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Re: Dynamic Analysis Question

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In general, I think the coupled analysis would be the more realistic.
However, there are many potentail pitfalls which could have introduced
extra conservatism into the combined model (e.g., eccentricities) and the
solution details (e.g., modal combination method).  Without knowing the
specific details, no one can say for sure which one of your results is the
most realistic.

Walter Sawruk
EQE International, Inc.
Shillington, PA
email: ws(--nospam--at)

At 02:40 PM 13-01-2000 -0800, you wrote:
>For those of you who are dynamic analysis experts, or have had substantial
>experience in this field, here is a question:
>We have a structure that is comprised of an irregular midrise tower (say 15
>stories) utilizing moment frames located on top of a low rise, substantially
>rigid base (concrete shear walls). Originally the building was dynamically
>analyzed as two separate sections. In the first run the tower was assumed to
>be a separate building located at grade and in the second run the forces
>from the tower were applied at the top of the base and then analyzed. This
>appeared to be crude approximation of the building behavior. So another run
>was performed modeling the building as a whole. 
>As one might expect when the building is analyzed as whole, a substantial
>portion of the forces induced by the base is getting dumped into the tower
>and penalizing the tower frames.
>The question is which one is more realistic? Is there a middle ground or
>better alternative?
>Thanks in advance
>Ben Yousefi, SE
>San Jose, CA