Retrofitting CLT Panels and Glulam Beams Subjected to Static and Dynamic Loads

Abstract

Mass timber products such as cross-laminated timber (CLT) and glued laminated timber (glulam) have become more common in contemporary structures, particularly mid- to high-rise ones, as a result of their development. Although engineered wood products are structurally efficient and reliable, their performance can deteriorate over time due to factors such as material deterioration, increased service demands, and exposure to extreme loading conditions. As a result, research on strengthening and rehabilitating timber members has gained significant attention in structural engineering. The current research aims to investigate the effect of CFRP in improving the structural performance of CLT panels and glulam beams under static and dynamic blast loads. Experiments were conducted at the University of Ottawa using a shock tube designed to replicate the high strain rates associated with blast loading. Different retrofit configurations were investigated, including confinement only and combined configurations with both unidirectional tension reinforcement and CFRP confinement. The confinement was applied in various configurations, including full length, localized (shear and moment regions), and U-shaped arrangements, using both unidirectional and bidirectional CFRP. According to the experimental results, CFRP fabrics significantly improved the resistance, stiffness, and ductility of the specimens. In the static tests, the retrofitted CLT specimens exhibited increases in peak resistance from 13% to 133%, while stiffness improvements reached up to 49%. The ductility ratio increased to a maximum of 1.67, indicating enhanced energy absorption. Under dynamic loading, peak resistance increased up to 166%, while stiffness improvement reached up to about 52%. In addition, the failure mode shifted from rolling shear in the unretrofitted CLT panel to predominantly flexural behavior in the retrofitted ones. For the glulam specimens, the retrofitting led to peak resistance and stiffness increases up to 46% and 13%, respectively, under static loading. Under dynamic loading, peak resistance increased by up to 123%, with the failure modes primarily governed by flexural behavior. A fiber section analytical model was developed to simulate the behaviour of the specimens up to peak resistance. The predictions showed good agreement with experimental data, accurately reflecting force response, stiffness, and displacement at peak resistance.