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Storm Shelters: Selecting Design Criteria FEBRUARY 2007 TORNADO RECOVERY ADVISORY FEMA DR 1679 RA2
Purpose and Intended Audience TheintendedaudienceforthisTornadoRecoveryAdvisory isanyoneinvolvedintheplanning,policy-making,design, construction,orapprovalofshelters,includingdesigners, emergencymanagers,publicofficials,policyordecisionmakers,buildingcodeofficials,andhomeorbuildingowners. HomeownersandrentersshouldalsorefertotheTornado RecoveryAdvisorytitledResidential Sheltering: In-Residence and Stand-Alone Shelter.Thepurposeofthisadvisoryisto identifythedifferenttypesofshelterdesignguidance,code requirements,andothercriteriathatpertaintothedesignand constructionofsheltersfortornadoesandhurricanes.Thereare variousstormsheltercriteria,eachofwhichoffersdifferentlevels ofprotectiontoitsshelteroccupants.
This Recovery Advisory Addresses:
Howshelterconstructionisdifferentfromtypicalbuilding construction
Structuralsystems Windbornedebrisresistance
Designcriteriafordifferenttypesofshelters
Shelterconsiderations
Seethese2007TornadoRecovery Advisoriesforinformation abouttornadorisk,sheltering fromtornadoes,andimproving manufacturedhomesagainst damagefromhighwinds:
TornadoRisksandHazardsin theSoutheasternUnitedStates (TornadoRecoveryAdvisoryNo.1)
ResidentialSheltering:In-ResidenceandStand-Alone Shelters(TornadoRecovery AdvisoryNo.3)
UnderstandingandImproving PerformanceofOlder ManufacturedHomesinHigh-Wind Events(TornadoRecoveryAdvisory No.4)
UnderstandingandImproving PerformanceofNewManufactured HomesinHigh-WindEvents (TornadoRecoveryAdvisoryNo.5)
Usefullinksandshelterresources
How Shelter Construction is Different from Typical Building Construction Ashelteristypicallyaninteriorroom,spacewithinabuilding,oranentirelyseparatebuilding,designedand constructedtoprotectitsoccupantsfromtornadoesorhurricanes.Sheltersareintendedtoprovideprotection againstbothwindforcesandtheimpactofwindbornedebris.Thelevelofoccupantprotectionprovidedby aspacespecificallydesignedasashelterisintendedtobemuchgreaterthantheprotectionprovidedby buildingsthatcomplywiththeminimumrequirementsofbuildingcodes.Themodelbuildingcodesdonot providedesignandconstructioncriteriaforlifesafetyforshelteringnordotheyprovidedesigncriteriafor tornadoes.
Shelterstypicallyfallintotwocategories:residentialsheltersandcommunity(non-residential)shelters.
Therearetwogeneraltypesofresidentialshelters:in-residence sheltersandshelterslocatedadjacentto,ornear,aresidence. Anin-residence shelter,alsocalleda“saferoom,”isasmall, speciallydesigned(“hardened”)room,suchasabathroomor closetthatisintendedtoprovideaplaceofrefugeforthepeople wholiveinthehouse.Anexternal residential shelterissimilar infunctionanddesign,butitisaseparatestructureinstalled outsidethehouse,eitheraboveorbelowground.Referalsoto theTornadoRecoveryAdvisorytitledResidential Sheltering: In-
Theterm“hardened”refersto specializeddesignandconstruction appliedtoaroomorbuildingto allowittoresistwindpressures andwindbornedebrisimpacts duringahigh-windeventandserve asashelter.
Residence and Stand-Alone Shelter.
Storm Shelters: Selecting Design Criteria HSFEHQ-07-J-0006/April 2007 Page � of 6
Acommunity shelterisintendedtoprovide protectionforalargenumberofpeople,anywhere fromapproximately12toasmanyasseveral hundredindividuals.Thesesheltersinclude notonlypublicsheltersbutprivatesheltersfor businessesandotherorganizations.
Structural Systems
Theprimarydifferenceinabuilding’sstructural systemwhendesignedforuseasashelter,rather thanforconventionaluse,isthemagnitudeofthe windforcesthatitisdesignedtowithstand.
