Steel strength loss after yielding?

[calky117]

What happens to structural steel after it has yielded plastically? Can it still be used and how much of its strength does it retain?

I'm trying to give several repair options on a steel/gate structure which has had an impact load causing deformation. The structure consists of a steel skin facing plate on the front and is stiffened with beams/angles on the rear. It has clearly yielded and deformed, but I'm trying to determine if it should be completely replaced or if some repairs can be done.

I understand it will depend on how much it has deformed, since this would have an effect on the cross section. Any help is appreciated. I couldn't find any literature on the matter.

 

[JAE]

It depends on how much strain the steel has experienced...might have become cracked or hardened/brittle if the deformation was too far.

This would also depend on what this gate structure is designed to do and what strength it needs - sizing of members vs. applied loading.
Probably too many variables for us to give you a solid answer but essentially you would need to analyze the various members and parts of the structure with the applied deformations to see if there are discrete locations where you may have reached strain hardening. In those locations you could then respond with stiffening, replacement, etc. to bridge over the embrittled areas.

You'd need to know the actual type of steel to confirm this - or possibly sample some of the steel to test to get a representative stress-strain diagram....all that sounds excessive for a simple gate so maybe just assuming the "bent areas" are "bad" and strengthen/replace from that view.


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[Tmoose]

got any pictures ?

If there are no cracks before or after straightening mild steel I'd say there is a decent chance it would be good to go.

If the members are stout heat straightening is pretty well accepted.

https://www.fhwa.dot.gov/bridge/steel/02.cfm

 

[rb1957]

it doesn't sound like these are carrying a significant load ? So the repair is cosmetic ?

another day in paradise, or is paradise one day closer ?

 

[JasonMcKee71]

The Bauschinger effect should also be considered, as the quake loads are cycling loads and the yield stress continues to get smaller.

Jason McKee
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