| The dynamic behavior prediction analysis of long-span bridge structure is usually based on numerical finite element model.However,most of the idealized material parameters are used in the finite element model,while the actual material parameters,such as density and elastic modulus,are deviated from them.At the same time,the finite element model is usually a simplification of the real structure,and the simplified boundary conditions are often difficult to reflect the real constraint conditions of the structure.In order to accurately predict and analyze the structural behavior of discontinuous suspension Bridges with asymmetric towers,a stepwise model modification method based on response surface is proposed in this paper.Firstly,an initial finite element model is established to analyze the structural static and dynamic characteristics of the asymmetric pylon separated suspension bridge,and the comparison is made with the measured structure.Then,a stepwise correction method based on sensitivity analysis is proposed to solve the problems of distortion in the results obtained by the traditional method of correcting all parameters at one time,and the huge amount of calculation and the difficulty of iteration and convergence.Finally,the improved Gaussian radial basis function was used to construct the response surface model for model modification,and the corrected results were verified by real bridge test.The main conclusions are as follows:(1)Under the action of temperature load or automobile load,the variation of ground anchor cable force of the sling at the separating side of the tower girder and the sling near the separating side of the tower girder are much higher than that of other sling.Beam under temperature load,the tower separation side beam end longitudinal displacement less than bridge tower side beam end longitudinal displacement,stiffening girder,beam bottom chord stress on the tower separation side on the beam end take the maximum,the temperature stress has obvious characteristics of asymmetric distribution,every increase 1 ℃,temperature separation tower beam side beam end upper chord stress change 0.41 MPa,0.72 MPa bottom chord stress changes.(2)The basic frequency of the structure is low,which is only 0.097364 Hz,and it belongs to the typical flexible system.The transverse stiffness of main girder is weak,and the structural response under the action of transverse wind cannot be ignored.The vibration of the structure is mainly transverse bending,longitudinal drift and vertical bending,until the torsional mode appears in the 8th mining stage.(3)The calculation results of the initial finite element model are basically consistent with the measured static and dynamic responses of the structure,but there is still a certain deviation between the measured response and the calculated value.Among them,the error between the measured bearing displacement and the finite element model calculation is the largest,reaching 43.20%.It is necessary to modify the finite element model to establish the finite element model which can accurately reflect the static and dynamic characteristics of the actual structure.(4)The sensitivity of sling elastic modulus,sling density and bridge tower density to all structural static and dynamic response characteristic quantities is small,so it can not be modified.The longitudinal stiffness of the composite cable saddle only affects the longitudinal displacement of the composite cable saddle,and the longitudinal displacement of the composite cable saddle is only affected by the longitudinal stiffness of the composite cable saddle,and there is a unique correspondence between the two.Therefore,the measured longitudinal displacement of composite cable saddle can be used to correct the longitudinal stiffness of composite cable saddle.Material density parameters and load parameters only affect the dynamic response of the structure,and the main cable density,stiffened beam density,bridge deck system and secondary constant weight can be modified only by using the characteristic parameters of structural dynamic response.(5)After the modified RBF response surface was adopted,the tower deviation and support displacement errors were all within 15%,and the static and dynamic response errors of the other structures were all within 10%.Compared with the errors before the correction,the errors were significantly reduced and the error distribution was more uniform.Taking the measured static and dynamic characteristics as the characteristic quantities and using the improved Gaussian radial basis function response to modify the asymmetrical separated tower suspension bridge step by step,the calculation accuracy of the finite element model can be improved effectively.The recommended values of longitudinal stiffness of beam end and composite cable saddle are 1156.3k N/m and 211760 k N/m,respectively.. |
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