Research on Seismic Behaviors of RC Circular Pier with Longitudinal Rebar of Reduced Diameter and CFRP Wrap

Investigations on the seismic damage of bridges after earthquakes indicate that reinforced concrete (RC) piers are easily damaged, which influences the rescue and reconstruction after earthquakes. Repairing damaged piers with the technology, which substitutes the damaged original longitudinal rebar using a longitudinal rebar with a reduced diameter (turned rebar) and envelops the RC piers with the carbon fiber reinforced polymer (CFRP), can shorten the repair period after earthquakes and reduce the reconstruction costs. The RC circular pier in a continuous girder bridge with irregular piers was selected as the case study. Quasi-static tests on seven RC circular pier specimens with a reduced scale factor of 1: 6, considering the length and diameter of the turned rebar, and the layer of CFRP wrap as parameters were adopted. The finite element models were implemented using the OpenSees finite element software, and the accuracy was verified by the test results. Parametric analysis was performed using the finite element model. The results indicate that the plastic deformation of piers with the turned rebar was concentrated within its length, and the failure of piers was limited within the plastic hinge zone. Comparing the piers without the turned rebar, the load bearing capacity of piers with the turned rebar could decrease by 20%-27%; however, the displacement ductility, curvature ductility, and energy dissipation capacity increased by 42%-85%, 47%-242%, and 32%-56%, respectively. It was established that the turned rebar could effectively improve the seismic performance of piers when the load bearing capacity of piers satisfies the design requirements. The measured maximum strains of the CFRP wraps within the length of the turned rebar in the piers with the turned rebar, were significantly larger than those in the piers without the turned rebar. It can be concluded that the CFRP wraps could be chosen for piers with the turned rebar to prevent the premature failure of piers and improve the ductility. With an increase in the length of the turned rebar or a decrease in the diameter of the turned rebar, the energy dissipation capacity of the pier first increases and then decreases. Selecting the length of the turned rebar is proposed, considering the fatigue life of rebar as the lower limit and the length of the plastic hinge zone as the upper limit. The maximum diameter obtained, under the condition of ensuring that the stress of the longitudinal rebar outside the plastic hinge zone is always within the elastic range, can be considered as the diameter of the turned rebar. Using concrete with higher strength in the repair zone of the pier can increase the load bearing capacity of the pier with the turned rebar.