Study On The Mechanical Properties Of Full-grouting Sleeve Connection With Defects After High Temperature

Prefabricated building is a green construction mode,which perfectly fits the concept of green development in China with its unique advantages of "four saving and one environmental protection".Compared with ordinary cast-in-place concrete structures,the nodal connection performance of prefabricated structures is more important.As one of the main connection methods of prefabricated structures,the full-grouting sleeve connection’s safety performance is obviously important for the safety of prefabricated structures.In the construction process of prefabricated buildings,defects in the sleeve are difficult to repair and will stay with the building throughout its operational phase,are often caused by insufficient manufacturing accuracy and improper operation in factories.If a fire occurs during the service life of the building,the effect of high temperature on the connection nodes of the assembled building will be tremendous.Therefore,research into the full-grouting sleeve connection with defects after high temperature is very necessary for the high quality development of prefabricated buildings.In this test,144 full-grouting sleeve connectors were subjected to unidirectional tensile test using temperature and defect type as variables to investigate the effects of temperature and grout defects on failure mode,bearing capacity,end displacement and bond strength of the specimens.At the same time,18 steel bars of the same batch were reserved and 18 test blocks of grouting materials of the same batch were made,treated and maintained under the same conditions as the specimens and subjected to material properties tests to investigate the effect of temperature on the properties of both steel bars and grouting materials.Based on the test,numerical and parametric analyses of the fully grouted sleeve specimens were carried out using ABAQUS software.The results show that :（1）the failure modes of connectors can be divided into the tensile failure of the steel bar and the bond-slip failure between the steel bar and the grouting material.（2）From room temperature to 300℃,the increase of temperature has little effect on the bearing capacity and end displacement of specimens,and the ultimate load and end displacement of specimens decrease to a smaller extent;From 400 ℃ to600℃,the ultimate load of the specimen showed an obvious decreasing trend with a larger decrease.（3）Defects accelerate the reduction of the ultimate bearing capacity of specimens after high temperature,with a maximum reduction of 19.2%.（4）With the same equivalent,the central defect has the greatest influence on the specimen.（5）When the length of the end defect is longer than 2.5d,the failure mode of the specimen changes from reinforcement pull-out damage outside the joint to reinforcement scraping and ploughing type pull-out damage.（6）The overall trend of the load-displacement curves is consistent with the finite element simulations.and the ultimate load values all differed by less than5%,indicating that the finite element model established in this paper and its related parameter settings were correct.（7）Parametric study shows that reducing the length of the middle defect can effectively reduce its bad influence on the specimen;When the defect length is 2d,the defect of beginning part has the greatest influence on the specimen,followed by the middle defect and the end defect.In this paper,through the analysis of test data and finite element simulation,the mechanical properties of the full-grouting sleeve specimen with defects after high temperature were studied and summarized,and the future research direction of the sleeve-grouting connection technology was prospected,which provided a theoretical basis for ensuring the safety of prefabricated buildings.Figure[86] table[17] reference[52]...