Buildingsaredesignedtowithstandacertainwind speed(termed“design[basic]windspeed”)based onhistoricwindspeedsdocumentedfordifferentareasofthecountry.Thehighestdesignwindspeedused inconventionalconstructionisnearthecoastalareasoftheAtlanticandGulfCoastsandisintherangeof 140–150mph,3-secondgustinmostlocations.Bycontrast,thedesignwindspeedrecommendedbyFEMA1 forsheltersinthesesameareasisintherangeof200–250mph,3-secondgust;thisdesignwindspeedis intendedtoprovide“near-absoluteprotection.”
Windpressuresarecalculatedasafunctionofthesquareofthedesignwindspeed.Asaresult,the structuralsystemsofashelteraredesignedforforcesuptothreetimeshigherthanthoseusedfortypical buildingconstruction.Consequently,thestructuralsystemsofashelter(andtheconnectionsbetweenthem) areveryrobust.
Windborne Debris Resistance
Windbornedebris,commonlyreferredtoasmissiles,causesmanyoftheinjuriesandmuchofthedamage fromtornadoesandhurricanes.Windowsandtheglazinginexteriordoorsofconventionalbuildingsarenot requiredtoresistwindbornedebris,exceptforbuildingsinwindbornedebrisregions.2Impact-resistantglazing caneitherbelaminatedglass,polycarbonate,orshutters.TheASCE7missilecriteriaweredevelopedto minimizepropertydamageandimprovebuildingperformance;theywerenotdevelopedtoprotectoccupants.
Community storm shelter being constructed to FEMA 361 criteria in Wichita, Kansas.
Ifglazingispresentina tornadoshelter,itshould beprotectedbyaninterior-mountedshutterthatcanbe quicklyandeasilydeployed bytheshelteroccupants.
Toprovideoccupantprotection,thecriteriausedindesigningshelters includesubstantiallygreaterwindbornedebrisloads.
Theroofdeck,walls,anddoorsofconventionalconstructionarealso notrequiredbythebuildingcodetoresistwindbornedebris.However, theroofdeckandwallsaroundashelterspace,andthedoorsleading intoit,mustresistwindbornedebrisifthespaceinsideistoprovide occupantprotection.Additionalinformationregardingthedifferentlevels ofwindbornedebrisloadsisprovidedbelow.
Design Criteria for Different Types of Shelters Shelterswillprovidedifferentlevelsofprotectiondependinguponthedesigncriteriaused.Thelevelof protectionprovidedbyashelterisafunctionofthedesignwindspeed(andresultingwindpressure)usedin designingtheshelter,andofthewindbornedebrisloadcriteria.
Design wind speed and wind pressure criteria:Windpressurecriteriaaregivenbydifferentguides,codes andstandards.Windpressurecriteriaspecifyhowstrongthesheltermustbe.Thedesignwindspeedisthe majorfactorindeterminingthemagnitudeofthewindpressurethatthebuildingisdesignedtowithstand. InFEMA’sshelterpublications(seeUsefulLinksonpage3),recommendeddesignwindspeedsrange from160to250mph.The2006International Residential Codeandthe2006International Building Code, whichestablishtheminimumrequirementsforresidentialandotherbuildingconstruction,includedesign windspeedsrangingfrom90to150mphthroughoutmostofthecountry.Thetableonpages4–5provides acomparisonofshelterdesigncriteriaoptions.Thetableonpage6presentscomparativedatafortwo locationsusingthedesigncriteriapresentedonpages4–5.
1. FEMA361,Design and Construction Guidance for Community Shelters(July2000),availableonlineathttp://www.fema.gov/fima/fema361.shtm
2. ASCE7,AmericanSocietyofCivilEngineersStandard7,Minimum Design Loads for Buildings and Other Structures(2005)
Page 2 of 6 Storm Shelters: Selecting Design Criteria HSFEHQ-07-J-0006/April 2007
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Windborne debris load criteria: Thetableonpage3presentswindbornedebriscriteriagiveninvarious guides,codes,andstandards.Thetableshowsthedifferenttestmissilesandthecorrespondingmomentum theycarrywiththemastheystrikeashelter.Thefirstentriesonthistable(TornadoMissileTesting Requirements)aretheFEMAmissileguidanceforresidentialandcommunitysheltersthatprovidenearabsoluteprotection.
