Sensitivity of bending stiffness to moisture content in adhesive-free wooden-doweled cross-laminated timber panels

Despite the rapid commercial success of cross-laminated timber (CLT) in the past decade, largely thanks to its excellent thermal and structural performance, the use of synthetic adhesives still raises sustainability concerns, in particular with respect to fire behavior of the bond lines, potential VOC emissions during service, and the challenges of separating bonded layers at end-of-life for recycling or energy recovery. While wooden-doweled CLT has never been considered a viable large-scale alternative to traditional CLT, it is important to better understand the properties of adhesive-free CLT panels as potential surrogates. In the case of wooden-doweled CLT, the mechanical integrity of the panel depends on the assembly conditions, where the moisture content of the dowels at insertion is lower than that of the timber boards. The swelling of the dowels, as they equilibrate with the moisture content of the surrounding timber, ensures the structural performance of the panel. However, what happens if there is a general decrease in moisture content over the building's lifespan and the differential shrinkage between the boards and dowels compromises the structural integrity? In this study, the authors tested adhesive-free wooden-doweled CLT panels, assessing the sensitivity of the bending stiffness to three moisture content scenarios: 8, 12 and 15%. Using classical methods for predicting the stiffness of layered beams, such as the γ and the shear analogy methods, the authors indirectly estimated the slip modulus based on three-point bending tests and modal parameters as a function of wood moisture content. Thus, the paper, examining the mechanical behavior of wooden-doweled CLT panels under varying moisture content conditions, provides practical recommendations for their use.