斜拉桥钢桥面板顶板-U肋-横隔板过焊孔细节群数字疲劳试验

为研究多场耦合作用下斜拉桥钢桥面板疲劳裂纹的扩展机理，建立了跨尺度斜拉桥全桥数字疲劳试验模型；通过模拟顶板-U肋-横隔板过焊孔细节群处多道焊缝的焊接全过程，将焊接残余应力引入数字疲劳试验模型中；基于扩展有限元法，在多场耦合作用下对顶板-U肋-横隔板过焊孔细节群处典型疲劳裂纹进行扩展机理的数字断裂参数分析与扩展行为的数字疲劳试验。研究结果表明:在顶板-U肋-横隔板过焊孔细节群处存在较大的残余拉应力，其最大值接近钢材的屈服强度，焊接残余应力对钢桥面板疲劳性能的影响不可忽略；后续焊缝会影响已有焊缝区域的应力场分布，在分析计算多道焊缝影响区域的焊接残余应力场时，需模拟多道焊缝的焊接全过程；在恒载应力场、活载应力场和焊接残余应力场的多场耦合作用下，按复合型裂纹扩展的工程准则，顶板-U肋-横隔板过焊孔细节群处4种典型疲劳裂纹的最大等效应力强度因子幅均大于疲劳裂纹扩展阈值，均将在疲劳循环荷载作用下发生疲劳扩展；在多场耦合作用下，过焊孔上方顶板-U肋连接焊缝的顶板侧焊趾处疲劳裂纹和U肋侧焊趾处疲劳裂纹均为以Ⅰ型裂纹为主导的Ⅰ-Ⅱ-Ⅲ型复合裂纹，Ⅱ型和Ⅲ型裂纹的影响不容忽略；过焊孔上方顶板-U肋连接焊缝的顶板侧焊根处疲劳裂纹和横隔板过焊孔边缘处疲劳裂纹均为Ⅰ型裂纹；建立的多场耦合作用下多尺度数字疲劳试验可为运营阶段大跨度桥梁钢桥面板疲劳裂纹的扩展提供分析与模拟方法。 

Digital fatigue test of detail group at deck-U rib-diaphragm access hole of steel bridge deck in cable-stayed bridge

To investigate the fatigue crack propagation mechanism of steel bridge deck in cable-stayed bridges under the multi-field coupling effect, a model for the multi-scale digital fatigue test of the whole cable-stayed bridge was constructed. The entire welding process of the multi-pass welds at the detail group at the deck-U rib-diaphragm access hole was simulated to introduce the welding residual stress into the model for the digital fatigue test. The digital fracture parameter analysis and the digital fatigue test were conducted under the multi-field coupling effect by the extended finite element method to clarify the propagation mechanism and propagation behavior of typical fatigue cracks of the detail group at the deck-U rib-diaphragm access hole. Research results show that the high residual tensile stress can be observed at the detail group at the deck-U rib-diaphragm access hole, with a maximum being close to the yield strength of steel. The influence of the welding residual stress on the fatigue performance of the steel bridge deck cannot be ignored. Subsequent welds affect the stress field distribution in the existing weld area. Therefore, the entire welding process needs to be simulated when the welding residual stress field in the influence range of multi-pass welds is analyzed and calculated. Under the multi-field coupling effect of dead-load stress field, live-load stress field and welding residual stress field, the maximum equivalent stress intensity factor ranges of four typical types of fatigue cracks of the detail group at the deck-U rib-diaphragm access hole are all larger than the fatigue crack propagation threshold according to the engineering criterion for the propagation of mixed cracks. In this case, the four types of fatigue cracks all propagate under the cyclic fatigue loading. Under the multi-field coupling effect, the fatigue cracks initiating from the deck-side weld toe of the deck-to-U rib welded joint above the access hole and those initiating from the U rib-side weld toe of the U rib-to-diaphragm welded joint are all mixed cracks of modes Ⅰ, Ⅱ, and Ⅲ dominated by mode-Ⅰ cracks. Nevertheless, the influences of mode-Ⅱ and mode-Ⅲ cracks cannot be overlooked. The fatigue cracks initiating from the deck-side weld root of the deck-to-U rib welded joint above the access hole and those initiating from the edge of the diaphragm access hole are all mode-Ⅰ cracks. The muti-scale digital fatigue test constructed under the multi-field coupling effect can provide analysis and simulation methods for the fatigue crack propagation in the steel bridge deck of a long-span bridge in operation. 1 tab, 28 figs, 32 refs.