Design of Concrete Tunnel Linings for Fire Safety

Abstract

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.

Design of the metro tunnel project tunnel linings for fire testing

“…This is in addition to the economic impact due to significant time periods of closure while the tunnel undergoes restoration works 2 . For example, the extreme event in the Channel Tunnel which reduced the 450 mm thickness of the tunnel lining to 100–200 mm, 3 required over 1,300 tons of fiber‐reinforced shotcrete for repair events and the tunnel was closed for approximately 6 months, at a cost of $1.5 M Euro a day in uncollected tolls 4 …”

“…These incidents have led to requirements in limiting the spalling depth and the magnitude of temperatures of the in situ reinforcement 5 for both rail and road tunnels. While road tunnel fires are more frequent, the number of fatalities in railway tunnel systems generally seems to be far greater 4,6 . Another complication arises when tunnels are constructed under water level, especially in soft ground with high water pressure.…”

Effects of Fire Duration on the Seismic Retrofitting With Hysteretic Damped Braces of r.c. School Buildings

“…Concrete does not recover strength (i.e., thermal decohesion) and stiffness (i.e., thermal damage) after fire and its heat properties are progressively reduced as function of the duration of the heating and cooling phases (Lee et al, 2008;Maraveas and Vrakas, 2014). Progressive and explosive spalling are also evident in high and ultra-high strength concrete rather than in normal one, on account of low permeability (i.e., hydraulic spalling) and restrained thermal dilation (i.e., thermal spalling) of the zone near the heated surface produced by the cooler inner layers of concrete (Maraveas and Vrakas, 2014). Moreover, the residual compressive strength of the concrete is significantly influenced by the cooling method, with an additional strength reduction of 38% for quenching but not for spraying (Botte and Caspeele, 2017).…”

Numerical Analysis of a Moderate Fire inside a Segment of a Subway Station

“…As for structural elements, related studies have been devoted to normal-strength concrete columns with circular cross-sections [19], high-strength concrete columns with quadratic cross-sections [20][21][22], RC beams, either unprotected [23] or protected by fiber-reinforced polymer laminates [24], high-performance self-compacting concrete slabs with superabsorbent polymers and polypropylene fibers [25], T-shaped beams, made of high-strength reinforced concrete [26] and prefabricated RC segments for linings of shield tunnels [27]. As for entire RC structures, testing and/or simulations were carried out for RC slabs resting on steel frames [28], slab-column connections, made of reinforced concrete [29], composite slabs with, as well as without a supporting secondary beam [30], RC frame structures [31][32][33], the Channel Tunnel between France and the United Kingdom [2,13], other monolithic tunnel linings with cross-sections in the form of a segment of a circle [34,35] , of an ellipse [36] and in the form of a double box [37], a segmental tunnel ring of a metro tunnel [38] and the twin-tube cross-section of the immersed tunnel of the Hong Kong-Zhuhai-Macao-Bridge [39].…”