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[SEAOC] Wind loading vs. Seismic loading[Subject Prev][Subject Next][Thread Prev][Thread Next]
- To: SEAOC <SEAOC(--nospam--at)SEAOC.ORG>
- Subject: [SEAOC] Wind loading vs. Seismic loading
- From: "Sprague, Harold O." <SpragueHO(--nospam--at)bv.com>
- Date: Tue, 13 Aug 96 09:01:00 PDT
- Encoding: 27 TEXT
Comparison of wind to seismic loading must be done judiciously. The probabilities of the events are not equal, neither is the expected performance. The ASCE 7-95 commentary provides guidance on the probability of wind speeds and the calculated wind loads. The Blue Book and the NEHRP Commentary provide good resources for probabilities on seismic events, calculated loads, and expected performance, although residential construction is not the primary focus of these documents. In general, seismic loads are determined with a 10% chance of exceedance in 50 years, however ASCE 7 wind loads have a 64% chance of exceedance in 50 years. At first glance this appears to be an extraordinary disparity, but one must then look at the expected performance. The performance in seismic events is aimed at life safety, stability, and collapse prevention, and assumes non linear response for forces larger than those calculated using the code. The intended performance for wind is elastic, and linear under design loads. Remember also the special detailing and limitations for seismic loads are required to insure proper non-linear performance. If an engineer is going to make any kind of assurances as to the performance of rigid cladding such as plaster or masonry, it would be prudent to perform extensive analyses including site specific response and non-linear dynamic analysis. This is generally a tall order for residential construction. HOS ...
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