Evaluation of Methods to Predict and Measure Out-of-plane Bending and Shear Stiffnesses in Cross-Laminated Timber Panels

Abstract

Cross-laminated timber is an innovative mass timber construction material that takes advantage of many of the strengths that timber provides while also helping to address many of timber's limitations. Most of the current research is primarily focused on the strength of CLT elements, however, there remains a gap in the current research with respect to the out-of-plane effective flatwise shear rigidity of short-span cross laminated timber elements. Along with this investigation of shear rigidity, this study aims to evaluate the accuracy of a direct method of measuring both bending stiffnesses and shear rigidity. To properly assess the various method’s abilities to accurately measure stiffness, the shear span-to-depth ratio, loading configuration, axis of loading and width of CLT panel elements were varied. A total of 45 beam-type one-way panel bending tests were conducted and different types of instrumentations were used to measure bending stiffnesses and shear rigidity. For example, linear variable differential transformers (LVDTs) were used to measure the apparent bending stiffness, inclinometers measuring both the end rotation and rotation of the member under the load points were used in two different methods to measure the effective bending stiffness. The average shear rigidity of a unit section was measured using diagonal string potentiometers. The study found that for CLT specimens with low shear span-to-depth ratios (equal to or less than 5.0), both the apparent bending stiffness and the measured shear rigidity were consistently greater than design guidance is currently accounting for. It was also found that the effective bending stiffness was consistently lower than design guidance predicts. Overall, this study contributes to furthering our understanding of the stiffness and rigidity of CLT panels.