Experimental investigations on transient burning characteristics of a butt-jointed wooden wall with horizontal gaps in timber buildings

In this paper, a series of experiments were carried out to study transient burning behaviors of vertical wooden boards widely used as dividing walls in timber buildings. The boards were butt-jointed by wood battens, forming several horizontal gaps. Gap sizes were carefully controlled as 0 mm, 2 mm and 5 mm to study their effects on the burning process. The boards were heated with one surface initially exposed to fire, and heat release rates (HRRs) of fire source were set from 5 kW to 15 kW to simulate the early fire stage. Results showed that there existed a transition from single-sided burning to double-sided burning for wooden boards exposed to fire. The start of the double-sided burning was accompanied with sharp increases in HRR and temperature. With the increase of the gap size, the start time for double-sided burning was obviously shortened, and the role of gap was analyzed as strengthening heat convection and air entrainment. A simplified estimation method for transient HRR during the whole burning process was put forward, which agreed well with the experiments. This work supports guidance to predict fire development in timber buildings in the early fire stage. •Transient burning behaviors of a butt-jointed wooden wall with gaps are obtained.•Studying the early fire stage helps to protect wooden components from fire risks.•There is a transition from single-sided to double-sided burning of the board.•Gaps on the butt-jointed board strengthen heat convection and air entrainment.•An estimation method for transient heat release rate during burning is proposed.