Experimental And Theoretical Study On Connection Performance Of Novel Bolt-UHPC Grout Composite Splice Sleeves

The reliability of the connection of the rebar between the vertical members of prefabricated assembly structure is the key to ensure that the prefabricated assembly structure has good mechanical performance.The grouted coupler for rebars splicing is not limited by the diameter of reinforcing bars,so it can be used for components that may be subjected to larger horizontal loads in earthquake.It has a wider scope of application and is more suitable for the lower structure of bridges.The diameter of reinforcing bars used in the lower structure of bridges is larger and the large diameter reinforcing bars are beneficial to the installation and construction of prefabricated structures.The traditional grouting sleeve mainly changes the sleeve shape or processes ring ribs inside the sleeve to increase the bond strength between sleeve and grouting material.However,with the increase of the diameter of reinforcing bars,the processing difficulty of sleeve increases,and the length of anchorage increases,which makes the sleeve too long to construction and installation.In order to make sleeves lighter and have good connection performance,based on summarizing the existing sleeves at home and abroad,a new type of bolt-UHPC grout composite splice sleeve for large diameter steel bar connection is proposed in this paper.33 grouting sleeve specimens are manufactured,and its structural performance is studied through experimental research,theoretical analysis and finite element simulation.The main work is as follows.1.A new type of sleeve is put forward in this paper.The sleeve adopts seamless steel pipe to cut directly and insert bolts on the surface.The bolts surface and the sleeve hole wall are connected by threads.The pre-tightening force is applied at the joint to ensure that the connection is tight and without the risk of grouting leakage at the same time.The bolts can prevent the pull-out of grouting material and have a certain positioning effect on the internal steel bar.Its processing technology is simple,which can reduce the production cost of large diameter steel bar connection.At the same time,UHPC is used as grouting material to enhance the bond strength between grouting material and steel bar,reduce the anchorage length of steel bar,further reduce the sleeve cost,make sleeve lighter,and promote the engineering application of large diameter steel bar in prefabricated lower structure of bridge.2.In order to study the performance of grouting sleeve connection of large diameter steel bar,the grouting sleeve with diameter of 28 mm,32 mm and 40 mm was tested by unidirectional tension test and repeated tension-compression test.The failure mode,load-bearing capacity,load-displacement curve and strain distribution of steel bar and sleeve were studied.The test results show that when the anchorage length is 5 times the nominal diameter of steel bar,the bearing capacity of sleeve with bolts can meet the strength requirements specified in the domestic and foreign codes.3.The effects of different parameters on the structural properties of the specimens were studied by unidirectional tensile test.The main parameters include anchorage length of reinforcing bar,number and length of bolts,location of bolts,strength of grouting material,influence of fibers in grouting material,thickness of grouting material and strength of reinforcing bar.4.According to the strain test results of sleeve,the strain variation law was analyzed,and the restraint mechanism of sleeve with bolts was studied.Based on the thick-walled cylinder theory,the calculation models of the axial and circumferential stresses on the sleeve surface are derived,and the theoretical analysis is verified by the test results.The ABAQUS finite element software is used to simulate the specimen.The load-displacement curve is basically in accordance with the test results,and the strain distribution of steel bars and sleeves is also consistent with the test results.5.Based on the test results,the strain variation and bond stress distribution of reinforcing bars are analyzed,and the restraint effect of sleeve is quantified.The calculation method of bond strength between UHPC and reinforcing bars under steel tube restraint is obtained.A new formula for calculating the bearing capacity of bolt-UHPC grout splice sleeve is proposed.The calculation results are in good agreement with the test values.The optimum design method of bolt and the calculation of the length of inelastic section are studied.The design suggestions of bolt-UHPC grout splice sleeve are given,including anchorage length,bond strength between sleeve and grouting material.