| With the rapid development of China’s transportation industry,the need to build channels across large rivers and straits has become more urgent.Super-large span suspension bridges with strong spanning capacity,reasonable force,beautiful shape,and other characteristics often become the preferred bridge type.However,the existing design specifications for 2000 m class super-large span suspension bridges are not suitable.Some of the design parameters take the value of the lack of target and systematic research.The main cable of suspension bridges is a crucial stress member of the structure.In the natural environment,with the increase of service life will occur a certain degree of corrosion damage,resulting in the main cable resistance degradation,threatening the safety of bridge operations,for the corrosion of the main cable under the influence of the reliability of the whole life of the study is more petite.Given this thesis to large span suspension bridge main cable as the research object,the main cable whole life reliability research analysis,the main research content,and conclusions are as follows.(1)The existing structural reliability theories and calculation methods are summarized.The advantages and disadvantages of the center point method,checkpoint method,Monte Carlo method and response surface method are compared and analyzed through examples.The calculation efficiency and accuracy of the checkpoint method meet the actual engineering requirements.So this method is used for the reliability analysis of the main cables of large span suspension bridges.(2)Based on the actual measurement data and literature research statistics,it is found that the probability characteristics of the main cable,stiffened beam,and second-phase constant load of large-span suspension bridges are approximately subject to normal distribution.The probability characteristics of automobile and temperature load effects are approximately subject to extreme value type I distribution.The probability characteristics of the critical factors affecting the resistance of the main cable,such as area and tensile strength,are approximately subject to normal distribution.Based on the reliability theory and each constant load probability model,the constant load coefficients applicable to large span suspension bridges are studied.The results show that the constant load coefficients of main cables and stiffened beams determined under different failure probabilities are less than the value of code1.1.(3)Using different span suspension bridges as the engineering background,the adjusted constant load coefficients and main cable material subfactors are used to design the main cable sections.The finite element model of the whole bridge is established,and the internal force of the main cable under each load is calculated and analyzed.The results show that the main cable of the large span suspension bridge is mainly subjected to a constant load,and the effect of constant load accounts for the most significant proportion of the effect of each load,more than 85%.Based on the main cable resistance and load probability model,the reliability equation of the main cable is established,and the reliability index of the main cable is calculated by the checkpoint method.The results show that as the values of constant load factor and main cable material sub-factor decrease,the design section of the main cable decreases,and the corresponding reliability index decreases.The reliability of the main cables for different span suspension bridges remains similar and insensitive to the span,indicating the applicability and feasibility of the method of designing the main cables with each constant load factor.(4)The corrosion mechanism and post-etching mechanical properties of the main cable wire were summarized,and the corrosion damage assessment method of the main cable under different maintenance levels was established.The reliability of the main cable during the whole life under the influence of corrosion was calculated,and the expected service life of the main cable was evaluated.The results show that the worse the maintenance level is,the more serious the corrosion damage of the main cable during the service life.The reliability index of the main cable decreases as the service life increases,significantly reducing the service life.Considering the corrosion impact of the main cable during the 100-year design reference period,it is desirable to design the main cable with a material sub-factor value greater than1.50.The whole-life reliability assessment provides a basis for the design of the main cable and has a particular engineering reference value. |
