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Februar y 2012 Working Draf t w w w.toolbase.org
RETROFIT Improvements MakingHomesSafer inDisasters
Hazards
Purpose•Tofix/strengthencripplewallsandpoorfoundationconnections
•Topreventabuildingfromslidingoffitsfoundationduringaseismicevent
Benefits•Ensuressafetytooccupantsandproperty
IllustrationRetrofit
SummaryForensicinvestigationindicatesthatpartialorcompletecollapseofhillsidehousesisacommoncalamitywhenearthquakeshit.Themostatriskhouseshavetheentryfloorlocatedatornearstreetlevelandtallwoodlight-framewallsprovidingsupportatthehillsideedgeofthefloor.Thesehomesmayhavea“walk-out”basement.Referredtoasdown-slopehouses,thelargestlevelissupportedbyadiscontinuousfoundationthat“flows”withthegradewhichslopesdownandout.Thestructurebetweenthefoundationandthemainlevelofthehouse,astypicallyconstructed,providesapoorinterconnectionthatissusceptibletoshaking.Wallsatthesidesofdown-slopehousesarealsoirregularlyshapedastheyare“stepping”downthehillside.Thesecripplewalls,andthefactthatthemainfloorisusuallypinnedtoanupperandlowerfoundation(whicharedisconnected),providemanypivotpointsfromwhichtherigidfloorsystemmayshakeoutofplaneandcausefailuresoftheelementsthatsupportit.Retrofittingdownslopehousesisajobthatrequiresanengineereddesignandspecialtycontractor.Asaresult,thecostofthisretrofitwillvarywiththescopeoftheproject.
Bracing of Hillside HomesFloodWind Rain Seismic SnowFireRetrofit Opportunity
•Seismicretrofitsofthisscopearefiniteprojectsinandofthemselves(specialtycontractorsexisttoservethismarket)
Detail of shear wall construction and anchorage at stepped foundation
Februar y 2012 Working Draf t w w w.toolbase.org
Photo:www.fema.gov
Potential Damage
Key Steps •Hireaprofessionalinspectortodeterminethescopeofaretrofit.•Generallyspeaking,thisretrofitwillincorporateprimaryandsecondaryanchoringofthemainfloorsystemandloadpathreinforcementcomponents.
•Yourcontractormayhaveadditionalideasonhowtoimprovethesafetyofyourhome.•Formoredetailsaboutthisretrofitimprovement,pleaserefertothelistofResourcesinthesectionbelow.
ResourcesFEMA,Earthquake Safety Guide for Homeowners http://www.fema.gov/library/viewRecord.do?fromSearch=fromsearch&id=1449FEMA,Homebuilders’ Guide to Earthquake-Resistant Design and Construction http://www.fema.gov/library/viewRecord.do?id=2103
