Shear Lag Analysis And Modeling Simplification Of Steel-Concrete Composite Stiffening Girder In Suspension Bridge

Steel-concrete composite girder has been widely applied on large-span suspension bridges due to its fully utilization of both concrete and steel material and better resistance to bridge deck wearing out. However, the research of shear lag effects, under the condition of large-span flexible bridges, is still insufficient as a result of its limited application on site. The main work of the research is demonstrated as follows:1.The influence of small stringer and transverse girder on shear lag effect was analysed based on two composite girder bridge examples in order to investigate the theoretical basis for calculation simplification of the composite girder structure.2.Finite element analysis software ANSYS was utilized to establish and validate the shell-solid model for Yingwuzhou Yangtze River Bridge. The Bridge NonLiner Anlysis System (BNLAS) was utilized to establish the frame model to the most unfavourable section under live load and the corresponding moment influence line.3.Based on the most unfavourable sections and the corresponding moment influence line, nine loading cases were proposed to acquire the most unfavourable moment. The effect of lateral loading position upon shear lag was discussed in this dissertation as well as the feasibility of load equivalently transformation on steel girder4.After properly determined the shear lag warping displacement, the elastic stiffness matrix, initial stress stiffness matrix and equivalent nodal load vector of the composite beam under U.L. determinant was calculated using calculus of variations.5. A composite beam element was compiled using the UPFs function of ANSYS based on the derived relative matrixes. Geometric nonlinearity and the shear lag of flanges of a composite girder element can be considered by the proposed beam element. The accuracy of the developed element was verified by comparing with the calculation results using the ANSYS shell-solid model. The force distribution of the main girder was also analysed using the proposed beam element.The analysis of longitudinal stress distribution of composite girder bridge deck demonstrates that:The effect of small stringers is negligible when simplifying a composite girder model while the effect of transverse girder on shear lag is relatively large and have to be considered in the model simplification. Under the condition of symmetric load, the results of using equivalent load applied on the steel girder satisfy the calculation requirement of stress, while a scaling factor is needed when analysing the effect of eccentric load. The scaling factor can be approximated by using twice the lateral distribution factor that calculated using G-M. After analysing the shear lag effect, the variation of the axle force and shear force within the stiff girder is very small, the variation of moment is relatively large, the inflection point and extreme point remain the same. Based on the calculus variation of energy, the proposed shear lag element provides a conceptual clearly, efficient and generic solution for the stiff girder shear lag problem in suspension bridges while retaining a satisfactory calculation accuracy.