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Re: Shear Walls

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In a message dated 3/28/99 10:54:35 PM EST, Francis.Ang(--nospam--at) writes:

<< Sir, 
 Thank you very much for your suggestions. I intend to use a dual system to
 provide sufficient rigidity for lateral deformations and forces. 
 With regards to the forces, I use STAAD for 3-D analysis but the results are
 in stresses (kPa and psi) and not forces (KN and lbs). Previously, I
 determine the wall forces manually (assuming that the walls are cantilever
 beams with each story forces) with the resulting conservative design. I
 intend to use STAAD but I need a confirmation on the results. I presume that
 the results are to be multiplied to the wall dimensions to obtain the
 moments and forces. 
 Any suggestions and comments are most welcome. Thanks.
 By the way, do you know any other structural engineering programs, aside
 from STAAD and ETABS, which are user friendly and efficient? Thanks again

I have found ETABS to be rather friendly to use, but I have used it for
several years.   In reviewing your analysis to include the elevator core, are
all sides of the elevator core attached to the diaphragms so the forces can
actually get to all walls.  This can be a problem if the elevator is located
at the perimeter of the building sometimes.  

Also be aware if you are modeling the elevator as a "C" shape or box shape
that you can develop large axial forces in wall due to overturning forces and
flange affects of the walls.  In some cases, the axial forces may be large
enough that according to code (1921.6.5.3) you can not use the wall as part of
the lateral resisting system.

To eliminate the axial loads, you can model the "C" shape as three separate
walls  with no connections to the cross walls to eliminate the seismic axial
loads on the walls.  In the real world, the slab still acts to tie the walls
together, so there will be some axial forces.  I am curious to know how others
have been addressing this issue.

Michael Cochran