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Re: soft story

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Sum the stiffnesses of the frames or shearwalls on the lower level.
Do the same for the frames and shearwalls above.


You can determine the stiffness using a computer model by putting dummy loads and compare the deflections. Or hand calc.

Usually it's pretty obvious, like when you have a discontinuity at the bottom floor.

"Weak story" is similar, but has to do with strength rather than stiffness


On Thu, May 8, 2008 at 10:46 PM, sam2000 . (sam2000) <sam2000(--nospam--at)> wrote:
 7 defines soft story as the one where "stiffness" is less than 70% of story above. If stiffness is to be defined as I/L this would mean whenever we have a 16ft 1st floor, we have a weak story, even though all the walls and columns are continuing from the story above? This is frequently the case in multi-story concrete buildings I design. I never thought of 1st story as weak, unless I was missing a wall or something.

I'm afraid I haven't been reading it right. Have I?

Syed A Masroor
Consulting Structural Engineer
Karachi, Pakistan

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