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[SEAOC] Re: [SEAOC] Seismic Rehabilitation of Buildings using FEMA 178, 172 or 273 Pr...[Subject Prev][Subject Next][Thread Prev][Thread Next]
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- Subject: [SEAOC] Re: [SEAOC] Seismic Rehabilitation of Buildings using FEMA 178, 172 or 273 Pr...
- From: IteUrsi(--nospam--at)aol.com
- Date: Tue, 3 Dec 1996 14:40:14 -0500
Ali Sadre's criticisms of FEMA 178 being out of date are valid from an engineering perspective. Work started on 178 before Loma Prieta, and lessons from that event weren't fully digested before the document was completed. And, of course, subsequent academic research and the lessons from Northridge are not reflected. But these shortcomings overlooks an important consideration that will keep 178 a useful document in the "real" world long after FEMA officially releases 273. >>It may be worth reiterating that despite being a "consensus standard", the existing FEMA 178 Handbook has certain limitations. For example, this procedure is based on a single performance level which is less than the life-safety standards, implicitly adopted by the current model codes. The obvious drawback here is the lack of explicit options for retrofit schemes beyond marginal life-safety or collapse prevention.<< This "drawback" is actually one of 178's strengths in the real world! Building codes most often use a single standard/performance level approach whether requirements are prescriptive or performance based, and not just for seismic design, but for most other areas regulated by codes, such as fire resistance, durability, serviceability, efficiency, etc. Why? Mostly because we live in an increasingly legalistic world, and building officials more than ever need approved/disapproved, acceptable/unacceptable, go/no go criteria in order to carry out their ministerial duties without being second-guessed or mired in local politics. Yes, most of life's situations are continuums rather than step functions. Buildings are seismically less safe or more safe, not unsave or safe. But that's a point a building officials usually aren't asked or allowed to expand on when sitting in the witness chair in court. The question usually is framed as, "did the design/installation/construction/situation meet code?". Safety is not only an engineering concept, but even more so are political and legal concepts. Engineers may have had substantial involvement in establishing an appropriate level of safety or performance in a given code requirement (i.e. how safe is safe enough), but once that requirement is codified through the political process, it takes on a life of its own. The above reality is the reason that multi-level performance requirements in 273 (and the developing performance-based engineering guidelines for new buildings) will not be incorporated into codes as mandatory requirements anytime soon, and why, if a jurisdiction is contemplating a mandatory seismic retrofit program, a single performance level like 178, based on minimum life safety objectives, will be pushed by the jurisdiction's building official and legal counsel. None of this is to say that an engineer shouldn't recommend a higher level of performance to an owner to reduce economic risk, but simply that building officials face enormous difficulties in enforcing multiple bright lines in the sand instead of one line that reflects some concensus on minimum acceptable safety. And engineers may find their legal counsels and E&O insurance providers will be less than thrilled with multiple "standards of care" associated with multiple levels of performance. For further thoughts on that, go to the SEAOC archives and look for a posting from Frank McClure with a subject along the lines of " And the building won't even catch a cold". Franklin Lew, SE Building Official ...
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