| The research group of Harbin Institute of Technology has developed the new-style connection of " the lap joint of grouting sleeve for reinforcement ".In view of the problems that the lap length of large diameter reinforced bars is too long and the stirrup ratio of spiral stirrups cannot increase indefinitely,a new type of reinforced lap joint technology-grouting sleeve reinforced lap joint technology is put forward.This connection method not only gives full play to the advantages of steel bar lap,but also reduces the length of steel bar connection,and replaces the original spiral stirrup constraint with sleeve constraint,which makes the its connection tighter,and impedes splitting failure.In order to study the internal mechanism of this new-style connection mode,uniaxial tensile test,mechanical analysis and finite element simulation were carried out.In this test,five specimens were designed with the overlapping lengths of reinforcement,diameters of steel bars and outer diameters of sleeve as the main parameters,and the influence of different parameters on the performance of specimens was further studyed.In order to obtain the surface strain of steel bars and calculate the distribution of bonding stress between grout and steel bar,the reinforcing steel bar is grooved with a width and depth of 5cm,and then a welding-free strain gauge is stuck in the groove.In order to understand the strain distribution on the sleeve surface,the specimens were subjected to uniaxial tensile test on a 100-ton experimental machine with circumferential and longitudinal strain gauges pasted on the sleeve surface,The test results showed that steel bars were pulled off when the failure of the specimens happened,and all the performance indexes satisfied the requirements of Grade I joints in ‘ Technical Specification for Mechanical Connection of Steel Bar ’,and the load-displacement curves of the specimens resembled those of single steel bar.The experimental results showed that the overall circumferential strain at the end of the sleeve is larger than that at the middle of the sleeve.Circumferential strain is always positive in the sleeve area closest to the reinforcement,that is,the hoop stress in the sleeve area closest to the reinforcement is always tensile stress,while the hoop strain in the sleeve position farthest from the reinforcement is smaller.Circumferential strain of the sleeve is positive or negative,that is,the tension part of the sleeve is compressed.Based on the reinforced micro-element extracted and the equilibrium formula established,the calculation expression of bonding stress is derived,and the bonding stress distribution curve of reinforced lap joint under sleeve constraint is drawn.Based on the research of the research group,the mechanical analysis was carried out,and the spiral stirrup constraint was replaced by the sleeve constraint,and the overlapping connection mechanism of reinforcement under the sleeve constraint was studied.Through ABAQUS finite element software simulation,the stress distribution nephogram of grouting material section was obtained,and the position of crack grout surface was determined.And the calculation model of reinforced overlapping connection of grouting sleeve is established after the grout is cut along the possible cracking plane,The stress of the model is analyzed,the corresponding equilibrium formula is listed,and the expressions of reinforced overlapping connection length and sleeve wall thickness are derived.Based on the research of the research group,the mechanical analysis was carried out,the spiral stirrup restraint was replaced with the sleeve restraint,and the mechanism of the steel bar lap connection under restraint was studied.Through ABAQUS finite element software simulation,the cross-sectional stress distribution cloud map of the grouting material is obtained,and the location of the cracking surface of the grouting material is determined.The grouting material was cut along the possible cracking surface,the calculation model of the grouting sleeve steel bar lap connection was established,the force of the model was analyzed,the corresponding balance formula was listed,and the rebar lap connection length and the sleeve wall were derived Thick expression. |
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