Fatigue behaviour of concrete beams post-tensioned with unbonded carbon fibre reinforced polymer tendons

Abstract

Much research has been conducted in the past decade to evaluate the suitability of fibre reinforced polymer (FRP) reinforcement in concrete structures. Most of the research has concentrated on the short-term performance of FRP prestressed and reinforced concrete beams. Only a limited amount of research has considered the fatigue behaviour of FRP prestressed beams. This paper presents an experimental research program designed to examine the fatigue behaviour of unbonded carbon fibre reinforced polymer (CFRP) post-tensioned concrete beams. The fatigue test program consisted of five large-scale (4.0 m span) concrete T-beams. Three of the beams were post-tensioned with CFRP tendons, and the remaining two beams were post-tensioned with steel prestressing strands. The fatigue load limits were chosen to produce an additional stress range of about 100 MPa in the lower prestressing reinforcement. During fatigue testing, some of the prestressing strands fractured at the anchor location. In the steel post-tensioned beams, fracture of wires in the seven-wire prestressing strands did not result in total failure of the steel post-tensioned beams, as the unbroken wires continued to carry prestress force. In the CFRP post-tensioned beams, however, fracture led to splintering of the tendon between the anchors and total loss of prestress force. In general, the CFRP post-tensioned beams performed satisfactorily in fatigue, in comparison with the steel post-tensioned beams, as long as premature failure of the tendons near the anchor location was prevented.Key words: fibre reinforced polymer (FRP), anchorage, tendon, fatigue, post-tension, concrete, beam, dynamic, testing.