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Re: UBC97 question

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          There are a number of reasons why the dynamic analysis would 
          be providing larger values than the static analysis.  In 
          order for anyone to provide a helpful response to such a 
          question one would have to know a lot more about how you 
          set-up your static model and performed the analysis versus 
          how you set-up your dynamic model.  Sorry, I know this is 
          not much help but I think your question can't be answered by 
          a casual "off the cuff" response.
          
          Robert C. Rogers, PE
          robert.rogers(--nospam--at)woolpert.com
          www.woolpert.com


______________________________ Reply Separator _________________________________
Subject: UBC97 question
Author:  seaint(--nospam--at)seaint.org at Internet
Date:    3/2/99 12:25 PM


I am forwarding this query for discussion.

 To Whom It May Concern:  

"My name is Michael Kingsmore and I work in the Structural Engineering
Department at Sherlock, Smith and Adams, Inc. (an A/E firm) in Montgomery,
Alabama.  Most of our work is done for the Department of Defense -
specifically medical facilities for the  DOD.  

"Generally, when our firm encounters projects where seismic analysis is
necessary, we consult with firms specializing in seismic design.
However, we are interested in doing seismic analysis in house and are in the
process of performing our own dynamic analysis on a current project.  

"The governing code for the project is UBC 97.  Our current frame design
software is capable of Static Force Procedure and Dynamic Analysis
(utilizing UBC Normalized Response Spectra, NEHRP Normalized Response
Spectra or El-Centro Response Spectra).  I am having trouble understanding
why there is such a huge difference in member forces and
displacements/drifts between the results obtained using the Static Force
Procedure and results obtained using the Dynamic Analysis.  The Dynamic
Analysis results are much higher than those obtained through the Static
Force Procedure (typically 3 times larger).  It would seem to me that the
static approximation would be much more conservative than the dynamic
approximation.  

"I would appreciate any information or thoughts that would shed some light
on this dilemma.  Thank you for your time.  

Michael A. Kingsmore  
e-mail:  kingsmore_m(--nospam--at)ssainc.com  
Structural Department  
Sherlock, Smith and Adams, Inc.  
3047 Carter Hill Road  
Montgomery, AL   36111-0006  
(334) 263-6481  
FAX: (334) 264-4509  

===============================================================
Ken Wong   Tel: 510-231-9564
PEER Bldg. 451 RFS  Fax: 510-231-9461
1301 South 46th Street     E-mail: info(--nospam--at)nisee.ce.berkeley.edu
Richmond, CA  94804-4698      http://www.eerc.berkeley.edu
===============================================================