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

Serge Lamothe,Luca Sorelli,Pierre Blanchet,Philippe Galimard

doi:10.1016/j.engstruct.2021.112409

Serge Lamothe, Luca Sorelli + Show 2 more

Open Access

https://doi.org/10.1016/j.engstruct.2021.112409

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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, full-scale 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.

Highlights

In the last decades Cross-Laminated-Timber (CLT) floors have been more and more employed in multistory timber buildings [1,2,3,4]
The measured dumping ratio is low 1% for all slabs indicating negligible inelastic behaviour. This works introduces an innovative composite slab made of CLTHPC and CLT-Ultra High-Performance Fiber Reinforced Concrete (UHPFRC) with the use of ductile notch connectors by a methodology which combines structural design and experimental vali dation of simulated results
It is recommended that a shear reinforcement or steel fibers are added to the concrete slab at the notch location to avoid this kind of cracking; 3

Summary

Introduction

In the last decades Cross-Laminated-Timber (CLT) floors have been more and more employed in multistory timber buildings [1,2,3,4]. By mechanically connecting timber and concrete, Timber-Concrete Com posite structures (TCC) allows reducing the thickness, the lightness and the construction time of the floor [7,8,9]. As timber and concrete have a limited material ductility, TCC structures can be plastically-designed by employing ductile connectors as well as assuring a hierarchal sequence of inelastic mechanisms so that the ductile connections efficiently yield before the timber failure [17,18,19]. Selçukoglu and Zwicky developed stiff and ductile notch connection between concrete and Glued Laminated Timber (GLT) by designing the notch configuration so that the wood fibers yield under compression parallel to grain [22]. A special class of concrete, such as, High-Performance Concrete (HPC) or Ultra-High-Performance

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