Nonlinear structural analysis of a 2D cut-and-cover tunnel exposed to fire

Abstract

Behaviour of cut-and-cover tunnels exposed to fire should be analysed by using a realistic model which takes account ofsimultaneous mechanical and thermal effects acting on the structure.  This has been performed by 2D structural modelsfor a 2-cell tunnel with the aid of FE software package called SOFiSTiK (SOFiSTiK, 2014), in parallel, for two types of elements, beam and plate elements, as a scope of research project financed by BAST. The two considered models were levelled in terms of boundary conditions and the possible mechanical behaviour as well as mesh generation aspects.A nonlinearthermo-mechanical analysis has been performed considering pre-damaged effects on the cross sectionsby taking into account 10 and 15-minute time intervals for a whole duration of 90 minutes. The results of both models are in an acceptable agreement with each other,but they deviate from the simplified, linear-elastic calculation method considering a constant temperature gradient,DT_M = 50 K,proposed by ZTV-ING Part 5 (BASt, 2013).To improve this method, a linear interpolation of different DT_M-values with respect to the thickness of theconcrete member has been introduced.