A NEW METHOD FOR INTEGRATING STIFFNESS MATRIX OF NONLINEAR FRAME ELEMENT

A simple and efficient method for integrating the nonlinear beam element stiffness matrix is presented in this paper. It originates from the concept of displacement method of structural mechanics. With either exact or numerical integration and linear combination of integral operators, the element stiffness matrices of nonlinearframe element taking into consideration of bending moment, shear force torsion moment as well as axial force can be obtained easily. The method is universal and valid for various polynomial functions and straight members with varying cross-section or stiffness. An example of straight linear elastic frame is provided to verify the method.