| Corrosion is one of the important factors affecting the service life of bridge.In this thesis,a long-span steel cable-stayed bridge is taken as the engineering background,and the atmospheric corrosion of the bridge in the marine environment is studied.Through the finite element software Midas Civil,the corrosion model of steel bridge under different time nodes is obtained after determining the corrosion law of bridge components with time.Through the basic load combination,the change law of bridge bearing capacity with time is obtained,and the influence of different corrosion degree on bridge deformation can be studied.The research results can not only guide the design and construction of bridge engineering,but also provide a useful reference for the operation and maintenance of existing bridges in marine environment.The main results are as follows:(1)The subspace iteration method is used to carry out modal analysis of cable-stayed bridge,and the first 15 modes of the bridge and the dynamic characteristics of the structure considering the bridge corrosion with time are obtained.The results show that the frequency distribution of the cable-stayed bridge is dense,and only in the first six modes,the first-order lateral vibration of the main beam,the first-order vertical vibration of the main beam,the first-order torsion vibration of the main beam and the related vibration of the cable-stayed tower appear;with the development of corrosion,the section of the main girder becomes thinner and the stiffness of the section decreases,resulting in a slight decrease in the modal frequency related to the main girder,but the first six modes of the bridge have no obvious change.(2)Combined with the calculation formula of section normal stress,the maximum normal stress after conversion of structural importance coefficient is compared with the design value of steel strength,and the degradation law of normal section bearing capacity is obtained.The results show that the minimum residual bearing capacity of the steel girder section generally changes linearly with the corrosion,and the minimum bearing capacity occurs in the second section of the girder.The bearing allowance increases gradually when the steel girder ends close to the middle of the span.(3)Through the observation of the normal stress distribution of the steel main beam,it can be concluded that although the maximum normal stress of each section of the steel main beam does not reach the design value of the steel strength,during the100 year corrosion period,the section from the end of the steel main beam to the 9Section of the main beam has been in a high stress working state,and the normal stress of the bridge is sensitive to corrosion,which is prone to stress corrosion or corrosion fatigue damage.In the actual engineering,the monitoring and protection of the area should be strengthened.(4)Combined with the requirements of the code,the shear stress of the steel girder web is studied.The results show that the shear stress is very sensitive to corrosion.During the corrosion period of 100 year,the shear stress increases parabola significantly,and the stress level increases by about 50%.Although it does not reach the design value of shear strength of web steel,the monitoring of shear stress level of steel beam should be strengthened in the later stage.(5)According to the requirements of the specification,the vertical deflection of the bridge is checked.The results show that the deflection of the end of the main beam is much lower than that of the mid span section,and the overall deflection curve of the main beam is parabolic with the mid span as the wave trough.The deflection value of mid span section increases linearly with the depth of corrosion,but the corrosion will not change the deflection too much.The maximum deflection is only0.689 m,which is far from the vertical deflection limit of 1.9 m required by the code. |
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