| With the development of bridge construction technology,when designing long-span bridges that span valleys or straits,suspension bridges have become a very competitive type of bridge.Among them,the steel truss suspension bridge has become a common form of bridge due to its construction advantages such as less transportation and site constraints.However,as the span of the bridge increases,the long-span suspension bridge becomes softer and easily vibrates under the action of wind loads.Therefore,the wind resistance of the bridge must be checked during the design process.However,in actual tests,the aeroelastic model may have a certain deviation from the design target due to the conditions of production,storage and assembly,so that the model cannot accurately reflect the dynamic characteristics of the actual bridge,affecting the accuracy of the results.Based on the engineering background of a long-span steel truss suspension bridge,this paper studies the design and modification technology of the aeroelastic model of the full bridge of the bridge,and focuses on the preliminary design process of the geometric parameters of the "U" spring on the stiffening beam.Subsequently,based on the geometric characteristics of the "U" spring,a simplified and fast calculation method for spring design and a simulation method for spring shear deformation were proposed.Because damping has a greater impact on the wind-induced vibration of the bridge,this paper combines the transient analysis module of ANSYS software to simulate the damping in two ways,and uses the impact load method to simulate the vibration mode attenuation process of the main beams of the model.Finally,combined with the existing model correction theory,the dynamic characteristics of the bridge aeroelastic model in the wind tunnel test are used as the correction target,and the frequency and damping are corrected.The deviation of the actual wind tunnel aeroelastic model and design is obtained.The research results can indicate the following conclusions:(1)The parameters obtained by designing the "U" spring according to the static stiffness method still have room for further research and modification.First of all,there is still some room for improvement in the simulation efficiency of the static stiffness method.Secondly,compared with the actual bridge,the aeroelastic model designed by the static stiffness method due to the influence of the bridge tower and the cable structure will cause certain errors in the fitting of each frequency.Finally,compared with the actual aeroelastic model,the static stiffness method does not consider the influence of the shear deformation of the "U" spring,nor does it consider the difference in damping between the finite element model and the actual aeroelastic model.(2)The simplified model composed of "U" springs and internodes can improve simulation efficiency and save computing resources during model design.The simulated spring parameters installed on the aeroelastic model can not only fit the frequency of the basic mode of the bridge well,but also fit the high-order mode of the bridge well,reflecting the reliability of the method.(3)The shear deformation produced by the "U" spring will have a certain influence on the calculation results of the dynamic characteristics of the finite element model.By comparing the situation of multiple groups of springs after being affected by the shearing effect,it is found that the thicker spring is more affected by the shearing effect.This effect is mainly manifested in that the frequency of the torsional mode of the spring with a larger thickness is reduced to a large extent when the shear deformation is considered.If the influence of shear deformation is not considered in the design of the aeroelastic model,the maximum torsional frequency of the aeroelastic model produced by the design will only reach about 90% of the design value,which has a greater impact on the experimental results,so it is necessary to use high-precision beam elements for simulation.(4)The free vibration attenuation method and the impact load method were used to perform finite element simulation on the model,and the vibration attenuation of the bridge was analyzed.It was found that the model obtained by the two simulation methods had certain differences in the modal damping.After analysis,it is found that the basic mode frequency obtained by the impact load simulation method will produce errors because the basic mode is disturbed by higher-order modes during vibration,which results in a larger damping value.(5)When the frequency of the finite element model tested in the wind tunnel is inconsistent with the design value,the simplified model modification method or the full bridge model modification method can be used to modify the model.The simplified model correction method can modify the stiffness matrix of the model.In addition to the correction of the stiffness matrix,the full bridge model can also consider the change in the mass distribution of the bridge.Therefore,the correction effect is more accurate than the simplified model.(6)The damping of the finite element model can be set by Rayleigh damping and material damping.In the damping correction of the aeroelastic model,it is found that due to the large difference in the damping of each part of the aeroelastic model,the use of Rayleigh damping for the entire model will make the correction result unsatisfactory.Since the material damping can be set separately for different materials,the model correction effect will be more accurate.The conclusions of this paper can provide suggestions for the simplification and precision of wind tunnel aeroelastic model design.In the correction of aeroelastic model frequency and damping,a variety of correction methods are provided and the characteristics of the various correction methods are compared.The article can provide a reference for the design and modification of the wind tunnel test model of the aeroelastic model. |
