FIRST-ORDER ELASTIC-PLASTIC ANALYSIS OF MULTISTORY BUILDING FRAMES BY NUMERICAL MODELING

摘要

A numerical model for first order elasto-plastic limit analysis of structural plane frame subjected to combined bending moment and axial force actions is presented. The model takes into account the influence of axial forces on the ultimate load carrying capacity of the structure. It also allows for reversal of plastic hinge formation. The applicability of the model has been demonstrated through elastic-plastic analysis of rectangular frames. The numerical solutions of the frames are compared to those obtained in the traditional simple elasto-plastic analysis which neglects the effects of axial forces on the ultimate load carrying capacity of the structure. The numerical solutions obtained in the frame showed that when the amount of axial force in the elements of a frame exceed 15% of the respective element plastic axial force, the conventional first order elasto-plastic limit analysis method over estimates the load carrying capacity of structures, grossly mispredicts the bending moment distributions and moment-normal force interaction behaviour of the structure at fully plastic stage and gives results which violate the plastic condition of the fundamental conditions of simple plastic theory. Further, the new technique increased the rate of structure stiffness degradation and altered the number, location and sequence of formation of plastic hinges and the type of collapse mechanism mode when axial forces were large.