This paper presents the seismic performance of concrete bridge columns reinforced with both steel and fiber-reinforced polymer (FRP). A bond-based parametric experimental study was conducted on five FRP steel–reinforced concrete (FSRC) bridge columns—using basalt FRP (BFRP) bars and BFRP sheets—and two steel-reinforced concrete (SRC) bridge columns served as references to investigate the fundamental characteristics of the proposed reinforcement. The investigated bond parameters included the texture of the FRP bars (smooth and ribbed), diameter of the FRP bars, location of the FRP bars with respect to the steel bars, and application of external FRP confinement. All columns were tested under the combined effect of constant axial load and reversed cyclic loading. The experimental results showed that the FSRC bridge column could realize the existence of a stable postyield stiffness (hardening behavior) as well as a reasonable displacement ductility of up to 10 before encountering strength degradation. Moreover, the FRP bars added for column longitudinal reinforcement did not have a substantial impact on the column elastic stiffness. The bond condition of the FRP bars to the surrounding concrete had pronounced effects on the column failure mode, postyield stiffness, residual displacement, and ductility; thus, it could be adopted as a design parameter.

Despite the improved performance of fiber-reinforced plastic (FRP)-retrofitted bridges, residual deformations in the event of an earthquake are inevitable. Little consideration is currently given to these deformations when assessing seismic performance. Moreover, important structures are currently required not only to have high strength and high ductility but also to be usable and repairable after high intensity earthquakes. This paper presents a definition of an FRP-RC damage-controllable structure. An intensive study of 109 bridge columns, extracted from recent research literature on the inelastic performance of FRP retrofitted columns with lap-splice deficiencies, flexural deficiencies, or shear deficiencies, is used to evaluate the recoverability of such retrofitted columns. The residual deformation, as a seismic performance measure, is used to evaluate the performance of 39 FRP-retrofitted RC columns from the available database. Based on this evaluation, a requirement for the recoverable and irrecoverable states of FRP-RC bridges is specified. Finally, the Seismic Design Specifications of Highway Bridges for RC piers is adapted to predict the residual deformations of FRP-RC columns.

This study aims to explore the cyclic bond–slip behavior of basalt fiber-reinforced polymers (BFRP) bars. Experimental pullout tests under monotonic and cyclic loading patterns were conducted in order to examine the effect of the cyclic loading on the bond behavior of BFRP bars. The effects of cyclic loading characteristics, concrete compressive strength, and bar diameter on the bond–slip relationship were examined. In addition, the bond performance of bars with four different surface profiles (smooth, sand-coated, wrapped, and wounded) under different loading protocols was studied and compared to that of deformed steel bars. The results revealed that cyclic loading had a significant effect on the bond performance of BFRP bars and the bond–slip relationship was greatly dependent on the bar surface treatment, as well as the characteristics of the applied cyclic loading protocol. Also, cyclic loading magnified the effect of concrete compressive strength on the bond behavior. A numerical model was proposed to predict the bond–slip relationship of wounded BFRP bars under cyclic loading. The model predictions showed good agreement with experimental results.

This paper presents a near surface–mounted (NSM) retrofit technique to enhance the seismic performance of existing reinforced-concrete (RC) columns with lap-splice deficiencies using basalt fiber-reinforced polymer (BFRP) reinforcing bars. The bond condition between the BFRP bars and the surrounding materials was examined using bars with smooth and rough textures. Three columns were designed with poor detail in the longitudinal lap splices and improper transverse confinement; one sample served as a reference, and the others were strengthened with NSM BFRP bars and an external BFRP jacket around the plastic hinge zone. The test results were assessed in terms of the seismic performance of a well-designed column (i.e., a column with continuous longitudinal reinforcement and well-designed stirrups). The test results indicated that the texture of the FRP bars is a key retrofit design parameter that can be used to control the inelastic performance of lap-splice columns. FRP bars with a rough texture ensured a gradual increase in column strength after yielding and mitigated residual displacement. Furthermore, the original functions of retrofitted columns could be rapidly restored after an earthquake with a drift of up to 4.5%, whereas the postearthquake recoverability of a well-designed column cannot be guaranteed after a drift of 2% is reached.