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Why Have We Gone to Strength-Level Wind Loads
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Why Have We Gone to StrengthLevel Wind Loads?
Posted on 20140423Topics: 2012 IBC, ASCE 710, Wind Provisions, Seismic Provisions, Load CombinationsReturn to Blog Index
Question: Codes and standardsare continually changing, and it makesthings difficult for us designers. Backin the 1997 Uniform BuildingCode (UBC), the switch from servicelevel earthquake loads to strengthlevel earthquake loads was first made.Now, in ASCE 710, the same switchis being made for wind loads. Why?
Answer: ASCE 7 leadershipbelieves that all environmental loadsshould be specified at strength level.Specifying userimposed loads suchas live loads at service level makessense. Those are the loads expectedto be imposed on the structure duringits service life. We are concernedabout "serviceability" (no excessivecracking, no excessive deflections)under those loads. When it comes towind or earthquake loads, our main
concern is providing strength to withstand designlevel loads, not serviceability. As you point out, theswitch to strengthlevel earthquake loads was made in the 1997 UBC. ASCE 710 has gone to strengthlevel wind. If things go according to plans, snow should be at strength level in ASCE 716.