coaƟng is in turn de-
termined by the thickness of the structural steel
member. Thin or light members will require more
coats than heavier members. It is someƟmes
more cost-eīecƟve to increase the thickness of
the steel as it can decrease the number or thick-
ness of the intumescent coaƟngs – the increased
cost of steel being signiĮcantly less than the extra
cost to increase the thickness of the intumescent
material. Structural steel is inherently a more sus-
tainable material, so the reducƟon of the amount
of coaƟngs is preferable.
Intumescent Įre protecƟon applicaƟon is preced-
ed by the applicaƟon of an approved primer. Not
all primers can be used, so you must check with
the intumescent coaƟng supplier to determine an
acceptable primer. If the wrong primer is applied,
it will interfere with the successful applicaƟon of
the intumescent coaƟng system.
TradiƟonally, intumescent coaƟngs have been
applied on-site to steel structures during the con-
strucƟon phase of the building. In-shop applica-
Ɵon is a more common pracƟce as beƩer control
of applicaƟon condiƟons is possible. Shop applica-
Ɵons can provide for the controlled venƟng need-
ed for solvent-based systems. Shop condiƟons
can also provide more control of temperature and
relaƟve humidity, and hence beƩer drying. Con-
trolled drying in the shop means beƩer Įnish as
the coated steel secƟons cannot be moved unƟl
they are hard enough to resist damage. These
members must be more carefully handled during
transporaƟon and erecƟon as any damage must
be properly repaired in order to preserve the
integrity of the Įre protecƟon system.
Intumescent coaƟngs are either acrylic or epoxy-
based. Acrylic coaƟngs can be either water or
solvent-based, and they are Įeld-applied. The
water-based material is “greener” but takes some-
what longer to dry and is mostly used for interior
applicaƟons. The solvent-based coaƟng is more
robust and can also be used on the exterior.
Epoxy coaƟngs are normally shop-applied and
can be used on interior or exterior applicaƟons.
They are more durable than acrylic coaƟngs and
can also be used to provide corrosion protecƟon.
Shop Versus Site PainƟng
The painƟng of an AESS structure can take place in the fabricaƟon shop or on the site. Many
fabricators can oīer shop painƟng which can ensure a more consistent, higher quality Įnish.
Naturally it is expected that the paint Įnish will be free of drips and runs. Access to the installed
structure for paint applicaƟons can be a logisƟcal issue. Shop-applied paint Įnishes will likely
need to be touched up aŌer erecƟon, but this is less problemaƟc than the complete painƟng of
the structure on site which rarely occurs.
Pre-painted structures will require extra care and protecƟon during transportaƟon, handling
and erecƟon. Pre-painted structures will be more in need of “just in Ɵme” delivery to the site to
prevent site-generated damage. Pre-painted structures may also require beƩer staging areas on
site – again to prevent damage to the painted Įnishes.
Careful preparaƟon of the steel, including basic removal of sharp edges (CharacterisƟc 1.2), will
allow for a more even applicaƟon of the paint and beƩer coverage on the corners. The spray
applicaƟon of the product on sharp corners is diĸcult and, if these are not ground or rounded
oī, can lead to premature wear on the edges of the structure. In an exterior applicaƟon, this can
lead to corrosion.
Primers
The selecƟon of the primer will be a funcƟon of the choice of the Įnish coaƟng. Not all Įnish
coaƟng systems take the same base primer, so revisions in the Įnal Įnish type may require reme-
dial correcƟon of primers to ensure compaƟbility. Care in applicaƟon of the primer is important
as any drips and runs will show through both paint and intumescent coaƟng Įnishes. AddiƟon-
ally, not all Įnish systems require a primer. If not required, this can represent a cost and Ɵme
saving.
Intumescent CoaƟngs
Intumescent coaƟngs simultaneously provide a Įre resistance raƟng and a painted appearance
to exposed steel. They contain a resin system “pigmented” with various intumescent ingredi-
ents which, under the inŇuence of heat, react
together to produce an insulaƟng foam or “char”.
This char layer has low thermal conducƟvity as
well as a volume that is many Ɵmes that of the
original coaƟng. The char layer reduces the rate
of heaƟng experienced by the steel, extending its
structural capacity and allowing for safe evacua-
Ɵon. As this material can extend the Įre resis-
tance raƟng of exposed steel to a maximum of 2
hours, it has become quite popular for use with
AESS applicaƟons. The Įre resistance raƟng is in
part dependent on the type and thickness of the
coaƟng as well as on the type of Įre that might be
anƟcipated in the building use. Increasing the Įre
resistance raƟng is usually achieved by applying
mulƟple coaƟngs of the product.
Applying intumescent Įreproof coaƟng on a steel
structure
The intumescent coaƟng on the legs was shop-
applied. In spite of eīorts during transportaƟon
and erecƟon, many touch-ups were necessary.
The thick coaƟng is also quite vulnerable to
abuse at street level.
93
92
The intumescent coaƟng on this structure is quite
thick. The detailing used seems appropriate to
the level of detail that is revealed through the
coaƟng. The connecƟons are all welded. LiƩle
grinding was necessary as the seams are in part
hidden by the coaƟng. Bolted connecƟons would
have been unsuitable.
94
The intumescent coaƟng on this structure is quite
thick. Nonetheless, the weld seam on the HSS
column remains visible. Given the scale of the
project and the grinding of the weld between the
conical base of the column and the cylindrical
leg, it was deemed unnecessary to grind the
seam weld for this 27 metre-long member.
91

that would be unacceptable if a standard paint
Įnish were employed. If a very smooth high-gloss
Įnish is desired, this system requires addiƟonal
surface treatment.
Care should be taken when using thick coaƟngs
in high-traĸc areas or where they can be subject
to vandalism. The damaged intumescent coat-
ing must be properly repaired to maintain the
required Įre resistance raƟng. Colour matching
can also be an issue.
CemenƟƟous/Fibrous Fire ProtecƟon
Although not the usual case for AESS installaƟons,
cemenƟƟous or Įbrous Įre protecƟon might be used. This could be the case if the steel is lo-
cated at a distance from view or touch, as in the case of AESS Categories 1 or 2. If such a Įnish is
to be applied, there need not be the same level of surface preparaƟon required, and the Matrix
should be customized to remove characterisƟcs very early on in the scheduling of the project to
avoid wasted Ɵme and expense.
Galvanizing
Galvanized Įnishes are increasingly seen in AESS applicaƟons. It is important to remember that
in the view of the steel industry, galvanizing was not intended as a Įnish, but as a preventaƟve
measure against corrosion. The speckled grey Įnish is guaranteed to vary from batch to batch,
even from the same manufacturer. It will also vary as a funcƟon of the applicaƟon technique and
the style, size and shape of the member to which it is being applied.
Achieving a good quality coaƟng requires a surface that is free of grease, dirt and scale of the
iron or steel before galvanizing. When the clean steel component is dipped into the molten zinc
(approx. 450°C), a series of zinc-iron alloy layers are formed by a metallurgical reacƟon between
the iron and zinc. When the reacƟon between iron and zinc is complete, there is no demarcaƟon
between steel and zinc but a gradual transiƟon
through the series of alloy layers which provide
the metallurgical bond. This helps to make the
galvanized Įnish highly durable as it cannot easily
be chipped away. The thickness of the coaƟng is
determined by the thickness of the steel. The gal-
vanized coaƟng can be made thicker by roughen-
ing the steel, thereby creaƟng more surface area
for the metallurgical reacƟon to take place.
Galvanized coaƟngs protect steel in three ways:
1. The zinc weathers at a very slow rate, giving a
long and predictable life.
2. The coaƟng corrodes preferenƟally to pro-
vide sacriĮcial protecƟon to small areas of steel
exposed through drilling, cuƫng or accidental
damage.
Where access for Įnishing may be an issue, shop-applied
epoxy coaƟngs may oīer savings.
Water-based coaƟngs are typically applied when relaƟve
humidity is between 40% and 60%. Solvent-based coaƟngs
can be applied with relaƟve humidity up to 85%. If there is
concern about the presence of high VOCs on the project, a
water-based product can be used if the humidity levels are
kept low. It is important to allow the layers to dry thoroughly
between coaƟngs. Water-based products take longer to dry
where humidity levels are high and temperatures are low.
Solvent-based products can dry faster but can also strike
back to dissolve prior layers if insuĸcient drying Ɵme is
permiƩed between layers.
The intumescent coaƟng system can include a top coat.
This provides a hard protecƟve coaƟng to the product. It is
important to note that white or light colours will tend to yel-
low with Ɵme, so if colour matching is an issue, this should
be taken into account when mixing intumescent and painted
Įnishes in a project. If combining intumescent and regular paint-Įnished steel, note that exact
colour matches are not possible. The nature of the intumescent Įnish will alter the colour of
the coaƟng. It will be necessary to detail the structure to account for this slight change in hue or
tone. Without a top coat, intumescent coaƟng surfaces don’t clean as well as with a top coat and
will also show Įnger prints. Any porƟon of the structure at “hand” level should have a top coat
for ease of cleaning and maintenance and to prevent permanent blotching and stains.
AddiƟonally there are two types of intumescent coaƟngs: thin and thick systems. A thin coat-
ing is considered to exist for thicknesses from 0.5 to 6 mm, and a thick coaƟng for thicknesses up
to 13 mm. Because the wet Įlm needs to be relaƟvely thick, of several hundreds of microns ac-
cording to the parƟcular formulaƟon, intumescent coaƟngs are oŌen thick to avoid slumping and
runs while sƟll wet. Several coats may need to be applied to build up to a total dry coat thickness
in order to give the required Įre protecƟon.
Although these coaƟngs provide the appearance
of a painted Įnish, the texture is not the same.
Thin-coat intumescent systems will result in a
Įnish that resembles an orange peel. The thicker
system has enough substance to conceal some of
the Įner details that might go into the design of
the AESS connecƟons. If badly applied, a thick sys-
tem can give a very uneven, textured appearance.
Intumescent coaƟngs, although allowing exposed
steel use in an increased number of occupancies,
are not always deemed by architects to be the
best soluƟon as they can someƟmes result in a
thick-looking Įnish that can obscure some con-
necƟon details. The use of intumescent coaƟng
oŌen precludes the need for Įne Įnishing, as it
is thick enough to cover up surface imperfecƟons
The colour and texture of intumes-
cent coaƟngs are not the same as
normal paint, so it is necessary to
detail items like these columns to
recognize that the Įnishes are not
the same. Here a band of a diīerent
colour highlights the change.
As can be seen in this galvanized exposed steel
exterior shading system, a variety of Įnishes
can be seen on the diīerent hot dip galvanized
members. This is to be expected in this sort of
applicaƟon.
98
95
This thick intumescent coaƟng is constantly being
repaired due to its high traĸc locaƟon as well
as repeated incidences of graĸƟ removal. The
colour matching on some of the supports is more
diĸcult to achieve.
96
CemenƟƟous Įnishes can be commonly found on
exposed steel used in parking garages. While not
falling in a regular AESS category, care has been
taken here with the design of the support system
in the garage.
97

