Influence of ply configuration and adhesive type on cross-laminated timber in flexure at elevated temperatures

This paper describes experiments on cross-laminated timber (CLT) beams exposed to uniform non-charring temperatures under sustained loading. Two different ply configurations and two different adhesive types were examined under sustained loads of both 30 and 50% of the ultimate ambient temperature flexural capacity. It was found that the adhesive type has a significant influence on the magnitude of the deterioration in structural stiffness during heating. From image correlation analysis this influence was attributed to increased shear strains along the adhesive lines between timber plies for specimens bonded with a polyurethane (PU) adhesive, when compared to those that used a melamine urea formaldehyde (MF) adhesive. It was also found that considerable deflections that were measured during heating were irrecoverable during cooling of the CLT, suggesting that these deformations were driven by creep of the timber – and possibly also the adhesives.