Research On Characteristics Of Spatial Mechanics Of Self-anchored Suspension Bridge With Super Wide Concrete Box Girder

The self-anchored suspension bridge with two concrete side girders is widely used in bridge engineering,and the main girder is composed of two side girders supporting a super wide bridge deck.The concrete side girders of the super-wide self-anchored suspension bridge show significant spatial mechanical characteristics.Based on a real bridge,the longitudinal and transverse stress distribution and the function of the cross diaphragm during construction process,operation and vehicle loading condition are studied.A solid finite element model of the self-anchored suspension bridge with super wide concrete box girder is built through finite element code Midas/FEA and the mechanical analysis of the concrete self-anchored suspension bridge is conducted.The main processes and results of the research are as follows:Firstly,spatial finite element model is built to analyze the longitudinal stress distribution of separated concrete side-box girder.Compared with the measured values,the results show that the longitudinal stress of the girder changes considerably and the spatial effect of the longitudinal stress distribution is remarkable.During the system conversion process,the longitudinal stress across the transverse section of the mian girder changes from shear lag effect to negative shear lag effect,with the shear lag coefficient of the top and bottom plates of the girder in the middle-span ranges from 0.84 to 1.21 and from 0.91 to 1.10,respectively.Under the symmetrical vehicle loads,the varying trend of bending deflection along the longitude is prominent,and the maximum deflection of the super-wide girder is-36.5 mm.Besides,the shear lag effect of super-wide concrete girder diminishes and the shear lag coefficient of the top plates of the girder in the middle span ranges from 0.85 to 1.15.Under vehicle loads,the longitudinal stress increments of the top and the bottom plates of the girder where wheels directly stand are greater than those of other parts.Secondly,the transverse stress distribution of the concrete side box girder under construction process and vehicle loading condition is analyzed through finite element simulation.The results show that transverse stresses of the girder derived from lateral pre-stressing distribute unevenly along the transverse direction of the girder,and the maximum of the longitudinal stress increments 1.55 MPa is located in the junctions of the inner web and the top plates.During operation condition,transverse bending deformation is more significant than that under pre-stressed tension process,and the maximum deflection of the super-wide girder is 17.6 mm and the transverse compressive stress is less than 1 MPa.Under biased loads,due to the transverse frame effect of the girder,transverse stresses of the top and the bottom plates of the girder change greatly.Under symmetrical vehicle loads,local effect of transverse bending deformation of concrete girder is obvious,and transverse tensile stress appears in the local bottom plates of the girder.The influence of vehicle loads on transverse stress ranges from 0 to 12 m along the cross section.At last,the effect of cross diaphragm on the longitudinal and transverse stress distribution of the main girder is analyzed.The analysis results show that the longitudinal stress on the top plates of the girder with no cross diaphragm diminishes and the distribution trend along the cross section changes.The transverse tensile stress at the junction of the web and the top plates of the girder with no cross diaphragm is 1.43 MPa,and the transverse stress on the upper edge of the bridge deck changes greatly.The cross diaphragm can increase lateral stiffness of the main girder,strengthen the transverse relationship between the deck and edge-box girder,reduce the relative displacement of girder and deck,and promote the synergistic effect of girder and deck.At the same time,cross diaphragm can greatly reduce the lateral stress of the bridge deck,and improve longitudinal machnical performance of the super-wide girder.