Changing Failure Modes of Cross-Laminated Timber

Cross-laminated timber relies on the adhesive layer between adjacent timber plies to provide composite action between the lamella for increased member strength and stiffness. Previous research has shown that adhesive loses normal and shear stiffness at elevated temperatures increasing the slip between adjacent timber plies. Slip in the bond layer results in reduced composite action increased deflections and a potential loss in ultimate strength in the CLT member. In order to study the effects of temperature on the flexural behavior of CLT, two series of tests were conducted. The first series focused on identifying the changing failure modes while the second series established conditions that led to those failure modes in large CLT beams. The results clearly showed the failure mode of CLT changes from timber failure to failure in the adhesive as a function of the in-depth temperatures. The adhesive failure yielded larger deflections and a loss in stiffness and ultimate strength.