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RE: Post yielded beam performance

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Flame straightening is probably the way to go unless the beam is relatively 

small and inexpensive.

The fact that the beam has yielded should have no bearing on the strength 
the beam --- in fact, the flange buckling would have much more of an effect 

than the beam having yielded.  (Recall the stress-strain curve from 
of Materials that when steel has been stressed into the yield range and
unloaded, it will back off parallel to the original loading curve, and then 

when reloaded it will progress back up the unloading curve.)  Since mild
steel is required to have an elongation in the range of 20 percent, and 
strain is .12 percent, you are probably nowhere near the failure point.

Be careful here.  The elongation to failure is in the 20% to 24% range. 
 But the ultimate strength is reached in the 12% to 16% strain range. 
 Beyond that point, the slope of the stress-strain curve is negative.  As 
loading proceeds up the new curve to a point that exceeds the new maximum 
point on the curve, major failure can proceed very rapidly because all of 
the strain hardening has been used.