Deformation of heated and loaded wooden stick : towards fire safety design of timber structure

Abstract

Mass timber construction has been emerging in architecture because of exceptional durability, sustainability, and versatility. This work applies the 3-point bending test to a reduced-scale wooden stick with a supporting span of 16.5 cm, under loads up to 560 times its self-weight under raised environmental temperatures up to 300 °C in the oven. The experiments quantify the deformation, critical shear stress of rupture, and degradation mass losses of the heated wood before ignition and combustion, while the numerical model further analyses the detailed thermomechanical responses. Results show that with increasing temperature, the deflection of loaded wooden sticks increases, driven by drying, thermal creep deformation, and thermal degradation. Moreover, the critical shear stress and temperature for wooden sticks rupture decrease, primarily caused by the thermal degradation of wood. The effects of fire-scene temperature on bending strength and modulus of elasticity on the loss of load-bearing capacity for wooden sticks are further quantified with numerical simulation. This work reveals the pre-ignition thermomechanical behaviours of wood under fire scenes, which supports early warnings for ignition and collapse, fire resilience design, and structural-fire stability assessment for wooden structures.