Experimental study and theoretical analysis of fire resistance properties of prestressed glued laminated timber beams

The addition of prestressing not only improves the force resistance of glulam beams, but also provides a potential solution to improve their fire resistance. An in-depth study of the fire behavior of prestressed glulam beams (PGBs) under fire and the force behavior after fire is essential for their fire resistance design and evaluation. In this paper, fire tests and post-fire four-point bending experiments were conducted on the PGBs aiming to investigate the thermal response of the PGBs as well as their force resistance after fire. The results showed that fire significantly affected the mechanical properties of the PGBs, not only reducing the prestressing force during the fire, but also decreasing the residual load carrying capacity after the fire. After 60 min of standard fire exposure, the prestress and load capacity of the PGBs decreased by 10 % and 33.33 %, respectively. Increasing either prestress or reinforcement ratio can effectively improve the resistance performance of the PGBs after fire. In the same fire action time, if the prestress was increased by 59.46 % or the reinforcement ratio was increased by 0.53 %, the residual ultimate load capacity of the PGBs was increased by 17.14 % and 22.19 %, respectively. The study also indicates that fully utilizing the synergistic effect of prestressing and reinforcement ratio enhancement can significantly improve the overall performance of the PGBs. In addition, a theoretical calculation model is proposed to accurately predict the residual flexural capacity of the PGBs after fire, which provides a theoretical support for the fire-resistant design of the PGBs before fire and the assessment of residual load capacity after fire.