Bond performance and physically explicable mathematical model of helically wound GFRP bar embedded in UHPC

Abstract

Due to the superior corrosion resistance, glass fiber reinforced polymer (GFRP) reinforced ultra-high performance concrete (UHPC) structure has been regarded as an attractive alternative to traditional RC structure exposed to harsh environments. In this work, upon the pull-out tests of 54 specimens, the bond behaviors between helically wound GFRP bar and UHPC were investigated, with an emphasis on the evaluation of the effects of GFRP bar diameter, embedment length, concrete cover thickness, and fiber characteristic parameters (i.e., volume fraction and aspect ratio) of steel-polypropylene hybrid fiber. The bond failure mode, ultimate bond strength, and bond stress-slip curve were analyzed. The results showed that the bond damage at GFRP-UHPC interface mostly occurred on the GFRP bar surface due to the relatively lower strength of GFRP ribs. The bond strength presents an upward trend with an increase in the thickness of concrete cover and volume fraction of steel fiber, whereas it decreases with the increase of GFRP bar diameter and embedment length. Moreover, the fibers in the UHPC matrix exerted a significant impact on the bond behaviors that could alter the bond failure mode from the concrete splitting failure to the pull-out failure. Finally, based on the experimental observations, a new physically explicable mathematical bond stress-slip model was proposed to reproduce the main features of the whole debonding process. The satisfactory predictions against the test results from independent research demonstrated that the proposed three-phase analytical model represents a compromise between accuracy and generality, providing a beneficial reference to the design of the GFRP reinforced UHPC structure.