An Experimental Study on Thermal Damage and Spalling of Concrete Under Loading Conditions in a Tunnel Fire

Abstract

While fire outbreaks in tunnels are not as frequent as those in other structures, temperature rises up to over 1,000ºC within 5 minutes upon the outbreak of a fire in a tunnel due to its semi-closed structure. Temperature rise in a concrete structure caused by a fire under constant load leads to deterioration in strength, accelerates deformation and finally results in collapse. In this study to identify structural damage caused by a fire in a tunnel, fire tests were conducted using a heating furnace that satisfied the KS F 2257-1 and EFNARC regulations to evaluate the thermal damage to a tunnel concrete lining. The two objects of the test were: 1) to identify the thermal damage to concrete lining associated with fire intensity 2) to evaluate the characteristics of spalling and failure of concrete lining associated with load ratio. The range of thermal damage under the ISO fire, heating rate of 1ºC/Sec., MHC fire³⁾ and RWS fire³⁾ was 30mm, 20mm, 100mm and 50mm, respectively. The depth of spalling in the RWS and MHC fires was 30mm. Spalling was observed under unstressed conditions, while it was not observed under 20 ~ 40% loads because of the smooth flow of vapors enabled by micro cracks. Under 70% load, the rapid spread of cracks caused failure during 10 minutes of heating.