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  Precast Concrete Tunnel Segments Slenderness Ratios

  The slenderness of the tunnel segments is defined as the ratio between the breadth or curved length of segment along its centroid and its thickness. It is a key parameter for design of segment length between two longitudinal joints in a segmental tunnel ring. Review of tunnel projects show that rings are often divided into a number of segments that yields a segment slenderness of between 8 and 14. Using latest fiber technologies and high-strength steel and concrete materials, fiber-reinforced concrete (FRC) segments with slenderness of more than 10 are now being frequently adopted and slenderness ratios up to 12-13 have been used in the most recent projects. Nonetheless, segments with slenderness ratios of more than 10 are not commonly used due to lack of engineering background and reliable calculations supporting the significance of this parameter and its reliable limits. This paper verifies the applicable range of slenderness ratios for FRC segments based on the latest segment design guidelines such as ACI 544.7R and ACI 533.5R. Special attention is paid to high residual strength of FRC segments built with latest generation of structural fibers and the factored design loads developed during segment production and transient stages.

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