Cyclic behavior of existing RC bridge piers strengthened by exterior ECC and BFRP/ECC composite jacketing at pier base

Engineered cementitious composites (ECC) are a class of high-performance fiber-reinforced cementitious composites. This study proposes using ECC and BFRP grid-reinforced ECC (BFRP/ECC) as external jackets at the base of existing RC bridge piers to enhance seismic performance. Seven 1/5-scale RC bridge piers were tested under reversed cyclic loading, including one unmodified pier as reference and six reinforced piers with varying jacket thickness, height, interface, and BFRP grid mesh size. The test results demonstrate that both ECC and BFRP/ECC composite jacketing effectively enhance ductility. The hysteretic response of the reinforced piers with different interfacial properties, however, varied significantly. The piers with interfacial shear keys exhibited enhanced flexural strength, ductility, and energy dissipation capacity but sustained severe damage as jacketing thickness and height increased. Conversely, the piers with smooth interfaces showed insignificant improvements in flexural strength but significant enhancement in ductility with marginal damage. This behavior can be attributed to the fact that the exterior jacketing in specimens with interfacial shear keys was under bi-axial tension-compression stress state due to flexural compression and lateral expansion of the plastic hinge, while the jacket in specimens with smooth interfaces acted solely as lateral confinement.