Study On The Force And Fatigue Characteristics For The Anchorage Zone Of Highway Composite-mixed Beam Cable-stayed Bridge

The thesis utilizes the engineering background of a large cable-stayed bridge in a coastal area to establish a finite element rod system model for the entire bridge and a detailed solid model of the steel anchor box at the outer web of the main beam for the stay cable.The study focuses on the cable force distribution and the stress status of each component of the steel anchor box under the most unfavorable load combinations of the entire bridge.Using the nominal stress method of the S-N curve and Miner’s linear cumulative damage theory,the thesis conducts fatigue analysis using FE-SAFE software and Python programming language for both software calculation and code calculation.The research aims to compare and analyze the fatigue damage and fatigue life of the steel anchor box in the cable beam anchorage zone under typical vehicle loads.The main content and results of this article are presented as follows.(1)Using the finite element software Midas Civil,a complete bridge model was developed to analyze the distribution of stress of the entire bridge.Based on the cable force values and amplitudes,the cable force values of the most unfavorable cable locations were determined,and the cable force influence lines for each lane of the study object were calculated.Fatigue load amplitudes were also calculated according to the fatigue specifications.Furthermore,a solid finite element model of the steel anchor box at a local level was created through the utilization of ABAQUS finite element software in order to analyze its stress distribution.Through the analysis of stress responses of the steel anchor box under the cable force amplitude,construction details with significant stress concentration were identified: stress concentration was significant at the end of the welds surrounding the top and bottom anchorage plates and the pressure plate connected to the outer web plate,whereas stress responses at other locations were relatively small.(2)Through the analysis of model proportion and load proportion of typical vehicle load and the superposition calculation of the influence lines of cable force in each lane of the stay cable,interactive programs are written by using the computer programming language Python,so that users can realize the purpose of generating typical random traffic flow based on Monte Carlo numerical simulation method and loading random traffic flow on the influence line.Based on the loading results,the cable force history data was generated under the influence of typical random traffic flow.Subsequently,The technique of "rain flow" counting was employed to derive the fatigue load effect spectrum that corresponds to the given conditions.(3)According to the specifications,the weld detail structure of the main weld of the steel anchor box is rated,and the fatigue life of the main weld of the steel anchor box is evaluated based on the S-N material fatigue curve combined with Miner’s linear cumulative fatigue criterion.At the same time,the fatigue life is analyzed using the stress response output data of the fatigue analysis software FE-SAFE combined with the finite element software,and finally the conclusions obtained by the two life evaluation methods are compared.It is found that the fatigue life obtained by the two methods is greater than the design service life of the bridge studied in this thesis.Therefore,it is safer to select a smaller value as the theoretical life limit of the steel anchor box component.