Tornado and Hurricane Windborne Debris Criteria Guidance, Code, or Standard
Criteria for the Design Missile Debris Test Speed
(mph) Large Missile Specimen Momentum at Impact (lbf s)
Tornado Missile Testing Requirements
FEMA320/FEMA361 100 15#2x4 68
InternationalCodeCouncil(ICC)Shelter Standard
100(maximum) 80(minimum)
15#2x4 15#2x4
68 55
Hurricane Missile Testing Requirements
FEMA320/FEMA361 100 15#2x4 68
ICCShelterStandard 102(maximum) 64(minimum)
9#2x4 9#2x4
42 26
FloridaStateEmergencyShelterProgram (SESP)Criteria
50(recommended) 34(EHPAminimum)
15#2x4 9#2x4
34 14
IBC/IRC2006,ASCE7-05,FloridaBuilding Code,ASTME1886/E1996
55 34
9#2x4 9#2x4
21 14
NOTES:
IBC/IRC–InternationalBuildingCode/InternationalResidentialCode
lbf-s–Pounds(force)seconds
Useful Links and Shelter Resources: Taking Shelter From the Storm: Building a Safe Room Inside Your House (FEMA320),FEMA,Washington,DC, SecondEdition,March2004.
Design and Construction Guidance for Community Shelters (FEMA361),FEMA,Washington,DC,July2000.
Tornado Protection: Selecting Refuge Areas in Buildings (FEMA431),FEMA,Washington,DC,November 2003.
Standard on the Design and Construction of Storm Shelters, International Code Council and the National Storm Shelter Association (ICC-500),(AnticipatedRelease)Late2007.
FEMA 320
FEMA 361
DRAFTFEMA 431
Storm Shelters: Selecting Design Criteria HSFEHQ-07-J-0006/April 2007 Page � of 6
Wind Design Coefficient Considerations�,� Debris Impact Criteria5 Remarks
FEMA �20:N/A–prescriptivedesignguidanceformaximumhazardFEMA �6�:UseFEMA361windspeedmapwithfourzones.CalculatepressuresusingASCE7methodsanduseI=1.0,Kd=1.0,ExposureC,notopographiceffects,GCpi=+/-0.55(thiswillaccountforatmosphericpressurechange[APC])
Testallshelterswiththerepresentativemissile:a15-lb2x4at100mph(horizontal)and67mph(vertical)
FEMA �20:Intentistoprovide“near-absoluteprotection.”Nocertificationisprovided.FEMA �6�:Intentistoprovide“near-absoluteprotection.”Shelteroperationsguidanceisprovided.Occupancyissuesaddressed.Wallsectiondetailsprovided.Nocertificationisprovided.
Tornado:UseFEMA361windspeedmap.CalculatepressuresusingASCE7methodsanduseI=1.0,Kd=1.0,Exposureasappropriate,notopographiceffects,GCpi=+/-0.55or+/-0.18+APCHurricane:UserevisedASCE7mapandmethodsanduseI=1.0,allotheritemsasperASCE7,noAPCconsiderationrequired.
Testshelterswithrepresentativemissile(missilespeeddependentonsitedesignwindspeed):Tornado:15-lb2x4at85–100mph(horizontal)and2/3ofthisspeed(vertical).Hurricane:9-lb2x4at68–105mph(horizontal)andalowerspeed(vertical)
Intentistoprovideastandardforthedesignandconstructionofhigh-windshelters.Willnotuseterm“near-absoluteprotection.”Occupancy,ventilation,anduseissuesarealsoaddressed.Shelteroperationsguidanceisprovidedinthecommentaryonly(commentaryisaseparatedocument—notaconsensusdocument).
Recommendsthatdesigneradd40mphtobasicwindspeedidentifiedonmap,ExposureC,I=1.15,Kd=0.85,GCpiasrequiredbydesign(typically+/-0.18),butrecommends+/-0.55fortornadoshelteruses
Inwindbornedebrisregion(120mph+):Small–peagravel;Large–9-lb2x4at34mph(horizontal),upto60feetabovegrade,butrecommends15-lb2x4at50mph(horizontal)
Thebuilding,oraportionofabuilding,isdefinedasanessentialfacilityandasashelter.Designerisrequiredtosubmitsigned/sealedstatementtobuildingdepartmentandStateofficesstatingthestructurehasbeendesignedasashelter(EHPAplusaddedrecommendedcriteria).
