Composite connections between CLT slab and steel beam: Experiments and empirical models

A composite floor comprising of steel beams connected to cross laminated timber (CLT) panels is a sustainable alternative to composite floors with reinforced concrete slab. The structural performance of the steel-CLT floor depends strongly on the load-slip behaviour (particularly the stiffness and strength) of the shear connection between the steel beams and the CLT slabs. In this paper, the short-term behaviour of steel-CLT joints is studied by laboratory push-out experiments conducted on CLT-steel-CLT specimens, being analogous to familiar push tests on steel-concrete specimens. In addition to coach screws and bolts, a high-performance steel-CLT composite connection comprising of high-strength bolted shear connectors embedded in pockets of grout is proposed and tested. The push-out experiments are used to determine the load-slip, failure mode, stiffness and ultimate strength/capacity of the steel-CLT composite joints and to calibrate an empirical formula for the load-slip response of the CLT-to-steel connections. Furthermore, simple empirical formulae for the stiffness and ultimate capacity of the CLT-to-steel composite connections are proposed.