Experimental study on bonding properties between ribbed steel bars and grouting material constrained by TypeⅡ APC sleeve

Abstract:

To study the bond-slip performance between ribbed steel bars and grout under Type II APC sleeve restraint, a total of 69 Type II APC sleeve-constrained grout reinforcement tensile tests in 23 groups were conducted in this study. An electro-hydraulic servo universal testing machine was used for unidirectional tensile loading. Strain gauges and displacement meters were used to collect data on the strain of the sleeve and the slip value of the reinforcing bar, respectively. The damage morphology of the specimens, factors affecting bond strength, bond-slip ontological relationship, and sleeve load-strain curve were studied. The results show that: The damage forms of the sleeve-constrained grout specimens include two types: the pull-out damage of steel bars (before and after yielding) and the pull-out damage of steel bars; The bond strength of the specimens decreases with the increase of the diameter of the steel bars and the anchorage length, and increases with the increase of the steel content rate; The bond slippage between the steel bars and the constrained grout is divided into four phases: slippage, cleavage, descending, and remnant;Comparison of anchorage specimens made of different materials reveals that when reaching the ultimate bond strength the slip values decrease in the order of unrestrained grout, sleeve-constrained grout, and concrete, and the slip value of concrete was the smallest due to the limitation of crack development by the aggregates. Energy analysis of the bond-slip curves shows that the ductility of the specimens is superior, and the coefficient of brittleness decreases with increasing reinforcement diameter and increases with increasing anchorage length. At the ultimate load, the annular direction of the long side of the sleeve is tensile strain, and it increases with the increase of the diameter of the reinforcement bar, the annular direction of the short side is mostly compressive strain, the longitudinal strain of the long side and short side of the sleeve is tensile strain, and the longitudinal and annular strain of the long side of the sleeve is larger than that of the short side. Based on the ABAQUS platform, a finite element model of type II APC sleeve-constrained grout was constructed, and the simulation results were in good agreement with the test data. When calculating the value of critical anchorage length of reinforcement in the critical state of yielding and pulling off, the existence of the sleeve significantly reduces this length.