Proceedings of the Institution of Civil Engineers - Construction Materials
The fire performance of heavy timber frame structures is often limited by the poor fire performance of its connections. Conventional timber connections, dowelled or toothed plate connections typically use steel as a connector material. In a fire, the steel parts rapidly conduct heat into the timber, leading to reduced fire performance. Replacing metallic connectors with alternative non-metallic, low thermal conductivity connector materials can, therefore, lead to improved connection performance in fire. This paper presents an experimental study into the fire performance of metal-free timber connections comprising a hot-pressed plywood flitch plate and glass-fibre-reinforced polymer dowels. The thermal behaviour of the connections at elevated temperatures is studied using a standard cone calorimeter apparatus and a novel heat transfer rate inducing system. The latter is a fire testing system developed at the University of Edinburgh. The mechanical behaviour of the connection during severe heating was also studied using an environmental chamber at temperatures up to 610°C. The results demonstrate that heat transfer in the non-metallic connections is governed by the thermal properties of the timber, resulting in significant enhancements in connection fire performance.
Project contact is Christian Dagenais at Université Laval
The structural elements of a building must provide fire resistance in order to prevent collapse and to provide an escape route for occupants. The basic philosophy is that components that support elements with a degree of fire resistance must also offer the same degree of resistance. It is also assumed that the connections between these elements provide at least the same degree as the supported elements. Traditionally, heavy timber construction used ingenious construction principles and assemblies made of cast iron. With the advent of innovative fasteners (eg self-tapping screws), the principles of assembly have changed greatly and are now similar to a metal frame. So, several studies have been carried out in recent years in order to increase knowledge of the fire behavior of these assemblies (Audebert et al., 2012, Dhima 1999, Frangi et al. 2009, Peng 2010, Ohene 2014, Ali et al. 2014 , Moss et al. 2008). Although a significant amount of information is available in the literature, it often indicates short-term flammability resistance (± 30 min), which is largely insufficient for buildings having to provide a degree of fire resistance of at least 2 hours. The objective is to carry out a literature review in order to fully understand the factors influencing the fire performance of assemblies in wood construction. A model of thermomechanical behavior and a simplified analytical approach would have to be developed.
With the arrival of innovative fasteners (e.g. self-tapping screws), assembly principles have greatly changed and now resemble a metal framework. Although a significant amount of information is available in the literature, it often indicates short-term flammability resistance (± 30 min), which is largely insufficient for buildings that need to provide a fire resistance rating of at least 2 hours. The objective is to carry out a literature review to understand the factors influencing the fire performance of assemblies in wood construction. A modeling of thermomechanical behavior and a simplified analytical approach should be developed. Testing from an intermediate furnace is likely to be required to validate model assumptions.
Cross-laminated timber (CLT) wall systems are composed of massive timber panels that are fastened together and to the horizontal elements (foundations or intermediate floors) with step joints and mechanical connections. Due to the high in-plane stiffness of CLT, the shear response of such systems depends strongly on the connections used. This paper proposes a numerical model capable of predicting the mechanical behavior and failure mechanisms of CLT wall systems. The wall and the element to which it is anchored are simulated using three-dimensional (3D) solid bodies, while the connections are modeled as nonlinear hysteretic springs. Typical racking tests of wall systems are reproduced by varying the assumptions used to schematize the behavior of the connections. Results are compared with test data published in the literature, and the differences are discussed. The influence of the boundary conditions (vertical load applied on top of the wall and friction at its base) and aspect ratio of the panel are investigated via a parametric numerical study. Finally, the performance of a wall system assembled with two CLT panels is analyzed, highlighting how the properties of the anchoring connections and vertical step joints affect the load-displacement response and energy dissipation.
This paper presents the results of an on-going program of the mechanical behaviour of bolted glulam beamto-column connections. The program included testing and modelling of connections of various bolt size, edge distance and lamina alignment patterns. This paper presents part of the obtained results, including monotonic and reversed cyclic loading test results of 10 full-scale beam-to-column connections and the corresponding modelling results. The test results indicated that the perpendicular-to-grain properties of glulam and the localized contact between the bolts and surrounding glulam had significant influence on the stiffness and the maximum moment of the connections. A finite element method based model, which can be easily incorporated in commercial available software packages, was developed and verified based on the test results. Good agreement was achieved. Parametric study results indicated that the tolerance of the bolt holes can significantly affect the mechanical behaviour of the bolted beam-to-column connections.
Cross laminated timber (CLT) has become very popular for all types of structures all around the world in last years. CLT consists of uneven number of plank layers oriented in 90° angle to each other and bonded together. Various types of adhesives and technologies are used for bonding and manufacturing of final product. In some cases, gluing is not ideal manufacturing method and there is a demand of other manufacturing processes. Mechanical jointing is logical result of current research at the Czech Technical University. Research is focused on developing and verifying mechanical behaviour of mechanically jointed CLT solid wood panels. Sets of experiments focused on mechanical behaviour of these mechanically jointed CLT panels were performed. This paper summarizes results of wall, floor and timber-concrete composite elements, which have been tested.
This paper illustrates arrangements of self-tapping screws to reinforce the mechanical behaviour of transverse compression. Several experimental approaches are studied such as the reinforcement below the support, beside the support or the combination of these two reinforcements. The last experimental approach is explored to solicit the shear over the entire height of the screw. These different approaches of reinforcement allow seeing a panel of constructive solutions to transverse compression reinforcement by screws. This panel allows adapting the type of reinforcement with the studied building.