Local Analysis And Seismic Analysis Of A Long-span Suspension Bridge

Since the beginning of the 21 st century,domestic large-span suspension bridges have developed rapidly.At present,several suspension bridges with a span of more than1,000 m have been built.The structural form of the suspension bridge determines that it has the characteristics of flexible structure and long natural vibration period.In that case,the seismic response of suspension bridges,causing by a long-period ground motion,may be too large,posing a threat to the safety of the structure.Therefore,the seismic response analysis of long-span suspension bridges should select appropriate earthquake records,which is of great significance to ensure the safety of the structures.In addition,for suspension bridges with stiffened beam in the form of double-layer truss,the stresses at the truss joints are complex.In order to ensure safety,a detailed model needs to be established.Relying on a large-span suspension bridge,the main contents of this paper are as follows:(1)Using Ansys,a detailed model of the stiffened-beam,bearing the dead load and vehicle load,was built and analyzed.The results show that the stress and deformation of some members at the truss joints are too large and need to be redesigned.By improving the structural form of the truss node,the stress and deformation at the truss node are significantly reduced to meet the requirements of the code.(2)Using Midas/Civil,a full-bridge model was built.In order to get the initial forces of each member,an initial equilibrium state analysis was performed.In addition,a modal analysis was performed to get the vibration periods and modes of the suspension bridge.(3)Using Abaqus,a series of dynamic time-history analysis were performed to the suspension bridge.Firstly,under the condition of uniform excitation,three short-period earthquake records and three long-period earthquake records were selected and used in the analyses.The results show that the impact of long-period earthquakes on long-span suspension bridges is significantly greater than that of short-period earthquakes.Secondly,three factors are considered,including travelling-wave effect,multi-directional earthquake and soil-pile-bridge interaction.The results show that traveling-wave effect,multi-directional earthquake and soil-pile-bridge interaction may all have adverse effects on some components of the suspension bridge.(4)The effects of the viscous damper and elastic connecting device on the seismic response of the suspension bridge were discussed.Under the long-period earthquakes along the bridge,the effects of dampers with different damping coefficients and elastic connecting devices with different stiffness on the displacement of the suspension bridge stiffened beam and the internal force of the tower are analyzed.The results show that under the condition of similar beam displacement,the internal force of tower is smaller when using dampers.