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RE: masonry shear walls

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Title: RE: masonry shear walls

Story moment contributes to the axial load on the piers: one end of the building gets tensile stresses while the other gets compression unless you have intermediate vertical control joints. T or C=story shear*story height*[Ai*di]/sum(A*d^2).  To design a perforated wall for the story shear, draw a free body diagram for each pier with shear, moment and axial load and use these to design the reinforcement in the piers and check stresses.

.85 was previous to the 97 UBC for seismic overturning, it is .9 now.  You use 2/3 for wind except when the building height/width<.5 you can use 1.

Scott M. Haan P.E.
Civil Engineer
Public Works, Engineering Department
Fort Richardson, Alaska
phone: 907-384-3161
e-mail: scott.haan(--nospam--at)richardson.army.mil




-----Original Message-----
From: Andrew D. Kester [mailto:andrew(--nospam--at)baeonline.com]
Sent: Thursday, January 02, 2003 1:07 PM
To: seaint(--nospam--at)seaint.org
Subject: masonry shear walls


Ok, here is an easy one for all of you reinforced masonry wall gurus. I am
mainly dealing with work in FL, so no seismic but high lateral wind loads.

When looking at a segment of a shear wall, or a pier, and doing overturning
analysis on that pier, what portion of the dead load do you  include to
resist overturning of that pier? I have been taking the dead load of the
entire wall and the roof dead load X 2/3, but I guess UBC/IBC and some other
codes may use 0.85. That is not really my question as much as do you assume
the wall acts as a unit in overturning, so that you include the dead load
from the entire wall? I have been and I am wondering what others are doing.
From the texts I have researched this seems to be the normal practice.


Finally, the compressive jamb.. The traditional simple formula is C= T + P,
where C= compressive force, T= tensile force, P= axial load (roof load, wall
weight). But on a fairly long one-story wall, it seems only logical to use
the axial load P which is directly applied to THAT JAMB, not of the whole
pier or wall segment. Also you assume that the entire compressive force is
resisted by the end jamb which is an oversimplified and conservative version
of the triangular stress pattern in the wall. So what I have been doing is
after my shear wall analysis, I take the T/C force from overturning, and
then add that into the worse case wall analysis (includes lateral loading
and axial loads), then check that wall segment. Often in walls with small
height to length ratios we are talking about less then a few kips. This
often does not require anything additional to the jamb, but maybe adding two
filled cells instead of one. This may be a little conservative, but it is
easy and quick and the results seem quite economical as many times it is
just a check. I do the same for tensile analysis, and maybe I add an
additional bar.

Clear as mud? Any comments or suggestions or "the way I do it" s  ????

Thanks in advance ladies and gents, and happy new year to all of you.

Andrew Kester, EI
Longwood, FL




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