The use of cross-laminated timber (CLT) in residential and non-residential buildings is becoming increasingly popular in North America. While the 2016 supplement to the 2014 edition of the Canadian Standard for Engineering Design in Wood, CSAO86, provides provisions for CLT structures used in platform type applications, it does not provide guidance for the in-plane stiffness and strength of CLT shearwalls. The research presented in this paper investigated the in-plane stiffness and strength of CLT shearwalls with different connections for platform-type construction. Finite element analyses were conducted where the CLT panels were modelled as an orthotropic elastic material, and non-linear springs were used for the connections. The hysteretic behaviour of the connections under cyclic loading was calibrated from quasi-static tests; the full model of wall assemblies was calibrated using experimental tests on CLT shearwalls. A parametric study was conducted that evaluated the change of strength and stiffness of walls with the change in a number of connectors. Finally, a capacity-based design procedure is proposed that provides engineers with guidance for designing platform-type CLT buildings. The philosophy of the procedure is to design the CLT buildings such that all non-linear deformations and energy dissipation occurs in designated connections, while all other connections and the CLT panels are designed with sufficient over-strength to remain linear elastic.
This paper contains the research results of a study related to developing an approach to estimate the deflection of Cross-Laminated Timber (CLT) shear walls for platform-framed construction. In order to account for the total deflection at the top of the wall, the contributions of connections and the CLT panels are considered. The connection contributions are accounted for through wall sliding and rocking, whereas the contribution of the CLT panels is estimated from the bending and shear deformation under lateral loading. The influence of perpendicular walls and floors above on the in-plane deflection of CLT shear wall is also investigated. A step by step procedure to estimate the deflection of CLT shear walls without and with perpendicular walls and floors above is discussed with examples.
The research presented in this paper analysed the stiffness of Cross-Laminated-Timber (CLT) panels under in-plane loading. Finite element analysis (FEA) of CLT walls was conducted. The wood lamellas were modelled as an orthotropic elastic material, while the glue-line between lamellas were modelled using non-linear contact elements. The FEA was verified with test results of CLT panels under in-plane loading and proved sufficiently accurate in predicting the elastic stiffness of the CLT panels. A parametric study was performed to evaluate the change in stiffness of CLT walls with and without openings. The variables for the parametric study were the wall thickness, the aspect ratios of the walls, the size and shape of the openings, and the aspect ratios of the openings. Based on the results, an analytical model was proposed to calculate the in-plane stiffness of CLT walls with openings more accurately than previously available models from the literature.
Timber-concrete-composite (TCC) floors, composed of timber and concrete layers connected by a shear connector are a successful example of hybrid structural components and are commonly used in practical applications.The connection of the two components is usually achieved with mechanical fasteners where relative slip cannot be prevented and the connection cannot be considered rigid. The growing availability of panel-type engineered wood products (EWPs) offers versatility in terms of architectural expression and structural and building physics performance. Preceding research determined the properties for a range of TCC connector systems in several EWPs using full-scale short-term bending tests. In the research presented herein, nine TCC floor segments (one specimens of each previously investigated configuration) were exposed to serviceability loads for approximately 2.5 years. During this time, the environmental conditions and the deflections of each floor were monitored. After having been long-term loaded, the floor segments were tested to failure. The results show an increase of deflection over time but neither bending stiffness,load-carrying capacity nor vibration performance were impacted by the long-term loading. This research provides input data to develop design guidance for TCC floors.
Cross-laminated timber (CLT) is gaining popularity in residential and non-residential applications in the North American construction market. CLT is very effective in resisting lateral forces resulting from wind and seismic loads. This research investigated the in-plane performance of CLT shear wall for platform-type buildings under lateral loading. Analytical models were proposed to estimate the in-plane stiffness of CLT wall panels with openings based on experimental and numerical investigations. The models estimate the in-plane stiffness under consideration of panel thickness, aspect ratios, and size and location of the openings. A sensitivity analysis was conducted to reduce the number of model parameters to those that have a significant impact on the stiffness reduction of CLT wall panels with openings. Finite element models of CLT wall connections were developed and calibrated against experimental tests. The results were incorporated into models of CLT single and coupled shear walls. Finite element analyses were conducted on CLT shear walls and the results in terms of peak displacements, peak loads and energy dissipation were in good agreement when compared against full-scale shear wall tests. A parametric study on single and coupled CLT shear walls was conducted with variation of number and type of connectors. The seismic performance of 56-single and 40-coupled CLT shear walls’ assembles for platform-type construction were evaluated. Deflection formulas were proposed for both single and coupled CLT shear walls loaded laterally in-plane that in addition to the contributions of CLT panels and connections, also account for the influence of adjacent perpendicular walls and floors above and illustrated with examples. Analytical equations were proposed to calculate the resistance of CLT shear walls accounting for the kinematic behaviour of the walls observed in experimental investigations (sliding, rocking and combined sliding-rocking) and illustrated with examples. Different configurations (number and location of hold-downs) of single and coupled CLT walls were considered. The findings presented in this thesis will contribute to the scientific body of knowledge and furthermore will be a useful tool for practitioners for the successful seismic design of CLT platform buildings in-line with the current CSA O86 provisions.
Abstract Seismic reliability analyses account for the inherent uncertainties in both the actions (earthquakes) and the reactions (properties of the structural systems) of a structure. To predict the failure probability of a structure, the system response due to external loads is usually estimated by a numerical method. In this paper, seismic reliability analyses were performed on a novel timber-steel hybrid system labelled FFTT (Finding the Forest Through the Trees) system. The FFTT system utilizes mass-timber panels to resist gravity and lateral loads and interconnecting steel members to provide the necessary ductility for seismic demands. To reduce the computational effort for reliability analyses, Genetic Algorithms (GA) and Analysis of Variance in combination with response surface methods were applied and compared. Uncertainties involving ground motions, seismic weight, connection properties of the lateral load resisting system, and ductility factor were considered in formulating the performance functions. Mean and standard deviation of peak inter-storey drift were selected as performance criteria. Nonlinear dynamic analyses were run to generate the response database for the FFTT system and the reliability index was calculated using second-order reliability methods. The results showed that the GA method was superior and that the ground motion was the most significant factor for structural reliability, while the ductility factor, the structural weight, the hold-down and connection stiffness also played significant roles.
The research presented in this paper is related to estimating the in-plane stiffness and strength of CLT shearwalls with different connections for platform-framed construction. Finite element analyses (FEA) for CLT shear walls with various types of connectors for wall-to-floor, wall-to-foundation, and wall-to-wall joints were conducted. The CLT panels were modelled using plane-stress shell elements with elastic material properties and the connections were modelled using nonlinear springs. The joints, consisting of traditional steel brackets, hold-downs, and screws connections, were modelled using nonlinear zero-length spring elements with "pinching4" hysteresis properties calibrated from tests. A parametric study was performed on single and coupled CLT shear walls with the variation of the number and types of connectors. The results showed that strength and stiffness increased significantly with the increase in the number of connectors. Placing hold-downs on both sides of the coupled shear walls increased performance-i.e. 43% and 25% increase in strength and stiffness compared to coupled shear walls with hold-downs located at the outer edges only.