UsebasicwindspeedatsiteasidentifiedonFBCwindspeedmap,useexposureatsite,useI=1.15,Kd=0.85,GCpiasrequiredbydesign(typically+/-0.18)
Inwindbornedebrisregion(120mph+):Small–peagravel;Large–9-lb2x4at34mph(horizontal),upto60feetabovegrade
ThebuildingoraportionofabuildingisdefinedasanessentialfacilityandasanEHPA.Designerisrequiredtosubmitsigned/sealedstatementtobuildingdepartmentandStateofficesstatingthestructurehasbeendesignedasanEHPA.
Basedonregionalhazards,recommendationsareprovidedtoimproveandstrengthentheloadpathandtheperformanceofthebuildingexterior
Windowandglazingprotectionisrecommendedformosthurricane-proneareas,notjustareaswithabasicwindspeedof120mphandgreater
Thisprogramprovidesdesignandconstructionguidancetoimprovebuildingperformanceforhigh-windevents.Compliancewilllikelyimprovebuildingperformancebutdoesnotimplythatthebuildingissafeorthatitisappropriatetouseasashelter.
Methodisbasisofmostwindpressurecalculationmethods.Allitemsindesignprocessaresite-specific.UseI=1.15forcriticalandessentialfacilities
Inwindbornedebrisregion(120mph+):Small–peagravel;Large–9-lb2x4at34mph(horizontal),upto60feetabovegrade.Note:2006IBCrequiresthe9-lb2x4(large)missiletobetestedat55mphforcriticalandessentialfacilities
Coderequiresincreaseddesignparametersonlyforbuildingsdesignatedascriticaloressentialfacilities.
None None Providesguidanceonhowtoselectbuildingsandareasofabuildingforuseasahigh-windshelterorrefugearea.Doesnotprovideorrequireatechnicalassessmentoftheproposedshelterfacility.
Typicallytheseoldercodesprovidedahurricaneregionalfactorfordesignwindspeeds,butlittleattentionwaspaidtocomponentsandcladding
Notrequiredforallbuildings.Whererequired,theStandardBuildingCode6developedandrecommendeddebrisimpactstandardsforuseinhurricane-proneregions
Thesecodesspecifiedlimitedhazard-resistantrequirements.SomeguidancewasprovidedwithSSTD10fromSBCCIforthedesignandconstructionofbuildingsinhigh-windandhurricane-proneregions.Buildingsconstructedtotheseearlycodeswerenotrequiredtohavestructuralsystemscapableofresistingwindloads.
None None Bestavailablerefugeareasshouldbeidentifiedinallbuildingswithoutshelters.FEMA431,Tornado Protection: Selecting Refuge Areas in Buildings,providesguidancetohelpidentifythebestavailablerefugeareasinexistingbuildings.Becausebestavailablerefugeareasarenotspecificallydesignedasshelters,theiroccupantsmaybeinjuredorkilledduringatornadoorhurricane.
Wind Shelter Design and Construction Codes, Standards, Guidance Comparison Table�
Title or Name of Document Code, Reg, Standard, or Statute? Wind
Hazard Wind Map
FEMA Shelter Publications: FEMA �20Taking Shelter From the Storm: Building a Safe Room Inside Your House(1999) FEMA �6�Design and Construction Guidance for Community Shelters(2000)
FEMAguidancedocument,notacodeor standard.“BestPractice”forhigh-wind shelters
Tornadoand Hurricane
FEMA �20:Hazardmap,butwind speedsnotusedfordesign FEMA �6�:Mapwithfourwind speedzonesfordesign(windmri2is 10,000–100,000years).Thismap isoftenreferredtoasthe“FEMA 361map”
International Code Council/National Storm Shelter Association (ICC/NSSA) High Wind Shelter Standard (ICC-500) –currentlyindevelopment,tentatively availableforadoptioninJanuary2008.
