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Re: Lateral decision -Reply

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Mr. Welliver and Mr. Wykoff have very good points. In San Francisco it is very common and required by code to upgrade just the level and every level below where a change in occupancy or significant alteration takes place. For wood frame buildings the ramifications are probable much less, but for a non-ductile concrete frame building the results could cause a Northridge Kaiser Permanente type failure. Frank Lew are you out there? Did the authors of section SFBC 104(f) have take this into consideration?
Jeff Smith

I read the definition in 3403.2  "if an addition or alteration will cause the existing building or structure to become structurally unsafe or overloaded....." as possibly addressing the second story requirements. If the lower level of a two story is strengthened, perhaps the added new "stiffness" pushes load further up the building and therefore may cause to second story to become "unsafe". There are examples of such, in Los Angeles I believe, where the "soft" story of a damaged building was "strengthened" only to have pushed the damage upward in the building during a later earthquake.................

Barry H. Welliver

..................I would retrofit both stories, not just the bottom story.
Reasons include:
Stiffening the bottom story usually increases the acceleration of the second
The second story may approach "weak" or "soft" status, even though codes give

Jeff Wykoff