Tensile structures and Pneumatic Structures

TENSILE STRUCTURES New Age Materials and
Construction
NEW AGE MATERIALS AND CONSTRUCTION | PRESENTATION BY AR.GEEVA CHANDANA | 1

TENSILE STRUCTURES
•The term tensile structures describes the category of buildings
in which the load bearing capacity is achieved through
tension stress in the majority of the components, such as
cables, technical fabrics or foils.
•It can also be defined as a structure where the exterior shell
is a fabric material spread over a framework. The fabric is
maintained in tension in all directions to provide stability.
•The only exception is represented by rigid boundaries and
structural members which are generally subjected to
compression and bending.
•Tension structures are commonly subdivided in boundary
tensioned membranes, pneumatic structures and pre-
stressed cable nets and beams.

TENSILE STRUCTURES
•Tensile structure is the term usually used to refer to the
construction of roofs using a membrane held in place on
steel cables.
•Their main characteristics are the way in which they work
under stress tensile, their ease of pre-fabrication, their
ability to cover large spans, and their malleability.
•This structural system calls for a small amount of material
thanks to the use of thin canvases, which when stretched
using steel cables, create surfaces capable of overcoming the
forces imposed upon them.

TENSILE STRUCTURES : HISTORY
Historically inspired by some of the first man-made shelters—such as
the black tents first developed using camel leather by the nomads of
the Sahara Desert, Saudi Arabia, and Iran, as well as the structures
used by Native American tribes—tensile structures offer a range of
positive benefits compared to other structural models.
Romans even covered the Colosseum with massive canopies,
hoisted by an intricate system of pulleys, to protect the audience from
the elements. NEW AGE MATERIALS AND CONSTRUCTION | PRESENTATION BY AR.GEEVA CHANDANA | 4

TENSILE STRUCTURES : HISTORY
•Predominantly used in coverings of sports centers, of arenas,
and industrial and agroindustrial constructions, tensile
structures are based on the old systems used during the Roman
Empire.
•However, from the Roman period until the mid-20th century,
due to the low demand, usability, and lack of manufacturers of
cables, canvasses, and connections capable of resisting the
forces generated, there were few technological advances.
•It was only after the Industrial Revolution and the triggering
of the era of Fordism that new developments were able to
meet the intrinsic needs of this construction system.
•The low cost of mass production and the demand for systems
capable of adapting to the most varied terrains with large
spans, such as circus tents for example, encouraged the
development of the technique.

TENSILE STRUCTURES : TYPES
•There are three different main classifications in the field of
tensile construction systems: membrane tensioned structures,
mesh tensioned, and pneumatic structures.
•MEMBRANE TENSIONED STRUCTURES: A membrane is held
by cables, allowing the distribution of the tensile stresses
through its own form.
•MESH TENSIONED STRUCTURES: A mesh of cables carries the
intrinsic forces, transmitting them to separate elements, for
example, sheets of glass or wood.
•PNEUMATIC STRUCTURES: A protective membrane is
supported by means of air pressure.

TENSILE STRUCTURES : CONSTRUCTION DETAILS
•Structurally, the system is formalized by combining three
elements: membranes, rigid structures such as pole and
masts, and cables.
•The membranes of PVC-coated polyester fibers have greater
ease in factory production and installation; lower cost; and
medium durability—around 10 years.
•PTFE (Polytetrafluoroethylene)-coated glass fiber membranes
have superior durability—around 30 years; and greater
resistance to the elements (sun, rain, and winds); however, they
require skilled labor.
•There are two types of support: direct and indirect. The direct
supports are those in which the construction is arranged
directly on the rest of the building structure, while the second
case is arranged from a raised point such as a mast.

TENSILE STRUCTURES : CONSTRUCTION DETAILS
•The cables, which are responsible for the distribution of the tensile stresses and the
hardening of the canvasses, are classified in one of two ways according to the action
which they perform: load-bearing and stabilizing.
•Both types of cable cross orthogonally, ensuring strength in two directions and avoiding
deformations.
•The load-bearing cables are those that directly receive the external loads, fixed at
the highest points.
•On the other hand, the stabilizing cables are responsible for strengthening the load-
bearing cables and cross the load-bearing cables orthogonally.
•It is possible to avoid attaching the stabilizing cables to the ground by using a
peripheral fixation cable.
•The nomenclatures for different cables are generated according to their position: a
ridge-line cable refers to the uppermost cable; while valley cables are fixed below
all other cables; radial cables are stabilizer cables in the form of a ring.
•Ridge-line cables support gravitational loads while valley cables support wind loads.