Consensusstandardforshelterdesign andconstruction,availableforadoption inJanuary2008.Tobeincorporatedby referenceintothe2009IBCandIRC.
Tornadoand Hurricane
Tornado:UsesFEMA361map Hurricane:UsesrevisedASCE7 mapwithcontoursat10,000year mriwithminimumshelterdesign windspeedof160mph,maximum approximately240mph
Florida State Emergency Shelter Program (SESP)– FloridaInterpretationoftheAmericanRedCross(ARC) 4496Guidance.Note:sheltersinthiscategorywill rangefromEnhancedHurricaneProtectionArea(EHPA) recommendeddesignlevels,showninthisrow,tothe coderequirementlevels(nextrow),totheARC4496 requirements(seebelow).
GuidanceintheFBC“recommending” above-coderequirementsforEHPAs.See alsoAppendixGoftheStateEmergency ShelterProgram(SESP)reportforthe detaileddesignguidance.
Tornadoand Hurricane
FloridaBuildingCode(FBC)map, basedonASCE7(mapsbasically equivalent);mriis50–100years incoastalareasandadjustedwith importancefactor
Florida Building Code (FBC) EHPAs–code requirementsforpublic“shelters”(FBCSection 423.25).
StatewidecoderequirementsforEHPAs Hurricane FBCmap,basedonASCE7(maps basicallyequivalent);mriis50–100 yearsincoastalareasandadjusted withimportancefactor
Institute for Business and Home Safety (IBHS) Fortified Home Program–intendedasguidance toimprovetheperformanceofresidentialbuildings duringnaturalhazardevents,includinghigh-wind events–notconsideredadequateforsheltering.
Guidanceprovidedtoimproveperformance ofregular(non-shelter)buildingsinhigh winds
Tornadoand Hurricane
ASCE7ormodernStatebuilding codemap
FBC 2000 and later, International Building Code (IBC)/International Residential Code (IRC) 2000 and later/ASCE 7-98andlater.
Buildingcodeanddesignstandardsfor regular(non-shelter)buildings.Some additionalguidanceisprovidedin commentary.
Hurricane ASCEhasitsownwindspeedmap basedonhistoricalandprobabilistic data;mriis50–100yearsincoastal areasandadjustedwithimportance factor
American Red Cross (ARC ��96)Standards for Hurricane Evacuation Shelter Selection.
Guidanceforidentifyingbuildingstouseas hurricaneevacuationshelters
Hurricane None
Pre-2000 Building Codes Buildingcodeanddesignstandardsfor regular(non-shelter)buildings
Hurricane Eachoftheoldercodesusedtheir ownpublishedwindcontourmaps
Areas of Refuge/Last Resort GuidancefromFEMAandothersfor selectingbest-availablerefugeareas
Tornadoand Hurricane
None
NOTES:
1. Thewindshelterguidanceandrequirementsshownherearepresentedfromhighesttoleastamountofprotectionprovided.
2.Meanrecurrenceintervals(mri)forwindspeedsmapsareidentifiedbythecodeorstandardthatdevelopedthemap.Typically,themrifornonshelterconstructioninnon-hurricane-proneareasis50yearsandinhurricane-proneregions,approximately100years.
Page � of 6 Storm Shelters: Selecting Design Criteria HSFEHQ-07-J-0006/April 2007
Title or Name of Document Code, Reg, Standard, or Statute?Wind
Hazard Wind Map
FEMA Shelter Publications:FEMA �20Taking Shelter From the Storm: Building a Safe Room Inside Your House(1999)FEMA �6�Design and Construction Guidance for Community Shelters(2000)
FEMAguidancedocument,notacodeorstandard.“BestPractice”forhigh-windshelters
TornadoandHurricane
FEMA �20:Hazardmap,butwindspeedsnotusedfordesignFEMA �6�:Mapwithfourwindspeedzonesfordesign(windmri2is10,000–100,000years).Thismapisoftenreferredtoasthe“FEMA361map”
International Code Council/National Storm Shelter Association (ICC/NSSA) High Wind Shelter Standard (ICC-500) –currentlyindevelopment,tentativelyavailableforadoptioninJanuary2008.
