Assessment of push-out test response of hybrid steel trussed-concrete beams by FE model

Aiming to investigate the truss-concrete stress transfer mechanism in Hybrid Steel Trussed-Concrete Beams (HSTCBs), a three-dimensional nonlinear FE model is developed. The constitutive laws of the steel composing the plates and the bars 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. The CDP model uses the concept of isotropic damaged elasticity in combination with isotropic tensile and compressive plasticity and is able to properly account for the concrete confinement effect. 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 3-D solid model is realized to account for the actual contact surfaces between the truss and the concrete. HSTC beam constituted by either deformed or smooth steel diagonal bars is considered, and four models for steel-concrete interface are proposed. The model is calibrated on some of the existing experimental push-out tests carried out by Aiello (2008) 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.