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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 of 
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 Strength 
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 yield 
strain is .12 percent, you are probably nowhere near the failure point.

AISC had an article or articles on flame straightening in either their 
"Modern Steel Construction" magazine or their "Engineering Journal" and there 
may have been an article or two in ASCE's "Structural Journal" or 
"Performance of Constructed Facilities Journal."

Hope this helps.

A. Roger Turk, P.E.(Structural)
Tucson, Arizona

Dave Meney wrote:

. > I hope that some of you experienced with post yielded beam behaviour can 
. > help me with the following problem.
. > 
. > An I-beam supporting mechanical equipment above a large ore bin has at 
. > some stage been overloaded and has
. > 
. > a) local flange buckling
. > b) a large deflection (approximately 30-40mm over a 4.5m span) which may 
. > be found to be inelastic when the load is removed
. > 
. > The flange buckling doesn't occur in the middle of the beam, which is
. > laterally braced with a truss arrangement.  I think that the buckling was
. > caused by a construction load applied to the top flange eccentrically 
. > causing the member to twist between points !
. > of lateral restraint.  This does not necessarily support the excessive
. > deflection case but there is evidence of twist on adjacent beams which 
. > would only ever normally carry relatively light floor grating loads. 
. > Perhaps a load was hung from the two adjacent!
. >  beams using a cross member which rested only on the flages and not over 
. > the web.
. > 
. > What are the issues regarding the strength of this beam given it has 
. > excessive deflection / deformation, and that a section of the beam has 
. > twisted flanges?
. > 
. > The deflection is not an issue from an aesthetics point of view - you 
. > cannot see the beam and its on a mine site anyway! - but if it is the 
. > result of yield sections what then?
. > 
. > Is it necessary to remove and replace the beam, or could
. > 
. > a) local flange replacements be made;
. > 
. > b) a tee section be welded to the underside if it is found that the beam 
. > is deficient for the design loads;
. > 
. > a) and b)
. > 
. > Any responses would be greatly appreciated.
. > 
. > Regards
. > 
. > Dave Meney
. > Structural Engineer
. > Perth, Western Australia
. >