Lightweight and slender timber-concrete composite floors made of CLT-HPC and CLT-UHPC with ductile notch connectors

Abstract

Cross-Laminated Timber (CLT) structures have been emerging worldwide for residential floors in multi-storey buildings thanks to their lightness, fast construction and low ecological footprint. This work aims at fostering this application, which is often limited by vibrational and deflection limits, by investigating composite slab floors made of CLT and High-Performance Concrete (HPC) slab as well as CLT and Ultra High-Performance Fiber Reinforced Concrete (UHPFRC). Firstly, the composite floors CLT-HPC and CLT-UHPFRC with a span of 8 m were designed by considering a multicriteria analysis. To assure a certain structural ductility, previously developed ductile notch connectors were employed. As an economic choice, no shear reinforcement in the concrete slab was employed. Then, fullscale composite beams were fabricated in order to verify the predicted flexural behaviour and natural frequency. A numerical analysis was carried out to verify the connectors could effectively yield before the timber collapse. The comparison between the numerical simulation and the slip measurements confirmed that about 50% of the notch connections fully yielded and underwent inelastic deformation which favors the structural ductility. In the case of the CLT-HPC floor, a reduction of the notch contact surface due to the use of plastic sheet waterproofing as well as shear cracks developing in the concrete close to the notch corner both reduced the expected structural stiffness. Finally, the CLT-UHPFRC floor is endowed with outstanding values of slenderness ratio (~35) and lightness (~2 kPa), while eliminating the use of shear reinforcement and sheet waterproofing.