Determination of the load - displacement curve of moment resisting steel frames under horizontal loading

Seismic resistant steel frames are very common in regions of high seismic r isk due to their excellent characteristics in terms of strength and ductili ty. For the evaluation of the total ductility, various methods have been pr oposed in the bibliography. In this paper a method is proposed for the eval uation of the total ductility in steel structures, which takes into account the exact form of the moment-rotation curve, including possible softening branches. In the above method, the strength degradation due to second order phenomena is also taken into account. The numerical algorithm presented in the paper is based on the background of nonconvex optimization theory. Num erical examples demonstrate the potential of the proposed method.