FABRIC STRUCTURES : TYPES OF ROOF
•SADDLE ROOF
•MAST SUPPORTED
•ARCH SUPPORTED
•COMBINATIONS

FABRIC STRUCTURES : SADDLE ROOF
The roof plan, taken directly from the structural
engineering working drawings, illustrates the roof
configuration and its components. Section through
the project showing the stage roof tucked under
the auditorium roof.
•Four or more point system when the fabric is stretched between a set of alternating
high and low points.

FABRIC STRUCTURES : MAST SUPPORTED
•Tent-like in appearance, mast supported structures
typically have one or sometimes several peaks that
are supported by either interior or perimeter masts.
•The fabric is attached to the interior mast by special
connections, usually a bale ring or cable loop.
•Mast-supported structures can also be supported by
adjacent buildings. The peaks of a mast supported
structure are determined by the design and how the
fabric is attached.
•Openings are typically ovoid or elliptical. The fabric
that extends from the top of the opening is seamed
and can necessitate patterning.
•Mast supported systems are suitable for long span
roofs.

FABRIC STRUCTURES : ARCH SUPPORTED ROOF
•Curved compression members are used as the main
supporting elements and cross arches are used for
lateral stability.
•In a plane arch, large differences between the thrust
lines and the main geometry will produce large
bending moments that in turn produce large changes
in shape and high stresses in the arch chord section.
•One method to significantly reduce these effects is to
tie or restrain points along the arch chord to reduce
the initial large deformations of the chord.
•The buckling length of the arch chord can also be
reduced by discretely or continuously supporting the
chord with tension elements or systems comprised of
cables or membranes.

FABRIC STRUCTURES : COMBINATIONS
•Combination of several support types.

FABRIC STRUCTURES : COMPONENTS
BASE PLATE
•Connection to concrete foundation pillar
MEMBRANES
•Forms the enclosure of the structure. Connections can be glued or
heat welded :
PVC coated polyester (polyvinylchloride)
Silicon coated glass
Teflon coated glass P.T.F.E (polytetrafluroethylene)
BALE RING/ MEMBRANE PLATE
Provide a link between the membrane and structural elements..
Bale rings are used at the top of conical shapes.
Membrane plates accept centenary cables and pin connection
hardware.

FABRIC STRUCTURES : COMPONENTS
TYPES OF FABRIC MEMBRANE
PVC :
•Less expensive
•15 to 20 year life span
•Easy to erect
TEFLON GLASS:
•Similar to silicon glass, less brittle
SILICON GLASS:
•Higher tensile strength
•Brittle, subject to damage from flexing 30+ year life span

Tripod head with centenary cables
Centenary cables at a side connection
Extruded section with membrane
plate and centenary cablesTensioner

Edge c able with c lamps. Used mainly for PTFE-
coated fiber glass fabric , but also for PVC-
coated poly ester fabric when edge spans
are longer than 20 m.
CABLECLAMPS

Bale rings are a good way to control stresses in fabric roof at high
or low po ints. Used at high points they must be covered to make
the structure watertight. If used at low points, they canbe
used to gather rainwater and snow for redistribution on site.
Channel (with grommets) and lacing. Used with PVC-
coated polyester fabric where the edge has grommets spaced
at frequent intervals.
Rope is laced thro ugh the grommets and to a tie rod within the
channel.
Water dreainage via Membrane plates

TENSILE STRUCTURES
ADVANTAGES DISADVANTAGES
Longer life cycles of materials. Little to no rigidity
Materials can be re-used in form. Loss of tension is dangerous for stability
Most materials are completely recyclable. Thermal values limit use
Less impact on site.
Less construction debris after demolition.
Unique designs
Lightweight and flexible
Environmentally sensitive
High strength weight ratio

PNEUMATIC STRUCTURES

•Pneumatics are tensile structures par excellence, since only with
them it is possible to have all elements working exclusively in
tension.
•As what usually occurs with tensile structures, in a pneumatic
structure, shape cannot be imposed, since membranes do not
withstand bending, and thus geometry and loads have to interact
until a equilibrium configuration is reached.
•The design of a pneumatic structure involves the determination of
an initial or viable configuration, encompassing the structure’s
shape and the corresponding stress field.
•Besides, the viable shape has to accommodate both architectonic
requirements (form and function) and – minding materials –
structural requirements (resistance and stability).
•The design of the structure is necessarily integrated to analysis, in
a process that encompasses procedures for shape finding,
patterning and load analysis.

