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SEISMIC RETROFIT- SOFT STORY

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dherna45

Structural
Mar 6, 2017
19
US
Hello guys, I am working on a soft story seismic retrofit of two story building apartment with a tuck under parking on the first level. The solution that I am using is steel moment frame at the carport. Should I design the shear, moment connections and the foundation based on the assumption of plastic deformation at the beam and column? I am confused because on a book, It says that since the ductility of the LFRS above the steel moment frame is pretty low compared to the steel moment frame system, then the building will likely have severe damage before the yielding of the frame.

Thanks for your help
 
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Why would that be bad? Meaning wouldn't you want people to see bad things happening above, and then be able to get out below before the moment frame fails?

And since you're new here, welcome! I hope you find this site to be as useful as I have. But just FYI - not all engineers are male, so kindly use a different greeting.

Please remember: we're not all guys!
 
As a starting point, you might look at the City of Los Angeles' Structural Design Guidelines for there soft story ordinance More information on the city's ordinance: SEAOSC also has a design guide for this ordinance: I think San Francisco has similar laws; so you might try searching the internet about San Francisco's ordinance.
 
Check out FEMA P-807 guidelines. Simpson Strong-Tie has a good online training course about the exact topic you are looking at.
 
Some great docs etc recommended here. I won't have time to read them anytime soon though so I'm curious, what's the answer? Left to my own devices, I would have recommended:

1) Design the moment frames in the usual way treating the upper stories as essentially a rigid mass. Maybe allow hinge formation in your columns rather than your beams if that is not prohibited by local codes.

2) Investigate the upper stories for the lateral load associated with overstrength mechanism formation in the moment frames. In a new building, this would be tantamount to capacity designing the upper floors to the yield strength of the lower floor.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
 
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