FEM analysis of push-out test response of Hybrid Steel Trussed Concrete Beams (HSTCBs)

Aiming to investigate the steel truss-concrete stress transfer mechanism in Hybrid Steel Trussed-Concrete Beams (HSTCBs), a three-dimensional (3D) nonlinear Finite Element (FE) model is developed. The constitutive relationship of the steel composing the plates and the rebars is modeled by means of a quadri-linear law, while the concrete behavior is defined by means of a Concrete Damaged Plasticity (CDP) model, suitable for modeling concrete and brittle materials. Two main failure mechanisms are considered, namely the tensile cracking and the compressive crushing. In order to accurately grasp the complicate dowel and bond phenomena arising at the steel-concrete interface, a 3D solid model is realized to account for the actual contact surfaces between the truss and the concrete. The behavior of HSTCBs constituted by either deformed or smooth steel diagonal bars is investigated, and four models for steel-concrete interface are analyzed. The model is calibrated on some of the existing experimental push-out tests available in the literature and, afterwards, it is used to simulate the slip-load curve of a number of push-out tests in order to individuate the main geometrical and mechanical parameters influencing the maximum load that can be transferred from the steel plate to the concrete core. The FE simulations are also used to develop a first interpretation of the maximum load carried by the steel-to-concrete connection by means of analytical regression of the results numerically obtained, taking into account the geometrical configuration of the beam and the range of the geometrical and mechanical parameters.