Consensusstandardforshelterdesignandconstruction,availableforadoptioninJanuary2008.Tobeincorporatedbyreferenceintothe2009IBCandIRC.
TornadoandHurricane
Tornado:UsesFEMA361mapHurricane:UsesrevisedASCE7mapwithcontoursat10,000yearmriwithminimumshelterdesignwindspeedof160mph,maximumapproximately240mph
Florida State Emergency Shelter Program (SESP)–FloridaInterpretationoftheAmericanRedCross(ARC)4496Guidance.Note:sheltersinthiscategorywillrangefromEnhancedHurricaneProtectionArea(EHPA)recommendeddesignlevels,showninthisrow,tothecoderequirementlevels(nextrow),totheARC4496requirements(seebelow).
GuidanceintheFBC“recommending”above-coderequirementsforEHPAs.SeealsoAppendixGoftheStateEmergencyShelterProgram(SESP)reportforthedetaileddesignguidance.
TornadoandHurricane
FloridaBuildingCode(FBC)map,basedonASCE7(mapsbasicallyequivalent);mriis50–100yearsincoastalareasandadjustedwithimportancefactor
Florida Building Code (FBC) EHPAs–coderequirementsforpublic“shelters”(FBCSection423.25).
StatewidecoderequirementsforEHPAs Hurricane FBCmap,basedonASCE7(mapsbasicallyequivalent);mriis50–100yearsincoastalareasandadjustedwithimportancefactor
Institute for Business and Home Safety (IBHS) Fortified Home Program–intendedasguidancetoimprovetheperformanceofresidentialbuildingsduringnaturalhazardevents,includinghigh-windevents–notconsideredadequateforsheltering.
Guidanceprovidedtoimproveperformanceofregular(non-shelter)buildingsinhighwinds
TornadoandHurricane
ASCE7ormodernStatebuildingcodemap
FBC 2000 and later, International Building Code (IBC)/International Residential Code (IRC) 2000 and later/ASCE 7-98andlater.
Buildingcodeanddesignstandardsforregular(non-shelter)buildings.Someadditionalguidanceisprovidedincommentary.
Hurricane ASCEhasitsownwindspeedmapbasedonhistoricalandprobabilisticdata;mriis50–100yearsincoastalareasandadjustedwithimportancefactor
American Red Cross (ARC ��96)Standards for Hurricane Evacuation Shelter Selection.
Guidanceforidentifyingbuildingstouseashurricaneevacuationshelters
Hurricane None
Pre-2000 Building Codes Buildingcodeanddesignstandardsforregular(non-shelter)buildings
Hurricane Eachoftheoldercodesusedtheirownpublishedwindcontourmaps
Areas of Refuge/Last Resort GuidancefromFEMAandothersforselectingbest-availablerefugeareas
TornadoandHurricane
None
Part2oftable(continuedfrompage4)
Wind Design Coefficient Considerations�,� Debris Impact Criteria5 Remarks
FEMA �20:N/A–prescriptivedesign guidanceformaximumhazard FEMA �6�:UseFEMA361windspeed mapwithfourzones.Calculatepressures usingASCE7methodsanduseI=1.0, Kd=1.0,ExposureC,notopographic effects,GCpi=+/-0.55(thiswillaccountfor atmosphericpressurechange[APC])
Testallshelterswiththerepresentative missile:a15-lb2x4at100mph (horizontal)and67mph(vertical)
FEMA �20:Intentistoprovide“near-absoluteprotection.”No certificationisprovided. FEMA �6�:Intentistoprovide“near-absoluteprotection.”Shelter operationsguidanceisprovided.Occupancyissuesaddressed. Wallsectiondetailsprovided.Nocertificationisprovided.
Tornado:UseFEMA361windspeed map.CalculatepressuresusingASCE7 methodsanduseI=1.0,Kd=1.0,Exposure asappropriate,notopographiceffects, GCpi=+/-0.55or+/-0.18+APC Hurricane:UserevisedASCE7mapand methodsanduseI=1.0,allotheritemsas perASCE7,noAPCconsiderationrequired.
