Detection of defects in glue bonding of cross-laminated timber using experimental and numerical modal analysis

The preferred structural elements for taller timber buildings include cross-laminated timber (CLT), the performance of which significantly depends on the adhesive bond (AB) quality that may be influenced by manufacturing or factors within the service life. Both may contribute to a delamination, which represents a serious structural damage of the CLT. The study utilised both experimental and numerical modal analyses to assess the influence of damaged AB on CLT vibrational behavior. Both approaches confirmed that the CLT stiffness and eigenfrequencies decreased with AB damage, and both found agreement on certain modal shapes. FEA showed ideal patterns also in terms of localization of the damaged AB using modal shape damage index. Meanwhile, experiments showed its limits due to natural variability of wood, CLT, and measurement setup. The obtained results show a potential for in situ grading and inspection. However, the effect of variability of material properties of CLT should be studied further.