To investigate the bond between the concrete and the large-diameter strands and reasonably propose design development lengths

pull-out tests of 32 specimens with strands arranged centrically and eccentrically were carried out. The test focused on high-strength and low-relaxation strands of nominal diameters of 15.2 mm

17.8 mm

and 21.6 mm. Main parameters included the thickness of the concrete cover

the volumetric stirrup ratio

and the anchoring length.The test results show that the pull-out specimens had two failure modes

though testing parameters varied for different specimens.The first mode was concrete splitting failure for a few specimens having both thin cover and small volumetric stirrup ratio

and the other was apparent pull-out of strand for most specimens but no cracking was observed. Based on the failure characteristics and the relationship between the pull-out force and slip

the mechanism of bond failure between strands and concrete was presented. The peak point of the pull-out curve was taken as the sign of failure.A calculation method for the bond strength between strand and concrete was proposed considering the effects of three parameters. The approximate probabilistic method was adopted to analyze the design value of the development length of the strands to meet the requirements of the corresponding reliability index.It can serve for the design and analysis of large-span pre-tensioned concrete members applied in precast structures of public buildings.