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[SEAOC] Re: Re: [SEAOC] Seismic Rehabilitation of Buildings using FEMA 178, 172 or 273 Provisions.[Subject Prev][Subject Next][Thread Prev][Thread Next]
- To: seaoc(--nospam--at)seaoc.org
- Subject: [SEAOC] Re: Re: [SEAOC] Seismic Rehabilitation of Buildings using FEMA 178, 172 or 273 Provisions.
- From: edean(--nospam--at)teleport.com
- Date: Fri, 6 Dec 1996 19:57:07 -0800 (PST)
>December 3, 1996 >Dear Colleagues: >Frank McClure, in response to Dave Evans' inquiry regarding the use of the >above mentioned documents, provided a very informative and fairly complete >historical background on all these documents. However, reading through his >comments, one could discern that he was advocating FEMA 178 over 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. >....<< Frank, Dave Evans, Ali Sadre and other Colleagues: There has been a recent discussion on the applicability of FEMA 178 vs 273 for the retrofit of existing structures. One thing that should not be lost site of, is that the premise for FEMA 178 is as an evaluation handbook. Specifically, it is intended to function as a means to quickly SCREEN FOR GOOD BUILDINGS, using criteria developed to offer a consistent rational basis of evaluation between engineers, buildings and building types. "Good" buildings by FEMA 178 standards are those that provide for "substantial life safety." This is intentionally a lower standard than is implied for new buildings or buildings being retrofitted to comply with the performance intent for new buildings as covered by the Code (UBC). The "substantial life safety" criteria is achieved by using a mean eq response, as opposed to the mean plus one std. deviation used by the Code. Once, the task of identifying the "good" buildings is done, only the "bad" ones, by definiton remain. The "bad" ones, those not meeting the FEMA 178 screening criteria, could be further evaluated using the more refined and demanding FEMA 273 "zero retrofit" procedures to see if compliance is met or if a structural seismic strengthening is required to meet the appropriate performance standard. If FEMA 178 criteria is used to retrofit a building, then the engineer must understand the limitations implied and intended in its development. FEMA 178 and 273, by definition are different standards. One critical question to ask is: "Is it appropriate to have an evaluation (screening) document, that represents a lower standard than is required in a design document?" Edwin T. Dean, S.E. ...
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