ABSTRACT

The use of steel fibre reinforced concrete (SFRC) for tunnel linings has been established in the UK for more than 20 years. Although the Ultimate Limit State (ULS) of steel fibre reinforced concrete (SFRC) can be verified in a number of ways, the design analysis for Service Limit States (SLhS) lacks a widely-agreed set of design rules due to the difficulty of estimating crack widths. A method of analysis is presented based on design principles established by EN 1990 and the fib Model Code 2010. The analysis presented here relates mean crack width, curvature and tensile strain to circumferential hoop force and bending moment, for a given crack width limit. The latter is an important parameter to satisfy the durability performance. The development of post-cracking inelastic behaviour is described, and its use for prediction of redistribution of moments prior to plastic hinge formation is discussed. This is illustrated by an outline of the current design practice for cast in-place (CIP) SFRC tunnel lining (pressurised sewer tunnels) for two sewer projects in London (Lee Tunnel and Thames Tideway West).