A review of test Methods, issues and challenges of Large-Scale fire testing of concrete tunnel linings

Abstract

This article provides a summary of substantial aspects pertaining to the design of concrete tunnel linings subjected to serious fire exposure. Compared to building fires, the air temperature rise of tunnel fires is more significant within a few minutes due to the confined space. This is of concern to tunnel designers as rapid temperature rise has shown to be a dominant factor in relation to concrete spalling. The dramatic European tunnel fires that occurred in 1999 and 2001 led to the development of new regulations and recommendations, including new guidelines recommended by the European Federation of National Associations Representing producers and applicators of specialist building products for Concrete (EFNARC 132F r3:2006) and Efectis R0695:2020. These regulations were intended to offer tunnel designers some scope on how to test for concrete spalling with particular focus on explosive spalling of concrete given that, in general, tunnels are at greater risk than other structures. This is principally due to the high heating rate and the high initial moisture content present. To date, full scale experimental works have been limited and not as extensive as those of small to medium scale unloaded specimens exposed to elevated temperatures. This paper summarizes recent research on large scale concrete tunnel lining tests exposed to fire conditions. The methodologies, questions, and challenges regarding large-scale fire tests on tunnel lining concrete and the current design guidelines are highlighted. First, this review examines published large-scale testing including unloaded and loaded applications. Secondly, a discussion surrounding the issues faced in testing, including the effects of loading, size reduction, boundary conditions, inclusion of polypyrene fibers and steel reinforcement is presented. Finally, current design guidelines for tunnel fire safety are reviewed and recommendations for future structural fire testing of full-scale tunnel elements was presented.