Experimental and reliability assessment of fire resistance of glue laminated timber beams

Glue-laminated timber (GLT) is an engineered wood product widely used in mass timber construction for its strong structural and fire-resistant properties. However, the fire performance of GLT varies significantly due to the natural and uncertain phenomena (moisture, exposure time, isotropic, homogenous properties, etc.) of fire and timber. This makes it difficult to predict the fire behaviour of the GLT structural elements. To ensure building safety, it is crucial to assess GLT's fire behaviour and post-fire structural integrity during the design stages. This study conducted the experimental tests of GLT beams (280 mm × 560 mm) without loading (1.4 m) and under a four-point bending load (5.4 m). Tests identified thermal behaviour and charring rates of GLT beam. Then, the residual stiffness of the GLT beam was calculated, and the charring rates of the beams were compared with Australian and European standards. Reliability analysis was conducted for beams for a fire exposure of 120 min, considering the charring rates observed through the analysis and simulating the fire insulations. Results show that the charring rate of GLT made with spruce pine timber varied between 0.43 and 0.81 mm/min, with a mean rate of 0.7 mm/min, aligning with both Australian and European standards. However, considering timber density and moisture content, the charring rates in Australian standards were conservative. The study also found that structural capacity significantly degrades under fire, with a 22 % reduction in flexural stiffness after 120 min of exposure. Additionally, GLT beams can safely function for 30 min under 75 % of their design moment capacity and for 60 min under 50 % capacity.