An approximate method that takes into account the influence of finite displacements upon the load carrying capacity of planar unbraced frames is described. It is the iterative procedure where Quadratic Programming is applied for evaluation of the subsequent updated configurations of the frame, whereas Linear Programming serves to find ultimate load factors for each configuration. Numerical tests show that the procedure gives practically acceptable results being at the same time much cheaper than the exact geometrically and physically non-linear incremental analysis.
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