During the past few years, a relatively new technology has emerged in North America and changed the way professionals design and build wood structures: Cross-laminated Timber (CLT). CLT panels are manufactured in width ranging from 600 mm to 3 m. As such, fastening them together along their major strength axis is required in order to form a singular structural assembly resisting to in-plane and out-of-plane loading. Typical panel-to-panel joint details of CLT assemblies may consist of internal spline(s), single or double surface splines or half-lapped joints. These tightly fitted joint profiles should provide sufficient fire-resistance, but have yet to be properly evaluated for fire-resistance in CLT assemblies.
The experimental portion of the study consisted at conducting ten (10) intermediate-scale fire-resistance tests of CLT floor assemblies with four (4) types of panel-to-panel joints and three (3) CLT thicknesses. The data generated from the intermediate-scale fire tests were used to validate a finite element heat transfer model, a coupled thermal-structural model and a simplified design model. The latter is an easy-to-use design procedure for evaluating the fire integrity resistance of the four commonly-used CLT floor assemblies and could potentially be implemented into building codes and design standards. Based on the test data and models developed in this study, joint coefficient values were derived for the four (4) types of CLT panel-to-panel joint details. Joint coefficients are required when assessing the fire integrity of joints using simple design models, such as the one presented herein and inspired from Eurocode 5: Part 1-2.
The contribution of this study is to increase the knowledge of CLT exposed to fire and to facilitate its use in Canada and US by complementing current fire-resistance design methodologies of CLT assemblies, namely with respect to the fire integrity criterion. Being used as floor and wall assemblies, designers should be capable to accurately verify both the load-bearing and separating functions of CLT assemblies in accordance with fire-related provisions of the building codes, which are now feasible based on the findings of this study.
The current study aims at evaluating the integrity failure (i.e. passage of hot gases or flames through the assembly) of CLT assemblies connected together using four types of commonly used panel-to-panel joints when exposed to the standard CAN/ULC S101 “Standard Method of Fire Endurance Tests of Building Construction Materials” [1] fire resistance time-temperature curve. The four types of joints include: 1) half-lapped, 2) internal spline, 3) single surface spline and 4) double surface splines.
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.
Cross laminated timber (CLT) connections in shearwalls require an understanding of the shear strength and stiffness of panel-to-panel connections within the wall. This research measures the strength and stiffness of three different panel-to-panel CLT connections considering both monotonic and cyclic loading. Connections included a laminated veneer lumber (LVL) spline, a half-lap connection and a butt joint with overlapping steel plate. All connections were ductile in nature. The butt joint with steel plate demonstrated the highest connection strength of the connections tested. The cyclic stiffness of the laminated veneer lumber spline was less than the monotonic stiffness, while the halflap joint experienced a sharp drop in load after ultimate load was achieved. Full details of the monotonic and cyclic behaviour will be discussed, including load, stiffness and ductility terms.
A cross-laminated timber (CLT) wall plays the role of resisting shear stress induced by lateral forces as well as vertical load. Due to the press size, CLT panels have a limitation in size. To minimize the initial investment, some glulam manufactures wanted to make a shear wall element with small-size CLT panels and panel-to-panel connections and wanted to know whether the shear wall would have equivalent shear performance with the wall made of a single CLT panel. In this study, this was investigated by experiments and kinematic model analysis. Two shear walls made of small CLT panels were tested. The model showed a good agreement with test results in the envelope curve. Even though the shear walls were made of small panels, the global peak load did not decrease significantly compared with the wall made of a single CLT panel, but the global displacement showed a large increase. From this analysis, it was concluded that the shear wall can be designed with small CLT panels, but displacement should be designed carefully.
