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

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.