Research On Seismic And Resiliency Performance Of Precast Segmented Self-centring Concrete Filled Steel Tube Bridge Column

In the transportation infrastructure network,the bridge structure is a key component of the urban infrastructure,and as a lifeline project,the seismic and the postearthquake recovery performance of the bridge are very important.The segmented selfcentering column combines the segmental prefabrication technology and the rocking self-centering to form a column form with low damage,low residual displacement,selfcentering,high construction quality,low construction period,and environmentally friendly bridge columns.This paper proposes a segmented self-centering concretefilled steel tube(PSCFST)column that takes into account energy dissipation,selfcentering,recoverability after an earthquake.The pseudo-static test and finite element analysis of its seismic performance are carried out,the post-earthquake restorability was tested and the single-span bridge underwater shaking table test using PSCFST columns was completed.The main research work and innovation results are as follows:(1)A pseudo-static test study on the seismic performance of the new PSCFST bridge column was carried out.Proposed PSCFST columns with internal and external energy dissipation steel bars,different assembly forms,and different steel strand layout positions.Then carried out the pseudo-static test of 4 PSCFST specimens and 1 castin-place reinforced concrete(RC)column comparison specimen.The seismic performance of the PSCFST and RC column is compared.The results show that the PSCFST column has no obvious damage after the test,PSCFST columns have good self-centering ability under the action of post-tensioned prestressed steel strands and gravity.The average residual displacement of the PSCFST columns is only 1/19.1 that of the RC comparison specimens.The proposed hybrid assembled column and the vertical assembled column show consistent seismic performance and self-centering performance.The residual displacement and cumulative energy dissipation of the specimens whose prestressed steel strand arranged around the specimen are less than those of the prestressed steel strand arranged in the center.The bearing capacity of the PSCFST column specimen whose prestressed steel strand arranged around the specimen is 1.49 times the average bearing capacity of the other three PSCFST specimens.(2)The plastic hinge analysis and hysteretic analysis models suitable for PSCFST columns are proposed.Considering the position and quantity of the nominal plastic hinges of PSCFST columns,the analysis process of single and double plastic hinges under the horizontal reciprocating load of PSCFST columns is given,and the hysteretic model is verified by pseudo-static tests.The results show that the hysteretic model is in good agreement with the experimental results;the hysteretic model based on the double plastic hinge model is more accurate,indicating that the double plastic hinge model is more suitable for simulating the mechanical behavior of PSCFST columns.(3)A finite element analysis model of PSCFST bridge columns with internal energy dissipation steel bars is established.Based on the ABAQUS finite element software,the PSCFST bridge column with internal energy-dissipating steel bars was analyzed,and a finite element model that can accurately simulate the opening and closing,stiffness,bearing capacity,and energy dissipation characteristics of the segments were obtained.Then the influence of main parameters on the seismic performance and recoverability of PSCFST bridge columns is analyzed.The results show that the vertical axial compression ratio has a greater impact on the bearing capacity of PSCFST columns;increasing the vertical axial compression ratio and the initial prestress level is not good for the energy dissipation of PSCFST columns,but it is beneficial to the self-centering ability of the column;excessive wall thickness of steel tube is detrimental to energy dissipation and self-centering ability.(4)The repair method of damaged PSCFST column after an earthquake is proposed.The PSCFST column specimens damaged after the earthquake were repaired.The seismic performance and recoverability of the specimens after the restoration were studied through pseudo-static tests,and compared with the performance of the RC specimen repaired after the earthquake.The results show that the strength of the PSCFST specimen after the repair is 99.99% of the original specimen,the initial stiffness is 125.81% of the original specimen,and there is no visible damage after the pseudo-static test of the restored specimen,and the residual displacement ratio is less than 1%.The strength of the RC column specimen repaired by the hybrid confinement method is 113.3% of the original specimen,and the initial stiffness is less than the original specimen.Compared with the repair of the earthquake-damaged RC column,the PSCFST column repairment requires a shorter time,simpler steps and better repair effect.(5)A single-span bridge model underwater shaking table test using PSCFST columns was carried out.The seismic response of a single-span bridge structure using PSCFST columns is analyzed to verify the feasibility of applying PSCFST columns to single-span bridges.The underwater shaking table test of a 1/4 scale model of singlespan bridges using PSCFST columns in four water depths has been completed to obtain the influence of dynamic rocking characteristics and water-structure interaction on the seismic performance and recoverability of the PSCFST column bridge.The results show that the bridge using PSCFST columns has good seismic performance,there is no obvious damage after the earthquake,and the residual displacement is almost zero;the displacement and acceleration response of the bridge model under different water depths indicate that the presence of water can reduce the acceleration response of the bridge model,but it has little effect on the displacement response of the bridge model.(6)The seismic design process of bridges using PSCFST columns is proposed.Based on the current bridge specifications in China and the introduction of the residual displacement angle limit of the Japanese code,the two-level fortification objectives and two-stage design ideas suitable for PSCFST column bridges are proposed,and the twostage design process and method are given.