Study On Mechanical Properties Of Curved Steel Bridges Under The Incremental Launching Construction Stage

The expressway construction is in the rapid-developing stage in our country.For the purpose of realizing the rapid transformation of traffic flow between different expressways,a large number of interchanges have been built all over the country.Curved girder bridges are increasingly used in interchanged ramp bridges.Due to the limitation of site conditions,some ramp bridges are designed as small-radius curved girder bridges.In order to reduce the impact of the construction of new ramp bridge on existing road traffic,the incremental launching method is used widely as the preferred choice of ramp bridge construction method.The incremental launching construction of straight or large-radius curved girder bridges is relatively common,while the incremental launching construction of small-radius curved girder bridges has few cases.Steel box girder bridges are widely used in ramp bridges due to their high rigidity,small self-weight,short construction period and flexible operation.Under certain conditions,the incremental launching method of small-radius curved steel box girder bridges has comprehensive advantages,but the lag of theoretical research limits the development of engineering application.Large difficulty and risks still exist in the design of small-radius curved steel box girder bridges using the incremental launching method.Based on the Qinglan high-speed bridge section on the A and C ramps of the Taibai hub,the mechanical properties of the curved steel box girder bridges during the incremental launching process are analyzed.The main work is as follows:(1)The theory of curved girder bridges is summarized,which is mainly divided into three categories: analytical method,semi-analytical method and numerical calculation methods,including pure torsion theory,warping torsion theory,plate-beam combination theory,folding plate theory,beam-lattice system theory.The equilibrium differential equations of force,the relationship between force and strain and the differential equation of the displacement of curved girder bridges are derived.And the influence of radius of curvature on its “bending and torsion coupling” effect is analyzed.(2)The finite element model of the curved steel box girder bridge is established.The reaction force,deflection,torsion and local stress distribution under each working conditions are analyzed,and the change trend of the stress during the launching process is basically the same as the theoretical change trend of bending moment,which verifies the correctness of the finite element calculation result.(3)The finite element calculation of steel boxes girder bridges with different curvature radius are carried out.The influence of the change of curvature radius on the reaction force,deflection,torsion and local stress of the curved steel box girder bridge is studied.The finite element calculation of the steel box girder bridge with different radius of curvature and different thickness of the diaphragm is carried out,and the influence of the thickness of the diaphragm on the deflection,torsion and local stress of the curved steel box girder bridge is analyzed.