Research On The Bending Performance Of The Joint Of Grouting Bellows And Cast-in-place UHPC Tenon Of Precast NSC Pier

The prefabricated bridge structure has the advantages of simple structure,clear stress,low cost,easy erection,etc.the Federal Highway Administration of the United States and the transportation departments of each state are actively promoting the rapid bridge construction technology,and the prefabrication and assembly of the substructure in China is also an important application of the prefabricated bridge,such as the rapid transformation of Hangzhou Bay,Hong Kong Zhuhai Macao,Changsha Xiangfu Road,etc.However,there are few researches on prefabricated bridge structures in China,and they are mainly concentrated on the superstructure of the bridge.The prefabricated components of the substructure still need to be studied.Because the connection technology of prefabricated pier column joint has the advantages of fast construction,reliable performance and large construction tolerance error,so the proper connection design is the key to the success of the prefabricated structure,and its development also depends on the Application of new materials and development of new structures.By using UHPC at the joint of Precast Pier,the cracking of the specimen can be delayed and the rotation ability of the plastic hinge can be improved.Therefore,this paper proposes a combined connection method of grouting bellows and cast-in-place UHPC tenon for Precast Pier Column,which improves the integrity of the joint through UHPC tenon structure,strengthens the connection at the joint,and inserts the reinforcement protruding from the pier body of the upper precast column into the grouting embedded in the lower precast column In the metal bellows,the UHPC is poured through the top grouting channel,and finally the UHPC tenon structure is formed in the cavity at the joint.The advantage of this structure is that the bellows connection around can ensure the structural performance is reliable,and it can be used for positioning installation during assembly,which not only accelerates the assembly speed of prefabricated columns,but also solves the problem of weak connection of prefabricated pier segments.In this paper,the compression bending performance and seismic performance of the new type of grouted bellows + cast-in-place UHPC mortise joint column are studied by experiment and theory.Finally,the stress characteristics of different joint combinations are analyzed by the finite element analysis software ABAQUS.The results show that:(1)This paper explores the influence of the grouted corrugated pipe + UHPC tenon new type of combined column on the mechanical performance of the joint under different axial compression ratio,and compares it with the integral concrete column.Under the pure bending or bending compression load,the failure mode of the joint column is that the concrete in the compression area is crushed,the joint is obviously open,the connecting reinforcement in the tension area is yielding,and there is a small amount of slip between the joint connecting reinforcement and the bellows,but it is not pulled out.Compared with the whole column,the center axis moves up and the area of the concrete compression area decreases continuously due to the bond slip between the stressed steel bar and the grouting material at the assembly joint.Under the high initial axial pressure,the concrete will collapse early and the ultimate bearing capacity will be reduced.However,for the assembled columns with UHPC tenon structure,due to the super strong mechanical properties of UHPC,the cracking of concrete can be delayed,and the bearing capacity can continue after the collapse of ordinary concrete,which improves the rotation capacity and ductility of the assembled columns,and the deformation resistance of the joint columns is better than that of the intact RC columns.(2)The quasi-static test of low cycle cyclic loading is carried out.By analyzing the test failure form of the specimen,the hysteretic curve,skeleton curve,residual deformation caused by cyclic loading,energy dissipation capacity and rigidity of the specimen are studied.In the cyclic loading under the constant axial force,the specimens show stable hysteretic behavior.The grouted bellows + UHPC tenon joint pier structure has better deformation capacity.The structure has better ductility and energy consumption characteristics.The displacement ductility coefficient is as high as 5,which can meet the overall seismic performance requirements of the structure.(3)Through the finite element analysis of the stress characteristics of the new composite joint proposed in this paper,and compared with the test results,the control group of the traditional grouted bellows connection column and grouted bellows +UHPC mortise planting reinforced column is added,and further research on the bearing capacity and ductility performance of the assembled column by the parameters such as the proportion of UHPC section and the ratio of planting reinforced.In the finite element simulation study of the mechanical properties and ductility of the joint combination of the prefabricated column,it is found that the joint of the traditional single grouting bellows is easy to open,the stress of the reinforcement is concentrated near the joint,and the bearing capacity and ductility are very poor;the grouting bellows + UHPC tenon joint column,thanks to the UHPC ultra-high mechanical properties,improves the stress concentration of the reinforcement at the joint,and improves the test The bearing capacity and ductility of the parts are improved by planting steel bars in the grouted bellows + UHPC mortise joint column,and the overall bending strength is strengthened.The bearing capacity is larger than that of the complete cast-in-place column,but the ductility will be slightly reduced,and the influence of the proportion of UHPC section and the ratio of planting steel bars on the bearing capacity and ductility of the assembled column is further analyzed.