3. If the damaged area is larger, sacriĮcial protecƟon prevents sideways creep which can under-
mine coaƟngs.
No post-treatment of galvanized arƟcles is necessary. Paint or a powder coaƟng may be applied
for enhanced aestheƟcs or for addiƟonal protecƟon where the environment is extremely aggres-
sive.
The resistance of galvanizing to atmospheric corrosion depends on a protecƟve Įlm which forms
on the surface of the zinc. When the steel is liŌed from the galvanizing bath, the zinc has a clean,
bright, shiny surface. With Ɵme this changes to a dull grey paƟna as the surface reacts with
oxygen, water and carbon dioxide in the atmosphere. This forms a tough, stable, protecƟve layer
that is Ɵghtly bonded to the zinc. Contaminants in the atmosphere will aīect this protecƟve Įlm.
The presence of SO2 greatly aīects the atmospheric corrosion of zinc.
Complex shapes and most hollow items can be galvanized, inside and out, in one operaƟon.
Where AESS is being installed in an exterior environment, it is criƟcally important that all
surfaces be coated. For HSS members, this will mean coaƟng the interior of the shape as well –
increasing the surface area for coaƟng and potenƟally increasing the cost. Good member design
requires:
• means for the access and drainage of molten zinc
• means for escape of gases from internal compartments (venƟng)
It is important to bear in mind that the steelwork is immersed into and withdrawn from a bath of
molten zinc at about 450°C. This temperature can cause distorƟon in thinner steels. If the use of
the galvanized coaƟng is known early on during the design process, it may be decided to increase
the thickness of the steel to prevent distorƟon.
Any features which aid the access and drainage of molten zinc will improve the quality of the
coaƟng and reduce costs. With certain fabricaƟons, holes that are present for other purposes
may fulĮl the requirements for venƟng and draining; in other cases it may be necessary to pro-
vide extra holes for this purpose. For complete protecƟon, molten zinc must be allowed to Ňow
freely to all surfaces of a fabricaƟon. With hollow secƟons or where there are internal compart-
ments, galvanizing internal surfaces eliminates any danger of hidden corrosion during service.
From a design perspecƟve, it will be important to understand the physical limitaƟons of the
galvanizer’s facility. To be speciĮc, what is the size of the bath? It is not usual to dip pieces that
are 20 metres in length, but this limit must be veriĮed as it impacts member size. This limit on
the member size may result in the need for addiƟonal connecƟons. Double dipping is not an ef-
fecƟve soluƟon.
Metalizing
Metalizing is a subsƟtute for painƟng structural steel that protects steel for signiĮcantly longer
than paint alone. It is more expensive than galvanizing. Steel of every shape and size may be
metalized either in-shop before construcƟon or on-site instead as an alternaƟve to painƟng.
Metalizing is a very versaƟle and eīecƟve coaƟng for protecƟng steel structures that are to be
conƟnuously exposed to weathering.
The metalizing process begins with proper surface preparaƟon. Next, aluminum wire or zinc
wire is conƟnuously melted in an electric arc spray or gas Ňame spray gun. Clean, compressed
Seal welds have been used to connect the various
components of this exterior galvanized steel fea-
ture railing. There is a large opening at the base
of the square HSS post to allow any water that
may enter the railing an opportunity to drain.
99
Here galvanized steel members are mixed with
zinc painted grey steel. It was decided not to gal-
vanize some of the members due to the chance
of deformaƟon in the hot zinc bath and potenƟal
stress release of the welds.
100
101
The base connectors for these hybrid steel and
glulam Ɵmber members have been fabricated
from galvanized steel. The posiƟon of the connec-
tor in the building put it at greater risk of mois-
ture exposure, so painted steel was not desired.
Galvanizing is very popular as a Įnish, but remem-
ber that its basic purpose is as a corrosion-preven-
Ɵon coaƟng. The nature of the Įnish will not be
consistent from batch to batch.
One of the technical realiƟes of using galvanizing
as a Įnish lies in the inconsistency of the product.
The diīerence in this photo is due to Įnishing tem-
peratures. If galvanizing is used as a Įnal coaƟng
on an AESS project, diīerenƟals in Įnish must be
both understood and detailed into the project.
Galvanizing is a suitable Įnish for an exterior AESS
structure that will be constantly subjected to
weathering as in this expressive railing system.
104
103
102

in many climates does not consume a signiĮcant
amount of steel in its formaƟon. However, climate
is important – the oxide layer will form provided
there are wet/dry cycles.
Words of cauƟon: runoī of water from upper
porƟons of a structure tend to produce long-
lasƟng streaks or other paƩerns of redder oxide
on lower porƟons. Therefore, special aƩenƟon
must be paid to the drainage of storm water (or
condensate) to prevent staining of surrounding
structures, sidewalks, and other surfaces.
Weathering steel is also available in sheets, for
rooĮng and cladding. However, they were not
meant for architectural applicaƟons. Weather-
ing steel must be kept free from debris such as
leaves, pine needles, etc. These waste products
retard the wet/dry cycle necessary for weather-
ing steel, and corrosion is accelerated. Also, in an
accelerated environment, loss of material may be
more signiĮcant and could cause perforaƟon of
very thin sheets. In addiƟon, for green building
design, one should know that a thin weathering
steel roof has low solar reŇecƟvity, i.e. it is a “hot
roof”.
In terms of availability, few steel service centres
will stock a large inventory of weathering steel
because of its speciĮc bridge applicaƟon. How-
ever, they will order it from the mill on request
but usually for bridge applicaƟons. Unfortunately,
when steel is needed for an exterior wall element,
that usually represents low tonnage for a service
centre.
AŌer about two years, which is the Ɵme it takes to develop the oxide skin, the colour is going
to be much darker and reddish brown. As we are dealing with “living steel”, the colour will not
be consistent from project to project or even within a project. In weƩer climates the colour of
weathering steel will generally have an overall redder cast relaƟve to those exposed in drier
climates. However, one can be most certain that the Įnal colour will have a rich dark earthy tone
and will be low-maintenance, durable and beauƟful, provided one is careful about the details. If
it is desired to use weathering steel in an interior applicaƟon, it must be noted that the requisite
wet/dry cycles are absent and it will not age (very quickly). If desired it can be pre-aged outside
and then installed inside. Otherwise be prepared for the Įnal surface state to take many years to
develop.
Weathering steel is not readily available in W shapes and HSS from Canadian sources. It is not
appropriate for green roofs. However, it is low-maintenance; no paint is required, and properly
used verƟcally, it can add a disƟnct and green character to your project.
air strips droplets of molten metal from the wire,
deposiƟng these parƟcles onto the steel forming
the protecƟve coaƟng. This sprayed metal coaƟng
is both a barrier coaƟng and a galvanic coaƟng in
one. A single metalized coaƟng can protect steel
for 30 years or longer depending upon the ap-
plicaƟon, coaƟng thickness and sealing.
Metalizing is thought of as a cold process in that
the aluminum or zinc is deposited onto steel by
spraying rather than by dipping the steel into a
bath of molten zinc as with galvanizing. The steel
remains relaƟvely cool at about 120O-150OC. This
means that there is virtually no risk of heat distor-
Ɵon or weld damage by metalizing.
There are no VOC’s (volaƟle organic compounds)
in the metalized coaƟng. There is no cure Ɵme or
temperature to limit metalizing, so metalizing may
be applied throughout the year, virtually regard-
less of temperature.
There are three types of wire that are used to cre-
ate three speciĮc coaƟngs. Sprayed aluminum is
preferred for use in industrial environments, par-
Ɵcularly where there are high concentraƟons of
sulfur dioxide and other pollutants. Zinc provides
greater galvanic protecƟon than aluminum. Its
greater galvanic power protects gaps in the coat-
ing beƩer than pure aluminum. It is marginally
easier to spray pure zinc than pure aluminum by
some Ňame or arc spray systems. Zinc with 15%
aluminum wire combines the beneĮts of pure
zinc with the beneĮts of pure aluminum in the
metalized coaƟng. It is very oŌen used as a sub-
sƟtute for pure zinc because it is somewhat more
chloride and sulfur dioxide-resistant than pure
zinc, while retaining the greater electro-chemical
acƟvity of pure zinc.
Weathering Steel
Weathering steel has a unique characterisƟc such
that, under proper condiƟons, it oxidizes to form
a dense and Ɵghtly adhering barrier or paƟna
which seals out the atmosphere and retards fur-
ther corrosion. This is in contrast to other steels
that form a coarse, porous and Ňaky oxide which
allows the atmosphere to conƟnue penetraƟng
the steel. The oxidized layer on weathering steel
This garden wall is made from weathering steel.
Although durable in appearance, you can see
the destrucƟve markings on the surface made by
users of the space. It is essenƟal to detail these
types of installaƟons so that the run-oī water
does not stain surfaces below the wall.
This wall is made from weathering steel. The
Įnal colour of the steel will be slightly darker
than what is pictured here. The material must go
through a number of weƫng and drying cycles
for the coaƟng to cure. It is not possible to select
or carefully predict its Įnal hue.
Care must be taken in detailing weathering steel
to avoid having the natural oxidizing process cre-
ate stains on the surfaces below the material.
These welded steel secƟons may look like
weathering steel but they are actually fabricated
from regular carbon steel that is coated with an
applied “weathering steel Įnish”. Although con-
venient, it will not provide lasƟng protecƟon.
109
105
106
107
This weathering steel has been badly located as it
is staining the concrete wall below.
108

Weathering Steel Finish is a new coaƟng that is available for use. This is a shop- and Įeld-applied
Įnish that gives the appearance of weathering steel but does not create the same oxidized layer
as actual weathering steel. It is applied to standard structural steel materials. It provides a similar
looking Įnish and so might be useful where certain sizes, shapes and thickness of material are
not available. The coaƟng must also be applied to site welds to result in a uniform appearance.
This coaƟng does not produce rust runoī.
Stainless Steel
Stainless steel has the advantage of having its corrosion protecƟon quite integral to the struc-
tural member. It is an iron-based metal that has at least 10.5% chromium as well as quanƟƟes of
nickel, molybdenum and manganese that assist in resisƟng oxidaƟon. The chromium combines
with oxygen to create a barrier to the rust that would normally form due to the iron content. As
a result, it has a remarkable Įnish and requires far less ongoing maintenance than does regular
steel protected through methods of galvanizing, metalizing, or with painted or intumescent coat-
ings.
There are signiĮcant cost premiums for stainless steel as a material, and from a structural per-
specƟve it also requires a diīerent set of calculaƟons as its behaviour is very diīerent from regu-
lar mild carbon steel. Stainless steel has a very low carbon content. There are 50 diīerent grades
of stainless steel, of which Įve are most commonly used for structural applicaƟons. These vary
due to their alloy content. 304 is the most commonly used for exterior architectural applicaƟons,
being easy to form and fabricate and available in a variety of forms. 304L is a low-carbon version
of 304 and is speciĮed where higher corrosion resistance is needed as well as the welding of
heavy secƟons. 316 oīers heavy corrosion resistance and is used in harsh environments. 316L of-
fers extra corrosion resistance and heavy welding. 430 is a chromium ferriƟc material that is used
in interior applicaƟons. 305 and 410 are used for bolts, screws and fasteners.
Stainless steel is available in plate, wire, tubes, rods and bars. Extruded shapes are not common
but can be fabricated by special order.
Only stainless steel fasteners should be used to join stainless steel members. Other metals can
result in chemical reacƟons between the materials, which can lead to failure. Stainless steel is
also readily welded; however, the welding rods and techniques are quite diīerent from those
involving regular carbon steel. Stainless steel casƟngs can be fabricated to form connecƟons
between members.
Only dedicated tools must be used to cut and
Įnish the steel. Tools used with carbon steel will
embed small parƟcles of carbon steel in the stain-
less, causing rust spots to occur.
The fabricator chosen for creaƟng an AESS struc-
ture from stainless steel should be experienced in
the material.
5 ConnecƟons
ConnecƟon detailing must meet the end requirements of the AESS Category and also take into account
the cost, constructability, fabricaƟon and ease of erecƟon.
DETAILING REQUIREMENTS FOR AESS CONNECTIONS
General Issues
AESS structures, by their inherently exposed nature, put a greater than normal emphasis on con-
necƟon design. The detailing language of the connecƟons must feed into the overall aestheƟc
desired for the structure. ConnecƟon details must be constructable and within reason to erect.
Although the details normally used for AESS structures include some fairly standard connecƟon
methods, these are mostly modiĮed as a way of enhancing the architectural expression of the
structure, and by their nature are likely to present challenges for both fabricaƟon and erecƟon.
ConnecƟon types can be subdivided into structures that use shapes (such as W, C and
L-shapes), and those that use hollow secƟons. These typologies can be further subdivided into
the choice of predominantly welding or bolƟng the connecƟons. Plates can be worked into both
types of connecƟons. AESS connecƟons will oŌen incorporate specialty items such as rods and
tensile connectors.
In turn there are shop-fabricated connecƟons and site-erected connecƟons. As a general rule,
it is beƩer to maximize the number of connecƟons, parƟcularly welded connecƟons, that can
be done in the shop over those, usually bolted, that must be done on site. There is more quality
control in the shop. Jigs can be set up for repeƟƟve assemblies to ensure consistency in appear-
ance and Įnish. It is easier to turn and Įx the members into posiƟon for welding with crane as-
sistance. The applicaƟon of primer and even Įnish painƟng is more eĸciently done in the shop.
In the end, the maximum size of member that can be transported to site will oŌen determine
the scope of shop-fabricated connecƟons and the number and type that must be done on
site. Although it is possible to transport oversized pieces to the site with a police escort, it does
increase the cost of the project. Likewise, when the site is constricted and the staging area either
111 112
The Domes at Robson Square in Vancouver have
been fabricated from stainless steel tubular sec-
Ɵons.
110
CISC AESS Guide – 5 ConnecƟons - 30

