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RE: Story shear for ramps; ramps as braces?

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Jim,
Thanks for your reply. You say that you don't take any credit for the ramp acting as a brace, so do you mean to say that you do not model the ramp in your lateral analysis models? If this is the case, then wont your structure be more flexible than in reality, meaning lesser base shear than what the building would really see due to the ramp stiffness? Or do you have details to ensure no force transfer through the ramp?
 
My case is a little different because I have more LLR on one side of the building and I have a shear flow through the ramp (collectors and diaphragm) to that side. That is adding a little bit more complication to my analysis in addition that the story shears and wall shears are not matching up until I reach the ground because the ramp being a stiff element is trying to take the forces down all the way to the base by itself :). But the ramp itself does not tie into the s.o.g and it is transferring all that it carried down to the base to the walls. My percentage transfer into the walls increases as I go down the building and that's my explanation to this problem.

Do you folks concur?
 
Thanks
Anantha
 
Any suggestions

Jim Getaz <jgetaz(--nospam--at)shockeyprecast.com> wrote:
            Anantha,
                        We assume half the ramp mass goes to the story above and half goes to the story below for our jointed precast concrete parking structures. And we do not take any credit for the ramp acting as a brace. The ELF method is conservative, so I think this assumption is OK. We build in the MidAtlantic so this has never been tested by a large earthquake, but it seems to be the way most people approach it. If you are doing a full ETABS analysis, that should answer your question.
            HTH,
            Jim Getaz
            Precast Concrete Engineer
            Winchester, Virginia



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ANANTHA NARAYAN, E.I.
Structural Engineer
Bliss and Nyitray Inc.
Miami, FL - 33134


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