"Structural tunnel fire safety"
Ir. G.L. Tan - Tan-consultant
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 Structural tunnel fire safety
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Since the late eighties, tunnel protection against fire is standard in the Netherlands. The protection is based on a petrol fire. In 1979 the RWS-curve was found during tests in a model tunnel. The temperature measured during the tests rose up to 1350°C. This high temperature was also found during earlier fire tests in Switzerland (Offenegg tunnel 1965) and Austria (Zwenberg tunnel 1975). Recent tests in Norway (Eureka project) and United States (Memorial tunnel) found the same high temperature. |
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The most important part of the RWS-curve is the gradient during the first 10 minutes. The temperature rises so rapidly that the construction has no opportunities to adapt. Moisture in the concrete becomes steam and causes high pore pressures and as result, spalling of the concrete. This spalling follows each other rapidly and if the reinforcement is heated, it looses its strength and the construction collapse. |
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 Steam forming and
explosive spalling |
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To prevent this, the construction must be protected by a fire-resisting layer, which has the property to reduce the gradient and give the construction time to adapt. This protecting layer must not collapse during the fire. Many protecting layers will melt already at temperatures above 1200°C. That’s why protecting layers must be tested according to the RWS-curve. There must be no doubts that the protecting layer will not disintegrate in case of a tunnel fire. |
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There are several types of protecting layers, some of them are sprayed materials and applied afterwards. This means extra construction time and costs. For immersed tunnels, cast in situ parts and cut & cover parts, this can be avoided by using boards, which are placed in the form-work before installing the reinforcement and pouring the concrete. |
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The advantages of boards are the constant quality and thickness, because it is produced in a factory with better circumstances and facilities (quality control) as opposed to a construction site. |
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Tan-consultant ( www.tanconsultant.com )
Ir. G.L. Tan has experience in tunnelling for more than 27 years and has worked for the Dutch Ministry of Transport (Rijkswaterstaat, RWS). In 1999 he started his own consultancy in tunnel engineering and safety. |
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