Exploratory Study of Seismic Response of Deficient Lap-Splice Columns Retrofitted with Near Surface–Mounted Basalt FRP Bars

Abstract

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.