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Re: Interpreting Analysis Results

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Bill,

I'm travelling right now so I don't have access to this reference, but Park and Gamble's REINFORCED CONCRETE SLABS has a section discussing a rational approach for dealing with Mxy in the design of the reinforcing steel.  If I recall correctly, Mxy is added to Mx and My using expressions involving a constant which you choose.  My previous employer had a standard approach which was to simply increase Mx and My by Mxy/2.  I think most engineers simply ignore Mxy. 

Walt Sawruk
Senior Consultant
ABS Consulting
 

At 11:11 AM 12/24/2004 -0800, you wrote:

I?ve just modeled my first mat foundation using STAAD Pro and the foundation support option. I?m not using their foundation module, just the feature within the plain vanilla version which allows me to specify a modulus of subgrade reaction and the program applies the appropriate spring support at each node. Nice feature.

Anyway, the results I get are forces at the center of each plate. I get two shear components, Qx and Qy in psi and three bending components, Mx, My and Mxy in in-lbs/in. I know what to do with the Qx and Qy terms; I would compare these values with phi*2*sqrt(f?c). I know what to do with Mx and My. These are pretty straightforward.

The value that has me a little baffled is the torsion term, Mxy. It appears to me that I need to do some sort of Tc/J calculation and add this value to the Qx and Qy term, but I?m not certain.

Thanks in advance,
T. William (Bill) Allen, S.E. (CA #2607)
ALLEN DESIGNS
Consulting Structural Engineers
http://www.AllenDesigns.com
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