PNEUMATIC

STRUCTURES

Suganya Sridhar

Sneha P

Sahithya S Theertha

Revathi Velu

Deepika Patil

Deepa Kulkarni

INTRODUCTION :-

•PNEUMATIC STRUCTURES ARE ESSENTIALLY MEMBRANE STRUCTURES

WHICH ARE STABILISED BY THE PRESSURE OF COMPRESSED AIR AND

ARE TENSILE SKINNED

• ITS STABLIZATION IS DONE BY PRESTRESSING THE MEMBRANE EITHER BY:-

a)PPLYING 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 N POPULARITY, OWING TO

THE TREMENDOUS FREEDOM THEY

PROVIDE TO THE ARCHITECTS IN

DESIGNING LARGE FREE SPACES

WITHIN THEM.

PRINCIPLE:-

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 ENVOLPE IS BALANCED, BUT THE MEMBRANE IS

STRESSED TO A POINT WHERE IT CANNOT BE INDENTED BY ASYMMETRICAL

LOADING .

HISTORICAL BACKGROUND

THE TECHNOLOGY BEHIND PNEUMATIC STRUCTURES HAS BEEN LONG KNOWN TO

US. BUBBLES HAVE AROUSED PEOPLE‟S CURIOSITY FOR LONG. THE MORE

IMMEDIATE USE OF PNEUMATICS HOWEVER LIES IN BALOONS AND AIRSHIPS THAT

HAVE GRACED OUR SKIES IN THE RECENT PAST.

IN 1922, THE OASIS THEATRE IN PARIS SPORTED A PNUEMATIC HOLLOW ROOF

STRUCTURE THAT WAS ROLLED INTO PLACE WHEN IT RAINED.

DURING WORLD WAR PNEUMATIC STRUCTURES PLAYED AN IMPORTANT ROLE AS

„RADOMES‟, WHICH HOUSED LARGE RADAR ANTENNAE.

THEY CAN CREATE ARTIFICIAL ENVIRONMENT ADAPTABLE TO HUMAN USE IN ANY

PART OF THE WORLD.

BUILDING WITH PNEUMATIC

ROOF

GENERAL CHARACTERISTICS:-

LIGHT WEIGHT:-

a) THE WEIGHT OF THE STRUCTURE AS COMPARED TO THE AREA IT COVERES IS

VERY LESS

b) 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 .

SPAN :-

• FOR A BUILDING, THEN THE LIMITATION IS 500 FEET SPAN DUE TO ITS SELF WEIGHT.

• ANOTHER ADVANTAGE OVER OTHER STRUCTURES IS THAT, FOR PNEUMATIC

MEMBRANE , THERE IS NO THEORTICAL 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 POSSIBLE.

SAFETY:- PNEUMATIC STRUCTURES ARE

SAFER THAN ANY OTHER STRUCTURE.

HOWEVER, PROPER CARE SHOULD BE

TAKEN WHILE ESTABLISHING

• ACCIDENTAL CIRCUMSTANCES ARE

AVOIDED AS THEY ARE VERY LIGHT.

• THERE ARE WARNING SIGNALS WHILE THE

RELEASE OF RETURN VALVE. SAFETY

FACTOR+ WARNING TIME IS QUIET LONG

AS COMPARED TO OTHER STRUCTURES.

• PNEUMATIC STRUCTURES CANT BE

DESTROYED BY FIRE QUICKLY AND

TOTALLY.

THEFT:- IT IS VERY SAFE NO BODY CAN OR

PASS THROUGH A PNEUMATIC

STRUCTURE. IF AN AIR BAG IS CUT WITH A

KNIFE/ PIN, A BANG IS PRODUCED.

HUMAN HEALTH:-IN MOST CASES, PRESSURE OF NOT MORE THAN 80-100mm

AND NOT LESS THAN 60mm.BUT MAN CAN WITHSTAND PRESSURES

BETWEEN 0.20 ATM TO 3 ATM. THEREFORE NO HEALTH HAZARD IS

PRESENTED BY CONTINOUS STAY IN A PNEUMATIC STRUCTURE.

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.

ECONOMY:- IT IS NOT EXPENSIVE WHERE IT IS USED FOR SHIFTING

STRUCTURES. FOR PERMANENT STRUCTURES, IT IS VERY EXPENSIVE.

OTHERWISE THE COST PER SQURE FOOT OF AIR SUPPORTED STRUCTURES

IS AMONG THE LOWEST FOR LARGE SPAN ROOFS.