Testshelterswithrepresentative missile(missilespeeddependenton sitedesignwindspeed):Tornado:15-lb 2x4at85–100mph(horizontal)and 2/3ofthisspeed(vertical).Hurricane: 9-lb2x4at68–105mph(horizontal) andalowerspeed(vertical)
Intentistoprovideastandardforthedesignandconstructionof high-windshelters.Willnotuseterm“near-absoluteprotection.” Occupancy,ventilation,anduseissuesarealsoaddressed. Shelteroperationsguidanceisprovidedinthecommentary only(commentaryisaseparatedocument—notaconsensus document).
Recommendsthatdesigneradd40mph tobasicwindspeedidentifiedonmap, ExposureC,I=1.15,Kd=0.85,GCpias requiredbydesign(typically+/-0.18),but recommends+/-0.55fortornadoshelter uses
Inwindbornedebrisregion(120 mph+):Small–peagravel;Large–9-lb 2x4at34mph(horizontal),upto60 feetabovegrade,butrecommends15lb2x4at50mph(horizontal)
Thebuilding,oraportionofabuilding,isdefinedasanessential facilityandasashelter.Designerisrequiredtosubmitsigned/ sealedstatementtobuildingdepartmentandStateofficesstating thestructurehasbeendesignedasashelter(EHPAplusadded recommendedcriteria).
Usebasicwindspeedatsiteasidentified onFBCwindspeedmap,useexposureat site,useI=1.15,Kd=0.85,GCpiasrequired bydesign(typically+/-0.18)
Inwindbornedebrisregion(120 mph+):Small–peagravel;Large–9-lb 2x4at34mph(horizontal),upto60 feetabovegrade
Thebuildingoraportionofabuildingisdefinedasanessential facilityandasanEHPA.Designerisrequiredtosubmitsigned/ sealedstatementtobuildingdepartmentandStateofficesstating thestructurehasbeendesignedasanEHPA.
Basedonregionalhazards, recommendationsareprovidedtoimprove andstrengthentheloadpathandthe performanceofthebuildingexterior
Windowandglazingprotectionis recommendedformosthurricane-prone areas,notjustareaswithabasicwind speedof120mphandgreater
Thisprogramprovidesdesignandconstructionguidanceto improvebuildingperformanceforhigh-windevents.Compliance willlikelyimprovebuildingperformancebutdoesnotimplythatthe buildingissafeorthatitisappropriatetouseasashelter.
Methodisbasisofmostwindpressure calculationmethods.Allitemsindesign processaresite-specific.UseI=1.15for criticalandessentialfacilities
Inwindbornedebrisregion(120 mph+):Small–peagravel;Large–9-lb 2x4at34mph(horizontal),upto60 feetabovegrade. Note:2006IBCrequiresthe9-lb2x4 (large)missiletobetestedat55mph forcriticalandessentialfacilities
Coderequiresincreaseddesignparametersonlyforbuildings designatedascriticaloressentialfacilities.
None None Providesguidanceonhowtoselectbuildingsandareasofabuilding foruseasahigh-windshelterorrefugearea.Doesnotprovideor requireatechnicalassessmentoftheproposedshelterfacility.
Typicallytheseoldercodesprovideda hurricaneregionalfactorfordesignwind speeds,butlittleattentionwaspaidto componentsandcladding
Notrequiredforallbuildings.Where required,theStandardBuildingCode6 developedandrecommendeddebris impactstandardsforuseinhurricaneproneregions
Thesecodesspecifiedlimitedhazard-resistantrequirements. SomeguidancewasprovidedwithSSTD10fromSBCCIforthe designandconstructionofbuildingsinhigh-windandhurricaneproneregions.Buildingsconstructedtotheseearlycodeswerenot requiredtohavestructuralsystemscapableofresistingwindloads.
None None Bestavailablerefugeareasshouldbeidentifiedinallbuildings withoutshelters.FEMA431,Tornado Protection: Selecting Refuge Areas in Buildings,providesguidancetohelpidentifythebest availablerefugeareasinexistingbuildings.Becausebestavailable refugeareasarenotspecificallydesignedasshelters,their occupantsmaybeinjuredorkilledduringatornadoorhurricane.
