Performance Analysis Of Corrosion Fatigue For Straddle-type Sling Under The Vehicle Load

With the rapid development of economy and technology advances, construction of suspension bridge that is more than 1000m is possible, which is also the preferred bridge type of large span structure. For most permanent bridge, its design life is 100 years, even more; as the key component of a suspension bridge, the slings’theoretical design life is only 20 years. In fact, many slings of suspension bridge at home and abroad had to be replaced after use of 5 to 13 years because of severe corrosion and damage. In view of this, taking a straddle-type sling of long-span suspension bridge for the object, the main research as follows:(1) The finite element method is used in the paper, finite element model of the full bridge is established; The vehicle loading methods of the specification on fatigue analysis for small and medium span bridges is summarized and propose a vehicle loading method about fatigue analysis for a sling of large-span suspension bridge, then, compared with longitudinal and lateral vehicle loading methods on fatigue analysis of the sling for long-span suspension bridge. The results show that: vehicle loading methods of the existing domestic small and medium-span bridges on fatigue analysis cannot meet the needs of fatigue analysis for large-span suspension bridge, the proposed vehicle loading method provides a comparison reasonable loading method for fatigue analysis of a long-span suspension bridge.(2) In order to compare the parameters’(loading lane, the vehicle center distance, fatigue life curves and different positions etc.) influence on the fatigue life of a sling in the long-span suspension bridge, the finite element numerical simulation method is used. The results show that: compared with full loading lane, fatigue vehicle load in slow lane only make fatigue life more conservative, it is recommended that part of heavy vehicles should be directed to the fast lane before the vehicles on the bridge; The lane closest to a sling is the most unfavorable lane, the proportion of fatigue damage for sling is the largest and dominant in four lane; When the center distance of the vehicle is greater than 60m, the longitudinal more vehicle effect do not be considered; The fatigue life of a sling after the fatigue life curve correction is two times than which before correction, so it is very vital to choose the fatigue life curve; The sling in both the north and the mid-span, if material, diameter and other parameters is in consistent, whether the fatigue life curve correct or not, fatigue life sling increases with the increasing of the length of the sling and fatigue life of the short sling is minimum in each span, so short sling is the monitoring focus; For slings in the same span, when the other parameters is same, as long as the length is same, fatigue life of sling in different positions can be considered equivalent.(3) According to the order of the sling in contact with the corrosive medium in the external environment, analyze the mechanism of corrosion fatigue, corrosion fatigue of steel wire is divided into four stages, and calculate life cycle of the various stages to give the corrosion fatigue life. The results show that:Taking a sling in the mid-span for the object, analyze the four stages of corrosion fatigue, anti-corrosion coating and galvanizing layer corrosion loss cycle of the sling account for 73.69% of the whole cycle, so corrosion inspection and conservation work of the slings must be made during operation; The sling in both the north and the mid-span, if material, diameter and other parameters is in consistent, corrosion fatigue life of the short sling is shorter than the long sling; Compared with pure fatigue, the damage of corrosion fatigue is greater, the service life of the sling become shorter, so corrosion fatigue is the main reason of sling failure.