Interaction ratio for single angles

STAAD output is providing me an interaction ratio for a single angle member of more than 2000 for clause H1-1 of AISC ASD code criteria. When I verify this by hand, the interaction of fa/Fa alone is greater than 0.15 which tells me that H1-1 no longer applies and H1-2 should be used.

Does anyone has seen this problem before? Your help will be greatly appreciated! Thanks!

Parents Reply
  • What is the critical condition being reported as? AISC H1-1 or H1-2?

    If it is H1-1, take a look at the term "fa", the allowable axial compressive stress. Is it greater than either of the Euler buckling stresses Fey and Fez? If so, (1-fa/Fey) or (1-fa/Fez) is becoming negative which is unaceptable. STAAD may be artificially magnifying the ratio to bring this to your attention. Do you see a warning in the output file that the allowable axial compressive stress exceeds the Euler buckling stress for that member?

    If this doesn't help, post your model.

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