A practice orientated modified linear elastic constitutive model for fire loads and its application in tunnel construction

A spate of fires in tunnels over the past decade, causing serious loss of life and significant structural damage, has led to new safety concepts in tunnel construction. Nowadays these concepts are already being considered during the design. In this context numerical methods represent a powerful tool for assessing the structural forces in the lining and the change of material properties caused by thermal effects This article deals with the simulation of a fire within a tunnel by means of the program FLAC. The tunnel lining is modeled by four-node continuum elements for simulating non-linear and time dependent temperature variation within the lining. The thermal effect is applied according to the fire load curve of the BEG-project, a future major railway section between Italy and Austria passing the Alps, at the inside of the lining. The coefficient of thermal transmission between the thermal source and the lining is chosen such that the temperature-field within the lining corresponds to experimental data. Non-linear material behavior due to thermal loading is implemented by varying the coefficient of thermal expansion.