Experimental Study On Performance Of Large Diameter Grout-filled Splice Sleeve Joint With UHPC

The difficulties in the grouting technology at the present stage lie in the problem of steel bar positioning and grouting quality.The insufficient sealing results in leakage,grouting mouth is not sealed,the change of steel bar leads to cavity,the reflow after grouting,grouting material strength and contraction and other quality problems of grouting,all of which will lead to the formation of weak surface at the joint.At the same time,since the pressure grouting connection of the steel sleeve is a concealed project,it is difficult to inspect and repair the grouting quality.At present,there is no effective,intuitive and low-cost detection method on site.In order to reduce the risk of weak joints caused by the above problems,this paper proposes to by using the method of grouting grouting and cushioning,and then splicing components to reduce the possible defects caused by pressure grouting.Combined with the above method,it adopts ultra high performance concrete(UHPC)as grouting material.This method improves construction safety and ensures the quality of pouring.In view of the above,this paper mainly carries out research work from the following aspects:(1)The uniaxial tensile test of 57 large-diameter full grouting sleeves was used to study the feasibility of the connection method.The r esults show that the design specimens meet the specifications of strength and deformation requirements,and the gravity grouting connection mode was feasible.when the anchorage length is sufficient,the eccentricity of the steel bar has little effect on t he bearing capacity of the specimen.UHPC grouting material can further improve the bond strength and reduce the anchorage length of the steel bar.The sleeve meets the strength requirement and has high safety reserve.(2)Considering the restraint effect of the sleeve,the formula of the average bond strength of the ribbed steel bar and the grouting material is proposed,which is the design basis of the gravity grouting sleeve considering the restraint of the sleeve.Based on the average bond strength formula,the recommended critical anchorage length at the time of fracture failure of steel reinforcement is 5.5 d,which is 31.25% lower than the 8d required by JGJ355-2015,and s superior to most literature test results.(3)Through the ABAQUS numerical simulation,understand the mechanical properties of the sleeve,grouting material and reinforcement during the stretching process;The design parameters of gravity grouting sleeve are preliminarily determined.The sleeve length can take 2 times the anchorage length of the steel bar and then the surplus is 3-5cm.The wall thickness should not be less than 5mm,and the diameter-thickness ratio(c/d)should not be less than 0.45;(4)Bending test was carried out on the cast-in-place column and sleeve connection assembled column to explore the operability of gravity grouting sleeve connection technology in actual construction,as well as the failure mode and mechanical performance of prefabricated assembled members under horizontal action.The test results show that all the three specimens are ductile failure and the mechanical properties are almost the same.when the tensile steel is yielded,the sleeve strain is not yielded.The crack resistance is sleeve segment>seam segment>rebar segment.In the loading process,the number of cracks in the sleeve section of the prefabricated test piece is small,the crack width is small,and the spacing is large.The crack width of the steel section is larger and the crack spacing is smaller than that of the cast-in-place test piece;(5)Fitting the finite element against the bending specimen to determine the design control section.