08.25: The influence of the concrete slab on the behaviour of steel‐concrete composite joints for braced frames

Abstract

ABSTRACTIn current practice, the design of seismic resistant steel‐concrete composite braced frames generally aims to ensure a structural behaviour for beam‐to‐column joints as close as possible to perfect hinges, hence preventing any kind of interaction with the bracing system. The global performance of steel‐concrete composite joints, on the other hand, is markedly affected by the structural interaction between the concrete slab and all the steel components at the beam‐to‐column intersection. This is especially true during seismic events, when compression forces can typically arise in the concrete slab in the vicinity of the column, leading to the occurrence of struts in contact with the column itself. As such, for appropriate design assumptions, it is thus necessary to fully understand the influence of the joint components interactions.To this aim, in this paper a refined Finite Element (FE) model representative of a hinged beam‐to‐column joint in a braced frame is implemented in the ABAQUS computer software and validated with experimental results. A full 3D solid modelling approach is first taken into account, with careful consideration for the geometrical and mechanical properties of each joint component, as well as for the corresponding contact interactions, including properly calibrated damage material models. After a preliminary validation of the FE modelling approach carried out towards earlier full‐scale experimental tests, a parametric FE study is proposed. By taking into account four different geometrical configurations for a reference steel‐concrete composite joint, in particular, being characterized by (i) absence of slab, (ii) presence of slab with partial interaction with the column (i.e. isolated slab), (iii) presence of slab with interaction (even with small gap on one side) and (iv) fully interacting slab, major FE outcomes are critically discussed. It is shown, in this regard, that the isolation of the slab is typically associated to important effects on the structural performance of the joint itself, compared to a fully interacting concrete slab.