Seismic Performance of Reinforced Concrete Bridge Substructure Encased in Fiber Composite Tubes

Recent cyclic tests in the United States, China, and Japan have shown that fiber-reinforced polymer (FRP) tubes can effectively replace spiral reinforcement in reinforced concrete (RC) columns. This study was undertaken to advance the current state of the art for concrete-filled FRP tubes (CFFTs) by comparing their seismic performance with that of conventional RC bridge pier columns at the sectional, member, and bridge system levels. A nonlinear finite element model was developed for a bridge case study. Because FRP has a lower rupture strain than steel spiral and because of its linear elastic response, a CFFT section shows less ductility than an RC section. However, at the member level, a CFFT column distinctly outperforms its RC counterpart, with almost twice the base shear capacity and more than three times the lateral drift capacity. This phenomenon was attributed to the effective role of the FRP tube in extending the plastic hinge zone of the column well beyond its typical range in conventional RC columns. The implication of this behavior was shown through a seismic simulation of the entire bridge under a major historical shake with varying levels of magnified ground acceleration. The simulation showed the CFFT substructure to suffer moderate damage while maintaining structural integrity compared with the RC substructure, which suffered severe and irreparable damage.