The two-way action of Cross Laminated Timber (CLT) is often ignored in the design of CLT due to its complexity. But in some cases, for example, large span timber floor/roof, the benefit of taking the two-way action into account may be considerable since it is often deflection controlled in the design. Furthermore CLT panels are typically limited to widths of less than 3 m. therefore, for practical applications, engaging CLT panels in two-way action as a plate in bending would require connecting two panels in the width/minor direction to take out-of-plane loading. To address this technically difficult situation, an innovative connection was developed to join the CLT panels in the minor direction to form a large continuous two-way plate. The two-way action of CLT was also quantified. Static bending test was conducted on CLT panels in the major and minor directions to measure the Modulus of Elasticity (MOE). This provided a benchmark for the following connection test, and data for the future development of computer modeling. The average apparent MOE was 9.09 GPa in the major direction and 2.37 GPa in the minor direction. Several connection techniques were considered and tested, including self-tapping wood screws, glued in steel rods, and steel connectors. One connecting system was found to be effective. For the panel configuration considered, the system was consisted of steel plates, self-tapping wood screws, and 45° screw washers. Two steel plates were placed on the tension side with sixteen screws, and one steel plates was placed on the compression side with four screws. When the screws were driven into the wood, the screws were tightly locked with the washers and steel plates, and at the same time, the wood members were pulled together by the screws. This eliminated any original gap within the connection. The connector was installed to join two CLT members in the minor direction. They were tested under bending with the same setup as above. The connected panels had an average apparent MOE of 2.37 GPa, and an average shear-free MOE of 2.44 GPa, both of which were higher than the counterpart in the full panels. The moment capacity of the connected panels was also high. The minimum moment capacity was 3.2 times the design value. Two large CLT panels were tested under concentrated loading with four corners simply supported. The deflection of nine locations within the panels was measured. This data will be used to validate the computer modeling for CLT two-way action.
In Phase I of Developing Large Span Two Way CLT Floor System (2017-18) we studied the performance of a steel plate connection system for the minor direction of CLT plates. The connected specimens had higher stiffness and strength compared to intact members under bending. In Phase II (2018-19) we designed and tested another connector based on...
Timber-Concrete Composite (TCC) systems are comprised of a timber element connected to a concrete slab through a mechanical shear connection. When TCC are used as flexural elements, the concrete and timber are located in compression and tension zones, respectively. A large number of precedents for T-beam configurations exist; however, the growing availability of flat plate engineered wood products (EWPs) in North America in combination with a concrete topping has offered designers and engineers greater versatility in terms of architectural expression and structural and building physics performance. The focus of this investigation was to experimentally determine the properties for a range of proprietary, open source, and novel TCC systems in several Canadian EWPs. Strength and stiffness properties were determined for 45 different TCC configurations based on over 300 small-scale shear tests. Nine connector configurations were selected for implementation in full-scale bending and vibration tests. Eighteen floor panels were tested for elastic stiffness under a quasi-static loading protocol and measurements of the dynamic properties were obtained prior to loading to failure. The tests confirmed that both hand calculations according to the -method and more detailed FEM models can predict the basic stiffness and dynamic properties of TCC floors within a reasonable degree of accuracy; floor capacities were more difficult to predict, however, failure did usually not occur until loading reached 10 times serviceability requirements. The research demonstrated that all selected connector configurations produced efficient timber-concrete-composite systems.
This paper examines CLT-steel hybrid systems at three, six, and nine storey heights to
increase seismic force resistance compared to a plain wood system. CLT panels are used as
infill in a steel moment frame combining the ductility of a steel moment frame system with a
stiffness and light weight of CLT panels. This system allows for the combination of high
strength and ductility of steel with high stiffness and light weight of timber. This thesis
examines the seismic response of this type of hybrid seismic force resisting system (SFRS) in
regions with moderate to high seismic hazard indices. A detailed non-linear model of a 2D
infilled frame system and compared to the behavior of a similar plain steel frame at each
Parametric analysis was performed determining the effect of the panels and the connection
configuration, steel frame design, and panel configuration in a multi-bay system. Static
pushover loading was applied alongside semi-static cyclic loading to allow a basis of
comparison to future experimental tests. Dynamic analysis using ten ground motions linearly
scaled to the uniform hazard spectra for Vancouver, Canada with a return period of 2% in 50
years as, 10% in 50 years, and 50% in 50 years to examine the effect of infill panels on the
interstorey drift of the three, six, and nine storey. The ultimate and yield strength and drift
capacity are determined and used to determine the overstrength and ductility factors as
described in the National Building Code of Canada 2010.
