PNEUMATIC STRUCTURES:MODULAR CONSTRUCTION TECHNOLOGY

•PREPARED BY:• JESON MATHEWS• SEM VI• KMEA COLLEGE OF ARCHITECTURE

The first experiments with pneumatic structures were undertaken during the development of hot-air balloons. An effective start for the development of balloons just occurred at the end of the 18th century.

These balloons were made by linen and paper.

At the same year, Jaques A. C. Charles built the first hydrogen balloon a derigible called the zepellin.

HISTORY

A Derigible or airship

The idea of transposing the dirigibles technology to architecture tracks back to the English engineer F. W. Lanchester.

His patent of a pneumatic system for campaign hospitals was approved in England, in 1918, but was never actually constructed, due to the lack of adequate membrane materials or appeal to possible clients.

WORLD WAR II AND THE U.S. ARMY During the Word War II, and after the invention of nylon, pneumatics started to be

used in military operations, as emergency shelters and decoys.

At the end of the War, the increase in the number of military air operations demanded implementation of a large and sophisticated network of radars over the American territory.

In order to protect these radars from extreme weather conditions, the American Army sponsored the development of thin non-metallic

shelters, avoiding interference with the radar signals.

These were called ‘radomes’.

Frei Otto was the first to undertake academic investigations, specially about the process of form finding.

Through various publications, Otto broadened the landscape, not only of pneumatics, but of tension structures in general.

Pneumatics were also part of the repertoire of Richard Buckminster Fuller. His proposal of a pneumatic dome to cover New York (1962, Figure 6) is a famous example of Utopian pneumatic architecture.

Realization of this project would require a radical environmental transformation, a sterilized enclosure without dust, pollution, exhaust gases and so.

INTRODUCTION• 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 b) internal pressurizing if the membrane is volume enclosing.

• These structures can create artificial environments adaptable to human use .

PRINCIPLE• Its principle is the use of relatively thin membrane supported by a

pressure difference.

• 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 .

GENERAL CHARACTERISTICS1. LIGHT WEIGHT

2. SPAN

3. CHEAP

4. BUILD QUICKLY

5. TEMPORARY

GENERAL CHARACTERISTICS

1) LIGHT WEIGHT :- 1. The weight of the structure as compared to the area it covers is very less

2. The weight of the membrane roof , even when it is stiffened by cables, is very small

3. Low air pressure is sufficient to balance it

4. Even with spans of more than 100mts, the weight of the structure does not exceed 3kg/square metre .

2) SPAN :-

• Another advantage over other structures is that, for pneumatic membrane , there is no theoretical maximum span as determined by strength, elasticity, specific weight or any other property.

• It is hardly possible to span a distance of over 36km. With a steel cables as they would fail because of their inability to sustain their own weight. But with pneumatics, such spans are quiet possible.

3) QUICK ERECTION AND DISMANTLING:- • Suitable for temporary constructions because they are as easy to dismantle as

to establish.• 1 sq.Km. Of an area can be brought down in 6 hours. And establish in less

than 10 hours. The 4 hours difference is due to establishment of pegs etc.

4) ECONOMY:- Pnuematic structures are relatively cheaper for erecting temporary structures

when compared to permanent ones. Otherwise the cost per square foot of air supported structures is among the lowest for large span roofs.

5) GOOD NATURAL LIGHT:- Gives good natural light as translucent/transparent plastic sheets are used to cover spaces. Daylight can be brought in efficiently. There is a lot of flexibility in getting sun light(50%-80%).

TYPES OF PNEUMATIC STRUCTURES:- These are primary classes of pneumatic structures:-

Air supported structures and 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.

• The air supported structure uses a low positive pressure to support a membrane over a given area. Air must be supplied constantly because of the continuous leakage, primarily through the buildings.

• Used most often because of:. Their relatively low cost. Their simplicity of design and fabrication

AIR – INFLATED STRUCTURE:-

• It is supported by pressurized air contained within inflated building element.

• The internal volume of building air remains at atmospheric pressure. The pressurized air in the pillow serves only to stablizing the load carrying membrane . The covered space is not pressurized .

• Advantages of air- inflated / air frame structure :-1. the ability for self support2.The potential to support an attached structure

CLASSIFICATION OF PNEUMATIC STRUCTURES:- Pneumatic structures can be further subdivided based on:-

1) type of diffrential pressure 2) degree of diffrential pressure3) type of surface curvature4) proportions

1. TYPE OF DIFFRENTIAL PRESSURE:-. A) PNEUMATIC STRUCTURES USE EITHER Positive pressure or negative pressure. B) In positive pressure system, the membrane is always curved outwards, whereas in negative pressure systems the membrane is

curved inward. C) Being curved inwards the structure is prone to water logging & snow

accumulation. D) Moreover, negative pressure systems require high supports at the edge or in

the centre which makes it more expensive..

2. DEGREE OF DIFFERNTIAL PRESSURE:-

LOW PRESSURE SYSTEMS - These systems are provided with low pressure air ;hence have tobe provided with continuous supplyof air. Eg-air supported structures.

HIGH PRESSURE SYSTEMS -Used for easy erection & dismantlingThe pressure difference is b/w 2000-7000mm of water pressure (100 to 1000 times of low pressure systems)

These high pressure air inflated systems are either havinga single valve system or a double valve systems which avoids it’s collapse.

TYPE OF SURFACE CURVATURES:- These structures can also be classified according to the types of curvature on

the outer surface-a) Single curvedb) Doubly curved in the same direction or synclasticsc) Doubly curved in opposite direction or anticlastic

4. PROPORTIONS:- On the basis of different proportions, pneumatic structures can be:-

• Two dimension of similar size and one larger dimension eg:- “tubes”, ”masts”, ”columns”, ”towers”.

• Two dimensions of similar size and one Smaller dimension, eg:- “cushions”, ”lenses”

• Three dimensions of similar size, Eg:- “balloons”,”balls”, ”spheres”, ”bubbles

5. MATERIALS:-ISOTROPIC:- THESE SHOW THE SAME STRENGTH AND STRETCH INALL DIRECTIONS. EXAMPLES ARE:-

PLASTIC FILMS:- These are primarily produced from PVC,Poly-ethylene, polyester, polyamide etc.

FABRICS:- These may be made of glass fibres or syntheticFibres which are coated in a PVC, polyester orPoly-urethene film.

RUBBER MEMBRANE:- They are the lightest and most flexible.

METAL FOILS:- They possess a very high gas diffusion resistance and high tensile strength. One of the major problems in the use of metal foils is in need to produce veryexact cutting joints and edges

ANISOTROPIC MATERIALS:- These do not show the same strength and stretch-ability in all directions. They have direction oriented properties. Examples are:-

WOVEN FABRICS:- they have two main direction of weave.They can be made of:- . Organic fibres eg:- wool, cotton or silk. . Mineral fibres eg:- glass fibres. . Metal fibres eg:- thin steel wires. . Synthetic fibres eg:- polyamide, polyester and poly-vinyl

GRIDDED FABRIC:- these are coarse-weave made oforganic mineral or synthetic fibres or metallic networks. They are particularly used where maximum lighttransmission and high strength is required.SYNTHETIC RUBBERS:- combination of plastic and rubber.They can take better wear and tear. They are latest and aremore resistant to elongation. PLASTICS:- Similar to woven fabrics. Its advantage is that theyhave more of tensile strength than normally manufacturedplastic sheets.