Design of steel fibre reinforced concrete tunnel linings

The analysis and design for tunnel linings of steel fibre reinforced concrete (SFRC) lack a widely agreed set of design rules. The published documents only provide partial coverage and are inconsistent. The method of analysis presented in this paper is based on design principles established by two European standards (Eurocodes EN 1990 and EN 1992-1-1), a standard test to EN 14651 and the methodology for SFRC characterisation from the 2010 fib Model Code. Charts are given that relate the mean crack width, curvature and tensile strain to the circumferential hoop force and bending moment, for serviceability and ultimate limit states. The development of post-cracking inelastic behaviour is described and shown to be stable, and its use for prediction of redistribution of moments prior to plastic hinge formation is discussed. The effects of creep and of using stronger concrete are examined. The closed-form methods of analysis used are derived in Appendices to the paper. These design methods are potential, rather than fully validated. The work exposes the areas where stronger evidence from tests and site measurements is needed to enable SFRC tunnel linings to become more economic by reducing embedded ‘factors of ignorance’. This is illustrated by an outline of current design calculations for a tunnel and a large shaft.