Study On Transfer Mechanism Of Inner Studs And Impact On Mechanical Behavior Of Concrete-Filled Steel Tubular Truss Arch Ribs

As a composite structure,the superiority of Concrete-Filled Steel Tube(CFST)is that steel tube and core concrete are combined to form integral component,thus improving bearing capacity.CFST has been widely used in practical engineering.However,because of temperature difference,shrinkage of core concrete and construction quality,different degrees of debonding have been found at interface between steel tube and core concrete,which affects synergistic effect between steel tube and core concrete.Especially for CFST truss arch,debonding cause that the internal force of web members cannot be transferred to core concrete,which affects its mechanical behavior.Through welding studs(inner studs)in the inner wall of chord steel tube of joint,it can be solved that force-transmission problem caused by debonding.Hence,they are studied that transfer mechanism of inner studs and impact on mechanical behavior of CFST truss arch by theoretical calculation,test and finite element analysis.The main contents and conclusions are as follows:(1)The causes and preventive measures for debonding of CFST are summarized and analyzed,and the effect of debonding on CFST single-tube arch rib and truss arch rib is discussed.The results show that debonding of CFST cannot be avoided,and the temperature difference between steel tube and core concrete and shrinkage of core concrete are the main causes of debonding,but separate axial compression will not nearly cause debonding between steel tube and core concrete.The effect of debonding on CFST truss arch rib is larger than single-tube arch rib.(2)It is carried out that experimental study of CFST joints with bonding and debonding,with inner studs and without inner studs.The results show that when the interface between steel tube and core concrete is debonding,internal force of web members cannot be transferred to core concrete smoothly,and debonding have great influence on force transmission near joint.Through welding inner studs,internal force of web members can be transferred to core concrete no matter whether main steel tube is debonding or not,and inner studs have great influence on force transmission near joint.The force-transmission effect of inner studs is better than that of total bonding.The diameter ratio between branch tube and main tube does not almost effect on the arrangement range of inner studs.(3)Transfer mechanism of inner studs is analyzed.It is concluded that the main force areas of main steel tube,inner studs and core concrete are concentrated on the range of 200mm above the center of joint and 600mm below the center of joint in the axial direction of main steel tube,and the force is larger than other areas at the intersecting area between main steel tube and branch tube.In the circular direction of main steel tube,the main force areas are the range of-60°?60°of joint.(4)The setting method of inner studs of CFST joint is discussed.It is suggested that inner studs are arranged at the range of-600°?60° of joint,and they should be arranged evenly.Inner studs cannot be arranged outside the range of-60°?60° of joint.In axial direction of main steel tube,inner studs are arranged at the range of diameter of web members above the center of joint and 2 times diameter of web members below the center of joint,and inner studs should be set in intersection between chord and web member.(5)Taking Sichuan Hejiang Yangtze River Highway Bridge as background,finite element models are established to consider debonding and inner studs of CFST.Effects of different debonding degree and inner studs on mechanical properties are analyzed.The results show that debonding length of arch rib has great influence on internal force of steel tube and core concrete,and has a little effect on total axial force of upper and lower chords.With increasing of debonding length,the total bending moment of upper and lower chords is more uneven.Debonding length has great influence on the deformation and ultimate bearing capacity of CFST truss arch.Under half-span uniform load,when debonding position is located at quarter point of half arch bearing load and arch crown,debonding has great influence on deformation and ultimate bearing capacity of CFST truss arch.Through setting inner studs at joint located at range of debonding,stiffness and ultimate bearing capacity of truss arch are improved by comparing with total bonding truss arch,and the more the number of joints with inner studs,the greater the degree of improvement.