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Post yielded beam performance

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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