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Re: hillside construction[Subject Prev][Subject Next][Thread Prev][Thread Next]
- To: seaoc(--nospam--at)seaoc.org
- Subject: Re: hillside construction
- From: NRoselund <NRoselund(--nospam--at)aol.com>
- Date: Fri, 10 Apr 1998 21:52:55 EDT
Jamie Walsh: The City of Los Angeles and SEAOSC formed a Northridge Earthquake Taskforce on Hillside Dwellings because of the hazardous and fatal damage that occured to that kind of construction in the Santa Monica Mountain areas of the San Fernando Valley. The output of that Taskforce included L.A. City Ordinances for both new construction and residential retrofit. The January 1996 SEAOSC Seminar titled "Structural Considerations of Building Conservation Toward the 21st Century" included a presentation on some of the findings of the Hillside DwellingTaskforce. The Seminar Notes are probably available from the SEAOSC Office. The Taskforce dealt with above-foundation structure only; hillside foundations generally performed well. Houses built on concrete foundations that extended from below grade upward to the floor framing did well. Serious damage occurred to wood and steel framing between the foundation and the at-grade floor. Bad-news items: 1) stilt-columns with tension only bracing; 2) plywood shear walls built on the stepped tops of grade beams or footings; 3) plywood shear walls built on the sloping tops of grade beams or footings; 4) floor diaphragm framing not WELL anchored to the uphill footing -- don't let it act as a diaphragm because horizontal diaphragm deflection will separate it from the uphill footing damaging shear-resisting connectors; 5) framing on the uphill side against which debris can accumulate and is not removed (moisture trapped in debris gets into the framing and corrodes bolts & nails, and deteriorates wood -- use very high stem walls). Related to items 2) and 3), plywood shearwalls that are not rectangular don't work in the way that many designers tend to assume: they don't have a uniform shear distribution, and they un-zip from the foundation starting at the top. Nels Roselund Structural Engineer "Only works on buildings that are older than him."
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