Seismic Performance of FRP-Confined Precast Assembled Concrete Piers: An Experimental Study

To improve the structural performance of precast assembled concrete piers under earthquake, we designed and manufactured two piers confined by carbon fiber reinforced polymer (CFRP) sheets (SPCC1, SPCC2), two piers confined by glass fiber reinforced polymer (GFRP) tubes (SPCG6, SPCG10), and one comparison pier (SPC). The column and bent cap connections were designed with a monolithic construction, whereas the column and pile cap connections had precast joints with grouted sleeves. The effects of the CFRP and GFRP on the seismic performance of the specimens were studied using a quasi-static test and a fiber model based on OpenSees. The failure modes of the specimens included concrete crushing in the plastic hinge zone and buckling fracture of the longitudinal reinforcement. A CFRP tensile fracture occurred in the plastic hinge zone at the top and bottom of the piers; however, damage to the GFRP tubes was minor. Compared with sample SPC, the maximum bearing capacities of SPCG6, SPCG10, SPCC1, and SPCC2 increased by 8.4%, 3.1%, 15.0%, and 4.8%, respectively. At 7% displacement, the residual bearing capacities of SPCG6, SPCG10, SPCC1, and SPCC2 increased by 103.3%, 90.4%, 36.7%, and 82.8%, respectively, compared with SPC. At 6% and 7% displacement, the average stiffness of the CFRP/GFRP-confined specimens increased by 46.2%/58.9% and 59.8%/96.8%, respectively, compared with that of the unconfined specimen. The curvature results also showed that the confined pier exhibited a better flexural performance in most loading processes. The test and simulation results showed that the connection strength of the grouted sleeve in the precast structure should be ensured, and the reinforcement ratio of the pier should be prioritized, followed by an appropriate improvement in the compressive strength of the concrete. The constraint range of the FRP at twice the height of the plastic hinge zone was sufficiently conservative to ensure that the pier maintained good seismic performance under a high axial compression ratio. In practical engineering, the use of a GFRP tube as a template for a prefabricated pier is recommended, and a CFRP sheet is used to strengthen the plastic hinge area of an existing pier with insufficient seismic ability.