The large “wishbone” secƟons used at Pearson
InternaƟonal Airport were special enough to
warrant a full scale mock-up. The size and cost of
the mock-up were such that it was made to be
incorporated into the project. Although there may
be slight diīerences in the Įnal design, these are
impercepƟble in situ.
3D modelled detail which can be used to verify
connecƟon details through a digital mock-up.
113
114
115
small or non-existent, pre-assembling the pieces on site on the ground might also not be pos-
sible. Most urban sites will require “just in Ɵme” delivery of steel pieces and carefully planned
erecƟon to make the best use of the staging area as well as preserve an area for staging that
might be required to the last moment of steel erecƟon.
Hidden or discrete connecƟons can be used where there are transportaƟon and erecƟon
limitaƟons. If a standard bolted connecƟon is unsaƟsfactory from an aestheƟc point of view, and
a welded site connecƟon is impracƟcal and expensive, alternaƟves can be provided. Large pieces
can be transported and erected eĸciently using bolted connecƟons that are hidden or made
discrete.
ConnecƟon Mock-Ups
The issue of mock-ups (CharacterisƟc 2.1 - Visual Samples) plays heavily into the design issues
related to connecƟons. Most architects would ideally like to be able to see and feel specialty
connecƟons before they commit to their mass fabricaƟon. This is not always possible or pracƟ-
cal due to issues of Ɵming and cost. The fabricaƟon of large specialty items is expensive and
Ɵme-consuming. Physical mock-ups can create delays, not only by their fabricaƟon but also by
requiring all parƟes to be present for approvals. Viewing distance also needs to be taken into
account when looking at a physical mock-up. Normally those present are examining the sample
at close range when in fact the in situ connecƟon may be many metres out of range of view and
touch. The AESS Category must be kept in mind when viewing physical samples. It may be pos-
sible to verify most of the appearance issues associated with the connecƟons and receive design
approval through the use of 3D drawings – a combinaƟon of those produced by the fabricator’s
detailing soŌware and the ones produced with 3D modeling soŌware. This approach can save
Ɵme and money. It may also be possible to reference a fabricator’s previous work to establish a
baseline for discussion when using digital references.
If 3D or other sorts of digital models are to be used as the basis of agreement for details, it is
important to discuss the Įner aspects of welding, bolƟng and Įnishing as these are likely not rep-
resented fully in the digital model.
A combinaƟon of smaller physical mock-ups of aspects of detailing and Įnish might be used to
accompany digital representaƟons to achieve a good level of communicaƟon about the expecta-
Ɵons of the project details.
Which Type of ConnecƟon Should I Choose?
The connecƟon type will be dependent on the structural requirements of the assemblies, the
shapes and types of steel members that are to be connected as well as the aestheƟc that is de-
sired. The type of connecƟon that is most appropriate for a project might not be clearly evident
from the outset. As previously menƟoned, there are many diīerent types of connecƟons, and it
may be necessary as well as desirable to use diīerent types in a project as are suited to the spe-
ciĮc range of requirements and AESS Categories (recognizing that viewing distances throughout a
project may vary). For overall clarity of the design, these diīerent connecƟons may use a similar
language and form a “family” of typical condiƟons.
As with any project, the overall structural consideraƟons – loads, clear spanning requirements
and support locaƟon – will form the starƟng point for the design. More pragmaƟc issues such
as the type of project, use of the space, exposure to weather and atmospheric grime and choice
Tubular members can be connected using very in-
venƟve means. This combinaƟon of plates allows
for constructability, minimal on-site welding and
enhanced interest in appearance.
116
This building uses extensive diagrids formed with
W-secƟons. These are very simply aƩached using
splice plates on both sides of the Ňange.
Varying approaches to bolƟng are used to achieve
the splicing of the W-secƟons and the joining of
the square HSS members to the truss.
117
118

of Įre protecƟon method will begin to inŇuence the choice of AESS Category. It makes liƩle
economic sense to invest in highly arƟculated details if the connecƟons are either out of view
or concealed in part by thicker intumescent coaƟngs. If there is signiĮcant dirt present in the
environment, or if cleaning and maintenance of the structure is diĸcult, it is best not to create
ledges that will collect dirt and surfaces that will highlight lack of maintenance.
TransportaƟon and access to the site will require breaking up the overall concept into smaller
elements that may be shipped as well as Įt into erecƟon limitaƟons on the site. The majority
of site connecƟons tend to be bolted. This does not preclude the use of welded connecƟons on
site. Site welding does mean addiƟonal costs to put temporary shoring or supporƟng pieces in
place while welding is carried out, and to remove and make good surfaces when these are no
longer required. It is also possible to suggest aestheƟcally pleasing bolted connecƟons.
Budget will also directly impact detailing. If the project can be broken into diīerent Categories of
AESS, then the more visible areas can be more expensively detailed. Refer to the Matrix for sug-
gested cost premiums for the AESS Categories, and discuss the same with your Fabricator.
Bolted ConnecƟons
Bolted connecƟons are normally chosen to achieve a more rugged aestheƟc for AESS or as a
result of erecƟon issues and constraints. Bolted connecƟons are oŌen chosen when using W, C
or L-shapes. The more industrial look of these secƟon types seems more aestheƟcally suited to
bolted connecƟons. OŌen the detailing used on these types of bolted AESS connecƟons is very
close to the connecƟons that would be used in standard structural steel. The organizaƟon and
alignment of members is likely to be either more careful or more creaƟve than is to be found in
standard structural steel.
When designing bolted connecƟons, aƩenƟon should be given to specifying the type of bolt to
be used (CharacterisƟc 1.4) as well as the consistency of the side on which the bolt head is to
be found. As the structural requirements of the bolted connecƟon dictate how far it needs to be
Ɵghtened, it is not reasonable to expect the rotaƟon of all heads to align.
Bolted connecƟons are also used with hollow structural members. The typical, pracƟcal HSS
connecƟon is to weld the intersecƟng HSS elements in the shop and create stubs with oversized
end plates to facilitate erecƟon. If these end plates are not aestheƟcally saƟsfying, cap plates and
plates slit into the HSS can be detailed to make the connecƟons more discrete. These details are
automaƟcally more expensive.
This can be seen in the connecƟons of square HSS members for the Canadian War Museum (Fig.
124). Two types of bolted connecƟons have been employed. One featured a set of overlapping
plates (at the X intersecƟon), and the other was designed to facilitate erecƟon using a more stan-
dard approach where the plates are welded to the ends of the HSS members and then bolted.
The aestheƟc of the space and the desire to mimic a twisted war-torn landscape inspired these
connecƟons.
Welded ConnecƟons
Shop-welded connecƟons are used on a high proporƟon of AESS structures. Welding gives a
clean, uncluƩered appearance. Welding is oŌen used on hollow structural shapes and less oŌen
for W, C or L-shapes. That is not to say that welding is not used with W-shapes. Both the NaƟonal
These square HSS members are connected both by
using overlapping splice plates as well as welded
end plates for ease of erecƟon.
124
Although the overall form of this box truss appears
complex, the 100% welded connecƟons have been
designed with simple geometries.
Space frame systems used to be rouƟnely used
to connect large nodes of HSS members. This has
given way to the use of all-welded connecƟons in
current AESS projects.
Good quality welding should require no special
aŌer-treatment (grinding) for the majority of AESS
applicaƟons (Categories 1 through 3). Grinding
would be considered only for Category 4 applica-
Ɵons if a seamless appearance is important.
Welded connecƟons have been used here in
conjuncƟon with the selecƟon of W-members to
create a very technical feel for the Works Yard.
122
120 123
121
The aestheƟc of this project included a high level
of texture using standard structural shapes, and so
bolƟng was chosen.
119

Complex connecƟons using square HSS members
are very diĸcult when it comes to alignment. Cir-
cular members are more forgiving. This connecƟon
is located on a high-level skylight, so the alignment
issue is not really visible.
It was important for the form, Įt and Įnish in this
building to have a seamless transiƟon between
these two HSS members, so a welded connecƟon
was used. All evidence of the joining of the two
members was concealed.
Modern equipment makes precision cuƫng of
these intersecƟng round HSS members much
simpler.
These tubular members were welded, using both
tube-to-tube connecƟons as well as X-shaped
plate fabricaƟons to resolve the geometry of the
transiƟon.
129
127
125
126
Works Yard (Fig. 120) and Art Gallery of Ontario (Fig. 101) incorporated welded connecƟons
within the larger porƟon of the shop-fabricated assembly, and bolted connecƟons for the site
work. In the SeaƩle Public Library (Fig. 117), bolted connecƟons are used for splices between the
larger shop-welded secƟons of the larger diagrid found in the building. In situ, these splices can
hardly be diīerenƟated from the larger welded expanses of steel.
Welded connecƟons present diīerent challenges for the fabricator as a funcƟon of the connec-
Ɵon geometry as it is combined with the choice of member. For complex geometries to be more
aīordable and for beƩer quality and alignment, it will be necessary to maximize the amount of
work that can be done in the fabricator’s plant so that proper jigs, liŌing and clamping devices
can be used to manipulate the materials. It will be necessary to understand transportaƟon
restricƟons when working through the details of these connecƟons. There will be a maximum
member size that will be able to clear bridge overpasses and road widths to avoid clearance
mishaps or frequent police escorts or road closures. Where highly arƟculated assemblies must
be broken into smaller elements due to transportaƟon and liŌing limitaƟons, it will be helpful
to discuss the details of these more signiĮcant site connecƟons with the fabricator if a totally
welded appearance is the desired end result. It is possible to create site connecƟons that give
the appearance of being welded but that are discretely bolted, with the Įnal connecƟon con-
cealed with cover plates.
When deciding upon the level of Įnish of a welded connecƟon, it is extremely important that the
viewing distance and AESS type and associated characterisƟcs be respected. One of the major
reasons for cost overruns in AESS has historically been the tendency of welded connecƟons to be
overworked. Welds are oŌen ground, Įlled or smoothed out unnecessarily. Welds are structural,
and overgrinding of welds can diminish their strength. Only in Custom or very high-end AESS 4
should grinding be considered as an opƟon for welded connecƟons. Except in the instance of
structural necessity, or for seal welding to prevent moisture entry, welding may not even need to
be conƟnuous.
Tubular Steel
Tubular steel – generally hollow structural secƟons or occasionally mechanical pipe – is oŌen
chosen when creaƟng AESS projects. In the case of HSS, the secƟon shapes can be square,
rectangular, round or ellipƟcal. Mechanical pipe is only produced round and cannot be used in
seismic applicaƟons. The choice of the member shape will have a tremendous impact on the de-
sign and appearance of the connecƟons. The geometry of the connecƟon – planar, simple angle
or mulƟ-member intersecƟon – will impact the cost and complexity of resolving mulƟple HSS
shapes. In some instances the joint can be resolved by cuƫng and welding. In other instances
plates may be needed to simplify the intersecƟon and erecƟon.
In general, HSS tends to be produced using a welding process, whereas pipe tends to be the re-
sult of an extrusion process. All HSS secƟons start out round and are formed to alternate shapes.
There will be a welded seam along the HSS, whereas in pipes the shape will be seamless. When
designing with HSS the AESS characterisƟcs require that you look at the orientaƟon of this weld
seam in the design. A welded seam will tend to be visible even aŌer grinding, depending on the
coaƟng process used, as one can only grind perpendicular to a surface. Although there is vari-
ance of Įnal texture in extruded shapes and on the coaƟng system used, the Įnal look is likely
to reŇect the iniƟal relief of the surface. As grinding may not completely conceal the weld seam,
even aŌer Įnish coaƟngs are applied, it is preferable (and less expensive) simply to orient this
The large HSS members used on this bridge have
helical welds. Although unusual in appearance,
they were aestheƟcally worked into the design.
128
A higher cost is the result of this level of complexity
for a welded connecƟon. The reveal detail of the
connecƟon of the upper structure to the column
makes the connecƟon simpler to erect.
130

