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• Membrane Structures that are stabilized by pressure of
• Pressure difference between the enclosed space and the
exterior are responsible for giving the building its
shape and its stability.
• The pressure should be uniformly distributed for
• Round in shape because it creates greatest volume
for least amount of material.
• The whole envelope has to be evenly pressurized for
• Pre stressing of membrane can be done either by
applying external force or by internal pressurizing.
• Use of relatively thin membrane supported by
• Dead weight increases by increasing the internal
pressure and the membrane is stressed so that no
asymmetrical loading occurs.
• Membrane can support both tension and
compression and thus withstand bending moment.
• Air Supported Structures
• Air Inflated Structures
Air Supported Structures
• They have air higher than the atmospheric pressure
supporting the envelope.
• Air locks or revolving doors help to maintain the
• Air must be constantly provided.
• Life span of 20 – 25 years. 6
• 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
Air Supported Structure
Air Inflated Structures
• Supporting frames consist of air under high pressure.
• Internal pressure of building remains at atmospheric
• There is no restrictions
in no. and size of
• They have potential
to support an attached structure.
• The concept of pneumatic structures were developed
during the development of hot air balloons.
• A brazilian priest Gusmao conducted the first
experiment in 1709.
• During second world war, after the invention of nylon,
these structures were widely used in military
operations, as shelters.
• These were later used for protecting radar from
extreme weather conditions.
• Weight compared to area is less.
• Low air pressure is required to balance it.
• There is no theoretical maximum span.
• To span a distance of 36 km for a normal building is
hard while such spans are quite possible for
• Not expensive in case of temporary structures.
• More safer but proper care should be taken.
• They are fire resistance structures.
Quick erection and dismantling
• Suitable for temporary constructions.
• 1 km² area can be brought down in 6 hours and can
be establish in less than 10 hours.
Good Natural Light
• If envelope is made up of transparent material good
natural light entre into the structure.
• Around 50% – 80% of sunlight can be obtained.
• They are very safe structures.
• If the air bag is cut with a knife or a pin a big bang
• 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
• 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.
• 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.
•Doors can be ordinary doors or airlocks.
•Airlock minimize the chances of having an unevenly
•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
• 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.
• 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.
• Wind loads produce a lateral force on the structures
and snow load causes downward forces on
• Pneumatic structures are designed to withstand
wind load of 120 mph and a snow load of 40
Air Supported Structure
• The analysis can be carried out either
mathematically, numerically or experimentally.
• In simple forms forces are resolved normal to the
plane of the membrane.
• This leads to a formula relating the membrane
tensions to the principle radii of curvature for a
given internal pressure:
• N ,N₁ ₂ membrane tensions
• r ,₁ r₂ the principle radii of curvature
• P internal pressure
RESPONSE OF HEMISPHERICAL STRUCTURE
• Apart from rain & snow accumulations, the causes
of failure are inadequate anchorage and the
instability due to high wind speeds.
• The first part of this study, an aeroelastic model of
a large-span, hemispherical, air-supported roof was
designed and tested.
• Objective is to examine the roof response and the
internal pressure fluctuations caused by wind loading.
• In second part of study, procedure is based on the
measurements of the external pressures using a rigid
Construction of Aeroelastic Model
• Model was made using plexiglas mold to required
shape under pressure and elevated temperature.
• To make adjustments inside the model, a circular
access door was made in the chamber wall.
• A manometer was attached to the chamber to monitor
the mean internal pressure and to detect leakage.
• Pressure transducer was connected inside the model
to monitor the internal pressure fluctuations caused
by the movement of the roof due to wind pressure.
• Aluminum foil targets were glued to the roof at the
probe locations to provide electrical conductivity.
Free Vibration Tests of Aeroelastic Model
• To find the natural frequencies, damping ratios, and
mode shapes of the structure.
• 2 types of excitation
• The random excitation was done using noise with a
frequency range of 0-400 Hz.
• Harmonic excitation was then applied stepwise at
each natural frequency.
• As the internal pressure increases, the natural
frequency increases as the roof becomes stiffer.
Wind Tunnel - Aeroelastic Tests
•The models were tested in the high speed section that
has dimensions of 2.5 m high, 3.4 m wide, and 39 m
•3 terrain exposures were used by varying the height:
•No. of locations were selected and the test was
conducted for different rotation angle. 26
• The outputs were connected either to the on-line
computer or to the HP analyzer.
• The digital data acquisition system was used to
obtain the maximum, minimum, mean, and RMS
values of roof response and the internal pressure.
• The deflections and the internal pressure
fluctuations were measured over a period.
