Slide 1

PNEUMATIC STRUCTUREHistory:

In late 1940s Walter Bird was the first person who used tin supported members(Pneumatic structures) for covering swimming pools temporary warehouse exhibition building.

The first structure were used in 1946 by Walter bird for housing of a radar antenna structure USA.

The Romans are reputed to have developed pneumatic envelopes using treated animal skins and intestines for support in water, and the Chinese developed the first aerial balloons from paper. In the 18th century, close weaved cotton fabric made man-carrying hot air balloons possible.

In present times, pneumatic structures are predominantly used in space exploration in the development of space stations and envelopes that are easily deployable.

In addition pneumatic structures present the possibilities of creating new fluid forms that differs from conventional geometries. However, the use of pneumatic structures faces the inherent risk of cataclysmic failure in the event of a rupture in the membrane and also in some cases a requirement for a constant air supply to maintain structural stability.General study of Pneumatic structures:With the high cost of buildings different types of construction techniques are used.Popular way to hold this high cost of construction down is to use air.Air is used to hold the roof in place instead of steel and concrete.Air is cheaper than many other materials.This air can support a fabric covering or plastic that will withstand elements. Air-supported membranes were first devised by Walter Bird in the late 1940s and were soon put to use as covers for swimming pools, temporary warehouses, and exhibition buildingsIntroduction : What is pneumatics? (Pressurized construction)

Pneumatics is a science which deals with the study of gases, air etc. their behavior, characteristics with respect to construction of structure or objects which depend upon air, gases etc.

Several terminologies have been proposed and accepted around the world to define it such as blow-ups, inflatables, air domes, air houses etc.

It can be more appropriately defined as the science which deals with the control and stabilization of all kinds of structures by means of pressure differentials achieved by the uniform loading actions of air, gases.

ii. Definition:

What are pneumatic structures?

Pneumatic structures are one of the fundamental structural forms in nature and man has been in touch of this phenomenon from very early times by observing the natural pneumatic structural forms in both plants and animal life. In fruits, air bubble, soap bubble, blood vessels.

The most live example is of skin, kept taut by muscle tissues and blood pressure and largely supported in addition by a skeleton resisting bending or compression.

Basic definition of pneumatic structure can be, structures constructed or developed with air, gases as the fundamental material.

Pneumatic structure or an air supported structure has a space enclosing membrane anchored to the ground and kept in tension by internal air pressure such that it can support applied loads.

iii. Characteristics of pneumatic structure:

Pneumatic shapes are characterized by double curvature surface.

Pneumatic structures are tensile skinned.

There is no theoretical span as determine by strength, elasticity, specific weight or any other property.iv. Principle of pneumatic structures:

If u blow a sausage shaped balloon, it becomes stiff. The internal air pressure acts against the wall of balloon in all the directions so that its cylindrical shape stretches and is tensed both lengthwise and crosswise.

the balloon will be capable of acting as a column and of supporting a certain amount of load. This is because the load tends to compress its longitudinal walls, but these thin as they are will not buckle and collapse until the compression due to the load cancels the tension due to the internal air pressure. v. Construction techniques:

Membrane structure that is stabilized by the pressure of compressed air or air supported structure are supported by internal air pressure.

A network of cables stiffens the fabric and the assembley is supported by rigid ring at the edge.

The air pressure within this bubble is increased slightly above normal atmospheric pressure and maintained by compressors or fans.

Air locks are required at the entrance to prevent the loss of internal air pressure.

The envelop is tightly fastened to the foundation.

Pneumatic structuresAir inflated structureSingle storeyDouble skinArch (inflated rib structure)BeamColumn Air mat`Multi storeyDouble skinCellular annulusCentral corecompartmentedAir supported structuresSingle storeyDomeRadomeSquare domeCylindrical with 1/4th spherical endAir supported cable structureMulti storeySingle skin flexible cable networkSingle skin rigidHybrid structuresFrame supportedCable supported Lenticular cushionsTYPESi. Air supported structures:The air supported structures uses a low positive pressure (15-30kg/m2) to support membrane over a given area and provides a single wall enclosure.

Air must be supplied on stantly because of the continuous leakage, primarily through the building entries.

Since the pressure is exerted normal to the surface in all directions., the natural shape of the air supported structure is sphere.

