Modelling and behaviour of beam-to-column connections under axial force and cyclic bending

Many experimental and numerical studies were conducted to study the cyclic behaviour of steel beam-to-column connections; however, most of the proposed numerical works developed sophisticated three-dimensional solid models. In this paper, firstly, simplified finite element models of steel beam-to-column connections under cyclic loading were established using three- and two-dimensional shell models. Element types and steel cyclic constitutive models were described. The interactions between connection components (bolts, members and endplate) were accurately modelled to simulate the actual behaviour of connections. Both material and geometric nonlinearities were considered. The suggested finite element models showed good agreement with experimental results (hysteretic curves and failure modes) for a cyclically loaded endplate connection. Usually the steel connections are subjected to bending and axial force. In some situations, the axial force on the beam may reach sufficient large values which can lead to a considerable effect on the connections behaviour. Therefore, using the suggested two-dimensional shell model, a numerical parametric study on different connection types (fully welded, extended endplate, flush endplate and header plate connections), under combined axial force and cyclic bending, was performed. The carrying capacity, initial stiffness, hysteretic behaviour and energy dissipation capacity were compared and discussed. The results indicated that the level and direction of axial force significantly modified the connection response. The ultimate capacity of welded, extended endplate and header plate connections, under axial compression force equal to 35% of the beam axial plastic resistance, was, respectively, 74%, 126% and 169% of that of the same connections without axial force.