Fire risk analysis focused on damage of the tunnel lining

In this paper, risk is calculated as the probable damage caused by a fire in the tunnel lining. The model is intended to be as simple as possible and still able to reflect the reality. In the first part, focused on probabilistic modeling, the traffic flow is described as a stationary Markov chain of joint states consisting of a combination of trucks/buses (TB) and passenger cars (PC) from adjoining lanes. The heat release rate is then taken for a measure of the fire power and two probability mass functions of this variable are suggested for one TB and two TBs, respectively. The intensity lambda(f) reflecting the frequency of fires was assessed based on extensive studies carried out in Austria [15] and Italy [16,17]. Eventually, the traffic density AADT, the length of the tunnel L, the percentage of TBs, and the number of lanes are the remaining parameters characterizing the traffic flow. In the second part, a special combination of models originally proposed by Bazant and Thonguthai [28], and Kunzel & Kiessl [29] for the description of transport processes in concrete at very high temperatures creates a basis for the prediction of the thickness of the spalling zone and the volume of concrete degraded by temperatures that exceeded a certain temperature level theta. The model was calibrated by fitting its parameters against a macroscopic test on concrete samples placed into the furnace. Though effective and easy to apply, there is room for the model as a whole to be gradually improved. These possibilities are outlined in conclusions.