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Pounding of San Francisco-type soft-story midblock buildings

Maison, Bruce F.; McDonald, Brian; Schotanus, Marko

[San Francisco: Structural Engineers Association of Northern California], authors retain copyright, 2012-09, PDF (620.4 M13 2012)

This report presents a study into the effects of seismic pounding on the collapse performance of mid-block wood-frame soft-story buildings of a type common to San Francisco. We performed numerous computer simulations of various hypothetical pounding situations using both as-built (existing non-retrofitted) soft-story and retrofitted buildings. We found that pounding can change the collapse risk when compared to the risk of the same building in a no-pounding situation (i.e. having no adjacent buildings). A building's risk may increase, decrease, or remain about the same, depending on the neighboring buildings' relative properties. Three key factors were identified: building relative strengths, relative weights, and separation (gap) distances. When the buildings had similar relative strengths, we found that the risk was about the same as that for the no-pounding situation, independent of building relative weights and/or gap size. When the relative strengths varied, it was found that pounding can significantly change the collapse risk of certain buildings. The risk increased in the stronger and decreased in the weaker buildings, and the risk was biased toward the no-pounding risk of the heavier buildings. The risk generally increased with larger building separation distances, but there were exceptions. Results from our study provide insights about the influence of pounding on building evaluation and retrofit. They also have implications about public policy that can help inform soft-story building mitigation programs.

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