NOTES(continued):
3. ASCE7-05Building Design Loads for Buildings and Other Structures(2005)istheloaddeterminationstandardreferencedbythe modelbuildingcodes.Thewinddesignproceduresusedforanysheltertypeinthistableuseoneofthewinddesignmethodsas specifiedinASCE7-05,butwithchangestocertaindesigncoefficientsthatareidentifiedbythedifferentcodes,standards,or guidancesummarizedinthistable.
4. FromASCE7method:I=importancefactor;Kd=winddirectionalityfactor;GCpi=internalpressurecofficient
5. Roofdeck,walls,doors,openings,andopeningprotectionsystemsmustallbetestedtoshowresistancetothedesignmissileforthe FEMA,ICC,andFLEHPAcriteria.
6. FromtheSouthernBuildingCodeCongressInternational,Inc.(SBCCI).
Storm Shelters: Selecting Design Criteria HSFEHQ-07-J-0006/April 2007 Page 5 of 6
Thetablebelowshowscomparativedatafortwolocationsforthedesigncriteriapresentedintheprevious table.Wherenoguidanceisprovidedforshelteringorbasicconstruction,“N/A”(notapplicable)isstated. Wheretherequirementisnotrequired,“Notrequired”isstated.
Design Criteria Comparison Shelter Design Standard,
Code, or Document Data� Example Location #�:
Miami, FL Example Location #2:
Atlanta, GA
FEMA320/361 Designwindspeed 200mph 200mph
Pressureonwindwardwall 107psf2 107psf
Pressureonroofsection 257psf(suction) 257psf(suction)
Testmissilemomentumatimpact 68lbf-s2 68lbf-s
ICC-500(pending1/08) Designwindspeed 200mph(tornado) 225mph(hurricane)
200mph(tornado) 160mph(hurricane)
Pressureonwindwardwall 107psf(tornado) 136psf(hurricane)
107psf(tornado) 69psf(hurricane)
Pressureonroofsection 257psf(tornado,suction) 325psf(hurricane,suction)
257psf(tornado,suction) 202psf(hurricane,suction)
Testmissilemomentumatimpact 68lbf-s(tornado) 42-26lbf-s(hurricane)
68lbf-s(tornado) 42-26lbf-s(hurricane)
FBCEHPA/SESP (using+40mph recommendation)
Designwindspeed 186mph 130mph
Pressureonwindwardwall 91psf 44psf
Pressureonroofsection 217psf(suction) 106psf(suction)
Testmissilemomentumatimpact 34lbf-s 34lbf-s
FBCEHPA Designwindspeed 146mph N/A
Pressureonwindwardwall 39psf N/A
Pressureonroofsection 117psf(suction) N/A
Testmissilemomentumatimpact 14lbf-s N/A
IBHS Designwindspeed 150mph 90mph
Pressureonwindwardwall 41psf 15psf
Pressureonroofsection 124psf(suction) 44psf(suction)
Testmissilemomentumatimpact 14lbf-s 14lbf-s
ASCE7-05/IBC2006 (ASTME1996)
Designwindspeed 150mph 90mph
Pressureonwindwardwall 41psf 15psf
Pressureonroofsection 124psf(suction) 44psf(suction)
Testmissilemomentumatimpact 14lbf-s Notrequired
ARC4496 Designwindspeed N/A N/A
Pressureonwindwardwall N/A N/A
Pressureonroofsection N/A N/A
Testmissilemomentumatimpact N/A N/A
Pre-2000BuildingCodes Designwindspeed 140mphandless 90mphandless
Pressureonwindwardwall <40psf(varies) <15psf(varies)
Pressureonroofsection <120psf(varies) <45psf(varies)
Testmissilemomentumatimpact Notrequiredbyallcodes Notrequired
AreasofLastResort Designwindspeed Unknown Unknown
Pressureonwindwardwall Unknown Unknown
Pressureonroofsection Unknown Unknown
Testmissilemomentumatimpact Notrequired Notrequired NOTES: 1. Windpressureswerecalculatedbasedona40-footx40-footsquarebuilding,witha10-footeaveheightanda10-degreeroofpitch. 2. psf–Poundspersquarefoot;lbf-s–Pounds(force)seconds
Page 6 of 6 Storm Shelters: Selecting Design Criteria HSFEHQ-07-J-0006/April 2007