Project contact is Frank Lam at the University of British Columbia
A continuous CLT floor/roof system that has two way bending action across multiple CLT panels will create open floor space with long spans in both major and minor directions, making mass timber construction more competitive and cost-effective. A design guide on CLT two way floor/roof system, incorporating the results from the two phases of study, will be developed at the end.
During an earthquake, shear walls can experience damage around corners of doors and windows due to development of stress concentration. Reinforcements provided to minimize this damage are designed for forces that develop at these corners known as transfer forces. In this thesis, the focus is on understanding the forces that develop around opening corners in cross laminated timber (CLT) shear walls and reinforcement requirements for the same. In the literature, four different analytical models are commonly considered to determine the transfer force for design of wood-frame shear walls. These models have been reviewed in this thesis. The Diekmann model is found to be the most suitable analytical model to determine the transfer force around a window-type opening.
Numerical models are developed in ANSYS to analyse the forces around opening corners in CLT shear walls. CLT shear walls with cut-out openings are analysed using a threedimensional brick element model and a frame model. These models highlight the increase in shear and torsion around opening corners due to stress concentration. The coupled-panel construction practice for CLT shear walls with openings is analysed using a continuum model calibrated to experimental data. The analysis shows the increase in strength and stiffness of walls, when tie-rods are used as reinforcement. Analysis results also indicate that the tie-rods should be designed to behave linearly for optimum performance of the wall.
Finally, a linear regression model is developed to determine the stiffness of a simply-supported CLT shear wall with a window-type opening. This model provides insight into the effect of various geometrical and material parameters on the stiffness of the wall. The process of model development has been explained, which can be improved further to include the behaviour of anchors.
Developed in the mid-1990s in Austria and Germany, Cross Laminated Timber (CLT) is an innovative wood product known for its strength in both orthogonal directions, and its dimensional stability, making it a sustainable alternative to concrete slabs. CLT is created through the cross-lamination process, which glues together odd number of layers of wood planks placed in orthogonally alternating directions. With the growing interest in the application of CLT in North America, numerous studies has been conducted to characterize the acoustical properties of CLT panels. However, most of them focused on the sound-transmission aspect of CLT, very few on the sound absorption. This thesis will explore the sound-absorption characteristics of CLT, the effect on overall room-acoustical conditions, the utilization of resonant sound-absorbing layers on CLT to make it more sound-absorptive, and proposed solutions to improve this performance aspect. To demonstrate the low sound absorption and poor acoustical conditions in rooms with exposed and untreated CLT panels, several in-situ reverberation-time (RT) measurements were conducted in multiple buildings in British Columbia. Average sound-absorption coefficients and estimated Speech Intelligibility Indices (SII) were calculated as baseline performance measures for this study. Based on the results from five different buildings, involving 8 rooms configurations, average sound-absorption coefficients for exposed CLT panels are approximately between 0.02 to 0.13, resulting in barely acceptable conditions for verbal communication. To optimize the sound-absorption characteristics of prototype CLT panels, a transfer-matrix model has been developed to predict the performance of multi-layered CLT panels. This theoretical model was then validated by using three different sound-absorption measurement methods (impedance tube, spherical decoupling, and reverberation chamber) for multiple HR array configurations. After identifying the important parameters of an HR system and their effects on performance, a final prototype configuration with Helmholtz Resonator Array was then created with the goal of improving the room- acoustical performance of CLT, as well as responding to input from the CLT manufacturers and experts. Both the theoretical and experimental results confirmed that the proposed solution has the required sound-absorption performance and achieves all research objectives.
