The Investigation On Shear Lag Effect Of The Curved Extradosed Cable-stayed Bridge

As a new form of bridge, curved extradosed cable-stayed bridge developed rapidly and is widely used in recent years, due to its excellent economic performance and landscape effect, especially in span-length of100-300m. Its mechanical performance is between the rigid continuous bridge and the flexible cable-stayed bridge. The main beam of which bears bending moment, pressure and shear force, and the cables bears tensile force under vertical load. Due to its wide deck and long cantilever, the shear lag effect of the bridge is significant, which is the main issues in design and construction. The research method and status at home and abroad of shear lag effect is discussed in this paper. Taking Longjing River Bridge as the engineering background, the shear lag effect is analyzed, because its main beam is subjected to bending moment and axial pressure, while its characteristics are long cantilever, variable cross-section and single box with multi-cells. The main contents and conclusions include:(1) On the basis of consulting a large number of literatures, firstly this article introduces current development of the extradosed cable-stayed curved bridge, and summarizes its structural and mechanical characteristics. For this kind of bridge, the theoretical and experimental research status of its shear lag effect is also discussed here. Then some remain problems is put forward based on former research. Finally the selected topic basis, research goal and significance have been confessed in the preface.(2) FEA model considering nonlinear materials is established based on the Longjing River Bridge by3D software MIDAS/Fea3.0.The mechanical characteristic and shear lag effect of the curved extradosed cable-stayed bridge are studied under different working conditions of maximum cantilever and a bridge.(3) The shear lag effect of the main girder under completion state is calculated with the three-bar stimulation analysis method. And the shear lag effect coefficient of middle section in mid-span and edge section at the bridge tower is calculated by breaking the main beam into multiple simple supported systems at points of inflections. Compared the calculated result of three-bar stimulation analysis method with that of the FEA method, the results are close to each other, but both method have its limitation. Relatively, the three-bar stimulation analysis method has the advantage of less calculation and high efficiency. It can meet the engineering preliminary requirements and can be used to estimate the cross-section size in the preliminary design stage, which result is over-conservative numeric value.(4) To research the affection of pre-stress, radius of curvature, pier height and cable force on the shear lag effect, multiple parameterized FEA models are established with software Midas/Fea aided, and then the normal force and shear lag effect coefficient of some typical sections are extracted. Through the comparison analysis of calculated results, a lot of meaningful conclusions are obtained, which can provide a reference for the design and construction.