Design of concrete tunnel linings for fire safety

This paper provides an overview of some significant aspects concerning the design of concrete tunnel linings subjected to severe fire exposure. The distinguishing feature of tunnel fires is the possible rapid rise of the air temperature within few minutes. The factors that contribute to this phenomenon in combination with the fire duration and the fire spread along the longitudinal direction are cited. Additionally, the widely used fire curves are presented, showing their influence on the predicted temperature profile of a concrete cross-section through uncoupled heat transfer transient numerical analyses. Then, the effect of fire on the concrete behaviour is briefly described with examples from real fire accidents. The focus is on the explosive spalling of concrete, provided that, in general, tunnels are at greater risk than other structures, principally due to the high heating rate and the high initial moisture content. The main features and mechanisms of spalling are presented in conjunction with the available modelling techniques and the design approaches against spalling. Finally, the effectiveness of several passive protection measures is discussed, based on the recent experiences.