Time-Dependent Behavior of FRP Retrofitted RC Columns after Subjecting to Simulated Earthquake Loading

Abstract

Seismic retrofit of reinforced concrete (RC) columns using fiber-reinforced plastic (FRP) jacketing has been widely investigated. However, the residual performance of FRP retrofitted columns after surviving earthquake attacks remains as an issue with little research. As a follow up of a previous experimental study, this paper reports the analysis of the axial loading creep behavior of FRP retrofitted RC columns with different degrees of simulated earthquake damage. The damage degree and residual strains in FRP after lateral loading are assessed based on previous maximum lateral displacement excursion. A creep model for damaged columns with FRP jacket is presented based on the age-adjusted effective modulus method for creep of concrete and the Findley’s power law function for creep of FRP jacket. The creep model considers the effects of previous damage, sealed concrete, multiaxial stress state of stresses and stress redistribution. The proposed model is validated against previous creep tests of fiber-wrapped concrete columns by other researchers and the long-term tests conducted by the authors. Finally, a detailed study is carried out to identify the practical design parameters affecting creep of hybrid columns. The analytical results show that the creep of the FRP confined column increases as the damage degree becomes larger and exhibits notable nonlinear feature. The creep life declines and may cause creep rupture of the FRP when retrofitted columns suffer serious earthquake damage or under high axial load.