| Because of its advantages of large span capacity,shapely configuration and diversified structure system,the cable-stayed bridges occupy an important proportion in modern bridge construction.Among them,the steel truss cable-stayed bridge with the characteristics of convenient construction and large flexural stiffness has been promoted vigorously in the western mountainous area.However,under the current traffic conditions with serious vehicle overload,due to the comprehensive influence of early imperfect design theory,construction technology limitation,improper maintenance and natural environment change,many cable-stayed bridges suffer from various diseases after a certain period of service,such as bridge deck cracking,damage to the anchoring structure,cable breakage,corrosion and other diseases.It reduces the bearing capacity of the bridge structure and seriously affects the drivcomfort and safety of the bridge.Therefore,it is necessary to timely detect the disease status of the in-service cable-stayed bridges,correctly evaluate the bearing performance of the bridges and propose reasonable reinforcement and maintenance measures so as to extend the service life of the in-service cable-stayed bridges.In view of this,an in-service double-tower double-cable-plane steel truss cable-stayed bridge,that is,Guozigou Bridge in Xinjiang,was used as the research background in this paper.According to the results of appearance inspection,constant load cable force and bridge deck alignment measurement,the use of cable-stayed bridge in service was studied.The finite element method was used to analyze the characteristics of the internal force distribution of the bridge and to determine the loading control section of the load test.The static and dynamic characteristics of the bridge were analyzed based on the load test results carried out on site.Then,the work performance of the bridge was evaluated and corresponding prevention measures were proposed for the typical diseases.In this dissertation,the main research contents and results are as follows:(1)The overall appearance disease investigation of the bridge was conducted on-site firstly.The main cause analysis of the cable-stayed bridge in service were discussed.The layered comprehensive assessment method was used to assess the technical condition of the cable-stayed bridge.The technical status of the upper structure of the cable-stayed bridge in service are three and the overall technique condition rating results are two.(2)By testing the cable force value under the constant load and the bridge surface linearity,the cable force incremental detection under the load is performed on the cable,and some cable force values are larger than the design value,up to 21.1%.In each loadingcondition,the actual measured value of the cable force increment is less than the calculated value,which indicates that the cable force of the stay cable has a certain safety reserve.The elevation of the bridge deck near the 3/4 position of the midspan is slightly higher than the design elevation alignment,and the measured alignment of the remaining positions is generally lower than the design alignment.(3)Under the action of static load,the steel truss girder and pier structure of the bridge are in the normal working stage and bearing structures have enough safety reserve.Under the dynamic load,the first five orders frequency of the main bridge are generally slightly larger than the theoretical analysis frequency.The damping ratios corresponding to the frequency of each order of the structure are more than 2%.The average value of the full bridge impact coefficient of 0.053 is close to the theoretical value of 0.050.The results show that the overall stiffness of the bridge structure is sufficient and the dynamic response is good,indicating that the cable-stayed bridge in service meets the requirements for safe operation.The research results of this study can provide reference for similar bridge detection and bearing capacity evaluation,and have certain reference value. |
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