natural occurrence consistently or away from the dominant angle of view.
The surface of a welded HSS tends to resemble that of a rolled shape, whereas a pipe may ex-
hibit a light texture akin to an orange peel. This textural diīerence may be signiĮcant if combin-
ing hollow secƟon types with other structural shapes in an AESS applicaƟon where a high level
of consistency of Įnish is desired. Pipe secƟons are rarely used and are considered a backup plan
for most applicaƟons.
There will be a variability in the availability of diīerent secƟon sizes, and it is not the same for
diīerent diameter ranges. Check with your local service centre for current availability. For large
quanƟƟes (i.e. over 50 to 70 tonnes) an order can be placed directly to the structural tubing mill.
HSS secƟons with a diameter greater than 400 mm generally require special ordering. Larger
diameter tubes (diameter > 500 mm) will be custom-manufactured and will require a minimum
100-tonne quanƟty when ordering unless they can be bundled with another job. As helical welds
are someƟmes proposed for large tubular secƟons, it is important to discuss this with your fab-
ricator and explicitly exclude these in your AESS speciĮcaƟon documents if they are not accept-
able.
Tapered tubes are not a regular manufactured product. They must be custom-fabricated from a
trapezoidal plate that is rolled to form a tapered pole and the seam welded.
Cast ConnecƟons
Cast connecƟons are being used increasingly in projects in Canada. The characterisƟcs of today’s
steel casƟngs have nothing to do with its earlier cousin: cast iron. Steel casƟngs are higher
strength, weldable and more ducƟle. You generally see casƟngs in conjuncƟon with cable and
glass structures, or in complex tubular joints for buildings or bridges. While they bring with them
the added advantage of handling complex, curved geometries without the diĸculƟes found
using mulƟple combinaƟons of tubes and plates, they do require a diīerent level of engineering
and tesƟng experƟse. Economy is found in the mass producƟon of the elements. One-oī casƟngs
or small runs can be very expensive.
For casƟngs to work, a reason is needed. Is there repeƟƟon (so the cost of making the mould
is partly amorƟzed – a must)? Are there many elements coming to one point? Do you want to
use casƟngs in a high-stress zone? Is there a foundry in your area that has the experƟse? Would
casƟngs provide aestheƟc advantages? If the answer is yes for at least 3 of these quesƟons, then
maybe these are appropriate for your project. A rough rule of thumb is that, if the connecƟon
starts to cost four Ɵmes as much as the material it is made of, then steel casƟngs start to be
economical.
A cast member has a diīerent Įnish. This is due to the manufacturing process and a funcƟon of
the material that creates the form for the casƟng. For example if a sand casƟng is used, the sur-
face texture of the Įnished steel will have a rough sand-like appearance. Special Įnishing will be
required if a seamless Įnal appearance is sought between the casƟng and the adjacent tubular
member. For higher levels of AESS categories, this can mean signiĮcant grinding and Įlling to
smooth out the rougher Įnish of the casƟng, or remove casƟng mill marks.
CasƟngs can be formed hollow or solid. Solid casƟngs are usually found in smaller connectors
like the ones used to form the terminus of tension rod-type structures. Hollow casƟngs are used
for larger members, as it would be diĸcult to achieve uniform cooling with solid casƟngs and
All of the primary connecƟons on this project are
fabricated from cast steel.
These complex connecƟons made appropriate use
of casƟngs to resolve complex geometries cleanly.
A large steel casƟng was used in this tree-like
structure to join several mechanical pipe secƟons.
The joints were Įlled and sanded to conceal them.
CasƟngs used as tension anchors can vary greatly
in size, from these pictured here to much smaller
ones used to aƩach rods for stayed structures.
134
135
136133
131
This is a cast connector that would form the end
condiƟon of a round HSS secƟon or pipe. You can
see the “orange peel” like Įnish of the raw casƟng.
132
Custom casƟngs are used to connect the Ɵmber
columns to the concrete foundaƟons.

CISC AESS Guide – 6 Curves and Cuts - 35
also more expensive. Non-uniform cooling
can create internal stresses. Non-destrucƟve
evaluaƟon of each casƟng, including 100%
ultrasonic tesƟng, should be considered as a
minimum. When selecƟng a caster, be sure
that appropriate tesƟng will be performed.
Large specialty casƟngs require speciĮc test-
ing to ensure that they are properly designed
and capable of resisƟng stresses. Cast steel
exhibits isotropic properƟes, making it quite
suitable for transferring forces through the
connecƟons in a reliable manner, so as to
resist shear, moment and torsional stresses.
It accomplishes this by working the geometry
as a funcƟon of variaƟons in the wall thick-
ness, independently of the Įnished form of
the exterior. Unlike fabricaƟons made from
tubes or plates, the interior dimensions of
the void in a casƟng do not have to match the
exterior form of the object.
Solid casƟngs are being eīecƟvely used in
seismic installaƟons.
References
• “Convenient ConnecƟons”, Carlos de Oliveira
and Tabitha SƟne, Modern Steel ConstrucƟon,
AISC, July 2008
• “Branching Out”, Terri Meyer Boake, Modern
Steel ConstrucƟon, AISC, July 2008
DESIGNING FOR CURVES AND COMPLEX CUTS
Modern bending equipment, plasma cuƩers and CNC equipment allow for a wide range of
interesƟng variaƟons in AESS projects. As much of this work is highly equipment-dependent, and
such equipment is very costly, it is a good idea to verify the capabiliƟes of fabricators that might
be bidding the job to ensure that their shop can handle the work on site, or that they can make
arrangements to sub out work that they cannot handle.
Bending
Bending steel is a specialty subset of fabricaƟon and is becoming increasingly popular in AESS
work. Most steel fabricators do not own bending equipment and will subcontract this work out.
Bending steel requires specialized equipment. There are also limits on the Ɵghtness of the radius
that steel can be bent to as a funcƟon of:
• the diameter or overall secƟon dimensions of the steel
• the thickness of the steel
• the type of secƟon
• the direcƟon of the bending (perpendicular or parallel to its weak axis)
In general terms, “easy way” is bending the steel around its weak axis and “hard way” is bending
the steel around its strong axis.
If bending Ɵghter than the advised Ɵghtness of radius, deformaƟon or distorƟon will occur. If the
deformaƟon is small enough, and the steel is AESS 3 or 4, out-of-plane surfaces may be Įlled and
sanded prior to painƟng to hide the defects. If the distorƟon is small and the steel is AESS 1 or 2,
viewed at a greater distance, there may not be any need for correcƟve work.
It is preferable if the bent steel member can be designed to be conƟnuous. If splicing needs to
occur to achieve a longer piece, or to join two secƟons of a complex project together, it is next to
impossible to ensure that the pieces will align properly due to the natural distorƟon of the steel
shape during the bending process. This is more easily done using W secƟons, but very diĸcult
when designing with HSS shapes or pipe. It is important to be realisƟc about the expectaƟons of
the connected pieces. ConnecƟon styles may be considered that do not aƩempt to create the
impression of Ňawless conƟnuity.
A certain length of steel is lost to the bending process. The lengths of the member clamped at
either end in the equipment are not bent. Extra steel will need to be purchased for each piece to
ensure that the lengths delivered to site are long enough.
Reference
• “What Engineers Should Know About Bending Steel”, Todd Alwood, Modern Steel ConstrucƟon, AISC,
May 2006.
6 Curves and Cuts
The high proĮle and very exposed nature of the
round bent steel tubes that support this pedestrian
bridge meant extra care in bending, splicing and
erecƟng the structure.
Although steel can be curved to very Ɵght radii, it
makes a diīerence if the steel shape is to be bent
“the hard way” or “the easy way”. It will depend on
the depth of the secƟon and the curvature. If curves
are very Ɵght, some deformaƟon is likely to occur.
It is best to check with the fabricator early on in the
design process when specifying curved steel.
137
138
Steel bending is done at a special facility. The equip-
ment and dies slowly push the steel into the desired
curve aŌer several passes through the machine.
139

EllipƟcal Tubes
EllipƟcal tubes are relaƟvely new to the AESS
scene. Their use started in Europe and is mak-
ing its way into North American architecture.
EHS have greater bending capacity than circu-
lar hollow secƟons of the same area or weight,
due to their strong and weak axis direcƟons,
but sƟll maintain a smooth closed shape. There
is also reduced visual intrusion compared to
regular circular HSS, if the member is viewed
from one predominant direcƟon.
All EHS are produced, with major-to-minor
axis dimensions of 2:1, as hot-Įnished hollow
structurals. They are produced as conƟnuously
welded secƟons, joined by high-frequency
inducƟon welding and Įnished to their
Įnal shape at extremely high (normalizing)
temperatures, with the outside weld bead
removed but the inside weld bead typically leŌ
in place. Due to the hot Įnishing process, EHS
have a Įne grain structure, uniform mechani-
cal properƟes, excellent weldability, negligible
residual stress, are suitable for hot-dip galva-
nizing and are applicable to dynamic loading
situaƟons. EllipƟcal tubes have similar material
properƟes to regular HSS members, and similar
connecƟon methods can be used in their con-
necƟon detailing. They are oŌen used in front
of glazing, as their shape is less obtrusive and
blocks less of the view and light coming into
the space.
References
• “Going EllipƟcal”, Jeī Packer, Modern Steel
ContrucƟon, AISC, March 2008
• “EllipƟcal Hollow SecƟons – Three-Part Series,
Part One: ProperƟes And ApplicaƟons “, Jeī
Packer, Advantage Steel No. 35, CISC, Fall 2009
• “EllipƟcal SecƟons – Three-Part Series, Part Three:
EHS ConnecƟon Design”, Jeī Packer, Advantage
Steel No. 37, CISC, Summer 2010
SPECIALIZED EQUIPMENT
When steel enters the fabricaƟon shop, it is normally iniƟally sized by sawing. New specialized
equipment, oŌen using roboƟcs to control welding, cuƫng, drilling and punching, are addiƟon-
ally used to alter the steel. This specialized equipment allows for a very high level of precision
when fabricaƟng complex geometries. When examining bids for any job that might require the
use of such equipment, it will be necessary to determine the shop capabiliƟes of the fabricators
bidding the job. Such equipment is very expensive. The use of such specialty equipment may en-
able increased fabricaƟon speed and the inclusion of Įne details but is likely to incur an increase
in cost to the project. It is common for fabricators to sub out work to another shop that may own
such equipment.
Shearing
Shearing, also known as die cuƫng, is a metalworking process which cuts stock without the
formaƟon of chips or the use of burning or melƟng. If the cuƫng blades are straight the process
is called shearing; if the cuƫng blades are curved then they are shearing-type operaƟons. Sheet
metal or plates as well as steel rods are com-
monly cut by shearing. The edges of sheared
steel are typically sharp and will require Įnish-
ing when used in AESS applicaƟons.
CNC Cuƫng
A “Computer Numerical Controlled” device
can be used to facilitate more complicated
or repeƟƟve cuƫng. The full potenƟal of the
device can only be realized if taking its instruc-
Ɵons from CAD/CAM soŌware. A CNC method
can be used in conjuncƟon with a number of
diīerent steel-cuƫng methods. These include
torch cuƫng, rouƟng, plasma cuƫng, water
jet cuƫng and laser cuƫng. It can also be used
to control hole drilling. CNC processes have
become very commonly used in steel fabrica-
Ɵon shops, parƟcularly in AESS work.
Plasma Cuƫng
Plasma is a gas in which a certain percentage of
parƟcles is ionized. Plasma cuƫng is a process
for cuƫng steel of diīerent thicknesses using
a plasma torch. In this process, an inert gas (in
some units, compressed air) is blown at high
speed out of a nozzle; at the same Ɵme an
electrical arc is formed through that gas from
the nozzle to the surface being cut, turning
some of that gas to plasma. The plasma is suf-
Įciently hot to melt the metal being cut and
The curved steel W-secƟons in this exposed installa-
Ɵon are joined with moment-resisƟng connecƟons.
The overall aestheƟc is rougher, and with the steel
located at a high ceiling level, the Įnish require-
ments would be less than for curved steel located at
a more easily viewed level using welded connecƟons
and HSS members.
EllipƟcal tubes are a new product that is seeing in-
creasing use. These tubes are used to support a high
curtain wall in an airport. The weld seam is located
on the top of the member as the predominant view-
ing angle is from below.
This curved secƟon is distorted at its splice, making
a smooth welded connecƟon diĸcult to achieve.
142
143
141
The minimum bending radius permiƩed will depend
on the secƟon type and its orientaƟon.
Angle Rings Heel Up
Angle Rings Leg Out
Angle Rings Leg In
Channel Rings
Flanges In
Channel Rings
Flanges Out
Beam Rings
The Hard Way
Beam Rings
The Easy Way
Channel Rings
The Hard Way
140

