Acm Unit 3 2

Advanced construction and
materials
Class – 4
Unit –III
B.Arch VII sem

The space structures may take the form of:
 Two-dimensional grids.
 Cylindrical vaults.
 Domes.

Construction techniques for erection of space frames
 Space frame, from a geometrical viewpoint,
consists of two plane grids, parallel to each
other, which form the upper and lower layers
of the space frame.
 These two plane frames (grids) are connected
to each other with the use of diagonal bars.
 The external loads are distributed amongst
the two parallel layers and the diagonal bars
which connect them.

The Structural System
The structural system is characterized by the combination of three
main components:
 member
 node
 connection

Members
 Hollow sections are essential for
a number of reasons.
 In particular, tubular sections are
generally used because of their
large and uniform radius of
gyration.

Nodes
 The dream of a 'universal' node has
not yet been realised.
 Several parameters govern the
design of nodes.
 Nodes can be connected mainly by :
 welding,
 bolting or
 by special fabrication.

Nodes
 Some authorities prefer welding for large
spans, even if it is difficult to guarantee the
quality of welds in site.
 One of the determining factors in the choice
of nodes is the number of members to be
assembled.
 The regularity of geometry resulting from
the node determines the entire geometry of
the structure.

Five 'kinds' of nodes may be identified:
Plated and folded nodes are usually connected to the member ends by means of bolted
connections, but also welding can be done.
The node is a critical element when evaluating the cost of spatial structures: one node for 2,5-
3,0m2 would seem to be an economical solution.

Connections
 The node-to-member joining system determines how the
ends of the members must be treated.
Five processes may be described, for example:
 Straight cutting
 Profiled cutting
 Squashed and drilled
 Addition of a connection plate
 Special fixing: threading, welding,
or bolt crushing
Different treatments of member ends

Methods of Fabrication and Erection
Methods used may be listed in three categories:
 Erection of separate members, each one lifted into position and connected to the work already assembled.
 Erection of sub-assemblies: this is an intermediate stage whereby the members are connected in sub-assemblies,
either in the factory or on site. The sub-assemblies are lifted into final position and connected to the work
already assembled.
 Lifting of the whole space structure, which is assembled on the ground on site. Various methods may be
considered ranging from the use of vertical construction parts as lifting masts to cranes.

The choice of one of these three methods depends on:
1. The nature of the project in terms of type of structure
and size.
2. Operational conditions: actual layout of the site,
available means of lifting, transport costs, experience,
etc.
3. Safety.

Lifting the whole space frame has the following
advantages:
 The greater part of the work is carried out on the ground, thus aiding control of the
operation, especially the making of welded joints.
 The use of heavy hoisting machinery is required for a shorter period, which may reduce
final costs.
 In some cases, the structure with other equipment attached may be lifted together.

 A new approach has been used in Barcelona for the
erection of the dome of the Olympic Palace.
 It involves the fabrication of the dome on the
ground in five portions which are temporarily pinned
to each other
 The central portion is then lifted and the remaining
segments of the dome locked in the final position.
 Different methods of execution may be considered
depending on the type of structure and place of
installation.
 There is no limit to the list of solutions. The erection
method chosen depends on the imagination and
know-how of the designer within a particular
context.
Novel method of dome erection

Membrane structures
 Membrane structures are spatial
structures made out of tensioned
membranes.
 The structural use of membranes can be
divided into pneumatic structures, tensile
membrane structures, and cable domes.
 In these three kinds of structure,
membranes work together with cables,
columns and other construction members
to find a form.

 High strength steel cables have been used
extensively over the past twenty five years
for space roof structures.
 There are two different possibilities when
using steel cables in roof structures.
 The first possibility, consists of using the
cables only for suspension of the main roof
structure, which can be either conventional,
e.g. beams, cantilevers, etc., or a space
frame.
 In this case, the main roof structure, instead
of being supported, is actually suspended
from steel cables above the roof, which
transmit the tensile forces to appropriate
anchorages .They are cable-stayed roofs.

 There are many examples of this type of
construction used as industrial buildings
where the roof structure, either as a single
or as a double cantilever, is suspended
from cables, which in turn are anchored on
robust pylons above the roof level.
 In this type of construction, the cables
behave as simple suspension elements,
while the roof structure itself behaves like
a normal load resisting unit, subject to
moments, shears, and other kinds of action
effect.
 It is expected that the suspending
elements remain in tension, even under
wind uplift, due to the dead weight of the
roof.

 The second possibility is represented by
those roof structures where the steel cables
are effective members of the roof structure
itself, and not just conveyors of forces from
the structure to the anchorages.
 In this type of construction (tension
structures), the cables themselves resist the
various external loads.
 Their particular behaviour has deeply
influenced the structural forms used and has
imposed new methods of execution.

Tension structures may be
categorised as:
(a) Single-layer cable systems
(b) Double-layer prestressed
cable truss systems
(c) Prestressed tensile
membrane systems

Tension structures are used to
cover stadia,
arenas,
swimming pools,
recreation halls and other buildings
where a large area for public
assembly and exceptional aesthetic
effect are required simultaneously.

CONCLUDING SUMMARY
 Standard industrial forms can be varied to provide structures capable of
spanning considerable distances.
 Curved forms, arches or domes, provide further possibilities.
 Cable staying extends the spanning possibilities of conventional trusses or
truss frames.
 Tensile structures open up a large repertoire of dynamic structural
possibilities for medium to large-span structures.
 Tensile structures may be planar or anticlastic, membrane or cable net
structures.

Cable structures
Cable structure, Form of long-span structure that is subject to
tension and uses suspension cables for support.
Highly efficient, cable structures include
 the suspension bridge,
 the cable-stayed roof, and
 The bicycle-wheel roof.

 The graceful curve of the huge main cables of
a suspension bridge is almost a catenary, the
shape assumed by any string or cable
suspended freely between two points.
 The cable-stayed roof is supported from
above by steel cables radiating downward
from masts that rise above roof level.
 The bicycle-wheel roof involves two layers of
tension cables radiating from an inner tension
ring and an outer compression ring, which in
turn is supported by columns.

 Cable, is an assemblage of three or more ropes
twisted together for extra strength or a rope made
by twisting together several strands of metal wire.
 The first successful stranded iron wire rope was
developed in 1831–34 by Wilhelm Albert, a mining
official of Clausthal in the Harz Mountains in
Saxony.
 High-tensile steel wire was introduced during the
1880s, and steel is now the predominant metal
used for wire rope.

Tension cables supporting structure for airport

Acm Unit 3 2

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Acm Unit 3 2