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RE: Setbacks on buildings subject to seismic

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Ben,

Thanks for the comments.

However, I would doubt that the irregularity will trigger a dynamic
analysis in my case because this building is in Detroit, which under UBC
would be Zone 1.  

I did find a section discussing setback type conditions in Section 104.8.2
and 105.3.1 of the 1996 Blue Book.  Both these sections deal with the
Static Force procedure.  I asked the question more to make sure that I
didn't miss any other sections that might pertain.

BTW, I do also have the Appendix that contained the "purpose" procedures
from the 1990 Blue Book.

Ultimately, I am not governed by either UBC or the Blue Book, but since the
BOCA code doesn't really directly give any methods to handle setbacks (I
still have to take a closer look at how it deals with "irregularities"), I
was looking for a rational method that I could use/incorporate with the
standard BOCA code method.  I knew about the Blue Book appendix because I
had used it several years before on a similar situation (again the
governing code is BOCA). 

Thanks again,

Scott

At 10:08 AM 12/17/99 -0800, you wrote:
>Most of the discussion in the blue book has been incorporated to UBC and IBC
>in the form of structural regularity (tables 16-L and 16-M of UBC). There
>are different procedures (Static vs. dynamic) depending on the building
>regularity and soil condition that needs to be used. If you have a highly
>irregular building, which based on your description you may have, you will
>end up using the dynamic procedure, which will address the setback issue in
>a more comprehensive manner, that static procedure.
>
>Ben Yousefi, SE
>San Jose, CA
> 
>
>	-----Original Message-----
>	From:	Scott Maxwell [SMTP:smaxwell(--nospam--at)engin.umich.edu]
>	Sent:	Friday, December 17, 1999 7:27 AM
>	To:	seaint(--nospam--at)seaint.org
>	Subject:	Setbacks on buildings subject to seismic
>
>	A question for all you real structural seismic people.
>
>	I have a building with a setback (i.e. a main pedestal of a building
>with a
>	"tower" portion sitting on top of the pedestal).  In reality, it is
>an
>	existing building in which we will be cutting out some of the middle
>bays
>	for the upper floors.  The result will be a pedestal with two towers
>	sitting on the two sides.
>
>	I have used a suggested procedure(s) for analyzing setback buildings
>in the
>	past that was contained in an Appendix of the SEAOC Blue book.  That
>	Appendix is no longer present in the 1996 Blue book.  I am assuming
>that
>	this has been incorporated into the main body of the newer Blue
>books (i.e.
>	1996).  The question is: Can any one tell me where this might be
>addressed
>	in the newer versions of the Blue book?  I ask because I am not as
>familiar
>	with the Blue book, since most of Michigan uses the BOCA code.  I
>believe I
>	found it in the Blue book but I want to make sure that I am not
>missing
>	other parts that may also address this.
>
>	Thanks,
>
>	Scott 
>
>
>