b"(Continued frompagel 0)ards(is50percentofthedy4) theDynamicorstagnationpressurenamicwindpressure.In theUnited of thewind,bothhighstabilityandStatesair-supported structuresareusverygooddeflectioncharacteristicsuallydesignedtowithstandaminiareobtained.Experiencehasshown,mum wind velocity of 60 or 70 mph. however,that for many usessatisfac (This requires an inflation differential toryperformancecharacteristics(in pressureofapproximately1inchof cluding acceptable deflections)can bewater.)In Canada the National Buildobtainedwithsomewhatlowerinfla ingCoderequiresthatbuildingsbe tion pressures(seeInflation System).designedtowithstandthewindload specifiedfortheparticularlocation Materialunderconsideration.Thismaybe The material of the envelope of anmoreor Jessthanthespeedsquoted air-supported structure has a most im aboveandmayrequirecorrespondportant influence on the performancespecifiedintheASMSAStandardsinglydifferentpressures. ofthestructure.Certaincombina (to ensure reliability.Blower capacity should be designed 4)to allowfor tions of properties are required to en Manymanufacturersrecommend( 1)anticipatedmaximumleakage suresatisfactoryperformanceandathat only a heat-sealed joint should beat the base, around doors and through long service life and characteristics toused for all load-carrying joints; whenvents( thetotalleakageairmustbe be considered in materials for air-sup properlydonethisprocessresultsinreplacedbyairfromtheblowerat portedstructuresinclude:tensileseamsactuallystronger than thema thedesigninflationpressure;experistrength in both warp and weft of theterialitself.Sewnjointsoftenofferenceindicatesthatconservativelyesfabric;tearresistance to reduce acci poor servicelife.In tentsandawn timated leakage losses - assuminga dentaldamage;coatingadhesiontoings,forexample, the sewn joint hasdifferentialpressure of1 inch of wathe fabric under all conditions of op longbeenrecognizedastheweakter- are10cuft/perlinear eration; weathering resistance,includ link.Cementedjointsareacceptablemin foot of base perimeter, 200 cu ft/ ingresistancetoultra-violet degrada when properly made but mustdevel min tion, abrasion resistance and retentionopthefullstrengthofthefabric.per door assembly, and 2400 x A cfm of physicalpropertiesafterlongpe InflationSystemforventswhereAisthetotalvent riodsofexposure;suitabilityoftheAir-supportedstructuresneedonlyarea insquare feet; (a ventilation airflow of at least materialforjointinginordertode small pressures to hold them up, i.e.,2) velopthefullstrengthofthebaseapproximately1inchof waterstatic30cuft/minperperson;and (aninitialinflation timespecimaterial; pliability to prevent damagepressureor0.036psi.Tovisualize3) duringpacking,storage andhandlinghowlowapressurethisrepresents,fiedbythedesignrequirements. at cold temperatures; flame spread re considerthatwhenonepuffsone'sInitialinflationrequirementswill sistance tomeet fire codes whereap cheekswithairabout30inchesofgenerallydictatetheblowercapacity plicableandpreventpropagationofwaterstaticpressurecanbecreatedrequired for structures having afloor flame; translucence or opacity, as ap insidethemouth,orthatanauto areaof morethan30 sqftper perplicationrequires.Therelativeim mobiletirecarriesabout800inchesson.Structures that provide less than portanceofeachcharacteristicmayof waterstaticpressure.Onlywhen30 sq ft per person may require addivarywiththeapplication,butallopeningthedoorcananyoneenter tionalblowercapacitytoaccommoshould be carefully evaluated.inganair-supportedstructureknowdateagreaternumberof occupants Amongthematerialsavailableforthatairpressureisinvolved.owingtotheincreaseinnumberof envelope construction one of the mostThegreatertheinflationpressuredoors and vents, and anticipated leaksatisfactoryforcommercialapplica the bettertheabilityof the envelopeageorventilationflowmaydictate tionsappearstobevinyl-coatedny toresistwindloadingswithoutsig theblowerrequirements. lon,inwhichheavynylonfabricisnificantdeformation.InpracticalItisrecommendedthatblowers coatedon both sideswithaspeciallyterms, therefore, the pressure requiredshouldbecapableofprovidingat compoundedpolyvinyl-chlorideelas willbeafunctionoftheprevailingleast twice the calculated airflow.The tomer.Thefabricprovidesthedesign wind speed.NationalBuildingCode requiresthat strength,thevinylcoating,theBased on extensive wind tunnel andstructures classified asassembly occuweather protection.The vinyl is com full-scale tests, the minimum inflationpancyshouldbefurnishedwithtwo poundedwith certainadditivesto re pressureforair-supportedstructuresblowers, each with sufficient capacity tardmildewandfungusgrowth,andrecommendedby theASMSAStand- to supply the required air.The standtoprovidepliability,weatherresist by unit is set to turn on automatically REFERENCES ance,toughness,flamespreadresist 1.Dietz,A.E.,R.B.Proffitt,andR.S.intheeventofmechanicalorelecance, colour or opacity, and ultra-vio Chabot,DesignManualforGroundtrical failure in the operating unit. An let absorption.MountedAir-SupportedStructures(Singleautomatic starting power generator is Useof otherfibresorelastomers,and Double Wol/j. U.S.Army NatickLob.,normallyprovidedforthispurpose. althoughnotcommonatthistime,TechnicalReportNo.69-59GP,JanuaryEachblowerisnormallyequipped 1969. may be acceptable if the requirements2.Dietz,A.E,.R.B.ProffittandR.S.withabackdraftdampertoprevent indicatedabovecan bemet.DacronChabot,WindTunnelTestsandAnalysisairlosswhenitisinoperative.To andglassfabricshavebeenused;forGroundMountedAir-SupportedStruc prevent over-pressurization, backward, polyethyleneandhypalon elastomers,tures.U.S.ArmyNaticklob.,Technicalcurved-bladecentrifugalblowersthat as well as others now in development,ReportNo.67-36.ME,October1966.deliveravariableairvolumeata 3.Bird, W.W.,DesignManualfor Spherical mayprovetobeacceptable.Air.SupportedRodomes(Revised).Reportspecifiedpressurearerecommended. Materialsmaybejoinedbyelec No.u4.909.o.2CornellAeronauticallab Allblowersshouldprovideadequate tronicwelding,cementingorsewing,oratory,March1956.protection for personnel,for example but becauseastructurecan obvious 4.MinimumStandardsforAir-Supportedinletscreenandbelt guards,andreStructures,1961.AirStructuresManuly be no stronger than its joints, mini facturers and Suppliers Assoc.,Box21, Co quireprotection fromthe weatherto mumjointstrengthperformanceislumbia,Ohio,U.S.A.ensureoperationatalltimes. AUGUST,197111"