Improved nonlinear plastic hinge analysis of space frame structures

This paper is concerned with second-order plastic hinge analysis of three-dimensional frame structures. The beam–column formulation is based on the use of stability interpolation functions for the transverse displacements, and considers the elastic coupling effects between axial, flexural and torsional displacements. The developed computer program can be used to predict accurately the elastic flexural buckling load of columns and frames by modelling each physical member as one element. It can also be used to predict the elastic buckling loads associated with axial-torsional and lateral-torsional instabilities, which are essential for predicting the nonlinear behaviour of space frame structures. The member bowing effect and initial out-of-straightness are also considered so that the nonlinear spatial behaviour of structures can be captured with fewer elements per member. Material nonlinearity is modelled by using the concentrated plastic hinge approach. Plastic hinge between the member ends is allowed to occur. Numerical examples including both geometric and material nonlinearities are used to demonstrate the robustness, accuracy and efficiency of the proposed analytical method and computer program.