The report describes the experimental and analytical research that was carried out for the development of large double pitched beams and three hinged frames made of cross laminated timber. The results are used to derive of design approaches for large finger joints in cross laminated timber.
A group of six glued laminated timber beams was tested in four-point bending until failure. Both standard measuring devices mounted to the beams and digital cameras were employed to provide for a continuous measuring of displacements and strains as well as visualization of damage evolution and subsequently for quantification of damage mechanisms leading to failure of individual beams. This was accompanied by identification of positions of all visible knots and finger joints. It is shown that their distribution plays an important role in the onset of damage evolution and final failure pattern.
The presented research describes the holistic development of a modular lightweight timber shell. So-called segmented timber shells approximate curved geometries with the use of planar plates, thus combining the excellent structural performance of double curved shells with the resource-efficient prefabrication of timber modules using only planar elements. Segmented timber shells constitute a novel building system that demands for innovative approaches on structural design and construction technologies. The geometric complexity of plate shells in conjunction with the particularities of the building material wood pose great challenges to the computational design and planning processes as structural requirements and fabrication constraints determine the shell design at early design phases. This paper discusses the design development and construction of the BUGA Wood Pavilion: A segmented timber shell structure made of hollow cassette components. Particular emphasis lies on the technical challenges of the employed building system, notably structural design and analysis, detailing solutions and the construction process. The authors further describe the integrative structural design and optimization methods developed for the timber shell in question. The BUGA Wood Pavilion demonstrates the possibilities of lightweight and sustainable wood architecture merging the merits of integrative design, structural engineering and high-tech robotic fabrication methods.
Finger joints are commonly used to produce engineered wood products like glued laminated timber beams. Although comprehensive research has been conducted on the structural behaviour of finger joints at ambient temperature, there is very little information about the structural behaviour at elevated temperature. A comprehensive research project on the fire resistance of bonded timber elements is currently ongoing at the ETH Zurich. The aim of the research project is the development of simplified design models for the fire resistance of bonded structural timber elements taking into account the behaviour of the adhesive used at elevated temperature. The paper presents the results of a first series of tensile and bending tests on specimens with finger joints pre-heated in an oven. The tests were carried out with different adhesives that fulfil current approval criteria for the use in loadbearing timber components. The results showed substantial differences in temperature dependant strength reduction and failure between the different adhesives tested. Thus, the structural behaviour of finger joints at elevated temperature is strongly influenced by the behaviour of the adhesive used for bonding and may govern the fire design of engineered wood products like glued laminated timber beams.
In this study, Malaysian Dark Red Meranti (DRM) was used to manufacture glulam beams, following closely the requirements of BS EN 14080:2013 so as to emulate commercial production. Phenol resorcinol formaldehyde (PRF), commonly used in structural glulam production, was used in the fabrication of finger joints and laminations of the glulam beams. Factors influencing the mechanical properties of finger joints and bonding performance of laminations were investigated. Full size glulam beams were manufactured and tested in bending with partial and complete carbon fibre reinforced polymer (CFRP) reinforcement on the tension face and compared with the performance of unreinforced beams. A bench-scale fire test was proposed to describe the behaviour of DRM finger joints in tension under fire condition, in order to simulate the failure of finger joints on the tension side of a glulam beam in a standard fire test. Overall, DRM finger joints exhibited better bending strength than Spruce finger joints which represented softwood used in European glulam. Wood density and end pressure were shown to affect the strength properties of the finger joints. Higher cramping pressure was needed to produce DRM laminations with higher shear strength. The glulam beam with CFRP reinforcement had a higher bending strength than the unreinforced glulam beams but partial reinforcement had an adverse effect on beam strength. In the bench-scale fire test, DRM finger-jointed specimens exhibited lower charring rate than Spruce. Furthermore, PRF finger-jointed specimens showed better fire performance than finger-jointed specimens bonded with polyurethane (PUR) adhesive. In conclusion, it is hoped that results from this research will motivate engineers and architects in Malaysia to design and build structures from less-utilised local timber, specifically in the form of glulam, encouraging the timber industry in Malaysia to produce them commercially.