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RE: CONCRETE Wall Shear question

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Title: RE: CONCRETE Wall Shear question

Read section 1911.10.5.  It says unless you choose to use 1911.10.6 you can assume Vc=2*sqrt(f'c) which is close to 1921.6.5.3.  UBC formula 21-7 has confused me for a while.  It does not necessarily appear that Av*Fy*d/s=Acv*rho*Fy?

Scott Haan, P.E.
DPW Ft Richardson, AK
phone: 907-384-3161
fax: 907-384-3051


-----Original Message-----
From: David Merrick [mailto:mrkgp(--nospam--at)winfirst.com]
Sent: Wednesday, March 26, 2003 9:08 AM
To: SEAINT
Subject: RE: CONCRETE Wall Shear question

Section 1921.2.1.4 clearly states that the wall must comply with the
1911.10.6 (11-32) shear strength. I have demonstrated cases where that shear
strength is about 30% reduced for high seismic areas, in section 1921.6.5.3
(21-7). Unless someone can tell me different, we must always check if
equation 11-32 controls. This concerns me because I have found recommended
shear wall designs not including the code required check for equation 11-32
for a high seismic zone. I then wonder how many proprietary concrete shear
wall programs also do not check this. This would lead to conclude an
under-reinforced shear wall by as much as 30%! Now, please tell me I am
wrong. If so, how?

The phi factor is the same for both equations. I hear what you are saying
that there is testing to prove the equations for section 1921. The minimum
strength requirement is controlled by the 1911 shear equation. I see example
calculations failing to comply with this requirement. We are allowed to use
scientific research to justify exceeding the code, not to undermine it.
Leave that to the code builders and legislative powers. I see this as
alarming and want to do diligence. I must test for if I have been mistaken,
if not then I can go ahead and peacefully do designs with 11-32 controlling
some shear wall strengths in high seismic zones.

The difference between the two equations is that the 21-7 uses the full
length of the wall and 11-32 reduces the length limited by the position of
the tension steel. This is allowed to be assumed as 80% of the wall length.
this affects both steel and concrete shear. The other 10% comes from the
maximum variance in shear steel strength.

David Merrick, SE
Sacramento, California


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