Tunnel structures are an important part of public transport facilities. During recent years, large tunnel fires happened, having caused loss of human life and damage of tunnel support structures. Keeping this in mind, determination of the safety of these structures in case of fire loading is necessary in order to adopt the chosen design and, hence, to increase the safety in/of tunnels in case of fire.
The temperature distribution within support structures originating from fire loading is nonlinear with the highest temperature at the fire-exposed surface.
Since this nonlinear temperature loading is difficult to be considered in numerical analysis tools, the nonlinear temperature distribution is converted into an equivalent (linear) temperature distribution. Most commercial design tools are able to take into account this equivalent temperature as input. Usually, the analysis is conducted assuming linear-elastic material behavior.
In this work, analyses are performed using both the equivalent and the nonlinear temperature distribution.
The analyses are performed with two finite element (FE) programs:
The FE program MARC: Hereby, user-defined subroutines developed at the Institute for Mechanics of Materials and Structures at Vienna University of Technology (TU Wien) are employed. This program allows consideration of nonlinearities as regards the material behavior and the temperature loading. The FE program SOFISTIK: This program is restricted to linear temperature distributions and linear-elastic material behavior.
In this work, different structural systems are investigated (clamped beam, frame corner, and circular tunnel cross-section) and different boundary conditions are applied (either allowing or restraining longitudinal expansion / rotation).