变电站避雷针法兰盘高强螺栓风振疲劳性能分析

Wind Induced Fatigue of High Strength Bolts in Flanges of Lightning Rods in Transformer Substations

为明确避雷针法兰盘高强螺栓风振疲劳性能以及预紧力对疲劳性能的影响,以某变电站高耸避雷针结构为例,在整体结构梁单元模型风振动力计算的基础上,对避雷针法兰盘连接部位建立局部精细化实体模型,借助整体结构所得截面剪力和弯矩时程,对局部实体模型进行计算,得到高强螺栓上的应力时程;运用雨流计数法得到变幅应力谱,根据Miner累积损伤理论和S-N曲线,得出螺栓疲劳损伤值,并分析了预加力和法兰盘厚度对疲劳损伤的影响。结果表明:预紧力和外荷载在高强螺栓中产生的应力不能简单叠加计算,须分荷载步连续计算或通过试验获得;结构的风振效应越大,螺栓风振疲劳损伤也越显著;预紧力大小对螺栓风振疲劳性能影响显著,预紧力施加的不足或者长期损失可能使结构的疲劳寿命明显下降甚至发生疲劳破坏事故。

The study was initiated for revealing the wind-induced fatigue of high-strength bolts in flanges of a lightning rod of a transformer substation and the influence of the pretension force to bolt fatigue life. A representative frame lightning rod structure was selected and the wind-induced dynamic responses in time domain were obtained firstly from the global model by beam element. Then, the refined solid model was established to model the local area around a flange. By using the section internal forces calculated by the global model, the stress history on the bolts were obtained. The rain-flow counting method was adopted to acquire the variable amplitude stress spectrum from the stress time history, and then the fatigue damage value was obtained according to the Miner cumulative damage theory, S-N curve. Finally, the influence of different preload value and flange thickness on the fatigue performance of high-strength bolts was analyzed. The results showed that the final stress of bolt resulted from pretension force and wind load couldn’t be deduced by superposition of them from each single load;it should be calculated by two continual load steps or determined by experiment. The greater wind gust effects, the more fatigue damage of bolts. The value of pretension force is critical to the bolt fatigue. The insufficiency or loss of pretension force could decrease the fatigue life of the bolt greatly and even lead to collapse of lightning rods.