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RE: (Negative Torsional Shear)

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I may have missed a previous response, but just in case:

1999 Blue Book, Section C105.7,  p. 112 (top paragraph, right column) ...
"The statement 'The most severe load combination for each element shall be
considered in design' is intended to permit torsional shear to be SUBTRACTED
from the direct load shear when the torsional shear is opposite to the
direction of the seismic load ..."

This is contrary to previous code requirements, but the remaining paragraghs
of Section C105.7 go on to further explain the reasoning.  

As the design engineer you might choose not to reduce the force on a lateral
resisting element (due to negative torsional shear), but it's my
understanding that computer programs typically DO subtract the (negative)
torsional shear from the direct shear ... when that situation occurs.

Steve Hiner, SE
Folsom, CA

-----Original Message-----
From: Williston L. Warren, IV - S.E. [mailto:Bill_Warren(--nospam--at)sesol.com]
Sent: Thursday, July 13, 2000 9:51 PM
To: seaint(--nospam--at)seaint.org
Subject: 


Julio,

The subtraction noted on page 79 is a typo, it should be an addition to take
into account the forces from the opposite direction.

Williston "Bill" L. Warren, IV - S.E.
Structural Engineering SOLutions
Newport Beach, California

To: seaint(--nospam--at)seaint.org
From: julio.guerra(--nospam--at)theaustin.com

Hello everybody,

     Since I was introduced to Structural Engineering I know that the
torsional shear  due to eccentricity, must not be deducted from the direct
shear in any case. Only torsional shear that increases the direct shear
should be taken into account. The Code is a litle ambiguous when it says:
"Provisions shall be made for the INCREASED shears resulting from
horizontal torsion where diaphragms are not flexible" . It doesn't adress
the reduction of the direct shear as it was in previous codes.
     I was reading  SEA "Seismic Design Manual", Volume , example 25 and I
noticed that they reduced the direct shear (page 79) due to torsional
shear.
     Am I too conservative because I don't use this reduction? I checked
with several structural engineers and NONE of them use the reduction.
How is everybody else doing regarding this matter?

     Thanks in advance for your response.







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