moves suĸciently fast to blow molten metal away from the cut. Plasma cuƫng is eīecƟve for
material no greater than 50 mm.
Torch or Flame Cuƫng
Torch cuƫng is also called oxy-fuel cuƫng. This process uses fuel gases and oxygen to cut the
steel. In oxy-fuel cuƫng, a cuƫng torch heats metal to kindling temperature. A stream of oxygen
is trained on the metal, and metal burns in that oxygen and then Ňows out of the cut as an
oxide slag. Oxy-acetylene can only cut low- to medium-carbon steels and wrought iron. Since
the melted metal Ňows out of the workpiece, there must be room on the opposite side of the
workpiece for the spray to exit. This type of torch can be part of a large roboƟc device or a small
portable handheld device.
The way that steel is cut will inŇuence the level of detail as well as the amount of remediaƟon
required. Most cuƫng today is performed using CNC control although manual cuƫng can sƟll
be done. Manual cuƫng requires more clean-up depending on the skill of the operator and the
level of AESS expected.
Thickness limits:
• Plasma cuƫng: The thickness of steel with this method is typically ¼” to 1-¼” (6 to 30 mm).
• Oxy-fuel cuƫng: This is the most common method and the thickness of material is unlimited.
• Water jet cuƫng: This method is less common and the limits on steel thickness are not
known.
• Laser Cuƫng: This method is used on material in the range of 1/16” up to a pracƟcal limit of
¾” (1.5 to 20 mm).
For excepƟonally thick steel, in the range of 150 mm or greater, oxy-fuel cuƫng would normally
be used. Plasma and oxy-fuel require moderate to heavy amounts of grinding if all cuƫng marks
are to be eliminated from the plate edges. Laser and water-jet cut edges require minimal grind-
ing. Any cut perpendicular to the material can be accomplished using CNC; however, plasma and
oxy-fuel have limitaƟons on width-to-thickness raƟos of cuts. For example, you cannot pracƟ-
cally oxy-fuel cut a hole with a diameter smaller than the thickness as this will result in too much
melƟng and poor quality.
Hole Punching and Drilling
Modern equipment has greatly improved hole punching and drilling, allowing for the high level
of precision that is required in complex AESS structures. It is essenƟal that the steel used in the
project meet the half-standard tolerance characterisƟc of precision drilling in order to be of
ulƟmate beneĮt to the project. Hole drilling can be done in conjuncƟon with CNC equipment
for greater precision and speed. For the cleanest results in hole punching, the plate thickness
should be no greater than 1” (25 mm). The correct size relaƟonship between the punch and the
die hole will produce a cleaner top edge, straighter hole and minimum burr on the boƩom edge.
The hole size should be no greater than the plate thickness plus 1/16” (1.5 mm) to the maximum
of 1” (25 mm).
Although very complex shapes are possible using modern equipment, this does come at some
cost to the project. It is good to remember that holes, circles and lines can be used in combina-
Ɵon to make clean cut-outs which do not require the extra expense of specialized equipment.
Plasma cuƩers can facilitate the cuƫng of more
complex shapes.
Plasma cuƩers combined with CNC equipment can
achieve a very Įne level of detail.
Modern hole-drilling equipment is clean, quick and
precise.
144
145
146
Several kinds of cuts are required to connect
this plate to the HSS member to create a pin
connecƟon.
Grinding is done by hand to remove or smooth out
the Įnish where operaƟons must be concealed. This
adds signiĮcantly to the Ɵme and, therefore, cost of
the fabricaƟon.
Automated torch cuƫng of a piece of steel plate.
If torch cuƫng is used on AESS material, the
edges will need treatment to make them smooth
for even-Įnish applicaƟons.
148
149
147
The drilling of holes is an automated process.
This ensures that holes are drilled with very even
spacing on each member.
150

CISC AESS Guide – 7 ErecƟon ConsideraƟons - 38
restricƟve, but also care had to be taken to
preserve the integrity of the intumescent coat-
ing during handling and erecƟon. A custom
set of supports (blue) was constructed to
hold the members in place unƟl proper lateral
bracing could be provided. The Įnish had to
be touched up intermiƩently throughout the
construcƟon process due to unavoidable nicks
and scratches, the result of rouƟne construc-
Ɵon processes – processes that would not
cause extra expense on a more rouƟne use of
structural steel.
Site Constraints
It is not uncommon for sub-assembly to occur
on site in the staging area for oversized or
geometrically complex members. The size of
the staging area will Įgure into design deci-
sions that will aīect the types of connecƟons
that are employed in aggregaƟng very large
members. Where quality welding can be easily
carried out in the shop, such will not be as
easy in the staging area without beneĮt of jigs.
If an all-welded appearance is desired, the de-
sign may need to make use of invenƟve hidden
bolted connecƟons to simplify erecƟon.
Constricted sites are common in dense urban
areas. Lane closures may be required on front-
ing streets to provide for staging and erecƟon,
parƟcularly when building to the lot line.
Care in Handling
AESS requires more care in handling to avoid
damage to the members. Oddly shaped or
eccentric members can easily be distorted
or bent if improperly handled. Many of the
members that come to the site might also be
pre-Įnished (paint, galvanizing or intumescent
coaƟngs), so padded slings will be required to
avoid marking the Įnish coat.
The more precisely fabricated the pieces, the
less force will be required to Įt them during
erecƟon.
OŌen steel will be shipped with temporary
supports, backing bars or bridging aƩached to
7 ErecƟon ConsideraƟons
HANDLING THE STEEL
TransportaƟon Issues
As quality of Įnish and precision of installa-
Ɵon are paramount with AESS, it is necessary
to maximize the amount of fabricaƟon and
painƟng that can be carried out in the fabrica-
tor’s shop. This may mean that members can
become increasingly large and diĸcult to
transport. It will be essenƟal for the fabricator
to map the clearances from the shop to the
site to ensure that the pieces will Įt for easy
transport, including turning radii for narrow
streets. It is obviously beƩer (and less expen-
sive) to avoid requiring an escort or street
closures. The standard limit for size would be
to ship on a Ňatbed trailer.
To prevent damage, members may have to be
shipped separately rather than maximizing the
allowable tonnage per trailer. More delicate
members may require the use of temporary
steel bracing to prevent distorƟon from road
movement, oī-loading and subsequent liŌing.
Sequencing of LiŌs
Just-in-Ɵme delivery is needed to ensure
proper sequencing and avoid damaging the
pieces. Many sites are constricted and have
insuĸcient staging area to provide holding for
the steel. The erector will arrange liŌ sequenc-
es to minimize the amount of steel that is on
the site at any Ɵme.
ConstrucƟon sequencing for architecturally
exposed steel members places further limita-
Ɵons on detailing and increases the challenge
of erecƟon. The 90-foot-long steel columns
that support the upper structure of the addi-
Ɵon to the Ontario College of Art and Design
were pre-Įnished at the fabricaƟon shop with
a coloured Įre-resistant intumescent coat-
ing. Not only was the street access extremely
These pieces were so long that they could not Įt on
a normal trailer bed but were ĮƩed with separate
wheels on the back. This conĮguraƟon also allowed
for these extra long members to navigate around
diĸcult corners.
153
A temporary piece of steel joins the two points to
stabilize the piece during shipping and erecƟon.
152
The erecƟon that took place at this end of the build-
ing was extremely challenging as the crane operator
was below the pieces he was erecƟng, and the small
staging area was bordered by hydro wires. With such
a small staging area and the complex geometry, it is
not uncommon to require more than one aƩempt to
Įt a piece.
154
Only one piece of steel will be shipped on this truck
to prevent damage to the piece.
151
The blue frames are temporary supports that were
constructed to shore up the sloped columns precise-
ly, using padded support points so as not to damage
the intumescent shop-applied coaƟng.
156
There was virtually no staging area at this busy
downtown intersecƟon, so the liŌs all had to take
place quickly at night. Hidden bolts were used on this
seemingly all-welded structure to facilitate erecƟon.
155

prevent deformaƟon during shipping and erecƟon. These supports are removed aŌer the steel is
liŌed into place and the weld marks removed prior to the applicaƟon of Įnishes.
ErecƟon Issues
ErecƟng AESS will vary with the complexity of the project. If the steel members have been
accurately constructed with no less than half the standard tolerances, Įƫng issues should be
minimized but may not be eliminated.
With odd geometries and asymmetry of members, the liŌing points will need to be more care-
fully pre-calculated. Standard structural steel elements tend to be more regular, with verƟcal
columns and horizontal, relaƟvely uniform beams. The liŌing points are predictable and make
assembly on site rouƟne and quick. With diagonal or unbalanced members, gravity will not be of
assistance and liŌing points may require more calculaƟon than normal. There may be erecƟon
delays in projects where each element is unique, as each will present a diīerent challenge to be
solved that may have no precedent. It is not unreasonable for some members to require more
than one aƩempt due to alignment or geometry issues. There can be holes or small aƩachments
to the steel strictly to facilitate erecƟon. Care must be taken to minimize and remove these ele-
ments.
Where steel is pre-Įnished, extra care must be taken during erecƟon so as not to damage the Įn-
ish. In some cases padded slings will be used in conjuncƟon with regular liŌing chains to prevent
damage to Įnishes. This might also be done with primed steel where a high-gloss Įnish is anƟci-
pated, again to prevent damage to the surface of the steel.
Combining Steel with Timber
Steel is oŌen used with structural Ɵmber. Pairing steel and wood in a single project can lead to
unique assemblies of sustainable and aestheƟcally pleasing hybrid structures. The strength of
steel lessens the bulk and provides an economy of structure that would not be possible with an
all-wood design. The warmth of wood can add a welcoming touch to an all-steel building.
Steel and wood are two very diīerent materials and combining them can be a challenge to de-
signers. Steel is a manufactured product – strong, predictable and inĮnitely recyclable. Wood is a
natural material – relaƟvely weak, variable in strength but renewable. Temperature diīerenƟals
cause steel to expand and contract but have liƩle eīect on wood; however, changes in humidity,
which have liƩle eīect on steel, can cause wood to shrink and permanently change its dimen-
sions. Wood is described as a heterogeneous, hygroscopic, cellular and anisotropic material. That
means it is made up of a diverse range of diīerent items, it aƩracts water molecules from the
environment though absorpƟon or adsorpƟon, it has a cellular structure and its properƟes are
direcƟonally dependent.
Because of their diīerent properƟes, connecƟons between wood and steel can be diĸcult. A
major issue is the diīerent expansion and contracƟon coeĸcients when combining AESS with
wood. AddiƟonally, steel excels in tension while wood reacts much beƩer to compression.
There are analyƟcal programs available now to help set up the structure needed when combin-
ing the materials, so in considering AESS with wood, make sure that the fabricator is familiar or
has experience with the applicaƟon. In some cases, sloƩed holes in the steel can allow for some
movement of the wood. The important thing in creaƟng a hybrid structural system is to remem-
ber the strengths of each material and in what context each of them works best. Because steel
is a much stronger material, a hybrid wood/
steel truss design should have the wood on
top of the truss (in compression) and the steel
at the boƩom chord (in tension). In this way,
the wood elements buƩ against each other
with very liƩle bolƟng. This also avoids large
connecƟons at the boƩom truss since steel is
transferring the high-tension forces.
Both materials have issues with moisture. Steel
is subject to oxidaƟon while wood is subject
to decay.
There are concerns where wood and steel
come into direct contact with each other. Steel
needs to be protected, by galvanizing or coat-
ing with a speciĮc paint system, in order to re-
sist the humidity changes in the wood. It also
helps to use dry wood instead of green wood
at the interface if possible because it moves
less over Ɵme. Because it is important to limit
the restraint imposed by the steel connecƟng
elements, a bolted steel connecƟon should
not span the full depth of a wood element. On
bridges, where Ɵmber decking is supported
by steel girders, the two materials should be
separated by a waterproof membrane.
Steel is a crucial element in the design of
hybrid structures because it allows the use of
slender, delicate proĮles that would not be
possible with wood alone.
When using steel and wood together, the
designer has to be very aware of balance. On
a primarily AESS structure, there has to be
enough wood to warm up the building, and
on a primarily wood structure, there has to be
enough steel to provide some interest.
From a fabricator’s perspecƟve, a hybrid
project can be carried out in the steel fabrica-
tor’s shop. It is helpful if the fabricator has
some experience with working with wood, as
the processes and connecƟon details diīer
from straight AESS work. There are concerns
about damaging the wood in the shop, either
through handling or by welding or heaƟng
steel too close to the wood in the structure.
The use of a heat shield can protect the steel
These special galvanized Įƫngs work well with the
glued-laminated Ɵmber system. Part of this canopy
will be exposed to humidity and so corrosion protec-
Ɵon is required. Also, the Įnish will last a long Ɵme
and the connecƟons would be diĸcult to access for
reĮnishing.
157
The steel and glulam arches of Brentwood StaƟon
were fabricated at the steel fabricator’s plant to
ensure proper Įt and coordinaƟon of the erecƟon
process.
159
The curved glulam facade of the Art Gallery of
Ontario is enƟrely supported by a steel frame that
takes its eccentric, twisƟng load back to the building.
A combinaƟon of painted grey and galvanized steel
is used.
158

