In the present paper, the theoretical basics for the implementation of time-dependent, nonlinear fire calculations are explained and there is given a comprehensive overview of the topic. The focus of this work is the structural design of a reinforced concrete tunnel structure under fire load including a prior cold design and an analysis to determine the ultimate load capacity of the tunnel structure in the case of fire. The analysis includes several time-steps and is used to determine the time of failure of the tunnel structure in the event of a prolonged fire, which is described by the open fire curve HCinc. The nonlinear calculation is carried out using the finite element method and using the software package SOFiSTiK (www.sofistik.de). Through the use of non-linear material stress-strain curves for the construction materials concrete and steel within this calculation, the rearrangement of forces within the structure can be considered. Thereby it is possible, to achieve an economical structural design even in the case of fire. Carrying out a sensitivity analysis to determine the parameter sensitivity of selected parameters with the program FReET (www.freet.cz) tops off the fire calculation. Furthermore described is the mathematical determination of temperature-distribution-curves within concrete cross sections also using the software package SOFiSTiK.