Seismic Behavior Of Embedded Concrete-filled Steel Tubular Pier-to-Reinforced Concrete Beam Connections

In recent years,along with the developing of long-span bridges,large and super-large concrete-filled steel tubular(CFST)members are regarded as bridge piers.The CFST pier-to-foundation connections and CFST pier-to-cap beam connections are the key members bearing force and displacement.On the one hand,the construction efficiency of the bridges are controlled by the construction of the connections;on the other hand,the seismic behavior of the whole bridge are constrained by the connections.This thesis has done a systemic study on the embedded CFST pier-to-beam connections,the main research contents are as follows:(1)Fifteen large-scale CFST column-to-RC beam connections were designed and tested under the combined axial loading and cyclic lateral loading.The design parameters were construction methods,connections types,steel tube materials,the embedded length of CFST column,the diameter over thickness ratio of the tube.The observation parameters were the damage status,damage models,deformation ductility,and the energy dissipating capacity.(2)Based on the mechanism analysis of the infill concrete under cyclic loading,an approach called “pre-cracking surface” was used to simulate the crack opening and closure of the infill concrete.The progressive damage evolution and ductile damage criteria were used to simulate the local buckling and tearing of the steel tube.The proposed finite element analysis models via ABAQUS software were verified by the experimental results.(3)The parameters which influence the seismic behavior of the whole connection were figured out by studies on the load-transferring mechanism of the embedded connection.Furthermore,the effective flexure stiffness of the CFST columns and the structure stiffness of the whole connections were estimated base on the parametric studies.(4)The diameters of testing specimens were 508 mm,609.6 mm,762 mm respectively,which were treated as large section members,having size effect.The loading bearing capacity and design provisions in the standards cannot been utilizeddirectly for the large section members.Based on the experimental results and numerical studies,the design requirements for the resistance of pullout failure and punching shear failure,the length of the plastic hinge,and the width of the shear ring were figured out.(5)A simplified finite element analysis model was propose based on the previous studies including effective flexure stiffness,structural stiffness,size effect.This simplified finite element model advantaged in easy modeling,fast calculating and reasonable accuracy.Furthermore,the seismic responses of the embedded CFST pier-to-beam connection under Near-Fault loading were studied.This embedded CFST pier-to-beam connection performed good seismic behavior,and can be used in accelerated bridge construction,as well can be recovered rapidly after earthquake.