Shear Performance Analysis of CLT–Steel Hybrid Joints: Effects of Fastener Geometry and FRP Reinforcement

Abstract

Cross-laminated timber (CLT) slabs and steel beams can be combined to form hybrid floor systems for long spans and heavy loads. The performance of these systems depends greatly on the shear connections between the CLT slabs and steel beams. In this study, push-out tests were conducted on CLT–steel joints connected with bolts or lag screws. The tests followed the loading procedure specified in EN 26891. Six specimen types were prepared by varying the fastener type, lag screw diameter and length, and reinforcement condition. Carbon fiber reinforced polymer (CFRP) plates were fabricated by laminating pultruded CFRP sheets with epoxy resin, whereas GF plates were fabricated by bonding woven glass-fiber cloth layers with phenol–resorcinol–formaldehyde adhesive. Both types of plates were bonded to the CLT with epoxy resin. CFRP reinforcement increased the strength and stiffness of the joints but resulted in brittle screw fracture. GF reinforcement produced smaller strength gains but showed a more gradual post-peak response. A modified Ramberg–Osgood model was used to describe the nonlinear load–slip behavior. The analytical curves agreed well with the test results (R² > 0.99). The model parameters reflected differences in fastener geometry and reinforcement condition. The results provide useful data for the design and numerical analysis of CLT–steel composite floor systems.