b'Air-Supportedmajor features:portability, and speed of erection and dismantling. StructuresPartIEnvelopeShapeandDesign Shape Itmustberecognizedthatthere ByD.A.LUTESarelimitationsontheshapeofair(Tobeconcluded DIVISIONOFBUILDINGRESEARCHinnextissue)supportedstructures.Everypointin NATIONALRESEARCHCOUNCILOFCANADAthesurfaceof thee~elope mustbe inequilibriumundertheloadsimposed.If these conditions are not pro 1 inthe1917patentofF.W.Lan videdbydesignandpatterning,the chester in England.envelope_ willwrinkleanddistort un } In the U.S.the Air Force in1946tilequilibriumconditionsareestabneededanew way to house the largelished.Distortion of thistyperesults radarantennae plannedfortheArc- not only in poor appearance but also . tic.WalterW.Bird,anaeronauticalin stress concentrations that could reengineer,directedateamthatde sult in failure of the structure. signed,built,andsuccessfullytestedThemostconventionalshapesinBLOWERCATENARYCABLEprototypesof radardomeswhichbe cludehemispheresorhalfcylinders cameknownasradomes.By1954capped at each end by hemispherical hundredsof thesebulbousstructureselements,but anair-supportedstrucwerescatteredacrosstheU.S.andtureisadaptabletoavarietyof ENTRANCE~Canada.shapes,generallysurfacesofrevoluDOORS~ AIRLOCKTen yearslaterin1956,Birdandtionaboutat least oneaxis. afewofhiscolleaguessetupaStructure .ported structureswerefurtherdevel velope are internalinflationair presc::-~ ENVELO PEmanufacturingcompanyandair-sup Themajor loadsactingonanen\'(".,opedandproducedcommercially.sure and wind (aerodynamic)loading. Other manufacturers entered the fieldPressuredifferencesoccuracrossthe \\~andanindustryassociation,theAirenvelopeduetostackeffect( CBD SEALStructures ManufacturersandSuppli 107),butthesebecomesignificant SK I RTers Association (ASMSA), was formedonly in relation to the design of very intheUnitedStatestoestablishhigh structuresheatedin cold weathstandards.er.Manyair-supportedstructures MajorApplicationshave been designed on the basisof a crude stressanalysisandalarge facTypical single-wall air-supported structure.Theair-supportedstructureisonetorofsafetytoensureanenvelope of the most efficient structural formscapable of withstanding a design wind availableintermsof weight ofma load.Concernformoreeconomical Awidevarietyofstructuresthatterial,althoughnotnecessarilyofstructures,however,hascreateda usepressurizedairtostiffenorsta cost,foritcombinestheinherentneedforamorerefinedanalysisof bilizeathinenvelopeof pliablema tensilestrength of materialswiththestresses.Fabricstressdistributions terial to form astructural shape maystructural efficiency of the shell form.have been determined using wind-tunbe included in thedescription"pneu Therearesomedisadvantages,how nel-measuredpressuredistributions matic structures."The single-wall orever.Anuninterruptedairsupplyandsuitableshelltheoryformany balloon-likestructurefilledwithairmust. be available,peopleand equip basicshapes.Such basicdesigndata ment must enter and leave the build arepresentedinreference(and maintainedatapressureslightly1), aboveambientwasoriginallycalleding through air-locks,andthe lifeofdetailedderivationmaybefoundin anair-supportedstructureandisfre availableskinmaterialsisgenerallyreference.(2)Stress values are those quentlyreferredtoasanair-struc shorterthanthatofmoreconven for the design wind load.In selecting ture.Double-wall structures where thetional building materials.a material to meet design stresses,alskin is shaped into tubular or cellularFewothertypesof structure havelowancemust be made for other faccompartmen!spressurizedtodevelopthesame abilitytoprovidefree-spantorssuchasuniformityofproduct, structuralstiffness( the usablespace,coverageforsolargeanarea.Sup weatheringresistance,handlingand incontrast,isnotpressurized)areportedbyair,requiringnocolumnsstress-strain characteristics of the fabgenerally called air-inflated structures.or beams,thesestructurescanattainricanditsultimate rupturestrength. This Digest will discusssingle-wall.In situationswhere detailedinformaair-supportedstructuresconsistingofgreatroofheights.Adomeerectedtion on thesefactorsisnot available fourbasic components:envelope, an atAndover,Maine,couldencloseareference (recommends that a safe3) chorage,inflationequipment,and16-storybuilding.ty factorof3be used. doors(Figure1).These componentsExisting uses of air-supported struc Instability, defined as the condition mustbeselectedinaccordancewithturesincludeantennaeshelters(ra at which structural deflectionand oscarefullyspecifieddesigncriteriatodomes),temporarywarehouses,on cillationcombinetoproduceobjecprovide for and ensure adequate safe sitestoragesheltersforconstructiontionablestructuremotion,hasbeen tyand operation.materials,constructionenclosures,studiedwithrespecttofabricporosswimmingpoolenclosuresandotherityandenclosurepressure(2).The HistoricalDevelopmentrecreationalshelters,socialactivitytests indicate that when the enclosure Thefirstproposalforanair-sup shelters,anddisastershelters.Thesepressureisequaltoorgreaterthan portedstructurewasprobablymadeuses,bytheirnature,illustratetwo(Contin11ed onnl\'xtpage) 10AUGUST,1971'