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.
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.