Reliability Assessment On Stability Of Gravity-type Anchorage And Research On Limit State Design Method Expressed As Partial Safety Factor

Gravity-type anchorage is an important load-bearing element in super-large span suspension bridge system,and its stability and safety have always been a difficult and critical point in structural design,as well as a necessary path for bridge engineering design level improvement and construction technology innovation.The current domestic anchorage design code has not yet transitioned from the traditional safety factor method to the reliability-based limit state method.The conservative design adopted by engineers has led to a situation of ambiguous structural uncertainty during the operation period,making the task of scientifically analyzing the stability and reliability of anchorages and proposing a limit state design method for anchorages expressed as partial safety factor far-reaching.This paper takes the south anchorage of the three-tower suspension bridge of Zhangjinggao Yangtze River Bridge as the research background,combines numerical finite element simulation with probabilistic statistics of structural parameters,establishes a limit state design method for gravity-type anchorages based on reliability theory,and obtains the partial safety factor about stability and the general design expression based on target reliability indicators.The main research contents are as follows:（1）Based on the comparison of domestic and foreign bridge foundation stability analysis methods and the identification of the relationship between failure probability,safety factor and reliability index,the south anchorage of Zhangjinggao Yangtze River Bridge was calculated under《General Design Specification for Highway Bridges and Culverts》JTG D60-2015,American《AASHTO LRFD Bridge Design Specifications》9^th Edition 2020,Eurocode and Japan《Road and Bridge Showbook-Common Part I》to obtain the deterministic evaluation.（2）In order to serve the anchorage design based on reliability theory,the probabilistic statistical properties of the resistance of structure and members,action and effects of action in anchorage design were investigated and collected,the most unfavorable rules of the combination of actions were clarified,the uncertainties of geotechnical parameters were organized,and the distribution of values and coefficients of variation of the base coefficient of friction were calculated.（3）The limit state equation of anchor stability analysis based on the reliability theory was established and the target reliability index in the specification or standard was revealed.Based on the statistical properties of the basic random variables,the probabilistic analysis of the finite element model identified the parameters that have a significant influence on the force system or members of the suspension bridge,and the anchorage stability reliability calculation was completed.（4）A method of calculating the partial safety factor based on the target reliability index was established.By inputting the statistical characteristics of the parameters of anchorage design and applying the least squares optimization method of reliability index recommended by《General principles on reliability for structures》ISO 2394-2015,the reliability indexes and the partial safety factor of resistance against sliding and overturning under different ratios of vehicle loads to the standard values of constant load effects were calculated,and the influence law of the base coefficient of friction on the anti-sliding design was studied.（5）The calibration method of anchor stability resistance coefficients for suspension bridges was established,which is suitable for national conditions,by integrating factors such as anchor project scale,bridge span,construction process and material technology.The design data of the completed super-kilometer suspension bridges Longtan River Crossing,Runyang Bridge and Jiangyin Bridge were obtained,and the practical design expressions for anchorage sliding resistance were proposed and tested.