Convergence of Load combination
Convergence of Load combination
(OP)
Hi everyone,
Trying to analyse an industriel steel buiding made of 8 stories and 32m hight (using VDesign).
Once I run the analysis some of the combinations are not converged, what does this mean and how to correct it.
Also how to check the P-delta effect if converge or not.
Thanks
Trying to analyse an industriel steel buiding made of 8 stories and 32m hight (using VDesign).
Once I run the analysis some of the combinations are not converged, what does this mean and how to correct it.
Also how to check the P-delta effect if converge or not.
Thanks






RE: Convergence of Load combination
I don't think this means that it's going to fall down tomorrow (especially if it's been standing for a while), but it does mean that, on paper anyway, it's unstable. I would double check boundary conditions and end restraints. Try to use an analysis method that might have been employed at the time of original design as a sanity check (e.g. use k factors without reduced stiffness and notional loads instead of the DAM for steel).
What kind of lateral system does the building have?
RE: Convergence of Load combination
it is an open structure to support equipments for refinery plant where a combination of X and chevron bracing are used.
RE: Convergence of Load combination
I would add that excessive internal (p-small delta) second order effects may also lead to divergence.
RE: Convergence of Load combination
RE: Convergence of Load combination
weird, i work in Refinery/Petrochemical/Oil and Gas industry and we dont usually use pdelta analysis but linear perform analysis on steel and these are major EPCs on multi-billion projects. we dont use LRFD either but ASD.
RE: Convergence of Load combination
RE: Convergence of Load combination
AISC requires that you account for second order effects (see AISC Section C1.1). This may be accomplished in several ways, not necessarily carrying out an actual rigorous 2nd order analysis (e.g. "amplified 1st order elastic analysis), but there are limitations on when you can use methods that don't explicitly account for the effects.
RE: Convergence of Load combination
RE: Convergence of Load combination