Elasto-plastic large deformation analysis of PR steel frames for LRFD

An efficient second-order finite element-based method is presented here considering geometric and material nonlinear behavior of steel frames with nonlinear flexible connections and local plasticity effects. The assumed stress method is used to derive the governing equations which satisfy joint equilibrium and displacement compatibility conditions. An explicit form of the tangent stiffness matrix of the structure is obtained that makes the proposed method extremely efficient in nonlinear analysis. In deriving governing equations for large deformation, each element is characterized as a beam-column which undergoes arbitrary large rigid displacement but small relative displacement. The behavior of flexible connections is represented by an exponential function. In solving the nonlinear equations, the Newton-Raphson method with arc-length control is used in tracing the post-buckling behavior. Several numerical examples are given to demonstrate the robustness, accuracy and efficiency of the proposed method.