正交异性钢桥面板横隔板弧形切口疲劳性能

Fatigue performance of floorbeam cutout on orthotropic steel bridge decks

为了揭示正交异性钢桥面板弧形切口母材的开裂机理,采用有限元程序ANSYS建立钢箱梁节段模型与钢桥面板单元子模型,为确保计算的精确性,进行了网格无关性检查,分析了弧形切口疲劳细节在移动轮载作用下的应力响应特征,分别采用热点应力法与名义应力法评估了弧形切口细节的疲劳性能,并研究了横隔板厚度与切口形状对构造细节应力的影响。研究结果表明:弧形切口细节应力影响线长度在纵桥向为横隔板间距的2倍,因而可用疲劳车的中轴组单独加载,根据AASHTO LRFD,1辆5轴疲劳车会在该构造细节上产生2或3个应力循环;弧形切口在纵、横桥向的最不利荷载位置分别为轮载中心作用于纵肋腹板与面板交界处和中轴前轮作用于距横隔板0.3m处;弧形切口边缘应力集中点的应力方向与水平面的倾角为67.2°;疲劳评估结果与名义应力提取位置密切相关,可采用热点应力法并基于FAT125的疲劳寿命曲线进行弧形切口的疲劳评价,也可根据疲劳等效原则提取距切口边缘5mm处的应力,并基于名义应力法开展疲劳评价;建议采用Eurocode 3中圆弧半径较大的公路桥梁切口形状,其热点应力与研究的切口形状相比降低了12.4%,且当横隔板厚度不小于12mm时,弧形切口细节的应力幅小于截止应力幅,为无限疲劳寿命;横隔板弧形切口的开裂与切口形状不佳、横隔板厚度偏小、制造工艺不完善以及货车通行量大等因素密切相关。

In order to reveal the mechanism involved in base-metal cracking of floorbeam cutout on orthotropic steel bridge deck, the finite element program ANSYS was employed to establish both the segmental model of steel box girder and the local submodel of bridge deck, and the check of mesh independent was conducted to ensure the calculating precision. Thereby, the stress response characteristics of floorbeam cutout were analyzed under moving wheel loads, the fatigue evaluations were performed based on hot spot stress method and nominal stress method, respectively, and the influences of floorbeam thickness and cutout shape on the stress of structural detail stress were discussed. Research result shows that the length of stress influence line of floorbeam cutout detail in longitudinal direction of bridge is 2 times of floorbeam spacing, thus, loading with merely middle-axle group is appropriate. According to AASHTO LRFD, a fatigue truck with five axles can generate 2 or 3 stress cycles at the structural detail. The worst longitudinal and transverse loading locations of floorbeam cutout are the wheel loads center locating at the intersection of rib wall and deck plate, and the front wheel of middle-axle group locating at 0.3 m from the floorbeam, respectively. The angle between the stress direction of stress concentration point of floorbeam cutout edge and the horizontal plane is 67.2~. Fatigue assessment result is closely relevant to the nominal stress extraction position. The hot spot stress method based on fatigue life curve of FAT125 is feasible for the fatigue assessment of floorbeam cutout. According to the equivalent principle of fatigue damage, the stress at 5 mm from cutout edge can also be extracted for the fatigue assessment base on the nominal stress method. It is suggested that the cutout shape in Eurocode 3 （highway bridge） with a large curve radius is preferable, and the hot spot stress reduces by 12.4% compared with the researched cutout shape. The stress range is below the cut-off limit as the thickness of floorbeam is not less than 12 mm, hence the cutout reaches a infinite fatigue life. Floorbeam cutout cracking is related to poor cutout shape, thin floorbeam, imperfect fabrication technology and high truck traffic volume.4 tabs, 21 figs, 27 refs.