Seismic vulnerability of multi-span continuous girder bridges with steel fibre reinforced concrete columns

The occurrence of earthquakes during the lifetime of bridges can result in the closure or even the failure of the structure. The vulnerability of multi-span continuous girder (MSCG) bridges strongly depends on the seismic performance of their columns. This paper investigates the seismic vulnerability of MSCG bridges with reinforced concrete (RC), steel fibre reinforced concrete (SFRC) and RC-SFRC columns. Quasi-static tests were conducted on eight different columns to obtain the limit-state capacities and validate numerical models. Numerical analyses were performed on MSCG reference bridges with RC, SFRC or RC-SFRC columns to derive probabilistic models for the demand on critical components. Fragility curves were established as a function of the peak ground acceleration by integrating the capacity distributions with the correlated component demand distributions. Results indicate that: (i) SFRC columns with 1.0% fibre ratio show a better performance-price ratio for improving the structural capacity compared with those with 1.5%; (ii) MSCG bridges with SFRC and RC-SFRC columns are less vulnerable to earthquakes when compared with those constructed using only RC, and the difference increases with the earthquake intensity; and (iii) the seismic vulnerability of MSCG bridges with SFRC placed only at the plastic hinges is similar to the one found with SFRC applied on the whole column. On a broader perspective, the conclusions drawn in this paper could offer a new strategy for the seismic enhancement or retrofit of MSCG bridges in earthquake regions, with optimal use of SFRC.