1 The Challenge
from scorching during adjacent welding. The
wood needs to maintain its protecƟve cover-
ing unƟl it arrives on site, only peeling away
areas requiring work. The wood should not
be walked upon, as is customary in working
large steel, as damage can result. Covering
saw horses with wood and carpeƟng and using
nylon slings to move the wood beams rather
than the chains and hooks usually used with
steel will minimize problems. In selecƟng a
fabricator it is important to make sure that ev-
eryone in the shop is aware of the diīerences
in the materials.
The staging and erecƟon of a hybrid system
is similar to regular AESS with the excepƟon
that the wood must be handled more gently.
Depending on the size and complexity of the
members, the physical connecƟons between
materials can either be done in the fabricaƟon
shop, then shipped, or combined on site in the
staging area. Precision in Įt is even more im-
portant as wood members cannot be forcibly
Įt, or cracking will occur. Padded slings need
to be used to liŌ the members so as not to
damage the wood. ProtecƟve wrappings need
to stay in place unƟl well aŌer the erecƟon
is complete to conƟnue to provide weather
protecƟon.
Most importantly, someone has to take charge
of the project. This is the only way to ensure a
proper Įt between the materials and to ensure
coordinaƟon from start to Įnish. It is possible
to have the steel fabricator coordinate shop
drawings, delivery schedule and erecƟon.
Reference
• “Steel and Other Materials, Part Two: Steel and
Wood”, John Leckie, Advantage Steel No. 30,
CISC, Winter 2007
Combining Steel with Glass
New technological developments have both in-
creased the opƟons available and reduced the
diĸculƟes in designing, detailing and erecƟng
AESS steel and glass buildings.
There are three basic ways to consider the
way in which steel acts as a support system for
expansive glazed applicaƟons:
• The steel framework is used simultaneously
as the structure and the method of holding the
glass in place, whereby the glass is virtually in
the same plane as the steel.
• Larger steel members are used directly be-
hind (or in front of) the glass system to provide
wind bracing; these members can be installed
verƟcally or horizontally at the mullions and
usually do not also support the Ňoor loads
above; structural steel secƟons, trusses or
cable systems are used.
• The steel structure sits back from the glass
to provide the lateral support and creates a
separate, unique structure of its own; an inter-
sƟƟal support system (oŌen cables) is used to
connect the glass to the steel.
Tempered glass is most commonly used in
these applicaƟons. Glass is tempered by heat-
ing it to 650 to 700o C and rapidly cooling it so
the centre retains a higher temperature than
the surface. As the centre cools, the resulƟng
contracƟon induces compressive stresses at
the surface and tensile stresses in the core
which can produce a pane of glass four or Įve
Ɵmes stronger than annealed or Ňoat glass.
ProtecƟon against breakage can be enhanced
by laminated units where mulƟple layers of
glass are bonded by a layer of plasƟc sheet
material. The combinaƟon of diīerent layers
improves post-breakage behaviour of the glass
and gives designers and building owners more
conĮdence to use it in larger applicaƟons.
Many AESS and glass structures are designed
as signature elements of the building. The
steel interface elements of these signature
structures transfer porƟons of the wind
loads to the steel superstructure, hence the
interface elements are generally small, but
a much higher emphasis is placed on their
visual appeal. The steel fabricator retained
must be familiar with AESS, as the Įnishes and
interface tolerances are more stringent than
for standard structural steel.
Much of the supporƟng AESS used in these
systems is welded for a cleaner appearance.
Bolted connecƟons are seldom chosen when
Steel connecƟons are used to join this Ɵmber struc-
ture. It can be seen that the steel connecƟon pieces
are ĮƩed with a plate that penetrates the end of the
Ɵmber. Bolts through the assembly secure the plate
to the Ɵmber. In this case the penetraƟon slot is leŌ
exposed. These will oŌen be Įlled or hidden to make
the connecƟons more mysterious.
160
The large arches over the Richmond Speed SkaƟng
Oval are fabricated from a combinaƟon of steel and
wood, with the majority of the steel hidden beneath
the wood cladding of the arches.
162
The heavy Ɵmber on this scupltural project is really
“for show” as the main support system is all steel
and the large square wood secƟons are used only to
bulk out the form and provide a contrast with the
steel used to support the glass.
161
The AESS system illustrated here uses a specialized
verƟcal truss-like column formed from round HSS
secƟons and plates, with holes cut into the plates to
lighten the appearance of the system, to act as the
lateral wind load support for this very tall expanse of
glass at Pearson Airport. The thin proĮle of the steel
appears as a simple extension of the curtain wall.
163
A suite of arƟculated steel arms canƟlevers out over
a hotel drop-oī area. Diagonal rods with stainless
connectors support the glazed roof.
165
A highly arƟculated verƟcal truss at either end of
a cable system is used to provide wind support for
a large expanse of glass at the Newseum. Stainless
steel clamps connect the spider connectors to the
cables.
164

creaƟng tall supporƟng systems for expanses
of glass. Precision in the welding of the steel
elements is parƟcularly important as the
welding process naturally distorts the steel. If
more welding is required on one side of a long
supporƟng member, it can result in bowing of
the member.
One of the problems of working with steel and
glass is the relaƟve tolerances in producing the
materials. Glass requires higher precision with
tolerances of ±2 mm while the tolerances for
steel are ±5 mm. The diīerences have to be
accommodated during the installaƟon in order
to keep the glass panels properly aligned.
Because the glass panels are normally aligned
with the steel elements, poor alignment will
be quite apparent.
There are a number of methods for connect-
ing the glass panels to the structural supports.
The most commonly used is the spider bracket
which has one to four arms coming out of a
central hub. Bolts through the glass panels
are secured to the arms and the brackets are
aƩached to the support structure. Angle brack-
ets, single brackets, pin brackets or clamping
devices are all alternaƟves that are used on
occasion. The panels are usually secured at the
four corners with an addiƟonal pair of bolts
in the middle of each side for larger panels. In
Europe parƟcularly, bolted systems are slipping
from favour and designers there tend to use
a clip system where the panels are supported
on the side, removing the need to drill holes in
the glass.
It is criƟcal to have a high level of commu-
nicaƟon between the architect, engineer
and fabricator on these types of projects,
as coordinaƟon must be very precise. Each
project will have slightly diīerent parameters,
and it is possible to adjust the glass support
system to suit the overall look of the balance
of the AESS on the project. The AESS porƟon
of the support system can be accomplished in
a variety of ways, all capable of connecƟng to
the stainless steel spider connectors. Methods
include: verƟcal trusses, thin verƟcal columns,
ellipƟcal tubes, cable net systems, tension
rods, stainless steel tension systems (either by
themselves or in conjuncƟon with larger AESS
carbon steel members). Structural glass Įns
can be used as the primary means of lateral/
wind support or in conjuncƟon with AESS
systems.
The support system can also bear on the Ňoor
or be suspended from the Ňoor above. More
recently some cable systems are spanning
across the width of the glazed facade and
transferring the load to adjacent columns or
verƟcal trusses.
In all cases a substanƟal amount of movement
must be accommodated in the design of the
system. Glazed façades are oŌen subjected
to high levels of solar gain, and so diīerenƟal
movement in the steel and glass will need to
be accounted for due to temperature. Wind
loads will cause diīering deŇecƟons at the
centre of the spans versus the top, boƩom or
side support points. Changes in Ňoor load-
ing both during construcƟon and during the
life of the building must be accounted for.
Systems must also allow for verƟcal diīerenƟal
movement, oŌen achieved by the use of slip
joints that simultaneously allow movement up
and down, while restricƟng the joint laterally
for wind loads. Silicon is oŌen used to Įll the
gaps between the panels once construcƟon is
complete.
Glass conƟnues to be very briƩle and sensiƟve
to local stress concentraƟons. Hence, much at-
tenƟon has to be spent designing the interface
between glass and steel to resolve issues of
material compaƟbility, and reach the desired
aestheƟc objecƟve.
As concerns about energy eĸciency and pre-
venƟng unwanted heat gain conƟnue to grow,
these sorts of facades promise to be even
more challenging to design as external shading
devices grow in use as a means of lowering
cooling loads.
Reference
• “Steel and Other Materials, Part One: Steel and
Glass”, John Leckie, Advantage Steel No. 29, CISC
Summer 2007
Spider connectors are used to connect this mullion-
less glass to a tubular steel frame at the top of the
expanse of window of this Las Vegas Hotel lobby. The
coordinaƟon for this detail is extremely Ɵght, with
liƩle room for discrepancy given the proximity of the
steel tube to the inside face of the glass.
166
This tubular steel framing system connects to the
sloped curtain wall in a more tradiƟonal fashion with
slim line supports being fairly concealed behind the
proĮle of the HSS secƟons.
168
Although the interior of this lobby would give the
appearance of being supported in heavy Ɵmber,
here we can see that the framing is steel with wood
cladding. This permits the connecƟon of spider con-
nectors to the steel structure hidden inside.
167
Alignment issues between the glass and steel sup-
port frame are taken care of by levelling mechanisms
that are part of the glass connecƟon system. These
are located on the rear of the canopy and are not
visible from the front, allowing for clean lines and
uniformity on the public side of the system.
169
Stainless steel cables are used in conjuncƟon with
laminated structural glass and stainless spider con-
nectors to support this large glazed façade at a Berlin
rail staƟon.
171
The steel supports for this double façade envelope
use a system of clips to support the extra layer of
glass. This alleviates issues of drilling of the glass
and allows for beƩer accommodaƟon of diīerenƟal
movement between the systems.
170

