Wirklichkeitsnahe Brandeinwirkungen für die Planung und Nachrechnung von Tunnelschalen

Realistic fire loads for design and re-analysis of tunnel linings

Meanwhile, the development of numerical systems for the simulation of flow phenomena has reached a level, which even allows the analysis of complex scenarios such as tunnel fires, within acceptable time-periods. On the one hand, this provides the possibility to critically question fire-curves from standards (derived and calibrated for the general case) against the background of tunnel-specific temperature fields. On the other hand, both temperature and smoke development as well as expected structural impairment may be assessed on a relatively realistic basis without large-scale conflagration tests being necessary. In addition to general options of non-linear structural analyses (i.e. utilisation of load re-distribution and activation of additional bedding reactions) [1] the simulation-based evaluation of fire loads particularly provides a valuable potential for the re-analysis of existing tunnel linings. This especially applies in such cases where the calculation with conventional fire-curves requires extensive strengthening and retrofit, whereas more favourable loading conditions may be expected by taking into account the tunnel-specific boundary conditions. In the present paper, firstly tunnel fire accidents and the derivation of fire-curves are generally discussed. Then, the possibilities, the theoretical background and limits of CFD modelling of fire scenarios are presented and finally, major influence factors on the thermal loading (in particular the cross-sectional size of the tunnel) are investigated by sensitivity studies.