In building terms, this normally reduces to a 3/4th

Easily transported, quickly erected volume package. Constant air input (vital to structural stability) required. Air sealing is vital- airlocks required which may cause limitations of entry, exit, and circulation.

Once erected, extension can only be achieved with deflation of entire structure and addition of extra modules.

Low cost, with a short life span (7-10 yrs), implies a throwaway product.

Deployability

The inflation tent can be said to be highly deployable. The frame and skin of the structure come affixed to each other. There is therefore no need to mount them together on site. The entire process of setting up the tent can be easily done by an untrained hand.

General Descriptions

The air-supported vinyl tent may look small from the exterior, but was actually quite spacious when we went into it. It can shelter 12 - 15 people quite comfortably.ii. Air-inflated Structure :

Membrane completely enclosing compressed air and comprises two types: Cushion and Double-layered Apertures can be placed more randomly Greater acoustic and thermal control possible Possibility of self-deployment Does not require air seal to the ground Relatively small air input required; inflation rapid Segments can be added without altering initial construction Higher pressure needed; hence higher performance needed for joints, seals and membrane itself

Air cell inflatables are advanced constructions (often referred to as pneumatic structures) made with two layers of material with fabric formers perpendicular in between. They are self-supporting and self-erectable by means of an air fan only with no need for foundation, hardware or guy wires.

Air cell inflatable buildings (or pneumatic buildings) act as permanent structures rather than temporary ones having high torsional stiffness, which allows them to withstand wind up to 80 knots and snow load up to 140kg/m2. Inflatable buildings can support loads on the roof and walls for lighting, lifting and other cabling requirements. They have great thermal and sound insulation properties, and tolerate temperatures from -30 C to + 70C.The life expectancy of inflatable buildings depends upon the climate in which they are installed and particularly the levels of UV light to which the pneumatic structures are exposed. An inflatable structure erected outdoors should survive for 10 years in Tropics and for 20 years in European conditions. If the inflatable's are kept indoors they will last almost indefinitely.iii. Inflated Ribbed Structures :High pressure tube frames Freedom of structural form Membrane independent of the rib structure Ability to change easily, allowing greater control of heat, light and sound Difficult to add to pressure tube structure; not easily extensible Initial air input is very small, inflation instant Self-deployment; pop-up package

Materials and Coatings:i Structural material:The choice of membrane material depends upon number of factors which can vary with function and design life.ii Usual Factors:Air permeabilityWeather resistance propertyChemical resistanceInsulation propertyFlexibilityIncombustibility Variation of propertiesStrength of joining methodsUSUAL MATERIALS:Four basic types of materials:Plastic filmsCoated fabricsWoven metallic fabricMetallic foils

Polyamide fabnylon

Metallic foilPLASTIC FILMSMain advantage is its transparency.But they are susceptible to ultra violet deterioration.Should be used in conjunction with cable nets.

WOVEN METALLIC FABRICSStainless steel fibres coated with suitable material are used for air tightness.

METALLIC FOILSAluminum plastic foils are used for high heat reflections.Its light weight, very strong, impermeable and has good ageing property.Feasibility of metallic foils is improper for large structures.

COATED FABRICSPolyamide fabric nylonPolyster fabrics terylene and decronThese are coated on both sides with vinyl, butyl, neoprene hypalon or other plasticized elastomers.POLYAMIDE FABRIC NYLON

POLYSTER FABRICS TERYLENE AND DECRON

Advantages: Very light weight therefore are of greater practical importance than any other structures withstanding compressive loads.Rapid development and erection.Possibility of acting as sophisticated mechanisms for controlling heat, light and soundRadical new forms are practical to be generated.

Disadvantages :Limited expansion by addition.Difficulty of placement of openings.Once erected, the structure is inflexible in terms physical response.In some cases requirement of air locks and continual air supply.Limitations on the pneumatic structures:The shape of membrane is limited by the size of the span.Clear span of 180 feet or more is requiredThere cost benefits are greatly increased at these greater spans.The inflated membrane must have enough curvature to shed snow, rain and ice but shallow enough to resist the upward suction from the wind.Wind is greatest enemy because it adds more tension to the system.Too much suction or internal pressure can rupture the membrane.Applying to much force to anchoring system can also rupture the membrane.Snow can ice can easily tear the membrane.All entrances and exits, there must be airlocks to prevent the internal pressure from escaping.An insulated, opaque membrane is used in cooler climates.