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.
With the advent of mass timber panels and the development of mid- to high-rise wood constructions, the renaissance of wood construction is underway from Europe to North America and throughout the world. Engineered wood-based panel products, especially mass timber panels, play an important role in the evolution of wood construction. Elastic properties are not only fundamental mechanical properties for structural design but also important indicators for quality control purposes. Accurate measurement of the global elastic properties of full-size panels is critical for their applications as load-bearing building components. An efficient and reliable non-destructive technique is required for the purposes both of characterizing elastic properties and of grading engineered wood-based panel products in the production line before processing for all kinds of structural applications. In this study, two vibrational non-destructive techniques employing modal testing for natural frequencies and other modal parameters were developed for simultaneous measurement of elastic constants of engineered wood-based panels. Both vibrational methods adopted modal testing of a rectangular plate with the boundary condition of a pair of opposite edges in the width direction simply supported and the other pair free. Compared with the elastic constant values by conventional static tests, both vibrational methods generally showed close agreement. The first method was developed for measuring the moduli of elasticity in both major and minor strength directions and the in-plane shear modulus of a panel based on free transverse vibration of rectangular thin orthotropic plates. A simplified modal testing procedure together with frequency identification methodology based on sensitivity analysis and an iterative algorithm were proposed as the means of achieving an efficient and reliable measurement with three and/ or four sensitive natural frequencies from only three impacts. The method was first verified with standard static test values in laboratory for full-size cross laminated timber, oriented strand board and medium density fibreboard. Then, 55 full-size cross laminated timber panels with different characteristics and from three manufacturers were tested in factory environments. The results showed that non-edge bonding and gap size had a negative effect on both Ey and Gxy and led to a large variation compared with edge bonded panels as well as with their corresponding prediction models (i.e., k-method, gamma method and shear analogy method). The second vibrational method was developed for determination of effective bending and shear stiffness values based on Mindlin plate theory with an exact frequency solution and a genetic algorithm for the inverse problem. The results showed that the transverse shear moduli of cross laminated timber panels can be accurately determined with proper shear correction factors and were verified by planar shear test values. According to an in-depth comparative study, the first vibrational method shows great potential for future development of a standard testing method and on-line quality control over other existing vibrational methods in terms of setup implementation, frequency identification, accuracy and the calculation efforts required. The second vibrational method is suggested for engineered wood-based panels with small transverse shear moduli and/ or small length/ width to thickness ratio. Both methods are deemed to be applicable to all kinds of composite plates.
This thesis focuses on the structural performance of mass timber panel-concrete composite floors with notches. Mass timber panels (MTPs) such as cross-laminated timber, glue-laminated timber, and nail-laminated timber, are emerging construction materials in the building industry due to their high strength, great dimensional stability, and prefabrication. The combination of MTPs and concrete in the floor system offers many structural, economic, and ecological benefits. The structural performance of MTP-concrete composite floors is governed by the shear connection system between timber and concrete. The notched connections made by cutting grooves on timber and filling them with concrete are considered as a structurally efficient and cost-saving connecting solution for resisting shear forces and restricting relative slips between timber and concrete. However, the notched connection design in the composite floors is not standardized and the existing design guidelines are inadequate for MTP-concrete composite floors.
To study the structural performance of notched connections and notch-connected composite floors, this thesis presented experimental, numerical, and analytical investigations. Push-out tests were conducted on the notched connections first, and then bending tests and vibration tests were conducted on full-scale composite floors. Finite element models were built for the notched connections to derive the connection shear stiffness. Finally, analytical solutions were developed to predict the internal actions of the composite floors under external loads.
This study shows that the structural performance of notched connections is affected by the geometry of the connections and material properties of timber and concrete. The notch-connected MTP-concrete composite floors showed high bending stiffness but were not fully composite. The floors with shallow notches tended to fail in a ductile manner but had lower bending stiffness than floors with deep notches. The composite floors with deep notches, however, often fail abruptly in the concrete notches. By reinforcing the notched connections with steel fasteners, the composite floor can achieve high bending stiffness, high load-carrying capacity, and controlled failure pattern. The proper number and locations of notched connections in the composite floors can be determined from the proposed composite beam model.
This thesis presented promising results in terms of the static and dynamic structural performance of notch-connected MTP-concrete composite floors. The test investigations added additional data to the current research body and prompted further evolvement of timber-concrete composite floors. The proposed empirical equations for estimating the connection stiffness and strength and composite beam model for predicting the serviceability and ultimate structural performance of composite floors provide useful tools to analyze the notch-connected MTP-concrete composite floors. The design recommendations for MTP-concrete composite floors with notches are provided in the thesis.