Computational models for the low-cycle fatigue behaviour of composite members and joints

We present an overview of our latest research and development in finite element simulation of moment-resisting frames consisting of steel-concrete composite beams with full and partial shear connection and partial-strength beam-to-column joints under cyclic lateral loads. Three-dimensional finite element models based on solid and shell elements, respectively, and alternatively, one-dimensional models relying on layered bearn-column elements are adopted to investigate several analysis and modelling issues. All of them take into account the non-linear behaviour of concrete, of structural steel, of stud shear connectors and of steel-concrete force-slip relationships. We review some of the results obtained. Moreover, the numerical analysis of the low-cycle fracture behaviour of bolted end plate connections that are component parts of composite joints are presented in order to define details able to reduce loading-induced toughness demands. Then, novel displacement-based and two-field mixed beam elements are proposed for modelling steel-concrete composite beams with shear tag and deformable shear connections. Finally, new damage and hysteretic degrading models for the steel-concrete shear connection are proposed. Their ability to trace the deteriorating inelastic behaviour of the shear connection up to and at failure is illustrated and their extension to the hysteretic modelling of dissipative component parts of steel and composite joints is suggested.