2种弧形切口对RF构造细节疲劳性能影响的现场监测

现场监测能真实反映结构的构造细节、边界约束和桥面加载条件,是正交异性钢桥面板疲劳评价最合理有效的方法之一。基于某正交异性桥面板钢箱梁桥,通过监测随机车流下同一车道紧邻的2个横隔板上疲劳敏感构造细节的应力响应时程,对比2种不同弧形切口正交异性钢桥面板构造细节的应力响应;通过雨流计数法获取构造细节应力谱,再基于米勒线性累积损伤准则计算疲劳等效应力幅和等效加载次数;最后基于AASHTO LRFD规范条文计算相关构造细节的疲劳寿命。研究结果表明:横隔板弧形切口构造细节总应力是面内应力分量主导,小弧形切口峰值应力时面外应力对总应力的比不大于23%,而大弧形切口仅略减小到20%,但大弧形切口削弱了横隔板腹板,使得传递面内竖向应力的面积减小,反而增大了弧形切口构造细节的应力,因而大弧形切口构造细节的疲劳寿命仅为10.6年,低于小弧形切口的14.2年;对纵肋-横隔板(Rib-to-floorbeam,RF)焊缝构造细节而言,大弧形切口减轻了RF之间的相互约束,能一定程度减小RF纵肋侧和RF横隔板侧的应力响应;但增大了RF围焊处因弯曲产生的压应力,从而导致横向泊松效应在该构造细节处产生大的二次应力;采用小弧形切口时估计的纵肋-横隔板焊缝构造细节的疲劳寿命大于100年,而采用大弧形切口对应寿命仅为31年。研究结果可为正交异性钢桥面板抗疲劳设计和加固提供有益的参考。

Investigation on Fatigue Performance of Rib-to-floorbeam Connection with Two Cutout Geometries Based on Field Monitoring

Field monitoring is recognized as one of the most effective and reliable approaches to evaluate the fatigue performance of orthotropic steel bridge decks, owing to its accurate representation of the details, boundary conditions, and in-site traffic loads. Based on an orthotropic steel deck box-girder bridge, the stress records at fatigue-prone details on two closely-spaced diaphragms were monitored under random traffic flows. The stress responses at the details with two different cutout geometries were compared. The stress range spectrums were first obtained by the rain-flow counting method. Then, the equivalent stress ranges and their loading cycles were calculated based on the Miner's rule on accumulative fatigue damage. Finally, the fatigue life at those details was estimated according to the AASHTO LRFD specifications. The results show that in-plane stress dominates the total stress at the nearby area of the cutout. The out-of-plane stress accounts for only 23% of the total stress for the small arc cutout under peak stress, while the associated one for the large arc cutout is slightly reduced to 20%. Since the large arc cutout weakens the floorbeam web, the section area transferring the in-plane vertical stress is decreased. Therefore, the stresses at the cutout detail will increase, resulting in a shorter fatigue life of 10.6 years compared with 14.2 years for the small arc cutout. Considering the three locations at the rib-to-floorbeam (RF) detail, the reduced stress levels at the RF rib side and RF floorbeam side can be expected owing to the presence of the large arc cutout, which could reduce the mutual constraint between the rib and floorbeam. However, the transverse Poisson effects driven by rib bottom compression under rib bending account for significantly high secondary stresses at the location of RF welding all-around at the large arc cutout. As a result, although the estimated fatigue life at the RF connection is over 100 years for the small arc cutout, the fatigue life is reduced to only 31 years for the detail with large arc cutout. The present results provide valuable insights for bridge engineering practice on the design and retrofit of orthotropic steel bridge decks.