Experimental study on Bond slip relationship of Steel sleeve

: The assembled concrete structure is usually connected with the steel bar through the sleeve (cid:452) In order to realize the optimum design of sleeve structure and develop new sleeve, the author put forward a new test method, and made 18 specimens for uniaxial tensile test. Study the influence of the strength of grouting material, diameter of reinforcing steel bar on bond slip relationship between steel bar and grouting material and its failure characteristics by experimental research. This result suggests that with the increase of age, the bond strength between steel bar and grouting material is increasing gradually, the increase speed gradually slowed down after 20 days. For CT20H sleeve, with the increase of the diameter of reinforcement, the bond strength between reinforcement and grouting material increased gradually. Conclusion: In the optimization design of the sleeve, under the premise of ensuring the smooth injection of grouting material and be convenient for the positioning of the reinforced members, reducing the inner diameter of the sleeve can improve the bond strength between reinforcement and grouting material.


INTRODUCTION
Steel sleeve grouting connection is made of high strength, rapid hardening inorganic slurry in the connection between reinforcement and special sleeve connecting pieces. In recent years, with the development of assembled concrete structure Both the domestic and abroad did a series studies of grouting sleeve. Huang Hejun discussed the bonding mechanism of anchoring adhesive through tensile shear test of 20 metal sleeve bonding specimens, put forward the constitutive relation of anchoring adhesive slip. It can be used as a reference finite element analysis [1] . Wu Xiaobao did monotonic tension and one-way repeated tension test in 36 specimens, researched the influence of age (1, 4, 7, 28d) and steel type(HRB500 and HRB400) on the mechanical properties of the steel sleeve grouting connection [2] . Shu Ruibin obtained the bond slip constitutive relation of two interface slip, including the rubber band and the plastic tube by the anchorage experimental study on steel sleeve, through the equipartition method, they get the steel sleeve anchorage system of the rubber band interface and a rubber cylinder interface separate bond slip constitutive relationship [3] . Wang Yuxin choose smooth and ribbed reinforcement with different corrosion rate to make concrete center pull out specimens with same strength grade, he obtained the bond slip relationship curve between corroded steel bars and concrete under cyclic loading [4] . Zheng Shansuo made 20 trusses specimens pull-out test of bond slip behavior of solid web type steel reinforced concrete member, set up a formula about reinforced concrete bond strength and slip quantity [5] . Xu Feng proved that the bond slip relationship is independent of the path of the lateral stress field, then concluded that changes in lateral stress field under the bond slip curve is the superposition of numerous fixed lateral stress field under bond slip curve [6] . At the same time, foreign scholars have done some research on bond slip, Hunebum Kocarried out the experiment of 54 members under cyclic loading and obtained the bond slip constitutive relationship of fiber reinforce d concrete [7] . Kankam C respectively tested the tensile members of the low carbon steel, cold rolled steel bars and hot rolled bars with a diameter of 25mm.After analyzed, he got the relationship between the bond strength, the stress of the steel bar and the slip [8] . Chen, G. And Baker, G studied the influence of bond slip on the crack spacing of concrete by simulation in 2003,and believed that the influence of bond slip on the crack spacing is very obvious [9] . Belleri Andreaet al [10] put the grout sleeve for column and foundation connections in earthquake zones, and found that the grouting sleeve connection is similar to the traditional connection, which can ensure the ductility and energy dissipation capacity of the connection area.
So far, few people have studied the bond slip between the steel bar and the grouting material or the sleeve and grouting material. The reason was that the space in the slurry anchored bar connecting sleeve internal is too small to determine the displacement of steel relative grouting material and the sleeve relative grouting material by direct method. In this paper, we used test methods to give the bond slip relationship between the internal reinforcement grouting material in the sleeve by indirect method, and the bond slip relationship between the sleeve grouting material will be studied as a follow-up work.

SPECIMEN MAKING
The cross section size of the test block is 250mm*250mm, along the length of the reinforcement direction is consistent with the sleeve length, as shown in figure 1.

TEST CONTENT AND ULTIMATE LOAD
The test contents of the experiment are loaded end load, load displacement and free end displacement, compression strength of grouting material test block, rupture strength. The load in Table 2    2) for the CT20H sleeve, with the increase of the diameter of reinforcing steel bar, the bond strength between reinforcement and grouting material increases gradually.

LOAD DISPLACEMENT CURVE
The reason is that the increase in the diameter of reinforcement will cause the increase of the mechanical bite force between reinforcement and grouting material.(The thickness of the grouting material between the steel bar and the sleeve is reduced, the height of the column formed after the cracking of the grouting material is reduced, and the compression strength is increased.) 3) It is possible to reduce the size of the inner diameter of the sleeve, but it is necessary to ensure the orientation of the reinforcing bar between the grouting material and the member during the construction.