A Practical Approach for Tunnel Fire Verification

Abstract

This paper highlights the nature of the problem related to tunnel liners exposed to fire, and presents a possible approach for assessing the static behaviour of concrete structures under this extreme loading condition. The paper starts with some comments regarding material parameters for concrete subjected to high temperatures proposed by the European Standards. Subsequently, the main aspects to be considered in a structural fire analysis for a tunnel are highlighted by means of a simple calculation scheme. Based on this scheme, an advanced calculation method for assessing the structural behaviour of concrete tunnel linings during a fire event is described and validated. The classic approach commonly used for structural static analyses based on thin elements (beam or shell) is not particularly suitable for determining section forces in concrete structures exposed to temperature changes. This limited adequacy emerges especially in the case of fire. In such cases, the impact of a temperature increase on the structural behaviour could be significantly overestimated. The proposed approach for tunnel fire verification, by properly considering the concrete cracking, provides more realistic results, avoiding unnecessary over-dimensioning of steel reinforcements in new structures, or the protection of existing structures by, for example, additional insulating layers.