Abstract
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.
Highlights
In recent years, the use of timber in multistorey residential and commercial buildings has increased worldwide, primarily inspired by consciousness surrounding the sustainability of timber as the primary structural material [1, 2]
Construction with mass timber is approximately 25% faster than similar on-site concrete construction. It requires 90% less construction traffic and 75% fewer workers which yields a much quieter job site [5]. e lighter weight and lower stiffness of timber-only floors can make them more susceptible to serviceability limit states such as vibrations and excessive deflections while satisfying the strength requirements. erefore, in timber-concrete composite (TCC) floor systems, a structural concrete topping layer is provided over the timber beam or mass timber panel (MTP). e two components are connected by mechanical connectors, as shown in Figure 1, such as dowels
The goal of this study is to investigate the impacts on design selection with respect to the main TCC floor components, namely, concrete and timber, for specific span requirements on the embodied carbon of the system. e allowable span for a TCC floor system can be developed by considering all ultimate limit states related to timber, concrete, and shear connectors, and serviceability limit states related to deflection and vibration. e ultimate and serviceability limit state requirements for TCC floors with different combinations of materials, dimensions, and connection characteristics were evaluated based on [20]
Summary
The use of timber in multistorey residential and commercial buildings has increased worldwide, primarily inspired by consciousness surrounding the sustainability of timber as the primary structural material [1, 2]. Timber structures are generally associated with lower levels of embodied carbon due to lower emissions during the manufacturing of the timber products and the construction process. A new generation of engineered mass timber products known as mass timber panel (MTP), for example, glued laminated timber (GLT) and cross laminated timber (CLT), has the structural capacities to be used as a lowcarbon alternative to steel and concrete for gravity and lateral load resisting systems in structures. Construction with mass timber is approximately 25% faster than similar on-site concrete construction. It requires 90% less construction traffic and 75% fewer workers which yields a much quieter job site [5]. Erefore, in timber-concrete composite (TCC) floor systems, a structural concrete topping layer is provided over the timber beam or mass timber panel (MTP). It requires 90% less construction traffic and 75% fewer workers which yields a much quieter job site [5]. e lighter weight and lower stiffness of timber-only floors can make them more susceptible to serviceability limit states such as vibrations and excessive deflections while satisfying the strength requirements. erefore, in timber-concrete composite (TCC) floor systems, a structural concrete topping layer is provided over the timber beam or mass timber panel (MTP). e two components are connected by mechanical connectors, as shown in Figure 1, such as dowels
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