REPORT ON PNEUMATIC STRUCTURE STRUCTURE SYSTEM PNEUMATIC STRUCTURE

REPORT ON PNEUMATIC STRUCTURE (STRUCTURE SYSTEM)

PNEUMATIC STRUCTURE INTRODUCTION : • PNEUMATIC STRUCTURE IS A MEMBRANE WHICH CARRIES LOAD DEVOLPED FROM THE TENSILE STRESSES. • ITS STABLIZATION IS DONE BY PRESTRESSING 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 N POPULARITY, OWING TO THE TREMENDOUS FREEDOM THEY PROVIDE TO THE ARCHITECTS IN DESIGNING LARGE FREE SPACES WITHIN THEM.

ORIGIN : • • • THE WORD PNEUMATIC IS DERIVED FROM THE GREEK WORD “PNEUMA”(MEANING BREATH OF AIR) , THUS THESE ARE THE STRUCTURE WHICH ARE SUPPORTED BY AIR. “PNEUMATIC STRUCTURE” HAS BEEN USED BY MANKIND FOR THOUSAND OF YEARS. BUT IN THE BUILDING TECHNOLOGY IT WAS INTRODUCED ONLY ABOUT 40 YEARS AGO. 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. GENERAL CHARACTERISTICS: CHARACTERISTICS 1) LIGHT WEIGHT: a) THE WEIGHT OF THE STRUCTURE AS COMPARED TO THE AREA IT COVERES 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 100 MTS, THE WEIGHT OF THE STRUCTURE DOES NOT EXCEED 3 KG/SQUARE METRE. 2) SPAN : • NO STRUCTURE CAN GURANTEE TO GIVE THE SPANS UPTO CERTAIN LIMITS CABLE STRUCTURES ARE EXCEPTIONS( CABLES FOR BRIDGES USUALLY). • 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 36 KM. 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) SAFETY: SAFETY PNEUMATIC STRUCTURES ARE SAFER THAN ANY OTHER STRUCTURE. OTHERWISE, A 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. 4. THEFT: 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. 5. HUMAN HEALTH: -IN HEALTH: - MOST CASES, PRESSURE OF NOT MORE THAN 80100 mm AND NOT LESS THAN 60 mm. 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. 6. QUICK ERECTION AND DISMANTLING: 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.

6. ECONOMY: 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: 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%).

TYPES OF PNEUMATIC STRUCTURES: THESE ARE PRIMARY CLASSES OF PNEUMATIC STRUCTURES: AIR SUPPORTED STRUCTURES AND AIR –INFLATED STRUCTURES AIR – SUPPORTED STRUCTURES: 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 STRUCTURE 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: -. PRESSURE a) PNEUMATIC STRUCTURES USE EITHER POSITIVE PRESSURE OR NEGATIVE PRESSURE. b) IN (+) PRESSURE SYSTEM, THE MEMBRANE IS ALWAYS CURVED OUTWARDS, WHEREAS IN NEGATIVE PRESSURE SYSTEMS THE MEMBRANE IS CURVED INWARDS. c) BEING CURVED INWARDS THERE IS A TENDENCY OF WATER LOGGING & SNOW ACCUMULATION. d) MOREOVER, NEGATIVE PRESSURE SYSTEMS REQUIRE HIGH SUPPORTS AT THE EDGE OR IN THE CENTRE WHICH MAKES IT MORE EXPENSIVE. e) BOTH OF THESE SYSTEMS ARE USED FOR STORAGE PURPOSES AS THEY CAN KILL THE RODENTS.

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 -7000 MM 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: CURVATURES THESE STRUCTURES CAN ALSO BE CLASSIFIED ACCORDING TO THE TYPES OF CURVATURE ON THE OUTER SURFACEa) SINGLE CURVED b) DOUBLY CURVED IN THE SAME DIRECTION OR SYNCLASTICS c) DOUBLY CURVED IN OPPOSITE DIRECTION OR ANTICLASTIC 4. PROPORTIONS: 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: 5 ISOTROPIC: - THESE SHOW THE SAME STRENGTH AND STRETCH IN ALL DIRECTIONS. EXAMPLES ARE: PLASTIC FILMS: 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: 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

ANISOTROPIC MATERIALS: MATERIALS THESE DO NOT SHOW THE SAME STRENGTH AND STRETCHABILITY IN ALL DIRECTIONS. THEY HAVE DIRECTION ORIENTED PROPERTIES. EXAMPLES ARE: WOVEN FABRICS: 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. GRIDDED FABRIC: FABRIC THESE ARE COARSE-WEAVE MADE OF ORGANIC MINERAL OR SYNTHETIC FIBRES OR METALLIC NETWORKS. THEY ARE PARTICULARLY USED WHERE MAXIMUM LIGHT TRANSMISSION AND HIGH STRENGTH IS REQUIRED. SYNTHETIC RUBBERS: RUBBERS COMBINATION OF PASTIC AND RUBBER. THEY CAN TAKE BETTER WEAR AND TEAR. THEY ARE LATEST AND ARE MORE RESISTANT TO ELONGATION. PLASTICS: PLASTICS LIKE WOVEN FABRICS. ITS ADVANTAGE IS THAT THEY HAVE MORE OF TENSILE STRENGTH THAN NORMALLY MANUFACTURED PLASTIC SHEETS.

PNEUMATIC STRUCTURES Usages in History: 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 BUILDING WITH PNEUMATIC ADAPTABLE TO HUMAN USE IN ANY PART OF ROOF THE WORLD.