GOOD NATURAL LIGHT:- GIVES GOOD NATURAL LIGHT AS

TRANSLUCENT/TRANSPARENT PLASTIC SHEETS ARE USED TO COVER AIR

BAGS.WE CAN EVEN BRING THE WHOLE SUN INSIDE. THERE IS A LOT OF

FLEXIBILITY IN GETTING SUN LIGHT(50%-80%).

CLASSIFICATION OF PNEUMATIC STRUCTURES:

PNEUMATIC STRUCTURES ARE FURTTHER SUBDIVIDED BASED ON :-

•TYPE OF DIFFERENTIAL PRESSURE

•DEGREE OF DIFFRENTIAL PRESSURE

•TYPE OF SURFACE CURVATURE

•PROPORTIONS

TYPES OF PNEUMATIC

STRUCTURES:-

AIR SUPPORTED STRUCTURES

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 INTERNALVOLUME OF A

BUILDING AIR IS CONSIQUENTLY 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 CONTANTLY

BECAUSE OF THE CONTINOUS 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 STRUTURE :-

. THE ABILITY FOR SELF SUPPORT

. THE POTENTIAL TO SUPPORT AN ATTACHED STRUCTURE

CLASSIFICATION OF PNEUMATIC STRUCTURES:-

PNEUMATIC STRUCTURES CAN BE FURTHER SUBDIVIDED AS:-

1)TYPE OF DIFFRENTIAL PRESSURE

2)DEGREE OF DIFFRENTIAL PRESSURE

3)TYPE OF SURFACE CURVATURE

4)PROPORTIONS

1. TYPE OF DIFFRENTIAL PRESSURE:-.

a) PNEUMATIC STRUCTURES USE EITHER

POSITIVE PRESSURE OR NEGATIVE PRESSURE.

b) IN (+) PRESSURE SYSTEM,THE MEMBRANE

IS ALWAYS CURVED OUTWARDS,

IN NEGATIVE PRESSURE SYSTEMS THE MEMBRANE IS

CURVED INWARDS.

c) BEING CURVED INWARDS THERE IS A TENDENCY

OFWATER 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 TO

BE PROVIDED WITH CONTINUOUS SUPPLY

OF AIR.EG-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.

TYPE OF SURFACE CURVATURES:- THESE

STRUCTURES CAN ALSO BE CLASSIFIED

ACCORDING TO THE TYPES OF CURVATURE ON

THE OUTER SURFACE-

a) SINGLE CURVED

b) DOUBLY CURVED IN THE SAME DIRECTION OR

SYNCLASTICS

c) 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”,

”DISCUSS”,”MATTRESSES”.

• THREE DIMENSIONS OF SIMILAR SIZE,

EG:- “BALOONS”,”BALLS”,”SPHERES”,

”BUBBLES

MATERIALS:-

ISOTROPIC:- THESE SHOW THE SAME STRENGTH AND STRETCH IN ALL

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 SYNTHETIC FIBRES WHICH ARE

COATED IN A PVC, POLYESTER OR POLYURETHENE 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 VERY EXACT CUTTING PATTERNS.

MATERIALSS

ANISOTROPIC MATERIALS:- THESE DO NOT SHOW THE SAME

STRENGTH AND STRETCHABILITY 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 POLYVINYLE.

ADVANTAGES

• LIGHT WEIGHT

• THE POSSIBILITY OF COVERING LARGE SPANS WITHOUT INTERNAL

SUPPORTS, COMPLETE PREFABRICATION

• RAPID ASSEMBLY

• PORTABILITY

• TRANSPARENCY TO LIGHT AND RADIO WAVES

• LOW COST

DISADVANTAGES

• NEED FOR CONTINUOUS MAINTENANCE OF EXCESS PRESSURE IN THE

ENVELOPE

•THE RELATIVELY SHORT SERVICE LIFE

•THE POOR FIRE RESISTANCE AND ACOUSTIC INSULATION.

THE USE OF PNEUMATIC STRUCTURES IS EXPEDIENT FOR PERMANENT AND

TEMPORARY BUILDINGS FOR A VARIETY OF PURPOSES (PRODUCTION AND STORAGE

AREAS, AS WELL AS HALLS FOR PERFORMANCES, SPORTS, TRADE, OR EXHIBITIONS),

MOBILE BUILDINGS (MAINTENANCE STATIONS, MEDICAL AID STATIONS,

CLUBHOUSES, AND LIBRARIES), TRANSPORTATION AND HYDRO-ENGINEERING

STRUCTURES (BRIDGES, DAMS, AND GATES), AND AUXILIARY FACILITIES IN

PERFORMING CONSTRUCTION WORK (HOISTS, WINTER SHELTERS, AND FORMWORK).