Fatigue of reinforced concrete beams strengthened with externally post-tensioned CFRP tendons

The fatigue performance of reinforced concrete beams strengthened with externally post-tensioned carbon fiber-reinforced polymer (CFRP) tendons was examined in an experimental and analytical study. Five unstrengthened and 13 strengthened reinforced concrete beams were tested under various fatigue load ranges until failure. The strengthened beams were post-tensioned with two external CFRP tendons on a double-harped profile. The results demonstrated that external post-tensioning significantly decreased the stresses in the internal reinforcement at all stages of loading, and hence extended the fatigue life of the strengthened beams. All beams failed due to the fatigue fracture of the internal steel reinforcing bars. The CFRP tendons demonstrated excellent fatigue performance, with no indication of distress at the deviated points or at the anchors. A fatigue model based on a strain-life approach was proposed to predict the fatigue life of the strengthened beams. The model allows the effect of strengthening on the fatigue life of the beams to be explicitly evaluated during the strengthening design process.