The presented work examines the rolling shear properties of beech wood for the novel application as cross-layers in hybrid cross-laminated timber. Rolling shear modulus and strength of beech were determined by three different approaches: i) two-plate shear tests on single beech board slabs, and ii) compression shear and iii) bending tests on hybrid CLT specimens based on the test methods defined in EN 16351. The CLT specimens were cut from two industrially manufactured hybrid three-layered CLT-plates with a beech cross-layer and spruce outer layers. The rolling shear modulus results obtained from the single board tests and the bending tests agreed well and were within the range of 350 - 370 N/mm². The characteristic rolling shear strength obtained from the bending tests was determined as 2.6 N/mm², where the failure was often governed by longitudinal shearing of the spruce laminations. Hybrid CLT-plates demonstrate a highly improved strength and deflection behaviour versus homogenous spruce CLT-plates and result in not only a mechanically superior product but also allow for a greatly simplified design approach.
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.