A fracture-mechanics-based design method for SFRC tunnel linings

The current design provision, on the estimation. of the load carrying capacity of steel-tiber-reinforced concrete (SFRC) tunnel lining is briefly introduced. The design method is based on the concept of fracture mechanics of concrete. Existence of a crack and transmitted stress by fibers are considered in the estimation of the maximum resultant forces of the critical cross section. In this study, the validity of the current design method is verified, and the possible improvements of the design method are proposed. It is shown, that the crack length at the maximum load depends on the specimen size and the fiber property. The source of the size effect which appears between a small specimen for the material test and the actual lining is the dependence of the crack length at the peak on the specimen size. The dependence of the critical crack length on the fiber property is not considered in the current design. It should be taken into account for the quality control of the fibers. Methods to determine the tensile strength carried by fibers and to estimate sectional capacities with various thickness of the lining and different kinds and volume fractions of fibers are proposed.