Bent/local buckling of joist chord analysis

[SeizeTheMoment]

Hello all, I would like your input on how you would analyze the tolerance of a bent chord of a joist, or if you have any resources available.

I've looked at TD12 and their commentary is that "if local buckling exists in chords subjected to compression, the buckled sections should be alleviated or reinforced. Buckled sections in chords subjected to tension only may not be detrimental to the joist performance depending on the degree of buckling. More than likely local buckling in tension chords occurred during shipping or erection."

Is there guidance on how much an angle can buckle in compression without needing reinforcement, and has anybody checked the case for tension chords as well?

See sketch below for the typical tolerance in question.

Thanks in advance.

 

[nategemb]

If a chord that is only ever in tension has buckled, I agree the damage would have had to come from shipping or handling. You still have the same area of steel (unless it got chipped or gouged) and therefore the capacity is still the same.

Damaged compression chords are more difficult. You could possibly create a FEM of the chord to try to determine the capacity but that would be taking the design of the truss into your own scope rather than the scope of the truss manufacturer who initially designed it. I typically send data and photos back to the company that supplied the truss and have them provide an analysis and a fix (if needed). They usually call for the chord to be repaired as much as possible and then specify some amount of reinforcement to be added in that area.

 

[SWComposites]

a very small offset will significantly affect the buckling capacity. you could run a simple beam nonlinear FEM with various offset sizes. is this a metal or wood joist?

 

[ANE91]

If we’re talking about local buckling, then there may be some post-buckling strength as adjoined elements serve to restrain the buckled element. In theory, once the member undergoes global buckling, it cannot take any more load.

AISC’s SCM discusses this.