Re: Twisting of rebar

All of my rebar has been yielded far beyond a strain of 0.02, at every single bend. Believe it or not, I indicate bends, sometimes, in excess of 180 degrees! Every single piece of cold formed steel I design has residual stresses, and many have strain hardening continuous along the length. Also, all of my steel designs nowadays (well, 95% of them, at least) are are designed - theoretically - into the plastic range. Heck, I've even checked stuff with two, fully plastic hinges along the beam length (thank goodness three hinges are required for failure).

Sorry for the hyperbole/sarcasm. I have no idea what the implications are for field applied torsional strains as I've never had to address the issues and haven't done the research. I was simply pointing out that cold bending a piece of rebar and enforcing a plastic deformation is part of the process of preparing all bent bars, and that it may not be as dire as it might seem on paper. Or it might.  You're correct on the shear forces, since the t/c/v is identical in pure shear of torsionally loaded bars, so the bars should fail before they yield...except the field results don't seem to support the math in all cases. I suppose my question was if anyone had data on why the practice appears common, and failures in torsional shear aren't more common in this condition.

Jordan

Steve Gordin wrote:

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    

    

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