Seismic Behavior Of Foundation Connections For Assembled Concrete-filled Thin-walled Steel Tubular Piers

The concrete-filled steel tubular piers have the characteristics of high bearing capacity,good deformation capacity and excellent seismic performance.They are suitable for urban bridge systems and have great application prospects.However,there are problems with the existing forms of concrete-filled steel tubular piers-to-foundation connections,including having a large burial pipe,which affects the distribution of the basic steel bar and having the complex structure of the foundation connection.Therefore,this paper puts forward new types of the concrete-filled steel tubular piers-to-foundation connections,in order to solve the defects in the construction of the existing concrete-filled steel tubular piers-to-foundation connections.(1)Based on the idea of anchor bars instead of steel pipe embedding in foundation,anchor bars welding or lapping with steel pipe.This paper puts forward 4 new types of the concrete-filled steel tubular piers-to-foundation connections,including anchor bars welding anchorage foundation connection,anchor bars lapping anchorage foundation connection,shear ring hoop-anchor bars lapping anchorage foundation connection,and PBL shear connector-longitudinal reinforcement anchorage foundation connection.(2)The finite element model is established by the ABAQUS software.The finite element results are in good agreement with the experimental data of the literatures.The validity of the finite element model is verified.Based on the models,the finite element parameter analysis is carried out.The design methods of the anchor bars are determined,and the design and processing of the specimens are completed.(3)The hysteretic tests of assembled concrete-filled steel tubular piers are carried out.The test parameters are the types of foundation connections and axial compression ratio.According to the test,the failure mode,hysteresis curve and skeleton curve of the specimens are obtained and analyzed.And the stress characteristics of the steel pipe and anchor bar are analyzed,and the bearing capacity,stiffness,ductility and energy consumption are analyzed.The analysis results show that the new-type concrete filled steel tubular foundation connections can replace the existing concrete filled steel tubular foundation connections.(4)The finite element analysis of assembled concrete-filled steel tubular piers is carried out.The finite element results are in good agreement with the test results,and the validity of the finite element model is verified.The stress analysis of the finite element model is carried out,and the stress level of each component under the peak load is obtained.Based on the finite element models,the finite element parameters are analyzed,including the concrete strength,axial compression ratio,steel tube wall thickness and the types of the foundation connections,and the design suggestions.According to the comparisons of different codes,the calculation methods of flexural capacity of specimens are determined.