Nonlinear dynamic analysis of steel-concrete composite frame structures with full and partial shear connection under earthquake excitation

Various finite element (FE) models can be used for the analysis of steel-concrete composite (SCC) structures. Among available FE models, frame elements permit obtaining significant information at reasonable computational cost compared to more sophisticated two-dimensional (plate/shell) and three-dimensional (solid) elements. As an extension of conventional monolithic beam models, beams with deformable shear connection were specifically introduced and adopted for the analysis of SCC beams. Flexible shear connectors allow development of partial composite action, influencing structural deformation and distribution of stresses under service and ultimate load conditions. Furthermore, the shear connection can be responsible for collapse, e.g., when partial shear connection design is adopted, connectors fail due to limited ductility. Thus, a composite beam model with deformable shear connection has some important advantages over the common monolithic beam model, i.e., it allows a more accurate modelling of the structural behaviour, provides information on the slab-beam interface slip and shear force behaviour, permits to evaluate the effects of the interface slip on stress distribution, and enables to model damage and failure of the connectors. Applications of beam elements with deformable shear connection to the analysis of SCC frames have mainly concerned quasi-static behaviour, and there is limited experience on nonlinear dynamic analysis [1]. More attention is required by very specific modelling issues, such as the characterization of the cyclic behaviour of the deformable shear connection and the assembly of SCC beam elements with conventional beam-column elements. In addition, the influence of various factors (e.g., shear connection boundary conditions, mass distribution between the two components of the composite beam) on the dynamic response of SCC frame structures needs to be better understood through a systematic parametric study. The objective of this work is to provide deeper insight into nonlinear dynamic analysis results of SCC structures and how different modelling assumptions affect these results. For this purpose, a materially-nonlinear-only FE formulation for static and dynamic analysis of SCC structures using displacement-based locking-free elements with deformable shear connection [2] is employed. Realistic uniaxial cyclic constitutive laws are adopted for the steel and concrete materials of the beams and columns and for the shear connection. Nonlinear dynamic seismic analysis results of two-dimensional moment resisting frames made of steel columns and composite beams are provided. These results and their discussion focus on: (i) the influence of partial composite action on the dynamic nonlinear analysis of SCC frames; (ii) the effects of different shear connection boundary conditions