Behavior of Structural Tunnel Element Exposed to Fire and Mechanical Loading

Abstract

Incidents like the fire in the Channel Tunnel [1], where concrete spalling with a depth of 30 cm over a length of 500 m was determined, have led to requirements in limiting the spalling depth and involved zone to local and compatible magnitudes. To account for the high heating rate of tunnel fires, the fire resistance of railway tunnel structures was investigated using the German EBA tunnel fire curve [2], which was derived from large-scale fire tests on railway cars [3]. The behavior of structural tunnel elements exposed to fire and mechanical loads have been investigated in several research programs during the last years [4],[5], [6]. In this paper, the results of an extensive research program investigating the fire behavior of two concrete mixtures four small- and two large-scale tests are presented. The small-scale tests prior to the main tests were conducted to determine an appropriate concrete mixture for the large-scale tests. For those tests, real-scale tunnel segments representing a design-relevant sector of an existing railway tunnel were used. During the large-scale tests, the tunnel segment is loaded with horizontal and vertical loads derived from a calculation taking into account the ground pressure, water pressure and dead loads corresponding to the situation of the existing railway tunnel. Additionally, the resulting restraint forces were calculated using the soil stiffness and the EBA tunnel fire curve [2] as fire scenario and induced via hydraulic jacks (force controlled). In order to avoid additional restraint forces during the experiment, thermal strains due to fire exposure were allowed by the statically determined boundary conditions.