CISC AESS Guide – 8 Special Acknowledgments - 42
8 Special Acknowledgments Architects and Engineers Who ParƟcipated
in Roundtable Discussions
Alain Bergeron
ABCP Architecture
Terri Meyer Boake
University of Waterloo School of Architecture
Peter Buchanan
Stantec
Guy Carrier, Ing.
Cima+
François Deslauriers
Saia Deslauriers Kadanoī
Leconte Brisebois Blais
Pierre Delisle
Pierre Delisle Architecte
Michael Heeney
Bing Thom Architects
Jean Lacoursière
Mesar Consultants
Jeī LeibgoƩ
SBSA Structural Consultants
Sol Lorenzo, Martoni
Cyr & Assoc. (Now Genivar)
Andrew MeƩen
Bush Bohlman
MarƟn Nielsen
Busby Perkins & Will
Bob Neville
Read Jones Christoīersen
Stéphane Rivest
Bureau D’études Spécialisées (BÉS)
Jacques White
Université Laval School of Architecture
Members of the
CISC Ad Hoc AESS CommiƩee
Walter Koppelaar
Walters Inc.
Ontario Region – Chairman
Suja John
CISC Ontario Region
Alan Lock
CISC AtlanƟc Region
Peter Timler
CISC Western Region
Sylvie Boulanger
CISC Quebec Region – Secretary
Peter Boyle
MBS Steel
Ontario Region
Paul Collins
Collins Industries
Alberta Region
Michel Lafrance
Structal-Heavy Steel ConstrucƟon
Quebec Region
Graham Langford
Weldfab
Central Region
Rob McCammon
Iwl Steel Fabricators
Central Region
Jim McLagan
Canron BC
BC Region
Mike Payne
Waiward Steel
Alberta Region
Rob Third
George Third and Son
BC Region
Harrison Wilson
Ocean Steel
AtlanƟc Region
The AESS Story in Canada started in 2005 with the CISC Ad Hoc CommiƩee. The idea
was to create a dynamic industry dialogue, including architects and engineers, in the
hopes of providing a series of documents that would assist in re-visioning the design,
speciĮcaƟon and construcƟon process for AESS.
In the following two years, CISC adapted components of what AISC had developed, but
it also introduced an underlining Category approach and reduced its scope. The com-
miƩee developed a Sample SpeciĮcaƟon (for engineers), an addiƟon to the CISC Code
of Standard PracƟce (for fabricators) and a Guide (for architects). Common to all these
documents is the unique Matrix of Categories and CharacterisƟcs to be used by all.
In parallel, several roundtables were held in Montreal, Toronto and Vancouver, which
would typically involve architects, engineers and fabricators. Those sessions helped
shape the orientaƟon and direcƟon of the commiƩee’s work on the documents.
We wish to acknowledge all the hard work from the commiƩee members, the round-
table parƟcipants, CISC staī and the author, Terri Meyer Boake. Walter Koppelaar, chair
of the commiƩee, introduced the importance of a strong diīerenƟaƟon of Categories.
Michel Lafrance suggested the step-like matrix of Categories, which became a central
tool in the process. Rob Third was immensely acƟve in the reĮnement stage of the
documents. All CISC regions reviewed the documents and suggested changes.
Finally, our warmest thanks go to Terri Meyer Boake. It is with unsurpassed enthusiasm
and a passion for teaching that Terri has travelled in Canada and around the globe to
gain understanding and deliver beauƟful, inspiring photos. She has asked thousands
of quesƟons and dug into the topic with the curious eyes of an architect, a teacher, a
photographer, a writer, a detecƟve and a friend of the industry.
So now the wait is over. The third of the series of CISC AESS documents is available
in the form of this Guide. May all design professionals wishing to have fun with steel,
to improve communicaƟon in order to saƟsfy aestheƟc, economic and construcƟon
criteria use this Guide at work, at home, at school and start specifying AESS Categories
in your projects. Enjoy!
Sylvie Boulanger
CISC

CISC AESS Guide – 9 References and Image Credits - 43
Architecturally Exposed Structural Steel: A Design Guide
Modern Steel ConstrucƟon | May 2003
Convenient ConnecƟons
by Carlos de Oliveira and Tabitha SƟne
Modern Steel ConstrucƟon | July 2008
Branching Out
Modern Steel ConstrucƟon | July 2008
What Engineers Should Know About Bending Steel
by Todd Alwood
Modern Steel ConstrucƟon | May 2006
Going EllipƟcal
by Jeī Packer
Modern Steel ConstrucƟon | March 2008
EllipƟcal Hollow SecƟons – Three-Part Series, Part One: ProperƟes and ApplicaƟons
by Jeī Packer
Advantage Steel No. 35 | Fall 2009
EllipƟcal SecƟons – Three-Part Series, Part Three: EHS ConnecƟon Design
by Jeī Packer
Advantage Steel No. 37 | Spring 2010
Understanding Steel ConstrucƟon: An Architect’s View
by Terri Meyer Boake, illustraƟons by Vincent Hui
Birkhauser, 2011
IMAGE CREDITS
Front and rear covers and, unless otherwise noted, all photos by Terri Meyer Boake
Sylvie Boulanger (CISC): Nos. 41, 42, 44, 45, 46, 47, 48, 53, 56, 70, 71, 89, 92, 95, 102
American InsƟtute of Steel ConstrucƟon: Nos. 43, 54, 57, 58, 63, 68, 73, 74
Walters Inc.: Nos. 32, 49, 51, 75, 114, 153, 156
Vincent Hui: Nos. 113, 140
9 References and Image Credits
REFERENCES
The following arƟcles, journal publicaƟons and books were referenced in the creaƟon
of this Guide:
Advantage Steel | Ask Dr. Sylvie Column
An excellent resource included in each Advantage Steel issue from Spring 2003 to Fall
2010
Advantage Steel issues are available online at:
hƩp://www.cisc-icca.ca/content/publicaƟons/publicaƟons.aspx
The Canadian Matrix: A Category Approach for Specifying AESS
A presentaƟon of CISC’s new Category Approach of AESS1 through AESS4 including a
handy pull-out centerfold of the Category Matrix
by Sylvie Boulanger and Terri Meyer Boake
Advantage Steel No. 31 | Summer 2008
Steel and Other Materials, Part Two: Steel and Wood
A detailed look at the technical aspects of eīecƟve design with composite steel and
wood structures
by John Leckie
Advantage Steel No. 30 | Winter 2007
Steel and Other Materials, Part One: Steel and Glass
A look at the detailed interacƟon of steel and glass in buildings
by John Leckie
Advantage Steel No. 29 | Summer 2007
Architecturally Exposed Structural Steel: How Is It DeĮned?
A look into the design process and criteria that will be used to create the upcoming
Canadian AESS SpeciĮcaƟon and Guide
Advantage Steel No. 22 | Spring 2005
A Categorical Approach: The Canadian InsƟtute of Steel ConstrucƟon Is Taking a New
Approach to Specifying AESS Requirements
by Sylvie Boulanger, Terri Meyer Boake and Walter Koppelaar
A detailed look at the new Canadian AESS Matrix.
Modern Steel ConstrucƟon | April 2008

CISC AESS Guide – Appendix 1 CISC Code of Standard PracƟce - 44
Appendix 1 - CISC Code of Standard PracƟce
CISC CODE OF STANDARD PRACTICE – APPENDIX I
Architecturally Exposed Structural Steel (AESS)
For a downloadable, electronic version of the CISC Code of Standard PracƟce, please visit:
hƩp://www.cisc-icca.ca/aess/
I1. SCOPE AND REQUIREMENTS
I1.1 General Requirements. When members are speciĮcally designated as “Architecturally Ex-
posed Structural Steel’’ or “AESS’’ in the Contract Documents, the requirements in SecƟons
1 through 7 shall apply as modiĮed by this Appendix. AESS members or components shall
be fabricated and erected with the care and dimensional tolerances that are sƟpulated in
SecƟons 1.2 through 1.5.
I1.2 DeĮniƟon of Categories. Categories are listed in the AESS Matrix shown in Table I1 where
each Category is represented by a set of CharacterisƟcs. The following Categories shall be
used when referring to AESS:
AESS 1: Basic Elements
Suitable for “basic” elements which require enhanced workmanship.
AESS 2: Feature Elements Viewed at a Distance > 6 m
Suitable for “feature” elements viewed at a distance greater than six
metres. The process involves basically good fabricaƟon pracƟces with
enhanced treatment of weld, connecƟon and fabricaƟon detail, tolerances
for gaps, and copes.
AESS 3: Feature Elements Viewed at a Distance ч 6 m
Suitable for “feature” elements – where the designer is comfortable
allowing the viewer to see the art of metalworking. Welds are generally
smooth but visible; some grind marks are acceptable. Tolerances are
Ɵghter than normal standards. The structure is normally viewed closer
than six metres and is frequently subject to touching by the public.
AESS 4: Showcase Elements
Suitable for “showcase or dominant” elements – where the designer
intends the form to be the only feature showing in an element. All welds
are ground, and Įlled edges are ground square and true. All surfaces
are sanded/Įlled. Tolerances of fabricated forms are more stringent –
generally one-half of the standard tolerance. All surfaces are to be “glove”
smooth.
AESS C: Custom Elements
Suitable for elements which require a diīerent set of CharacterisƟcs than
speciĮed in Categories 1, 2, 3 or 4.
I1.3 AddiƟonal InformaƟon. The following addiƟonal informaƟon shall be provided in the
Contract Documents when AESS is speciĮed:
a) SpeciĮc idenƟĮcaƟon of members or components that are AESS using the AESS
Categories listed in I1.2. Refer to Table I1;
b) FabricaƟon and/or erecƟon tolerances that are to be more restricƟve than provided
for in this Appendix;
c) For Categories AESS 2, 3, 4 requirements, if any, of a visual sample or Įrst-oī com-
ponent for inspecƟon and acceptance standards prior to the start of fabricaƟon;
d) For Category AESS C, the AESS Matrix included in Table I1 shall be used to specify
the required treatment of the element.
I2. SHOP DETAIL, ARRANGEMENT AND ERECTION DRAWINGS
I2.1 IdenƟĮcaƟon. All members designated as AESS members are to be clearly idenƟĮed with a
Category, either AESS 1, 2, 3, 4 or C, on all shop detail, arrangement and erecƟon drawings.
I2.2 VariaƟons. Any variaƟons from the AESS Categories listed must be clearly noted. These
variaƟons could include machined surfaces, locally abraded surfaces, and forgings. In addi-
Ɵon:
a) If a disƟncƟon is to be made between diīerent surfaces or parts of members, the
transiƟon line/plane must be clearly idenƟĮed/deĮned on the shop detail, ar-
rangement and erecƟon drawings;
b) Tack welds, temporary braces and Įxtures used in fabricaƟon are to be indicated
on shop drawings;
c) All architecturally sensiƟve connecƟon details will be submiƩed for approval by
the Architect/Engineer prior to compleƟon of shop detail drawings.
I3. FABRICATION
I3.1 General FabricaƟon. The fabricator is to take special care in handling the steel to avoid
marking or distorƟng the steel members.
a) All slings will be nylon-type or chains with soŌeners or wire rope with soŌeners.
b) Care shall be taken to minimize damage to any shop paint or coaƟng.
c) If temporary braces or Įxtures are required during fabricaƟon or shipment, or
to facilitate erecƟon, care must be taken to avoid and/or repair any blemishes or
unsightly surfaces resulƟng from the use or removal of such temporary elements.
d) Tack welds shall be ground smooth.
I3.2 UnĮnished, Reused or Weathering Steel. Members fabricated of unĮnished, reused or
weathering steel that are to be AESS may sƟll have erecƟon marks, painted marks or other marks
on surfaces in the completed structure. Special requirements shall be speciĮed as Category AESS C.

