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RE: PS CONCRETE: Torsion in Double-Tees

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From: Jim Getaz [mailto:jgetaz(--nospam--at)shockeyprecast.com]
Sent: Thursday, May 26, 2005 6:47 AM
To: seaint(--nospam--at)seaint.org
Subject: Re: PS CONCRETE: Torsion in Double-Tees

            Bill,

                        When I started doing precast concrete, I was told that the industry rule-of-thumb is that 25% of any load that looks like it should go to only one stem of a double tee is actually carried by the other. A few years ago I had the opportunity to run load tests on tees for another reason. The deflection measurements (we did not measure strain in the stems or any other more direct indication of load-sharing) indicated this is accurate. How the concrete stresses flow to get the load to the other stem is another issue. My mentor and the tests gave no indication of that.

                        Presumably, there are also flange connections between the loaded tee and the adjacent tee. Some load is shared by that tee’s stems, too.

            Jim Getaz

            Precast Concrete Engineer


 

Jim, appreciate the response very much.
 
The question I have, though, is: What does it mean?
 
May I "model" the torsion, then, assuming that it is (in essence) reduced by 25%?
 
It appears that the fabricator in this case used WWR for shear reinforcement. I assume that means they simply stick a sheet of the WWR in each leg of the tee. So, in that case, does this mean there is essentially NO torsion reinforcement provided?
 
In that case, do I need to look at (e.g.) CFRP or GFRP strengthening to handle the torsion?
 
Unlike yourself, I am NOT a prestressed concrete engineer. This is a fait accompli, and therefore I've got to decide what I need to do with what I have.
 
Any further comments would be most welcome.
 


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