Fire resistance of concrete lining in road tunnels

Abstract

Fire is an incidental load on structures. Experience has shown that in the event of a fire, extremely high temperatures are developed, as a result of which very often a colapse of the tunnel bearing structure happens, usually caused by spalling of concrete. Road tunnel fires are usually caused by vehicles using the tunnel, but can also be caused by exidants, technical breakdowns in tunnel equipment or improper tunnel maintenance. The intensity and frequency of fires in the tunnels are function of several factors such as: length and geometry of the tunnel, density and type of traffic, vehicle speed, slope, availability of ventilation equipment and so on. All of these factors define the fire risk. Based on the defined fire risk, known fire load and location of the fire, it is possible to define the fire curve that defines the temperature in the tunnel versus time. Several fire curves, usually used in EU countries, will be described in this paper, the fire curves characteristics will be defined and the most proper fire curve for typical tunnel, as case study, will be recomended. In the framework of this paper, a methodology for fire resistance analysis of road tunnels, based on the performance, is elaborated. A numerical procedure for defining the behavior of the tunnel lining in case of nominal fire curve (standard fire) is described and applied on one case study. The impact of the fire on the stress-strain state of the concrete structure of a tunnel is analyzed and measures for proper tunnel design in terms of increasing the fire resistance is proposed.