Long-term Behavior Of Curved Steel-Concrete Composite Box-Girder Bridges

Curved steel-concrete composite box girder bridges,in which steel beams and concrete slabs are combined to bear forces collaboratively by shear connectors,can make full use of material properties.This type of bridge structure has advantages for its light weight,high torsional rigidity,remarkable spanning capacity,and rapid construction.The complex mechanical behaviors with bending-torsion coupling of curved steel-concrete composite box girder bridges are different from the mechanical behaviors of reinforced concrete straight bridges.The time-dependent forcing behaviors of the bridge are remarkably affected by its evolutionary characteristics that change with respect to time.This thesis has implemented relatively systematic researches on the mechanical behaviors with bending-torsion coupling and long-term mechanical properties of curved steel-concrete composite box girder bridges.The research results have been shown below.(1)Long-term loading tests have been implemented on five curved composite box girders to explore the long-term mechanical properties of curved composite box girders,in which the development patterns of deflections,torsional angles,interfacial slippages,and strain distributions on cross-sections are measured over time.The influence of central angles,stud layouts,loading methods,and boundary conditions on bridges’ long-term mechanical behaviors are analyzed.Material property tests are carried out under the same environmental condition as the structural specimens,and the variation curves of shrinkage strain and creep function of concrete versus time are measured.The time-dependent variation mechanisms of inner force and deformation of curved composite box girders are revealed by those tests above,which can be used as references for studies on theoretical and numerical models of curved composite box girders.(2)To illustrate the complex mechanical behaviors with bending-torsion coupling of curved composite box girders,a one-dimensional theoretical model considering the influence of constrained torsion,distortion,shear-lag,and interfacial bidirectional slippage of curved composite box girder is proposed based on Vlasov beam theoretical model.The correctness and adaptability of the model have been verified according to the long-term loading tests on curved composite box girders.Deflections,torsional angles,distortional angles,interfacial slippage,and cross-sectional stress distributions are adopted as key parameters,based on that the mechanical behaviors and parameter sensitivity of curved composite box girders are analyzed.Some corresponding suggestions for value ranges of key parameters including central angle,interfacial shear-connection stiffness,and the number of diaphragms of the superstructure of curved composite box girders are proposed.(3)A one-dimensional theoretical model considering the influence of constrained torsion,distortion,shear-lag,interfacial bidirectional slippage,and time-varying effect of curved composite box girder is proposed based on the proposed one-dimensional theoretical model above in which the constitutive relationship for concrete shrinkage strain and creep function with respect to time have been introduced.Based on this model,a two-node,26-DOF,finite beam element for a curved composite box girder considering complex spatial mechanical behaviors and the time-varying effect is proposed,in calculations of which the finite element method is adopted in the space domain,and the stepwise calculation method based on the Kelvin rheological model without storage of stress and strain history is adopted in the time domain.The correctness and adaptability of the model have been verified according to the long-term loading tests on curved composite box girders.The time-variation mechanisms of mechanical behaviors of curved composite box girders are studied based on the model.Some corresponding suggestions for value ranges of key parameters at the conditions of short-term and long-term design of the superstructure are proposed.(4)After unloading in the long-term loading tests,the curved composite box girder specimens are loaded until destructions occur.The central angle,shear-connection degree,and positive/ negative moment loading state are chosen as parameters for those tests,in which the variation of deflections,torsional angles,and cross-sectional strain distributions with respect to the increase of loads are measured.Moreover,elaborate finite element models corresponding to the curved composite box girder specimens are established accordingly.The correctness and applicability of the elaborate finite element models are verified through a comparison of the results from tests and those from model calculations,which can be provided as references for numerical analyses on the curved composite box girder bridges afterward.(5)An ABAQUS finite element model for a curved steel-composite box girder bridge is established using Python parameterized modeling method,based on which a calculation for the lateral deviation behavior of curved composite box girders is carried out.Various loads are applied based on the exact situation to closely simulate the deviation behavior of curved composite box girders.Analyses on influence factors for deviation behavior of curved composite box girders are implemented using the finite element model.Some treatment measures,which have been verified by numerical models,are proposed based on these influence factors analyses.(6)A whole process simulation on the overturning of an overloaded and unbalanced loaded curved steel-concrete composite continuous box girder bridge with single-column piers is carried out in ABAQUS,a large general finite element software.The explicit dynamic finite element method is adopted in the analyses of transient behaviors of the structure during collapse process.Responses and failure characteristics of bridge components are described.Pieces of Advice for measurements to prevent girder overturning are proposed.