| Cable-stayed bridges have been widely used all over the world because of their good mechanical properties and low economic cost.Stay cables are the main stress-bearing components of cable-stayed bridges,and are prone to fatigue damage under the action of alternating loads such as vehicles,wind and rain.In recent years,the Morandi elevated cable-stayed bridge in Italy has caused collapse accidents due to cable fracture.This is mainly due to the brittle failure of the cable fatigue damage,which has the characteristics of suddenness,concealment and strong randomness,and it is difficult to Effective discovery through traditional detection methods.Therefore,the fatigue damage assessment of stay cables has always been one of the key concerns in the field of safety assessment.At present,the fatigue damage state assessment of stay cables is mostly based on the constant stress amplitude,ignoring the actual situation of the staying cable life cycle,the stress amplitude series are more and the order of action is complicated,and the tension corresponding to each stress amplitude is often The cable life is regarded as a constant,ignoring the randomness of the material.In addition,the current commonly used reliability analysis methods have problems such as low calculation efficiency and large errors.To solve these problems,this paper is based on number theory and probability density evolution method,through theoretical derivation to obtain high-dimensional space selection method and fatigue damage probability density conservation formula,combined with linear fatigue damage model to construct the frequency of stress amplitude,and propose multi-level cable stayed cables The prediction method of variable amplitude and time-varying fatigue reliability provides timely and accurate decision support for the maintenance and replacement of stay cables.The main research work and conclusions of this paper are as follows:(1)For the problem that the random parameters of the multi-level variable amplitude fatigue assessment of stay cables involve high-dimensional sampling,based on the good lattice point set method,through theoretical derivation,a layer-by-layer group point selection method and primitive root optimization theory are proposed to realize the efficient generation of point sets with good uniformity in the high-dimensional space.The results of numerical examples show that compared with the classical spatial point selection method,the calculation efficiency of the method proposed in this paper is increased by 4 to 12 times when the uniformity of the point set is the same.(2)When the reliability method is used to solve the high-dimensional time-varying fatigue reliability of stay cables,there are problems such as low calculation efficiency and insufficient accuracy.Based on the generalized probability density evolution method and the linear fatigue cumulative damage model,the stress amplitude frequency index is constructed through theoretical derivation,Which solves the problem of difficult determination of partial differential equations in the evolution of fatigue damage;by combining the layer-by-layer group point selection method with partial differential equations,a method suitable for solving multi-level variable amplitude high-dimensional time-varying fatigue reliability of stay cables is proposed.(3)In view of the problem of cable fatigue damage process involving load randomness and material randomness,based on the measured traffic data and material structure P-S-N curve of the cable-stayed bridge,through numerical simulation and theoretical derivation,the cable staying considering the randomness of load and material at the same time is realized Cable fatigue reliability assessment.(4)The proposed method is applied to the prediction of cable fatigue reliability of a cable-stayed bridge in Chongqing and compared with the Monte Carlo method.The results show that the fatigue life of the stay cables of the bridge under random vehicle load is longer than the existing service time of 20 years.The fatigue life of the long cables on the side span is the shortest,and the fatigue life of the short cables near the pylon is the longest.The correlation between the method proposed in this paper and the Monte Carlo method predicts cable fatigue reliability is as high as 0.999.When the fatigue life reliability index of the cable is selected as β=3.5,the errors of both methods are within 3years,but the calculation efficiency of the method proposed in this paper is It is 10 to 13 times the Monte Carlo method. |
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