Semi-rigid beam element model for progressive collapse analysis of steel frame structures

Semi-rigid connections are widely used in steel frame structures. The bending and axial stiffness of connections have a significant influence on the mechanical performance of frame structures. However, most finite-element models of an actual project established in general finite-element software are rigid or hinge-connected for simplicity. Thus, the results are not consistent with the actual situation and may cause large errors. To estimate the influence of joint stiffness, including bending and axial stiffness, a novel numerical beam model is proposed in this paper. This method can be used for inelastic analysis with axial and bending stiffness considered separately. The accuracy of the proposed element model is first validated by comparing it with an ordinary beam element. Then, the model is used for seismic analysis of a steel frame structure, and the influence of bending stiffness on the dynamic response of a steel frame is derived. Progressive collapse analysis is conducted, and the influence of bending and axial stiffness on the mechanical behaviour of the steel frame structure during collapse is also determined. The proposed element model can consider semi-rigid joints and inelasticity at the same time with high accuracy, and it can be conveniently incorporated in general finite-element software.