CISC AESS Guide – Appendix 1 CISC Code of Standard PracƟce - 45
I3.3 Tolerances for Rolled Shapes. The permissible tolerances for depth, width, out-of- square,
camber and sweep of rolled shapes shall be as speciĮed in CSA G40.20/21 and ASTM A6. The
following excepƟons apply:
a) For Categories AESS 3 and 4: the matching of abuƫng cross-secƟons shall be
required;
b) For Categories AESS 2, 3 and 4: the as-fabricated straightness tolerance of a mem-
ber is one-half of the standard camber and sweep tolerance in CSA G40.20/21.
I3.4 Tolerances for Built-up Members. The tolerance on overall secƟon dimensions of mem-
bers made up of plates, bars and shapes by welding is limited to the accumulaƟon of permissible
tolerances of the component parts as provided by CSA W59 and ASTM A6. For Categories AESS
2, 3 and 4, the as-fabricated straightness tolerance for the built-up member is one-half of the
standard camber and sweep tolerances in CSA W59.
I3.5 Joints. For Categories AESS 3 and 4, all copes, miters and buƩ cuts in surfaces exposed
to view are made with uniform gaps, if shown to be open joint, or in uniform contact if shown
without gap.
I3.6 Surface Appearance. For Categories AESS 1, 2 and 3, the quality surface as delivered by
the mills will be acceptable. For Category AESS 4, the steel surface imperfecƟons should be Įlled
and sanded.
I3.7 Welds. For corrosive environments, all joints should be seal welded. In addiƟon:
a) For Categories AESS 1, 2 and 3, a smooth uniform weld will be acceptable. For
Category AESS 4, the weld will be contoured and blended.
b) For Categories AESS 1, 2, 3 and 4, all weld spaƩer is to be avoided/removed where
exposed to view.
c) For Categories AESS 1 and 2, weld projecƟon up to 2 mm is acceptable for
buƩ and plug-welded joints. For Categories AESS 3 and 4, welds will be ground
smooth/Įlled.
I3.8 Weld Show-through. It is recognized that the degree of weld show-through, which is any
visual indicaƟon of the presence of a weld or welds on the opposite surface from the viewer, is a
funcƟon of weld size and material thickness.
a) For Categories AESS 1, 2 and 3, the members or components will be acceptable as
produced.
b) For Category AESS 4, the fabricator shall minimize the weld show-through.
I3.9 Surface PreparaƟon for PainƟng. Unless otherwise speciĮed in the Contract Documents,
the Fabricator will clean AESS members to meet the requirement of SSPC-SP 6 “Commercial Blast
Cleaning” (sandblast or shotblast). Prior to blast cleaning:
a) Any deposits of grease or oil are to be removed by solvent cleaning, SSPC-SP 1;
b) Weld spaƩer, slivers and surface disconƟnuiƟes are to be removed;
c) Sharp edges resulƟng from Ňame cuƫng, grinding and especially shearing are to
be soŌened.
I3.10 Hollow Structural SecƟons (HSS) Seams
a) For Categories AESS 1 and 2, seams of hollow structural secƟons shall be accept-
able as produced.
b) For Category AESS 3, seams shall be oriented away from view or as indicated in
the Contract Documents.
c) For Category AESS 4, seams shall be treated so that they are not apparent.
I4. DELIVERY OF MATERIALS
I4.1 General Delivery. The Fabricator shall use special care to avoid bending, twisƟng or oth-
erwise distorƟng the Structural Steel. All Ɵe-downs on loads will be either nylon strap or
chains with soŌeners to avoid damage to edges and surfaces of members.
I4.2 Standard of Acceptance. The standard for acceptance of delivered and erected members
shall be equivalent to the standard employed at fabricaƟon.
I5. ERECTION
I5.1 General ErecƟon. The Erector shall use special care in unloading, handling and erecƟng the
AESS to avoid marking or distorƟng the AESS. The Erector must plan and execute all opera-
Ɵons in a manner that allows the architectural appearance of the structure to be main-
tained.
a) All slings will be nylon-strap or chains with soŌeners.
b) Care shall be taken to minimize damage to any shop paint or coaƟng.
c) If temporary braces or Įxtures are required to facilitate erecƟon, care must be
taken to avoid and/or repair any blemishes or unsightly surfaces resulƟng from
the use or removal of such temporary elements.
d) Tack welds shall be ground smooth and holes shall be Įlled with weld metal or
body Įller and smoothed by grinding or Įlling to the standards applicable to the
shop fabricaƟon of the materials.
e) All backing bars shall be removed and ground smooth.
f) All bolt heads in connecƟons shall be on the same side, as speciĮed, and consis-
tent from one connecƟon to another.
I5.2 ErecƟon Tolerances. Unless otherwise speciĮed in the Contract Documents, members and
components are plumbed, leveled and aligned to a tolerance equal to that permiƩed for struc-
tural steel.
I5.3 Adjustable ConnecƟons. When more stringent tolerances are speciĮcally required for
erecƟng AESS, the Owner’s plans shall specify/allow adjustable connecƟons between AESS and
adjoining structural elements, in order to enable the Erector to adjust and/or specify the method
for achieving the desired dimensions. Adjustment details proposed by the Erector shall be sub-
miƩed to the Architect and Engineer for review.

CISC AESS Guide – Appendix 2 AESS Sample SpeciĮcaƟon - 46
Appendix 2 - Sample AESS SpeciĮcaƟon
SAMPLE AESS SPECIFICATION FOR CANADA
ARCHITECTURALLY EXPOSED STUCTURAL STEEL (AESS)
“AESS” SubsecƟon of Division 5 “Structural Steel” SecƟon 05120
For a downloadable, electronic version of the Sample AESS SpeciĮcaƟon, please visit
hƩp://www.cisc-icca.ca/content/aess/
PART 1 – GENERAL
1.1. RELATED DOCUMENTS
A. Drawings and general provisions of the Contract, including General and Supplementary
CondiƟons and Division 1 «SpeciĮcaƟons» SecƟon, apply to this SubsecƟon.
B. For deĮniƟons of Categories AESS 1, 2, 3, 4, and C as listed in the AESS Matrix (see Table
1), refer to the CISC Code of Standard PracƟce Appendix I.
1.2. SUMMARY
A. This SubsecƟon includes requirements regarding the appearance, surface preparaƟon
and integraƟon of Architecturally Exposed Structural Steel (AESS) only.
For technical requirements, refer to the other SubsecƟons of Division 5 «Structural
Steel» SecƟon.
This SubsecƟon applies to any structural steel members noted on Structural Design Doc-
uments as AESS. All AESS members must also be idenƟĮed by their Category.
B. Related SecƟons: The following SecƟons contain requirements that may relate to this
SubsecƟon:
1. Division 1 «Quality Control» SecƟon for independent tesƟng agency proce-
dures and administraƟve requirements;
2. Division 5 «Steel Joist» SecƟon;
3. Division 5 «Metal Decking» SecƟon for erecƟon requirements relaƟng to ex-
posed steel decking and its connecƟons;
4. Division 9 «PainƟng» SecƟon for Įnish coat requirements and coordinaƟon
with primer and surface preparaƟon speciĮed in this SubsecƟon.
1.3. SUBMITTALS
A. General: Submit each item below according to the CondiƟons of the Contract and Divi-
sion 1 «SpeciĮcaƟons» SecƟon.
B. Shop Drawings detailing fabricaƟon of AESS components:
1. Provide erecƟon drawings clearly indicaƟng which members are considered as
AESS members and their Category;
2. Include details that clearly idenƟfy all of the requirements listed in secƟons 2.3
‘’FabricaƟon’’ and 3.3 ‘’ErecƟon’’ of this speciĮcaƟon. Provide connecƟons for
AESS consistent with concepts, if shown on the Structural Design Documents;
3. Indicate welds by standard CWB symbols, disƟnguishing between shop and
Įeld welds, and show size, length and type of each weld. IdenƟfy grinding,
Įnish and proĮle of welds as deĮned herein;
4. Indicate type, Įnish of bolts. Indicate which side of the connecƟon bolt heads
should be placed;
5. Indicate any special tolerances and erecƟon requirements.
1.4. QUALITY ASSURANCE
A. Fabricator QualiĮcaƟons: In addiƟon to those qualiĮcaƟons listed in other SubsecƟons
of Division 5 “Structural Steel” SecƟon, engage a Įrm competent in fabricaƟng AESS
similar to that indicated for this Project with suĸcient producƟon capacity to fabricate
the AESS elements.
B. Erector QualiĮcaƟons: In addiƟon to those qualiĮcaƟons listed in other SubsecƟons of
Division 5 “Structural Steel” SecƟon, engage a competent Erector who has completed
comparable AESS work .
C. Comply with applicable provisions of the following speciĮcaƟons and documents:
1. CISC Code of Standard PracƟce, latest ediƟon.
D. Visual samples when speciĮed may include any of the following:
1. 3-D rendering of speciĮed element;
2. Physical sample of surface preparaƟon and welds;
3. First oī inspecƟon: First element fabricated for use in Įnished structure sub-
ject to alteraƟons for subsequent pieces.
4. Mockups: As speciĮed in Structural Design Document. Mockups are either
scaled or full-scale. Mockups are to demonstrate aestheƟc eīects as well as
qualiƟes of materials and execuƟon:
a. Mockups may have Įnished surface (including surface preparaƟon and
paint system);
b. Architect’s approval of mockups is required before starƟng fabricaƟon of
Įnal units;
c. Mockups are retained unƟl project is completed;
d. Approved full-scale mockups may become part of the completed work.
1.5. DELIVERY, STORAGE, AND HANDLING

CISC AESS Guide – Appendix 2 AESS Sample SpeciĮcaƟon - 47
A. Ensure that all items are properly prepared, handled and/or packaged for storage and
shipping to prevent damage to product.
B. Erect Įnished pieces using soŌened slings or other methods such that they are not
damaged. Provide padding as required to protect while rigging and aligning member’s
frames. Weld tabs for temporary bracing and safety cabling only at points concealed
from view in the completed structure or where approved by the Architect.
PART 2 – PRODUCTS
1.1 MATERIALS
A. General: Meet requirements of SubsecƟons of Division 5 “Structural Steel”.
B. Specialty bolts must be speciĮed.
1.2 SPECIAL SURFACE PREPARATION
A. Primers: Primers must be speciĮed.
1.3 FABRICATION
A. For the special fabricaƟon characterisƟcs, see Table 1 – AESS Category Matrix.
B. Fabricate and assemble AESS in the shop to the greatest extent possible. Locate Įeld
joints in AESS assemblies at concealed locaƟons or as approved by the Architect.
C. Fabricate AESS with surface quality consistent with the AESS Category and visual
samples if applicable.
1.4 SHOP CONNECTIONS
A. Bolted ConnecƟons: Make in accordance with SecƟon 05120. Provide bolt type and Įn-
ish as speciĮed and place bolt heads as indicated on the approved shop drawings.
B. Welded ConnecƟons: Comply with CSA W59-03 and SecƟon 05120. Appearance and
quality of welds shall be consistent with the Category and visual samples if applicable.
Assemble and weld built-up secƟons by methods that will maintain alignment of mem-
bers to the tolerance of this SubsecƟon.
1.5 ARCHITECTURAL REVIEW
A. The Architect shall review the AESS steel in place and determine acceptability based on
the Category and visual samples (if applicable). The Fabricator/Erector will advise the
consultant the schedule of the AESS Work.
PART 3 - EXECUTION
1.1 EXAMINATION
A. The erector shall check all AESS members upon delivery for twist, kinks, gouges or
other imperfecƟons, which might result in rejecƟon of the appearance of the member.
Coordinate remedial acƟon with fabricator prior to erecƟng steel.
1.2 PREPARATION
A. Provide connecƟons for temporary shoring, bracing and supports only where noted on
the approved shop erecƟon drawings. Temporary connecƟons shown shall be made at
locaƟons not exposed to view in the Įnal structure or as approved by the Architect.
Handle, liŌ and align pieces using padded slings and/or other protecƟon required to
maintain the appearance of the AESS through the process of erecƟon.
1.3 ERECTION
A. Set AESS accurately in locaƟons and to elevaƟons indicated, and according to CSA S16-
01.
B. In addiƟon to the special care used to handle and erect AESS, employ the proper erecƟon
techniques to meet the requirements of the speciĮed AESS Category:
1. AESS ErecƟon tolerances: ErecƟon tolerances shall meet the requirements
of standard frame tolerances for structural steel per CSA S16-01;
2. Bolt Head Placement : All bolt heads shall be placed as indicated on the structural
design document. Where not noted, the bolt heads in a given connecƟon shall be
placed to one side;
3. Removal of Įeld connecƟon aids: Run-out tabs, erecƟon bolts and other steel
members added to connecƟons to allow for alignment, Įt-up and welding in the
Įeld shall be removed from the structure. Welds at run-out tabs shall be removed
to match adjacent surfaces and ground smooth. Holes for erecƟon bolts shall be
plug welded and ground smooth where speciĮed;
4. Filling of connecƟon access holes: Filling shall be executed with proper procedures
to match architectural proĮle, where speciĮed;
5. Field Welding: Weld proĮle, quality, and Įnish shall be consistent with Category and
visual samples, if applicable, approved prior to fabricaƟon.
1.4 FIELD CONNECTIONS
A. Bolted ConnecƟons: Make in accordance with SecƟon 05120. Provide bolt type and Įn-
ish as speciĮed and place bolt heads as indicated on the approved shop drawings.
B. Welded ConnecƟons: Comply with CSA W59-03 and SecƟon 05120. Appearance and
quality of welds shall be consistent with the Category and visual samples if applicable.
Assemble and weld built-up secƟons by methods that will maintain alignment of mem-
bers to the tolerance of this SubsecƟon.
1. Assemble and weld built-up secƟons by methods that will maintain alignment
of axes. Verify that weld sizes, fabricaƟon sequence, and equipment used for
AESS will limit distorƟons to allowable tolerances.
1.5 ARCHITECTURAL REVIEW
A. The Architect shall review the AESS steel in place and determine acceptability based on
the Category and visual samples (if applicable). The Fabricator/Erector will advise the
consultant the schedule of the AESS Work.
1.6 ADJUSTING AND CLEANING
A. Touchup PainƟng: Cleaning and touchup painƟng of Įeld welds, bolted connecƟons, and
abraded areas of shop paint shall be completed to blend with the adjacent surfaces of
AESS. Such touchup work shall be done in accordance with manufacturer’s instrucƟons.
B. Galvanized Surfaces: Clean Įeld welds, bolted connecƟons, and abraded areas and re-
pair galvanizing to comply with ASTM A780.

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