斜拉桥锚拉板疲劳评估及足尺模型疲劳试验

Fatigue Assessment and Fatigue Test of the Full-Scale Model of Tensile Anchor Plate of Cable-Stayed Bridges

为了研究斜拉桥锚拉板关键疲劳细节的疲劳性能并对锚拉板关键疲劳细节进行疲劳评估,以乌江大桥为工程背景,根据MIDAS全桥杆系模型交通荷载下的索力幅值计算结果,选取了该桥最不利的中跨尾索锚拉板作为研究对象,采用通用有限元软件ANSYS建立了锚拉板三维分析模型并根据计算结果识别关键疲劳细节。结合JTG D64—2015《公路钢结构桥梁设计规范》、美国规范AASHTO LRFD Bridge Design Specifications以及欧洲规范Eurcode 3,采用名义应力法对锚拉板关键疲劳细节进行疲劳评估,同时建立热点应力局部分析模型并结合欧洲规范Eurcode 3和国际焊接学会规范,采用热点应力法对锚拉板结构关键疲劳细节进行疲劳评估,并对各规范的评估方法进行了对比分析,与此同时开展了锚拉板足尺模型疲劳试验研究。理论分析结果表明:锚拉板与边腹板对接焊形成的锚拉板结构,其最不利位置为锚拉板与锚拉筒上部焊缝圆弧过渡处(细节A),需重点关注该细节。乌江大桥锚拉板结构关键疲劳细节采用名义应力法评估均满足三种规范中无限疲劳寿命设计要求,从疲劳荷载效应、名义应力取值、板厚效应以及细节分类等方面对三种规范的无限疲劳寿命设计方法进行对比,分析发现:采用欧洲规范进行无限疲劳寿命设计更为保守,从结构安全性角度考虑,推荐采用Eurcode 3对锚拉板进行名义应力无限疲劳寿命设计。热点应力法分析结果表明:乌江大桥锚拉板满足Eurocode 3要求,相较于名义应力法,热点应力法的取值结果更为客观,疲劳强度-疲劳寿命(S-N)曲线相对统一,且受主观因素的影响较小。条件允许的情况下,推荐采用热点应力法对焊趾处细节进行疲劳评估。足尺模型疲劳试验结果表明:疲劳荷载加载200万次后结构仍处于弹性阶段,刚度未发生明显折减,结构表面未发现肉眼可见裂纹,增大疲劳荷载幅至640 kN,继续加载到300万次(等效为按初始疲劳荷载幅共加载约500万次),结构仍未开裂,锚拉板满足无限疲劳寿命设计要求。理论分析和模型试验均表明,乌江大桥锚拉板设计合理,抗疲劳性能满足工程要求。

In order to study the fatigue performance and fatigue assessment method of the key fatigue categories of the gusset plate anchorage device of cable-stayed bridges, with the Wujiang Bridge as the engineering background, according the cable force amplitude under the traffic load of the Midas full bridge model, the last cable anchor plate of mid-span of this bridge was selected as the research object. This paper establishes a three-dimensional finite element analysis model of the gusset plate anchorage device for fatigue assessment. The nominal stress method and the hot spot stress method was used to assessment the key fatigue details of the gusset plate anchorage device with JTG D64-2015, ASSHTO LRFD Bridge Design Specifications and Eurocode 3. The assessment methods of each code were compared and analyzed. At the same time, the fatigue test of the full-scale model of the gusset plate anchorage device was carried out.The theoretical analysis results showed that: the most unfavorable position of tensile anchor plate structure formed by the butt welding of was tensile anchor plate and the side web was the excessive arc of the upper welding seam of the tensile anchor plate and the anchor cylinder(detail A), which required special attention;the key fatigue details of the tensile anchor plate structure met the infinite life design requirements by nominal stress methods with those specifications, and the results were more secure when used Eurocode 3. From the perspective of structural safety, it was recommended to adopt Eurocode 3 to infinite life fatigue design of anchor plates by nominal stress.The analysis results of the hot-spot stress method showed that the tensile anchor plate of the Wujiang Bridge met the requirements of the specification. The results of the hot-spot stress method were more objective than the nominal stress method, and its fatigue strength-life(S-N) curve was relatively uniform and was less affected by subjective factors. Therefore, it was recommended to use the hot-spot stress method to evaluate the fatigue of the weld toe of the tensile anchor plate.The full-scale fatigue test results showed that the structure was still in the elastic stage after the fatigue loading 2 million times, the stiffness had not been significantly reduced, and no visible cracks were found on the surface of the structure. The fatigue load amplitude increased to 640 kN and the fatigue load was continued to 3 million times. It was equivalent to loading approximately 5 million times according to the initial fatigue load amplitude, the structure was still not cracked, and the gusset plate anchorage devices met infinite life design. Both theoretical analysis and full-scale model fatigue test showed that the design of the tensile anchor plate of the Wujiang Bridge had reasonable design, and its fatigue properties met requriement of actual engineering.