Study On Mechanical Properties Of Semi-grouting Sleeve With Defects

To some extent,prefabricated structure improves building quality and construction efficiency,which is an inevitable trend in the development of construction industry.In prefabricated concrete structures,the connection between prefabricated members is mainly to connect steel bars by grouting sleeves,and the connection performance of grouting sleeves determines the reliability of the whole structure.However,in actual construction,foreign matters(cement mortar and floating rust)may be attached to the surface of steel bars,which results in uncompact grouting inside the sleeve and degrading the performance of connectors.Therefore,this paper studies the mechanical properties of semi-grouting sleeve connectors with defects,and discusses the stress transfer mechanism of connectors.This paper is one of the research contents of "Research on Mechanical Properties of Fabricated Concrete Structure Reinforced Full-grouting Sleeve Connection after Fire" of Anhui Natural Science Foundation Project(1908085ME173).The main contents are as follows:(1)Through the investigation of practical projects,the grouting defects of semi-grouting sleeve connectors were summarized,and 10 groups of defect specimens(end defects,middle defects,uniform defects and horizontal defects)and1 group of standard specimens were manufactured.(2)The uniaxial tensile test of the designed specimen was carried out,and its failure characteristics and mechanical properties were analyzed.(3)Through ANSYS software,the semi-grouting sleeve connector was numerically simulated and compared with the test results.The results show that:(1)The failure modes of the specimen are pull-out failure and tensile failure of the steel bar,both of which occur after the steel bar yields.(2)When the connector is in the elastic stage,the displacement of the anchorage end of the steel bar is small.When the connector is in the strengthening stage,the displacement of the anchorage end of the steel bar is larger.(3)The central defect and uniformly distributed two-stage defect have the greatest influence on the ultimate bearing capacity of the specimen.The ultimate bearing capacity of ZB-2.5d specimen is 84.3 k N,which is 10% lower than the standard group.The ultimate bearing capacity of JB-2.5d-2 specimen is 81.5 k N,which is 12.8%lower than that of the standard group.(4)When the defect is at the end of the steel bar,the length of the defect is greater than or equal to 2.5 d,and the steel bar pull-out failure occurs in the specimen.When the defect length is less than 2.5 d,the tensile fracture failure of steel bar occurs in the specimen.(5)The average bond strength of BM specimens is ?=17.7MPa,which accounts for 72.8% of the ultimate bond strength of end defect specimens.Therefore,it indicates that the grouting material has a certain safety reserve.(6)When the connector is in the elastic stage,the strain of the sleeve and the steel bar increases linearly,and increases with the increase of the load.(7)In the anchorage section: the stress of steel bar gradually increases from the threaded end to the anchorage end,while the stress of sleeve gradually decreases from the threaded end to the anchorage end.When the steel bar yields,the stress of the sleeve is very small,and its maximum value is 184 MPa.(8)The semi-grouting sleeve connector transmits bonding stress to each other through the steel bar,grouting material and sleeve,and the transmission path is steel bar → grouting material → sleeve → threaded end steel bar.The stress transfer of the middle defect specimen and the end defect specimen is blocked at the defect,which leads to the small stress change of the steel bar and sleeve in the defect area.(9)The failure mode,stress distribution law and load-displacement curve of the simulation results are basically consistent with the test results,which shows the rationality of the finite element model in this paper.Through design test,theoretical analysis and numerical simulation,the semi-grouting sleeve connector with defects is studied,which provides technical guidance for the construction of prefabricated component joints on site and provides reference value for the development of prefabricated buildings.Figure [114] table [12] reference [58]...