Study On Transverse Behavior And Design Method Of Steel-concrete Composite Box Girder Bridges

With the increase of the width of the composite box girder and the popularization of the box girder section,the transverse behavior of the girder becomes more prominent.Improving the related theories and design methods is of great significance for promoting the development of the composite box girder bridges.According to the life cycle of the bridge,this dissertation investigates the transverse behavior such as distortion and transverse flexural of the composite box girder bridges in both construction and service stages.The main results and achievements of the research are presented as follows:(1)The torsion and distortion theories of the open-section steel box girder with lateral bracings and cross-frames are improved.Combining theoretical and numerical analyses,the equivalent action of the lateral bracings in rigid torsion analysis is discussed.Based on the Umanskii restrained torsion theory,the error of the distortion load which is provided by the widely-used traditional load decomposition method,in which the effect of the warping constraint is not taken into account,is derived.The revised formulations of the distortion load of the open-section steel continuous box girder bridges with lateral bracings considering the effect of the torsion warping constraint are developed.Furthermore,formulations to estimate the forces in the lateral bracings and cross-frames are developed,by which the accuracy of the result is significantly improved.(2)Simplified formulas of distortion control indicators of the composite box girder bridges under service load,as well as the optimal design of the internal cross-frames are proposed.Distortion theory of the trapezoidal composite box girder is developed based on the energy-variation method.Furthermore,simplified formulas of distortion control indicators are proposed,in which both of the distortion loads generated by eccentric load and those generated by curvature of the girder are considered.On this basis,quantitative requirements of the cross-frames to satisfy various control indicators can be obtained,making up the deficiencies of the existing design method of the cross-frames of the composite box girder bridges,and bringing good reliability,efficiency and economy in distortion control and cross-frames design.(3)Four groups of large scale model tests on the composite box girder are carried out to investigate its transverse flexural behavior.The test results and the comparison of the test and the current theories indicate that further studies on the rotational restraint stiffness,translational restraint stiffness and position,as well as the compressive membrane action are of vital importance for the rational design of the bridge deck.(4)Based on the spatial structure of the composite box girder bridge,simplified analysis model of the bridge deck is established,forming important basis for research on the transverse flexural behavior of the bridge deck.Simplified formulas of the elastic and elastic-plastic effective distributed widths of the load are proposed.Due to the deficiency of the conventional frame analysis,the formulations to evaluate the rotational and translational restraint conditions of the bridge deck are proposed based on the whole bridge model.(5)The transverse flexural mechanism of the bridge deck which is under typical rotational and translational restraint conditions is presented.Moreover,transverse flexural theory and numerical analysis model of the deck are developed,in which the rotational restraint stiffness,translational restraint stiffness and position as well as the geometric nonlinear effect are considered.Key parameters to describe the performance of bridge deck are analyzed and corresponding simplified formulas are proposed.Synthesizing the above research,the design theory and method of the composite box girder bridge deck are put forward,considering the compressive membrane action effect in both serviceability limit state and ultimate limit state.The proposed design method is verified by extensive tests and numerical examples,and can give more accurate predictions of the transverse behavior of the deck,providing more comprehensive and effective guidance for design.