Seismic fragility curves for vulnerability assessment of steel fiber reinforced concrete segmental tunnel linings

In recent years, application of fibers as a replacement for conventional reinforcement in segmented lined tunnels has gained great interest due to resulting cost and time savings. In seismically active regions, the seismic vulnerability of underground tunnels is of great concern. The aim of this paper is to investigate the effects of different composites of Steel FRC (SFRC), as the tunnel's lining material, on its seismic vulnerability, compared to each other and to that of unreinforced and conventionally reinforced concrete cases, employing analytical fragility curves. Results show that steel fibers, especially micro size fibers and for higher states of damage, display better seismic performance over conventional steel rebar in reinforced concrete linings. For best performance, a hybrid SFRC mix containing both micro and macro fibers, with a higher content of micro fibers over macro ones, is a technically preferable option for the design of segmental lining tunnels in seismic zones.