Shear Behaviour of Polyurethane Screw-Glued and Serrated Steel Plate Flange-to-Web Joints in Ribbed CLT Panels

The present study investigates the shear behaviour of screw-glued and mechanical flange-to-web connections intended for cross-laminated timber (CLT) ribbed panels, with the aim of improving composite behaviour and enhancing the structural performance of long-span timber floor and roof systems. Fifteen CLT-glue laminated timber (GLT) specimens were divided into five groups. One group incorporated SHARP501200 (SHARP) serrated steel plates, while four groups used screw-glued connections manufactured with LOCTITE HB (HB) or LOCTITE HB XE (HB XE) polyurethane (PUR) adhesive used in CLT manufacturing. For the adhesive groups, the screws were installed either from the CLT-flange side or from the GLT-web side to evaluate the influence of the assembly configuration. The specimens were subjected to monotonic quasi-static loading, and the resulting load–slip and load–displacement relationships were evaluated in terms of peak resistance, initial stiffness, post-peak response, and failure mode. The mechanically connected specimens achieved an average maximum load of 39.57 kN, whereas the screw-glued groups ranged from 141.20 kN to 198.90 kN. Installing the screws from the GLT-web side increased the average load-bearing capacity. The screw-glued connections exhibited high initial stiffness and predominantly timber-related failure, while the mechanical connection showed lower resistance and a more gradual post-peak response. Nonlinear finite element models were developed in Verisim4D (V2026), in which the CLT–GLT interfaces were represented by cohesive-zone contact elements governed by a tri-linear shear stress–slip law, consistent with the shear-dominated (Mode II) failure mode observed experimentally for both joint types. The results obtained provide design-relevant parameters and modelling strategies for optimising CLT ribbed panel joints in ultimate and serviceability states, thereby contributing to the development of efficient and environmentally sustainable multi-storey timber structures.