In my opinion, if you decide to analyse each part seperately, scaling and
dealing with periods should be performed based upon seperate analysis.
However combining the forces to get overall results needs engineering
judgment based upon combined model behavior. If I convert this for a time
history analysis, it means that you should consider the time that your
ultimate forces occure. So it's important, and sometimes too complicated,
that combine the forces in right way. My feeling about this precedure makes
me to use combined model with some modifications to consider the effects
that I mentioned in my previous email.
Fariborz Tehrani, Phone: (310)509-8826
Civil Engineer Fax: (530)481-9532
BSCE, MSCE, PE Voice Mail: (877)743-6206
From: "Yousefi, Ben" <Ben.Yousefi(--nospam--at)ci.sj.ca.us>
To: "'seaint(--nospam--at)seaint.org'" <seaint(--nospam--at)seaint.org>
Subject: RE: Dynamic Analysis Question
Date: Thu, 13 Jan 2000 17:14:23 -0800
Thank you everyone for your input.
Now let me provide you some additional relevant information, or
maybe the second part of the question. The dynamic analysis had revealed
that the dominant modes for upper tower and lower podium were dramatically
different. Assume the decision is made to use the distribution of forces
the model of building as a whole. When it comes time to scale the forces
back to the code level forces what do you scale it to? And would you scale
the forces for each section separately? According to which period?"
Ben Yousefi, SE
San Jose, CA
From: Walter Sawruk [SMTP:sawruk(--nospam--at)ix.netcom.com]
Sent: Thursday, January 13, 2000 3:17 PM
Subject: Re: Dynamic Analysis Question
In general, I think the coupled analysis would be the more
However, there are many potentail pitfalls which could have
extra conservatism into the combined model (e.g., eccentricities)
solution details (e.g., modal combination method). Without knowing
specific details, no one can say for sure which one of your results
EQE International, Inc.
At 02:40 PM 13-01-2000 -0800, you wrote:
>For those of you who are dynamic analysis experts, or have had
>experience in this field, here is a question:
>We have a structure that is comprised of an irregular midrise tower
>stories) utilizing moment frames located on top of a low rise,
>rigid base (concrete shear walls). Originally the building was
>analyzed as two separate sections. In the first run the tower was
>be a separate building located at grade and in the second run the
>from the tower were applied at the top of the base and then
>appeared to be crude approximation of the building behavior. So
>was performed modeling the building as a whole.
>As one might expect when the building is analyzed as whole, a
>portion of the forces induced by the base is getting dumped into
>and penalizing the tower frames.
>The question is which one is more realistic? Is there a middle
>Thanks in advance
>Ben Yousefi, SE
>San Jose, CA