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Re: Twisting of rebar

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Jordan,
 
Do you often design your steel beams to stresses beyond Fy? Or, even better, to strains beyond, say, 0.02? There is no such thing as "safe bending radius" for torsion, shear yielding occurs at about 60% of that at bending and affects the same section that we count on in our structural design. 
 
The situation at hand is not that of life and death, and there are at least two ways of fixing it reliably - epoxying or mechanical coupling of rebars. 
 
V. Steve Gordin, SE
Irvine CA    
    
----- Original Message -----
Sent: Friday, November 07, 2008 04:17
Subject: Re: Twisting of rebar

I would be curious to know as well. I see this condition on a lot of commercial jobs (not mine, of course) and it seems to be almost "standard practice" in the industry.

It is worth noting that the bending of rebar does just about the same thing to the steel - it increases the yield in a portion of the steel through cold work. Presuming that it does not extend beyond the yield plateau, one might presume that the condition is  acceptable. To try and calculate the allowable twist from standard linear stress-strain relationship is incorrect due to the elastic-plastic nature of steel.

That's not to say it should get blanket approval, but it may not be a dire a situation as it seems on paper.
Jordan


Harold Sprague wrote:
It is a point to ponder, but I doubt that twisting rebar has ever been definitively studied.  All we can do is look for cracking that would indicate that we have gone too far.  The cracking would be evidence of the rebar being non-usable although there would still be a lot of tensile capacity.  I wish I could define "a lot".  I know that "a lot" is more than some. 
 
I am glad that the Government will now regulate my health.  Why... I feal healthier allready. 

Regards, Harold Sprague
"Beer is proof that God loves us and wants us to be happy."  - Ben Franklin





From: sgordin(--nospam--at)sgeconsulting.com
To: seaint(--nospam--at)seaint.org
Subject: Re: Twisting of rebar
Date: Thu, 6 Nov 2008 11:43:33 -0800


Harold,
 
I can see how a long enough rebar can be twisted 360 degrees.  The thing is - will is stay that way, or can the needed plastic (permanent) torsional deformation to 90 degrees be achieved without rendering the rebar non-usable?
 
By the way, coming from so many grateful engineers, those beers may be really bad for your health.  Hopefully, as it goes now, the government will force you to stay healthy...  
 
V. Steve Gordin, SE
Irvine CA
 
 
----- Original Message -----
Sent: Thursday, November 06, 2008 10:24
Subject: RE: Twisting of rebar
 
<...If the twist occurs over a long enough length, it is not a problem...>


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