This study investigates the in-plane stiffness of CLT floor diaphragms and addresses the lateral load distribution within buildings containing CLT floors. In practice, it is common to assume the floor diaphragm as either flexible or rigid, and distribute the lateral load according to simple hand calculations methods. Here, the applicability of theses assumption to CLT floor diaphragms is investigated. There is limited number of studies on the subject of in-plane behaviour of CLT diaphragms in the literature. Many of these studies involve testing of the panels or the connections utilized in CLT diaphragms. This study employs numerical modeling as a tool to address the in-plane behaviour of CLT diaphragms. The approach taken to develop the numerical models in this thesis has not been applied so far to CLT floor diaphragms. Detailed 2D finite element models of selective CLT floor diaphragm configurations are generated and analysed in ANSYS. The models contain a smeared panel-to-panel connection model, which is calibrated with test data of a special type of CLT connection with self-tapping wood screws. The floor models are then extended to building models by adding shearwalls, and the lateral load distribution is studied for each building model. A design flowchart is also developed to aid engineers in finding the lateral load distribution for any type of building in a systematic approach. By a parametric study, the most influential parameters affecting the in-plane behaviour of CLT floor diaphragm and the lateral load distribution are identified. The main parameters include the response of the CLT panel-to-panel connections, the in-plane shear modulus of CLT panels, the stiffness of shearwalls, and the floor diaphragm configuration. It was found that the applicability of flexible or rigid diaphragm assumptions is primarily dependent on the relative stiffness of the CLT floor diaphragm and the shearwalls.
Wood as building material is gaining more and more attention in the 21st century due to its positive attributes such as light weight, renewability, low carbon footprint and fast construction period. Cross-laminated timber (CLT), as one of the new engineered wood products, requires more research emphasis since its mechanical performance can allow CLT to be utilized in massive timber structures. This thesis focuses on revealing one of the key failure mechanisms of CLT, which is usually referred to as the rolling shear failure. The scientific research conducted in this thesis combined both analytical modelling and experimental material testing. The stresses in CLT cross-layers obtained from a finite-element model were analyzed to differentiate various failure modes possible. Tension perpendicular to grain stress was found to cause cross-layer failure in combined with the rolling shear stress. Experimentally, specimens prepared from 5-layer CLT panels were tested under center-point bending condition. Detailed failure mechanism of CLT cross-layers were recorded with high speed camera to capture the instant when initial failure happened. It is evident that some of the specimens failed in tension perpendicular to grain which verified the modelling results. Variables such as the rate of loading and the manufacturing clamping pressure were designed in experiments to compare their influence to the failure of CLT specimens. In this research, the failure of CLT cross-layer was updated to a combined consequence of both rolling shear stress and tension perpendicular to grain stress. Future research topics and product improvement potentials were given by the end of this thesis.
In this study, the duration-of-load and size effects on the rolling shear strength of CLT manufactured from MPB-afflicted lumber were evaluated. The study of the duration-of-load effect on the strength properties of wood products is typically challenging; and, additional complexity exists with the duration-of-load effect on the rolling shear strength of CLT, given the necessary consideration of crosswise layups of wood boards, existing gaps and glue bonding between layers.
In this research, short-term ramp loading tests and long-term trapezoidal fatigue loading tests (damage accumulation tests) were used to study the duration-of-load behaviour of the rolling shear strength of CLT. In the ramp loading test, three-layer CLT products showed a relatively lower rolling shear load-carrying capacity. Torque loading tests on CLT tubes were also performed. The finite element method was adopted to simulate the structural behaviour of CLT specimens. Evaluation of the rolling shear strength based on test data was discussed. The size effect on the rolling shear strength was investigated.
The results suggest that the rolling shear duration-of-load strength adjustment factor for CLT is more severe than the general duration-ofload adjustment factor for lumber, and this difference should be considered in the introduction of CLT into the building codes for engineered wood design.