Nonlinear inelastic analysis of steel frameworks with non-prismatic members and semi-rigid connections

This paper presents a new computer method for nonlinear inelastic analysis of steel frames with non-prismatic members and semi-rigid connections. The behavior model accounts for material inelasticity (concentrated plasticity) due to combined bending and axial force, geometrical nonlinear effects in conjunction with initial geometric imperfections using only one element per physical member. The method ensures also that the plastic bending moment is nowhere exceeded once a full plastified section develops. The proposed formulation combines the power series approach with the Maxwell-Mohr method to compute the flexibility coefficients of the Euler-Bernoulli beam-column element in the presence of initial geometric imperfections, lateral loads acting along the member length and axial load. The second-order elasto-plastic tangent stiffness matrix and equivalent nodal loads vector of non-prismatic 2D beam-column element with semi-rigid connections is developed and the proposed nonlinear analysis formulation has been implemented in a computer program. In order to verify the efficiency and accuracy of the proposed approach, several examples analyzed by other researchers have been carried out and the results prove the performance of the proposed method.