Simplified Component-Based Modelling of Seismic Resistant Steel-Concrete Composite Joints and Frames

Beam-to-column joints in steel-concrete composite frames require specific calculation procedures for their optimal detailing and structural capacity maximization. For component-based modelling approaches, the most important mechanisms and behaviours of single members, but also the interaction of components, should be properly taken into account. In this paper, simplified non-linear formulations for beam-to-column joints in steel-concrete composite frames are applied to a case-study frame with X-concentric bracings. Two different modelling strategies are addressed for the calibration of joint components. First ("Type 1" model), nonlinear axial springs are assembled and calibrated in terms of force-displacement response (according to the DPC-ReLUIS Italian guidelines for seismic resistant steel-concrete composite joints). Beam-to-column joints with isolated (JA joint) or continuous slab (JB joint) are examined. Successively, non-linear rotational springs are proposed to simplify the "Type 1" strategy, and efficiently account for the moment-rotation behaviour of the same joints ("Type 2" model). By taking advantage of a preliminary validation towards past literature results, the optimized Type 2 approach is used to explore the in-plane lateral, seismic performance of a 2D composite frame, which is designed with X-concentric bracings. The seismic capacity of the frame (and the associated interaction of components) is addressed on the base of pushover analyses.