Assessing the Fatigue Life of CFRP Post-Strengthened RC Elements

Abstract

Abstract Upgrading historic structures is one of the most interesting applications of FRP in construction. The possibility to preserve construction technology and original structural conception after an intervention makes the use of FRP an interesting alternative for historic structures. Among these structures, historic bridges are frequently post-strengthened to increase load carrying capacity of structural elements, aiming to bear heavier commercial traffic. In such applications, the fatigue life tends to increase; however, this performance is not fully addressed, which can restrain the effective utilization of FRP in historic structures. Fatigue life becomes a crucial question since the lack of data regarding FRP post-strengthened elements leads to superficial analysis that considers the same S-N curves for different FRP systems and stress ranges, for example, besides other issues. Aiming to improve the fatigue life assessment of RC beams strengthened with FRP, this paper aims to adjust specific S-N curves for different FRP systems and techniques. An extensive database, with experimental data gathered from the literature, has been used to adjust linear regression models to characterize the large scatter between the results of fatigue tests from different sources. Distinct fatigue models have been developed considering three post-strengthening categories: externally bonded reinforcement with FRP strips/sheets and NSMR. Different declivities have been found for the adjusted fatigue life models, highlighting specific aspects of each category. The declivity of the fatigue curves accurately represents the fatigue behavior of FRP-strengthened RC beams and can be used to support proper post-strengthening design to avoid future unnecessary interventions. This paper also presents some real examples of FRP strengthening historic bridges around the globe.