Evaluation the maximum ceiling temperature and temperature longitudinal decay in a ventilated bifurcation tunnel with uphill mainline

Abstract Fire in complex tunnels poses unique threats to urban public safety and infrastructure. This study systematically investigates the fire characteristics in a branched tunnel with sloped mainline, focused on the effect of mainline slope, longitudinal ventilation and heat release rate on temperature distribution in mainline and ramp. Results reveal lower maximum ceiling temperature under higher airflow velocity. Greater heat release rate significantly elevates the maximum ceiling temperature in mainline. The maximum ceiling temperature rise is changed as the variation of mainline slope. The induced airflow velocity was employed to correlate the dimensionless temperature rise that the 0.36 power of sin θ was utilized to normalize the induced airflow velocity. The temperature beneath the mainline ceiling decreases with higher airflow velocity and is slightly influenced by the mainline slope. The Fr was utilized to correlate the dimensionless temperature longitudinal decay along mainline ceiling that sum of two exponential equations were established. The effect of mainline slope on temperature longitudinal decay along ramp ceiling is limited, but the heat release rate plays an important role. The prediction model for temperature distribution in ramp is developed based on the exponential equation. This study contributes to developing robust fire safety strategies and risk assessment in complex branched tunnel conditions.