• Pneumatic structure is a membrane
which carries load developed from
the tensile stresses.
• Its stabilization is done by pre-
stressing the membrane either by
a) Applying an external force
which pulls the membrane
taut
b) Internal pressurizing if the
membrane is volume
enclosing.
Such structures are called “pneumatic
structures”.
• These structures can create artificial
environments adaptable to human
use .
• The pneumatic forms are bound to
increase in popularity, owing to the
tremendous freedom they provide
to the architects in designing large
free spaces within them.
• The word pneumatic is derived from the
greek word “pneuma” (meaning breath of
air), thus these are the structure which are
supported by air.
• Although pneumatic structures have been
used by mankind for thousand of years; it
was only introduced in the building
technology about 40 years ago.
1. Its principle is the use of
relatively thin membrane
supported by a pressure
difference.
2. Through increasing the inside
air pressure not only the dead
weight of the space envelope is
balanced, but the membrane is
stressed to a point where it
cannot be indented by
asymmetrical loading.
PRINCIPLE

PNEUMATIC STRUCTURES : TYPES
AIR INFLATED
STRUCTURES
AIR SUPPORTED
STRUCTURES
It consist of a single membrane (enclosing a functionally useful
space) which is supported by a small internal pressure difference.
The internal volume of a building air is consequently at a pressure
higher than atmospheric.
• They have air higher than the atmospheric pressure supporting
the envelope.
• Air locks or revolving doors help to maintain the internal
pressure.
• Air must be constantly provided.
• Life span of 20 – 25 years.
• Relatively low cost.
• They are either anchored to the ground or to a wall so that
leakage is prevented.
• They have relative low cost and they can be installed easily.
It is supported by pressurized air contained within inflated building
element. The pressurized air in the pillow serves only to stabilizing
the load carrying membrane. The covered space is not
pressurized.
• Supporting frames consist of air under high pressure.
• Internal pressure of building remains at atmospheric pressure.
• There is no restrictions in number and size of openings.
• It has the ability to support itself.
• They have potential to support an attached structure.

• The weight of the structure as
compared to the area it covers is
very less.
• The weight of the membrane roof,
even when it is stiffened by cables,
is very small.
• Low air pressure is sufficient
to balance it.
PNEUMATIC STRUCTURES: GENERAL CHARACTERISTICS
LIGHT-WEIGHT
• There is no theoretical maximum
span.
• To span a distance of 36 m for a
normal building is hard while such
spans are quite possible for
pneumatics.
SPAN
• Pneumatic structures are safer than
any other structure. Otherwise, a
proper care should be taken while
establishing.
• They are fire resistance structures.
• Suitable for temporary
constructions.
• 1 km² area can be brought down in 6
hours and can be establish in less
than 10 hours.
QUICK ERECTION & DISMANTLING
• It is not expensive when it is used as
temporary structures.
ECONOMY
• If envelope is made up of
transparent material, good natural
light enter into the structure.
• Around 50% – 80% of sunlight can
be obtained.
SAFETY GOOD NATURAL LIGHTING
• In most cases, pressure of not more
than 80-100mm and not less than
60mm.
• Man can withstand pressures
between 0.20 atm to 3 atm.
Therefore no health hazard is
presented by continuous stay in
a pneumatic structure.
HUMAN HEALTH

• They can be made up of different
materials.
• Cannot be used as one continuous
material.
• Material are seamed together by
sealing, heat bonding or mechanical
jointing.
• The design of the envelope depends on
an evenly pressurized environment.
PNEUMATIC STRUCTURES : SYSTEM COMPONENTS
ENVELOPE
• They act as the supporting system.
• They experience tension force due to
the upward force of the air.
• Can be placed in one or two directions to
create a network and for better stability.
• They do not fail since they are pulled
tight enough to absorb the external
loads.
CABLE SYSTEM
• It is used to supply and maintain
internal pressure inside the structure.
• Fans, blowers or compressors are used
for constant supply of air.
• The amount of air required depends on
the weight of the material and the wind
pressure.
PUMPING EQUIPMENT
• Doors can be ordinary doors or
airlocks.
• Airlock minimize the chances of
having an unevenly pressurized
environment.
ENTRANCE

• Pneumatic structures are secured to ground using heavy
weights, ground anchors or attached to a foundation.
• Weight of the material and the wind loads are used to
determine the most appropriate anchoring system.
• For bigger structures, reinforcing cables or nets are used.
• For a dependent pneumatic structure (roof only air
supported structure) the envelope is anchored to the main
structure.
• When anchoring is done to soil, the cable is attached to the
anchor directly inserted and frictional forces of the soil to
hold it down.
• Soil anchoring systems include screw, disk, expanding
duckbill and arrowhead anchors.
FOUNDATION
PNEUMATIC STRUCTURES : SYSTEM COMPONENTS

• Wind and Snow loads are the primary loads that are acting
on pneumatic structures.
• They are anchored very tight to the ground, so no horizontal
forces are exerted to the envelope.
• As pneumatic structures are tensile, the envelope has the
ability to gain stiffness in order to withstand the loads acting
on them.
PNEUMATIC STRUCTURES : LOADING
• Wind loads produce a lateral force on the structures and
snow load causes downward forces on envelope.
• Pneumatic structures are designed to withstand wind load of
120 mph and a snow load of 40 pounds/yard.
AIR SUPPORTED STRUCTURES AIR INFLATED STRUCTURES

