Objective-level resilience assessment of circular roadway tunnels with reinforced concrete liners for vehicle fire hazards

A framework is presented to quantify the objective-level resilience of reinforced concrete liners of circular tunnels when exposed to enclosed vehicle fire hazards.By assessing the loss of functionality due to fire-induced damage,the framework enables a decision-basis evaluation of the efficiency of various fire mitigation methods for spe-cific tunnel conditions.In this study,the fire-induced damage of concrete tunnel liners due to strength loss and spalling is stochastically simulated and classified based on typical post-fire repair procedures and damage evalu-ation.The resilience assessment is conducted using Monte Carlo Simulation in combination with a fast-running tool for calculating the thermal impact from vehicle fires on the inside surface of the tunnel liner(developed by the authors in previous work).The proposed approach accounts for uncertainties associated with both the vehicle fire(particularly the combustion energy)and the tunnel conditions(i.e.,geometry,dimensions,and the presence of longitudinal ventilation and/or fixed fire-fighting systems(FFFS)).A parametric case study is used to quantitatively demonstrate the effectiveness of FFFS for reducing post-fire losses of tunnel functionality.Other parameters such as tunnel dimensions,traffic restrictions for vehicles with heavy fire hazard risk,and installation or upgrade of the tunnel ventilation system show somewhat less effectiveness for reducing fire-induced damage.

Numerical simulation of smoke stratification in tunnel fires under longitudinal velocities

Use of the longitudinal critical velocity in tunnel fires may destroy the stratification of smoke downstream,which is not conducive to the evacuation of downstream tunnel users.Reducing the longitudinal velocity can maintain stratification,but the appropriate longitudinal velocity range is unknown.Stratification of smoke under the longitudinal velocity is studied using Fire Dynamics Simulator(FDS).The aims of this paper are to explore the relationship between the longitudinal velocity and smoke stratification and to obtain a proper velocity range that can maintain clear downstream stratification.Based on Newman's theory,the"stratification velocity"is proposed,which is the maximum velocity that maintains downstream smoke stratification.A good correspondence between the average Froude number within 200 m downstream and the longitudinal velocity and heat release rate(HRR)is found.The correlation between the temperature stratification and Froude number is obtained.Fr=0.49 can be used to distinguish whether the stratification is clear.The relationship between the critical velocity and the stratification velocity is also discussed.