scope:

Scope and limitations

The fiber-reinforced concrete (FRC) segment designers should be provided with a clear and simple approach using specified post-crack residual tensile strength σp (ACI 544.8R) and specified compressive strength fc′. This report proposes a procedure for designing FRC tunnel segments to withstand all the appropriate temporary and permanent load cases occurring during the construction and design life of tunnels. This procedure is based on the available design codes, standards, and guidelines. Application of this approach is summarized in this document. Full-scale bending tests are also discussed to evaluate the segment performance during each stage of its design life to include stripping, storage handling, transportation, and the in-service load condition due to earth pressure, groundwater, and surcharge loads. Other full-scale tests performed on the precast segments include thrust tests to reproduce the tunnel boring machine (TBM) action on the segment during the jacking process.

This report is focused on the analysis, design, and manufacturing of FRC segments of one-pass precast segmental lining used with TBM-bored tunnels. The design methods presented can be applied to tunnels of different types such as road, railway, and subway tunnels; headrace, water supply, and wastewater tunnels; and service, gas pipeline, and power cable tunnels. Two-pass lining systems, however, can also benefit from the proposed design procedure.

This document does not address the actions of TBM gantries, thermal variations, fire loads, or internal loads such as train loads within tunnels. Also, further research is needed to establish design checks for concrete breakout strength around bolts and dowels, and resistance against punching shear force in the proximity of stack support at storage phase.

The design procedures presented herein have been developed for steel fibers, and any extrapolation to synthetic or other types of fibers reported in ASTM C1116/C1116 should be confirmed by repeating small-scale (ASTM C1609/ C1609M; BS EN 14651) and full-scale bending, point load, and cantilever tests explained in Chapter 8 to show that static and long-term properties are adequately characterized

Typical volume fraction of steel fibers used in FRC tunnel segments does not exceed 0.5 percent, which typically results in a tensile strain-softening response (ACI 544.8R) of the material. Therefore, this report only covers properties, analysis, and design methodologies of tensile strainsoftening FRCs, and not tensile strain-hardening materials (ACI 544.8R). Note that a deflection-hardening response under flexural tests can be achieved using conventional fiber dosage rates, which is desired due to improved crack control characteristics of concrete materials (ACI 544.8R).