Wind-Induced Multiaxial High-Cycle Fatigue Analysis of Welded Spherical Joints of Spatial Grid Structures
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摘要: 在风荷载作用下的空间网架结构焊接球节点的疲劳为多轴高周疲劳,为保证结构风致安全,需对其进行风致多轴高周疲劳分析。首先进行焊接件单、多轴高周疲劳试验,获得焊材的基于双参数临界面法的多轴高周疲劳损伤寿命模型;再基于风洞试验数据,对网架结构进行风致响应分析,并采用子结构分析法,建立所分析焊接节点的精细化有限元模型,获得各焊接节点危险点的应力时程和等效应力时程;然后采用雨流计数法获得各个循环的起点和终点,在每个循环中确定原始应力时程并采用搜索方法确定临界面;最后基于焊材多轴高周疲劳损伤寿命模型,根据Miner线性损伤累积准则得到所有循环的累积疲劳损伤值,在此基础上预测出节点发生疲劳损伤的起始寿命。以武汉游泳馆屋顶网架结构为工程背景,对其不同位置节点进行了风致疲劳分析。结果表明:迎风面、背风面和中间节点的疲劳损伤起始寿命都远小于结构的使用寿命。说明焊接节点在结构使用年限内会发生风致疲劳损伤,应当引起工程界的关注和重视。Abstract: Because of the multiaxial high-cycle fatigue characteristics of welded spherical joints under wind load, it is necessary to do some research on the wind-induced multiaxial high-cycle fatigue of the joints in order to ensure the wind safety of spatial grid structure. A multiaxial high-cycle fatigue analysis methodology was proposed. Firstly, the high-cycle fatigue tests of weldments under uniaxial and multiaxial loading were carried out, and obtained the multiaxial high-cycle fatigue damage life model of weldments based on two-parameter critical surface method. Secondly, based on the wind tunnel test data,the wind-induced response of the grid structure was analyzed, meanwhile, the refined finite element model of the welded joints was established by using the substructure analysis method, so as to obtain the stress time-history and equivalent stress time-history of the dangerous points of each welded joint. The rainfall counts were then performed to determine the starting and ending points of each cycle and its original stress time-history, accordingly identify the critical surfaces in each cycle by using the search method. Finally, based on the multiaxial high-cycle fatigue damage life model obtained in the test, and the cumulative fatigue damage values of all the cycles were calculated according to Miner's linear accumulation criterion, on the basis of which the starting life of the joint was predicted when fatigue damage occurred. The wind-induced fatigue analysis was carried out on the joints of the roof grid structure of Wuhan Natatorium at different locations. The results indicated that the fatigue damage starting life of the windward joints, leeward joints and intermediate joints was far less than the service life of the structure. Therefore, wind-induced fatigue damage might occur on the welded joints within the service life of structure, which should be concerned in the engineering field.
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