Study On Torsion Effect In Concrete Filled Steel Tube Piers Of Curved Girder Briges

In curved steel-concrete composite girder bridge system, the torsion effect in piershas significant influences on the mechanical behavior of structures subjected tohorizontal earthquake load. Therefore, the nonlinear torsion behavior and numericalmodels of concrete filled steel tube columns were comprehensive studied, includingexperimental study, theoretical model, refined finite element model, user-definedsubroutine development and structural system application. The main research works andresults are as follows:(1) Based on the B31fiber beam-column element and user-defined subroutineUMAT in the general finite element program ABAQUS, the steel-concrete compositefiber beam-column element without consideration of the nonlinear torsion effect wasdeveloped and a serious of uniaxial stress-strain hysteretical relations of steel andconcrete material constitutive models were introduced. When applied for analyzing theelastic-plastic mechanical behavior of steel-concrete composite beams and columns, thehigh modeling efficiency and solution precision could be obtained. Compared with theconvention finite element modeling method, the obvious advantages of thesteel-concrete composite fiber beam-column model could be observed when analyzingthe structural members subjected to combined axial force and bending moment.(2) The quasi-static test on fourteen concrete filled steel tube columns with varioussection types and load modes was carried out. The torsion moment versus rotation anglehysteretic relations were obtained, and the strain state and developing trend of steeltubes were also observed during the entire loading history. Then the torsion mechanismof concrete filled steel tube columns was preliminary studied, providing a serious of testresults for the subsequent research work in this dissertation.(3) The refined “shell-solid” finite element model for concrete filled steel tubecolumns subjected to torsion was established, and the theoretical model calledlaminated tubes model was also proposed. The suitable material constitutive modelswere chosen for simulating the mechanical behavior of concrete filled steel tubecolumns subjected to pure torsion, compression-torsion, bending-torsion andcompression-bending-torsion. The torsion mechanism of concrete filled steel tubecolumns were further studied in order to provide the research basis for establishing the fiber beam-column model considering torsion effect.(4) The shear strain distribution law on the section of the fiber beam-columnelement was assumed based on the refined “shell-solid” finite element model, and theplane section assumption of the normal strain was also introduced. Based on thelaminated tubes model and two-dimensional material constitutive models of steel andconcrete, the fiber beam-column model for concrete filled steel tubes consideringtorsion effect was proposed. Using the FORTRAN language, the proposed fiberbeam-column element considering torsion effect was developed in the user-definedsubroutine UEL in the general finite element program ABAQUS. The good agreementbetween the test results and predicted results could be observed, and the nonlineartorsion behavior of concrete filled steel tube columns was effectively calculated by theproposed fiber beam-column model considering torsion effect. Furthermore, the highsolution efficiency and precision could be achieved.(5) Applying the proposed fiber beam-column model considering torsion effect inthe curved steel-concrete composite girder bridge subjected to earthquake load, theeffectiveness of the proposed model was investigated. The results showed that the highmodeling efficiency and solution precision could be obtained for analyzing thetime-history response of curved steel-concrete composite girder bridges under thefrequent and rare earthquake load. Then using the fiber beam-column model consideringtorsion effect, the key influencing factors on the torsion effect of curved steel-concretecomposite girder bridges were preliminary discussed.The proposed fiber beam-column model considering torsion effect for concretefilled steel tube columns and the developed subroutine in this dissertation have provideda powerful research tool for predicting the seismic behavior and mechanism of curvedsteel-concrete composite girder bridge system.This dissertation is sponsored by National Natural Science Foundation of ChinaProgram (51138007) and Ph.D Candidate “Young Scholar of Distinction” of ChinaEducational Administry.