钢桥面板纵肋与横隔板连接位置疲劳损伤特征

纵肋与横隔板连接是控制钢桥面板耐久性的关键构造细节，其在轮载作用下应力传递复杂，构造设计不当极易引起疲劳裂纹。目前常规式纵肋与横隔板连接在运营过程中可能发生的疲劳裂纹形式有横隔板弧形开孔裂纹、焊缝端部横隔板裂纹、焊缝端部纵肋水平裂纹或竖向裂纹，针对常规式连接的不足，设计上进一步提出内肋式和无缝式2种构造类型。采用有限元方法，以纵肋与横隔板连接可能出现裂纹的4类细节为对象，基于应力影响面分析，讨论了车辆轮载移动对各细节局部受力的影响，研究了常规式、内肋式和无缝式3种构造类型的疲劳损伤特征。结果表明：轮载作用下4类细节的局部效应非常显著，纵向影响区域约在3道横隔板之间，横向影响区域约在2个纵肋范围；考虑轮迹横向概率分布，各细节应力幅横向折减系数在0.94~0.97范围内。常规式连接弧形开孔细节应力幅最大，主要受面内变形控制，纵肋壁板水平细节次之，表现出明显的面外弯曲特性。与常规式连接相比，内肋式连接纵肋壁板水平细节和竖向细节最大应力幅分别降低28%和29%，减缓了纵肋在焊缝端部的应力集中程度。无缝式连接可能的疲劳破坏形式减少为横隔板焊趾开裂和纵肋壁板焊趾开裂2类，分析发现这2类细节均主要处于受压状态。常规式连接疲劳寿命预估为41.2年，纵肋壁板出现水平裂纹导致疲劳破坏的可能性较大；内肋式连接疲劳寿命由横隔板弧形开孔细节控制，较常规式连接提高58%；无缝式连接疲劳寿命预估为85.3年，较常规式和内肋式连接分别提高107%和31%，且两细节寿命相近，从全寿命设计角度考虑该构造更为合理。

Fatigue Damage Characteristics of Rib-to-diaphragm Joints in Orthotropic Steel Deck

Longitudinal rib-to-diaphragm joints are the key structural detail that controls the durability of orthotropic steel deck. Fatigue cracks easily occur in this joint because of complex stress transfer and improper structural design. For conventional rib-to-diaphragm joints during the period of service, fatigue cracks may occur in the cut-outs of the diaphragm, in the diaphragm web at the weld toe, or in the longitudinal rib at the weld toe, including horizontal cracks and vertical cracks. Considering the deficiency of conventional connections, two new configurations are proposed in the design:internal rib joints and seamless joints. Four details of possible cracks in the rib-to-diaphragm joints are interpreted as objects. The finite element method was used to analyze the influence of the moving wheel load on the local stresses of four details, and the fatigue damage characteristics of conventional, internal rib, and seamless joints were studied. The analysis results demonstrate that the local effects of the four details in the rib-to-diaphragm joints are significant under wheel loading. The longitudinal influence area of the wheel load is approximately two diaphragm distances, and the laterally influenced area is approximately two longitudinal ribs. When the transverse distribution of wheelmark is considered, the transverse reduction coefficients of equivalent stress range between 0.94 and 0.97. For the conventional joints, the largest stress range is in the cut-outs detail, which is mainly controlled by the in-plane deformation; the second largest stress range is in the horizontal detail on the longitudinal rib wall, which is mainly controlled by the out-plane deformation. For the inner rib joints, the maximum stress range of horizontal detail and vertical detail on the longitudinal rib wall are reduced by 28% and 29%, respectively, compared with the conventional one, which reduces the stress concentration of the longitudinal rib at the end of the weld. The stress state of each detail of the seamless joint is obviously different from that of other joint types with cut-outs on the diaphragm and is mainly in the compression state. The fatigue failure modes of seamless joints are reduced to two types:cracking at the weld toe in the diaphragm and cracking at the weld toe in the longitudinal rib. Findings conclude that the two details are mainly in the state of compression. The fatigue life of the conventional joints is estimated to be 41.2 years, and the fatigue failure is more likely to be horizontal crack on the longitudinal rib wall. The fatigue life of the inner rib joints is controlled by the cut-outs detail H3 of the diaphragm, which is 58% higher than that of the conventional joints. The fatigue life of the seamless joints is estimated to be 85.3 years, which is 107% and 31% higher than that of the conventional and inner rib joints, respectively. Because the fatigue life of each detail of the seamless joint is similar, using them is more reasonable from the perspective of life-cycle design.