Fire protection in tunnels: Protection goals and fire design (FGU2008/003_OBF)
Overview
Background & policy context:
The Swiss SIA standards focus on the issue of fire impact in tunnels, but it is only vague in most cases or it refers to additional literature that refers back to other references. A reader can be easily losed during studying of literature. This is confirmed by the literature review of the fundamentals and rules in other countries.
The deformations and internal forces of the tunnel construction during a fire depend mainly on the factors of bedding, wall thickness and type of concrete. The deformations in case of fire can be classified according to predefined temperature-time curves using calculating nonlinear, temperature dependent material laws. However, these are dependent on defined fire protection objectives and fire protection concepts which must be specified by the client in part. Here, however, lacking assistance and constraints.
In the literature there are already some temperature-time curves, their applicability have to be looked respectively. Here lack concrete details on what basis they are based (eg. As fire simulations).
The structural analysis for the fire design situation has to be evaluated using appropriate models, with thermal and mechanical effects and the structural behavior to be considered at elevated temperatures. The structural safety analysis can be done either in the following ways (SIA 261):
- In the time domain on the basis of fire resistance
- In resistance area on the basis of supporting resistance
- In the temperature range with reference to the critical temperature
Objectives:
The Swiss SIA standards provide reference to the impact of fire in tunnels and how to deal with it. However there is a lack of defining data for fire protection design. There is no actual specification for the dimensioning of a tunnel structure. However, the standard calls for such a specification to be established. The scope of the research includes an evaluation of how such a standard shall be put into practice. The result of the research shall then be presented as a recommendation, possibly even as an application guideline. In the first instance the “State of the Art” will be ascertained and advanced research projects evaluated.
Methodology:
The project uses the following activities: literature research, modeling, theoretical study.
The project will be developed in the following sub-items:
Phase 1:
Study of the existing literature, regulations in other countries, state of the art, differentiation of the requirements, specifications for the dimensioning, identification of loop holes and optimise potential, identification of design principles
Phase 2: (forecast)
The implementation focuses on the individual tunnel structures or construction units and delivers recommendations on whether a specific design is necessary at all. If the specific design is necessary, the manner in which this design should be carried out is decided. The objective is to evaluate design principles in order to maintain the structural safety, which leads to recommendations or guidelines.
The following calculation methods: general or simplified proof and the evidence with tables. The general calculation method is very complicated, simplified procedures have been very controversial and the evidence for tables is actually only valid for a standard fire curve from the building construction. Except for the simplified procedure no more analytical design methods were found in the literature. Design criteria as a function of the structure are completely absent.
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