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Organisationseinheit der BAM
Mittels Propan-Brennern mit einer Brennerleistung 750 kW wurden in einer U-Bahn-Station Heißgasversuche durchgeführt und die zeitlichen und örtlichen Verteilungen der physikalischen Größen (Stoffkonzentration, Temperatur und Rauchgasdichte) erfasst. Laborversuche sowie die Feldversuche sind Validierungsgrundlage für ANSYS CFX und FDS und die später im Rechenmodell der U-Bahn-Station zur Untersuchung der Grundströmung und Rauchausbreitung verwendeten mathematisch-physikalischen Modelle. Der Aufsatz stellt das Projekt ORPHEUS vor und diskutiert die ersten Ergebnisse.
The time dependent thermal behavior is analyzed with FLUENT for the fluid as well as the solid region (concrete component) in case of a 100 MW n-heptane fire. To study the effect of parameters in mathematical-physical models several sensitivity studies were carried out to investigate the effect on the fluid flow as well as on the component. The influence of soot was additionally considered. FDS simulations as well as empirical calculations considering underlying assumptions are additionally used to examine the plausibility of results from the FLUENT simulations. This is an appropriate method if no experimental results are available. Recommendations are given for choosing parameters in mathematical-physical models e.g. radiation models. The results of the CFD investigations show that considering the influence of soot provides maximum temperatures which were 200 K lower than without soot.
The Fractional Effective Dose model was used to predict the fire smoke toxicity numerically. In this context fire tests were carried out for three different building materials: polyurethane, flame retardant polyurethane and polyvinyl chloride. The fire tests were performed for flaming and smoldering combustion. The aim of the fire tests was to determine the light extinction, the smoke density and the combustion products at varying oxygen concentrations, different temperatures and different irradiance levels. The fire tests were performed in the German DIN-tube and also in the Cone Calorimeter. Stoichiometric coefficients at varying oxygen concentrations and temperatures were determined from measurements. With these stoichiometric coefficients reaction equations were defined and implemented in the Computational Fluid Dynamics (CFD) program, ANSYS CFX. The implemented reaction equations were used to account for different ventilation and temperature conditions in the simulation. The fire and smoke propagation was calculated numerically with CFD in the room corner test geometry. Equations to account for toxicity and light extinction were also implemented and were used to analyse the toxicity and the optical properties of fire smoke with CFD.
Vehicle fires in tunnels can have catastrophic consequences for the road users, the property and traffic inffastructure. To support an evacuation planning, this study simulates the fire smoke toxicity and the smoke layer of a vehicle fire in a full-size test tunnel. The three dimensional prediction of the fire smoke toxicity in the test tunnel is realized by implementing the Fractional Effective Dose and the Fractional Summation concept in a CFD environment. The developed model facilitates to calculate fire scenarios for various types of tunnels and to quantify the hazard e.g. during an evacuation scenario.
Im Rahmen der schutzzielorientierten Brandschutzbemessung müssen, neben dem Nachweis der Wirksamkeit von Schutzmaßnahmen, Nachweise zur Einhaltung von in Abhängigkeit des Sicherheitsniveaus festgelegter Grenzwerte für die zulässige Wärmestrahlung, die Temperatur der oberen und unteren Rauchschicht, die toxische Konzentration von Rauchgasen und die Mindestsichtweite zum Schutz von Personen im Bauwerk erbracht werden.
Probabilistic thermo-Mechanical analysis of a concrete tunnel lining subject to fire The probability distributions of the parameters related to the thermal analysis was considered in order to study the variability of the results and to carry out a reliability analysis. This assessment considered as random variables the thermo-mechanical properties of the concrete, the maximum heat release rate (HRR), the duration of the period of maximum HRR, the convective coefficient, the emissivity at the surface exposed to the fire, the air velocity within the tunnel, and the initial fire radius. The temperature-time curve was described by a correlation. An experimental design based on a Latin Hypercube Sampling algorithm was performed to define the input parameters to each analysis case. The definition of a limit state function based on the punctual strain status has permitted to carry out a reliability analysis.
A probabilistic approach for finite element analysis (FEA) for tunnel linings exposed to the nominal fire is presented. The probabilistic FEA accounted for the uncertainties distributions tied to the conductivity and specific heat as well as of the compressive strength, tensile strength, Young’s modulus, and ultimate strain in compression. To get an understanding on the influence of different probability density functions on the distribution of maximum displacements of the tunnel lining, a sensitivity analysis was performed. Four sets of FEAs were carried out with different probability distributions of the conductivity, the specific heat, and the compressive strength of the concrete, respectively. An experimental design based on a Latin Hypercube Sampling algorithm was performed to define the input parameters which describe each analysis case. A reliability analysis was executed considering a limit state function based on the temperature-dependent ultimate strain. The results show that, depending on the distribution adopted, the standard deviation of the maximum displacements can vary up to 47,4% of the minimum standard deviation. The large standard deviation is associated with the possibility of a greater displacement and, hence, to a structure more vulnerable to fire.