PNEUMATICSTRUCTURES : CLASSIFICATION
• Pneumatic Structures use either positive pressure or negative pressure.
• In Positive Pressure System, the membrane is always curved outwards, whereas in
Negative Pressure Systems the membrane is curved inwards.
• Being curved inwards there is a tendency of water logging & snow accumulation.
• Moreover, negative pressure systems require high supports at the edge or in the
center which makes it more expensive.
Pneumatic Structures can be further subdivided as:-
A. Type of Differential Pressure
B. Degree of Differential Pressure
TYPE OF DIFFERENTIAL PRESSURE
C. Type of Surface Curvature
D. Proportions
DEGREE OF DIFFERENTIAL PRESSURE
LOW PRESSURE SYSTEMS
These systems are provided with low pressure air; hence have to be provided with
continuous supply of air. Example: Air Supported Structures.
HIGH PRESSURE SYSTEMS
Used for easy erection & dismantling; the pressure difference is b/w 2000-7000mm of
water pressure (100 to 1000 times) low pressure systems.
These high pressure air inflated systems are either having a single valve system or a
double valve systems which avoids it’s collapse.
AIR SUPPORTED
STRUCTURES
AIR INFLATED
STRUCTURES

a. Single curved
b. Doubly curved in the same direction or
synclastics
c. Doubly curved in opposite direction or
anticlastic
TYPE OF SURFACE CURVATURE
These structures can also be classified according to the
types of curvature on the outer surface,
PROPORTIONS
On the basis of different proportions, pneumatic structures
can be:-
a. Two dimension of similar size and one larger
dimension
Example: Tubes, Masts, Columns, Towers
b. Two dimensions of similar size and one smaller
dimension
Example: Cushions , Lenses, Mattresses
c. Three dimensions of similar size
Example: Balloons, Balls, Spheres, Bubbles
DOUBLY CURVED IN THE SAME
DIRECTION
DOUBLY CURVED IN OPPOSITE
DIRECTION
PNEUMATICSTRUCTURES : CLASSIFICATION

• They high tensile strength, elastic
behavior and durability.
• Coated with Teflon or silicone to
increase resistance to extreme
temperatures and UV radiation.
FIBERGLASS
• Most common envelope material
for smaller structures.
• PVC-coated polyester is common
for flexible, smaller air-supported
structures.
• The PVC is applied to the
polyester using a bonding or
adhesive agent.
POLYESTER
ETFE (ETHYLENE
TETRAFLUOROETHYLENE)
• It is very energy efficient because
of transparency, insulation and
UV resistance.
• It is also light weight has an
lifespan on 20 years and is
recyclable.
NYLON
• Vinyl-coated nylon has more
strength, durability and stretch
than polyester.
• They have a higher cost.
ENVELOPE MATERIALS
PNEUMATICSTRUCTURES : MATERIALS

• Materials for ballasts of smaller structures include sand bags,
concrete blocks or bricks.
• The ballasts must be placed around the perimeter of the
structure to evenly distribute the load.
BALLASTS
ANCHOR MATERIALS
The anchor material depends on the application and size of the pneumatic structure.
STEEL CABLES
• Steel wires are twisted into strands which are then twisted around a core to form the
cable.
PNEUMATICSTRUCTURES : MATERIALS

SPORTS & RECREATIONAL
CENTRES
Ability to span great distances without
beams and columns.
MILITARY STRUCTURES
For storage, for emergency medical
operations & To protect radar stations from
weather conditions
EXHIBITION & CONVENTION CENTRES
STRUCTURES FOR BOTANICAL GARDENS,
ZOOLOGICAL GARDENS, GREENHOUSE,
HOTHOUSE
TRAVERSING BRIDGE STRUCTURES
PNEUMATICSTRUCTURES : APPLICATIONS

PNEUMATIC STRUCTURES : ADVANTAGES & DISADVANTAGES
ADVANTAGES DISADVANTAGES
• Light weight
• Covers large spans without internal supports
• Rapid assembly and have low initial and operating cost
• Portability
• Need for continuous maintenance of excess pressure in the
envelope
• Relatively short service life
• Continuous operation of fans to maintain pressure
• Cannot reach the insulation values of hard-walled structures
CONCLUSION a) Pneumatic structures have found wide range of application.
b) They are best suited for small and temporary construction.
c) They can be quickly erected and dismantled.
d) Provoke fascination among observers and bystanders.

Graphical representation of air-supported hall and hall constructed with airbeams

Tensile structures and Pneumatic Structures

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