Experimental study on lap behavior of CFRP indented bars in UHPC

Abstract

The lap behavior of Carbon Fiber Reinforced Polymer (CFRP) indented bars in Ultra-High Performance Concrete (UHPC) were investigated based on pullout test under direct tension on 27 specimens in total. The test variables include splice length, UHPC strength and stirrup ratio. The lap failure mechanism of CFRP bar embedded in UHPC and the influence of test parameters on lap performance were analyzed. Test results showed that the failure modes, pull-out and rupture of CFRP bar, in those lap-spliced specimens were governed only by the splice length of the CFRP bar embedded in UHPC. The pullout failure was caused by the shearing off of indented ribs on the surface of the bars and the fracture failure was governed by the tensile strength of the bars. The bond strength of lap-spliced indented CFRP bars in UHPC is mostly dependent on the shear strength of indented ribs on CFRP bars, little on the UHPC strength and stirrup ratio. For CFRP bars with a 2480 MPa tensile strength and a 9.8 mm diameter (d), a splice length of 30d in UHPC can fully develop the tensile strength of the bar. A simplified equation for predicting the critical splice length of CFRP bars in UHPC was proposed. Compared with the results on anchorage of CFRP bars in UHPC, the critical splice length of CFRP bar in UHPC was 1.45 times the corresponding anchorage length.