• The aeroelastic model remained aerodynamically
stable for all of the internal pressures and wind
speeds employed 27
.Effect of Wind Speed
• The mean response is proportional to the square of
the wind speed, as in conventional structures.
• RMS deflections are small in comparison with the
mean deflections of the roof and appear to decrease
with turbulence intensity for the same wind speed.
Effect of Exposure
•The open-country exposure gives higher mean and
smaller RMS deflections at roof center.
•Because for the open-country, the mean wind speed
at the rooftop is higher than other exposures, yielding
higher mean deflections.
Internal Pressure Effect
•There is a tendency toward reduced mean and
dynamic deflections with increasing internal pressure
for a specific wind speed.
• The mean response decreases as the internal
pressure of the model increases.
Wind-Tunnel Pressure Tests on Rigid Model
• The terrain roughness affected the external
• The mean external pressures for the open-country
exposure were higher than those for other
• The urban exposure resulted in higher RMS
pressure values than other exposures.
Comparison of Analytical and Experimental Results
•Internal pressure of the model increases, the mean
and RMS deflections decrease.
•The maximum difference between the analytical and
experimental results is about 14%.
•The mean membrane deflections in strong winds are
very large compared with conventional structures.
•The dynamic response is generally small compared
with the mean deflections.
THERMAL PERFORMANCE ANALYSIS
• The major environmental factors governing the
comfort criteria are
the mean radiant temperature
• Air movement plays a major role in the process of
heat exchange in hot climates.
• The air inside the structure are periodic functions
• Climatic data of Trinidad are used for the analysis.
• The skin temperature of the structure can be
calculated by using the energy-balance equation.
• Assumptions made are
• the temperature gradient in the thin water film is
• an arithmetic average value has been used for the
temperature of the water
• the partial pressure of water vapour in atmospheric
air is assumed to be constant.
• The use of water spray and reflective coatings
help to reduce the heat flux and the skin
temperature of the structure. 33
•There is no significant reduction in the inside air
temperature leading to comfort conditions.
VIBRATIONS OF PNEUMATIC STRUCTURES
INTERACTING WITH AIR
•The effect of the air surrounding the structure on the
structure’s natural frequencies is significant. For the
higher frequencies the influence of the air is less
•The effect of compressibility of the air varies with
the frequency of the force applied. 34
• Envelope Materials
• Anchor Materials
• They should be light weight.
• Should have high tensile strength, tear
• They high tensile strength, elastic behavior
and durability. 35
• Coated with Teflon or silicone to
increase resistance to extreme
temperatures and UV radiation.
• Most common envelope material for smaller
• PVC-coated polyester is common for flexible,
smaller air-supported structures.
• The PVC is applied to the
polyester using a bonding
or adhesive agent.
• 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.
• Vinyl-coated nylon has more strength, durability
and stretch than polyester.
• They have a higher cost.
• The anchor material depends on the application and
size of the pneumatic structure.
• Steel wires are twisted into strands which are then
twisted around a core to form the cable.
• 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.
• Light weight
• Covers large spans without internal supports
• Rapid assembly and have low initial and operating
• 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
• Weather Condition
• Continuous pressurization
Span Limitations : No limitation
Height Limitations: No limitation
Load Capacity: Internal pressure of 1psi for every
144 psf loading
Sports and Recreation
• Ability to span great distances
without beams and columns.
Eg. American Football or
• For storage, for emergency medical operations.
• To protect radar stations from weather conditions
• Used within dams and flood prevention systems.
• It can be used in a relatively small river or stream.
Military Radar Station Swimming
Case Study: Minnesota Metrodome
• It requires 120 m³/s of air to keep it inflated.
• Air pressure is supplied by twenty 90-horsepower
• The entire roof weighs roughly 580,000 pounds.
• It reaches 59 m or about
16 storey, at its highest point.
• Pneumatic structures have found wide range of
• They are best suited for small and temporary
• They can be quickly erected and dismantled.
• Provoke fascination among observers and
• An Outline of the Evolution of Pneumatic Structures,
Jung Yun Chi and Ruy Marcelo de Oliveira Pauletti.
• Pneumatic Structures: A Review of Concepts,
Applications and Analytical methods, C.G. Riches &
• Response of Hemispherical, Air supported structures
to wind by Magdy Kassem1 and Milos Novak,2
• Stability of Cylindrical Air supported structures by
Robert Maaskant and John Roorda.
• Stimpfle Bernd, "Structural Air - Pneumatic
• Thermal Performance Analysis of Pneumatic
Structures, P. Gandhidasan and K. N. Ramamurthy.
• Vibrations of Pneumatic Structures Interacting
with air, R. Sygulski