Experimental study on the bond behaviour between cfrp nsm strengthening system and concrete under fatigue loading

Abstract

Strengthening techniques based on the use of Carbon Fibre Reinforced Polymer (CFRP) materials have been used in bridges to extend their service life, since it has been proved their excellent performance under fatigue loading. Despite that, only few studies regarding the CFRP-concrete bond behaviour under fatigue loading can be found in the literature. Therefore, there is a further need of investigating how fatigue conditions can affect the behaviour of the bonded joints, since this affects not only serviceability aspects, such as crack width and spacing, but also the ultimate capacity of the strengthened elements. This paper aims to contribute to the understanding of the bond behaviour of Near-Surface Mounted (NSM) CFRP-concrete specimens under fatigue loading. NSM CFRP-concrete specimens have been tested through direct pull-out tests under different fatigue loading conditions (20%-40%, 30%-50% and 40%-60% of the ultimate instantaneous load) at 5 Hz until 2.000.000 cycles. After the fatigue tests, specimens that did not fail under fatigue loading were tested monotonically until failure to study the residual bond response. A significant increase of slip between the CFRP and the concrete at the loaded end was observed with the increasing number of cycles, being higher with the average load increase. Furthermore, a decrease on the stiffness of the cycle’s loop and an increase of the residual slip were observed as the number of fatigue cycles increased. Finally, from the monotonic post-fatigue tests, a decrease on the load-slip stiffness was observed.