In this paper a theoretical and experimental study on behavior of FRC as the material for tunnel linings being subjected to fire of 12000 °C in duration of 2 hours is to be carried out. Theoretical considerations on this problem are presented in terms of free hexagon method and start with the experiments presented hereinafter.
The procedure assumes a «soft contact» between hexagonal particles, i.e. springs simulate either tensile and shear contacts in the normal concrete or FRC, where fibers over-bridge possible cracks appearing during cooling process after removing the source of fire. Since the structure is loaded only by change of temperature and no other type of loading is considered (volume weight of the system is neglected), the «soft contact» is fully sufficient to describe the mechanical behavior of the material.
The formulation of the problem involves the change of porosity, degree of saturation of water, bulk modulus, and other relevant quantities appearing in the physical processes taking part in the FRC. Both the lining and surrounding rock are modeled by free hexagons; their mechanical properties are described by boundary elements. Formerly, the mechanical characteristics inside of the hexagonal elements were uniform during the processes envisaged.
Now, the particles changes the properties according to the state equations and the interfaces obey also nonlinear laws, which are described by changing coefficients in generalized Mohr-Coulomb law. The results from numerical procedure are compared with accessible experimental data and the mechanical properties of the material are tuned accordingly.
Petr Prochazka, Association of Czech Concrete Engineers, Czech Republic.
Sarka Peskova, Czech Technical University, Prague, Czech Republic.