Large deflection distributed plasticity analysis of 3D steel frameworks

This paper presents an efficient computer method for elasto-plastic and large deflection analysis of three-dimensional steel frames that provides the accuracy of second-order plastic-zone analysis methods but requires less computational effort. The method employs modelling of structures with only one element per member, which reduces the number of degree of freedom involved and the computational time. Gradual yielding of cross-sections is modelled using the inelastic Ramberg-Osgood force strain relationships, and then using the flexibility approach the elasto-plastic tangent stiffness matrix of 3D beam-column element is developed. The combined effects of material and geometrical nonlinearity sources are simulated into an object oriented computer program automatically. This program was used to study the ultimate response of several steel frames, which have been studied previously by other researchers. The example of computations and the comparisons made, have proved the effectiveness and time saving of the proposed analysis method.