Abstract: Wood undergoes internal moisture loss due to weathering, leading to cracking most commonly longitudinal cracking. When such cracks extend deep into the heartwood, they significantly influence the wood's combustion behavior. Current research on timber structure buildings primarily focuses on moving away heat source after ignition and self-sustained combustion observations. In this experiment, wood samples with longitudinal cracks of 15 cm in length and varying cross-sectional depths of 4, 5, 6 cm were tested under different inclination angles, all under continuous external flame exposure. The results indicate that when the inclination angle reaches 30°, the combustion behavior changes markedly, with notable increases in temperature, mass loss, and charring length. The influence of longitudinal cracks on wood components manifests mainly in two aspects: first, by altering gas flow direction and increasing oxygen supply to the combustion zone; and second, by modifying heat transfer patterns. Cracks facilitate faster heat transfer from the alcohol flame into the wood interior, accelerate air flow along the cracks, and enhance convective heat effects.

Key words: timber building, longitudinal crack, peak temperature, mass loss rate, charring length