Anti-punching Shear Performance Of Embedded Concrete-filled Steel Tube Column Base With Headed Studs

Concrete-filled steel tubes have been widely used in engineering structures due to the high bearing capacity,high stiffness,and good economic benefits.Column base joints are important component connecting the column and foundation.Whether its design is reasonable has a direct impact on structural safety,construction quality and project cost.Embedded column bases show excellent load resistance and high stiffness,and are commonly used in concrete-filled steel tube structures.In terms of this column base,stud connectors are often designed on the embedded section of the pipe wall in order to strengthen the connection between the column and foundation.However,the contribution of the stud connectors on the punching resistance is ignored in current design codes,resulting in the large embedded depth and construction difficulties of large-diameter columns.Therefore,it is significant to consider the contribution of bonding and studs in the punching process.This thesis conducted the experimental investigation and FE analysis on embedded concretefilled steel tube column base joints,and the main contents are listed as follows:(1)The push-out tests of 2 concrete-filled steel tubes were carried out to determine the bonding force between the steel tube and the core concrete.Then punching tests were conducted on 10 joints to study the influence of the studs,and the influence of the diameter,location,and distribution of the studs on joints were investigated.The punching resistance,deformation development and failure mode of joints were obtained based on the tests.The results show that the studs can significantly improve the bearing capacity of the joints.The contribution of the studs was improved with increase of the distance between the studs and the bottom of the joint.Therefore,it is recommended to consider the contribution of the studs to the punching capacity in the design.(2)The finite element model of the column base joint was established using ABAQUS software,and the interaction between studs and concrete was considered in the model.The FE model was validated by the experimental results.It is shown that the FE analysis results were in good agreement with the test results,and the FE model could well predict the bearing capacity,deformation development and failure mode of the joint.Then the typical joint was analyzed and the vertical force transmission mechanism was discussed.(3)Based on the validated FE model,the parametric analysis was performed,and the influence of the length,diameter,number,and position of the studs on the punching resistance of the embedded column base joints was studied.The key parameters were determined,and the calculation formula of punching resistance was put forward.According to the force transmission mechanisim of the studs under the vertical load,it is recommended to consider the contribution of the studs which are located in the range of upper 1/3 embedded depth.