Over the last few decades, there has been growing interest in the use of low‐carbon materials to reduce the environmental impacts of the construction industry. The advent of mass timber panels (MTP), such as cross laminated timber (CLT), has allowed structural engineers to specify a low‐carbon material for a variety of floor design considerations. However, serviceability issues such as vibration and deflection are limiting the construction of longer span timber‐only floor systems and have encouraged the development of timber‐concrete composite (TCC) systems. The use of concrete would negatively impact on the carbon footprint of the TCC floor system and should be minimized. The purpose of this study was to study the impact on embodied carbon in the TCC system, when the ratio of timber and concrete was varied for specific floor spans. Two MTP products were considered, CLT and glued laminated timber (GLT). The floors were designed to satisfy structural, acoustic, and vibration criteria, and the results were presented in the form of span tables. It was found that using thicker MTP instead of adding concrete thickness to meet a specific span requirement can lead to lower embodied carbon values. Increasing concrete thickness for long‐span floor systems led to a reduction in allowable floor span due to the vibration criterion being the controlling design parameter. Increasing timber thickness also resulted in higher strength and stiffness to weight ratios, which would contribute toward reducing the size of lateral load resisting systems and foundations, resulting in further reductions in the embodied carbon of the entire structure.

Mass timber panels (MTPs) are a new generation of engineered wood panels that are available in large plane dimensions to facilitate fast floor construction with the obvious environmental benefit of being from a renewable material. In floor construction, concrete slab or topping is often applied over the MTPs to improve various performance attributes, including structural, acoustic, and vibration serviceability. A mass timber panel-concrete (MTPC) composite floor system often consists of a MTP connected to the concrete layer with mechanical fasteners and a sound insulation layer in between. The capacity of this type of composite system mostly depends on the strength of the connection, and often tests are performed to characterize connection properties required for structural design. In lieu of testing, analytical models can be developed to calculate connection properties based on component properties. To that end, two analytical models were developed for solid and layered timber by characterizing all possible kinematical failure modes for directly predicting the strength of a connection with inclined screws and an insulation layer. According to Johansen’s yield theory, the strength of a laterally loaded connection is controlled by the dowel-bearing effect of the fastener in timber, but joints with an inclined screw have a more complex behavior because of the combined bearing and withdrawal action of the screw. In the developed models, both the dowel-bearing and withdrawal action of the screw are considered along with the bending capacity of the screw and friction between the members. Both models were experimentally validated with a wide range of material properties. It was found that the models are capable of predicting the mode of failure of a connection and the load-carrying capacity within 10% of the experimental value.

Lack of design standards and guidelines is the most important barrier limiting widespread use of mass timber panel–concrete (MTPC) composite floor systems, a preferred choice by designers in modern multistory mass timber construction. The commonly used Gamma method of designing timber–concrete composite floors has some limitations and cannot predict the load-carrying capacity and failure modes of composite floor systems. Therefore, an analytical model was developed considering the interlayer connector behavior under the elastic-plastic range along with an acoustic layer between timber and concrete, to accurately predict the capacity and failure modes of MTPC composite floor system. One-way acting composite floor panels were tested under four-point bending with different configurations to investigate the influence of different parameters and to validate the developed capacity prediction model. It was found that the model can predict the capacity of the MTPC composite system within 17% of the experimental value and the associated failure mode. This developed capacity prediction model for MTPC composite floors will facilitate the use of these system in mass timber construction.

In the construction of modern multi-storey mass timber structures, a composite floor system commonly specified by structural engineers is the timber–concrete composite (TCC) system, where a mass timber beam or mass timber panel (MTP) is connected to a concrete slab with mechanical connectors. The design of TCC floor systems has not been addressed in timber design standards due to a lack of suitable analytical models for predicting the serviceability and safety performance of these systems. Moreover, the interlayer connection properties have a large influence on the structural performance of a TCC system. These connection properties are often generated by testing. In this paper, an analytical approach for designing a TCC floor system is proposed that incorporates connection models to predict connection properties from basic connection component properties such as embedment and withdrawal strength/stiffness of the connector, thereby circumventing the need to perform connection tests. The analytical approach leads to the calculation of effective bending stiffness, forces in the connectors, and extreme stresses in concrete and timber of the TCC system, and can be used in design to evaluate allowable floor spans under specific design loads and criteria. An extensive parametric analysis was also conducted following the analytical procedure to investigate the TCC connection and system behaviour. It was observed that the screw spacing and timber thickness remain the most important parameters which significantly influence the TCC system behaviour.