Finite Element numerical analysis of hybrid connections for the reinforcement of timber-to-timber slabs

Self-tapping screws (STS) are largely used in timber construction, both for fastening and rein-forcements. Their continuous thread with high withdrawal capacity makes possible to construct many geometrical configurations for connections with stiffness and load-carrying capacity marked-ly higher with respect to traditional timber-to-timber joints. The arrangement of screws with differ-ent inclination and spacing, however, requires the designer to account for several aspects in the actual load transfer mechanism of the full connection, including the bending capacity of screws, the embedment strength of wood, the withdrawal capacity of fasteners, as well as friction between the system components. In this paper, an advanced Finite Element (FE) numerical study is proposed for novel hybrid connections. As known, FE analyses can offer a robust support to design en-hancements, as an alternative to costly and time consuming experimental testing. On the other side, complex mechanical behaviors that are typical of composite structural systems can be hard to cor-rectly reproduce, due to a combination of multiple aspects. Major advantages of the current re-search study are taken from small-scale and full-scale experimental tests carried out on a wide set of geometrical and mechanical configurations. As shown, a key role for the discussed FE investiga-tion is assigned to the reference modelling approach. While the material properties are properly taken into account (including possible damage evolution in the steel and timber components of in-terest), special care is spent for a set of contact interactions, based on the use of the Cohesive Zone Modelling (CSM) method and its adaptation for timber-to-timber composite systems. The reliability of FE results is then discussed, towards the development of a robust generalized modelling ap-proach that could be used in support of the refined analysis and design of hybrid connections in timber-to-timber composite slabs.