Research On The Mechanical Behavior Of Steel Tube Confined Reinforced Concrete Double-column Piers

Reinforced concrete(RC)pier has been widely used in bridges,but it has some disadvantages such as heavy structural weight and low ductility.Although the structural performance of the concrete filled steel tube(CFST)pier is superior,it is challenging to connect CFST piers with the foundations and the cap beams,which was the key problem hindering its wide application.Based on the above problems,this paper presents two types of double column steel tube confined reinforced concrete bridge pier and investigates their mechanical performance,which includes the following parts:(1)An innovative composite bridge pier referred to as double-column solid-web dumbbell steel tube confined reinforced concrete(DSTCRC)pier was proposed in this paper,and the seismic performance of 7 DSTCRC specimens and 1 double-column solidweb dumbbell shaped RC specimen was experimentally studied.The test parameters included the width and height of the web,shear span-depth ratio and axial load ratio.Based on the test results,the failure mode,load-displacement curve and the stress development of the dumbbell steel tubes were discussed,and the bearing capacity,ductility,energy dissipation capacity,stiffness and strength degradation performance of the specimens were analyzed.The results show that the restraint from dumbbell shaped steel tube changes the shear failure of the double-column solid-web dumbbell shaped RC specimen into the bending failure of the DSTCRC specimen;the failure mode of the DSTCRC specimen is primarily affected by the shear span-depth ratio;the steel web and the concrete web contribute to the better energy consumption capacity so that the DSTCRC specimen can exhibit good seismic performance.(2)A refined finite element(FE)model of DSTCRC bridge pier was established,considering geometric nonlinearity,material nonlinearity,and the contact between steel tubes and concrete.The predictions of the FE model were in good agreement with the test results,which verified the accuracy of FE model.The effect of concrete strength,dumbbell steel tube strength and thickness,axial load ratio,web size and shear span-depth ratio on the mechanical behavior of DSTCRC piers were assessed in terms of the force mechanism.The results show that the axial load ratio affected positively on bearing capacity when the axial load ratio is less than 0.5;the shear span-depth ratio determined the failure mode of DSTCRC pier and was an important factor affecting the bearing capacity;the size of steel web affected the formation and distribution of the tension band.(3)According to the test and FE model results,it can be concluded that the seismic performance of the DSTCRC pier was influenced by the internal reinforced concrete section bending capacity,diagonal tension field of steel web and the shear force of concrete web.Based on the calculation method of eccentric compression and the theory of superposition,a formula was proposed to calculate the DSTCRC bearing capacity,which was in good agreement with the test results and FE.Based on the displacement calculation,the stiffness analysis method of the DSTCRC pier was proposed,which was in good contrast with the test results.(4)An innovative type of steel tube confined reinforced concrete(STCRC)doublecolumn bridge bent pier was presented,which was a double-column lattice bridge pier.An experimental investigation into the seismic performance of four STCRC doublecolumns piers was carried out.The test parameters included the disconnection mode of steel tube(disconnected at the binding steel plates or not)and the axial load ratio.The test outputs,including the failure mode,load-displacement curves and the stress development of bent piers were reported and analyzed,and the bearing capacity,ductility,energy dissipation capacity,stiffness and strength degradation of the test specimens were compared.The test results show that the disconnection mode controlled the position of the plastic hinge of STCRC double-column piers,and the increase of axial load ratio was beneficial to the bearing capacity.(5)A FE model of STCRC double-column piers was established.The influence of binding steel plate strength,circular steel tube thickness and strength,concrete strength,thickness and height,axial load ratio and longitudinal reinforcement ratio on the mechanical behavior of STCRC double-column piers were evaluated from the theoretical mechanism.The results show that within the range of parametric analysis,the axial load ratio had a favorable influence on the bearing capacity of STCRC double-column piers;the disconnection mode directly affected the location and development mechanism of the plastic hinge,which was an important factor affecting the failure modes of the piers,while the binding steel plate has a slight influence on the bearing capacity of the piers.(6)Based on the test and FE results,it is concluded that the mechanical behavior of the STCRC double-column piers was affected by the disconnection mode and the binding steel plate strength and thickness.The bearing capacity calculation formula for predicting the STCRC double-column pier with clear theoretical model was presented,and the stiffness analysis method of the STCRC double columns pier was proposed.Two types of construction measures and application range of double column steel tube confined reinforced concrete bridge pier were proposed.