Zhang Jingfeng, Jing Yuan, Li Pandao, Han Wanshui, Zhang Nan, Zhou Yunlai
Department of Bridge Engineering, School of Highway, Chang'an University, Xi'an 710064, China.
Beijing General Municipal Engineering Design & Research Institute Co., Ltd., Beijing 100866, China.
Sensors (Basel). 2019 Aug 29;19(17):3735. doi: 10.3390/s19173735.
U-shaped girder has been extensively used for its excellent adaptability in the urban railway transit system. As an open thin-walled structure, significant difference of working mechanism exists between U-shaped girder and conventional section girder (e.g., T section or box section). The thin-walled web plays significant role in the flexural performance of U type girder particularly. Moreover, severe collision may occur between the moving train and the girder, and subsequently results in the decrease of the structural bearing capacity. In this paper, a full-scale test was carried out to examine the ultimate bearing capacity and the failure mechanism of the U-shaped girder, and a refined numerical model was developed to simulate the damage evolution and the failure process. It was shown that the flexural failure occurred on the U-shaped girder under vertical loads. In addition, the ultimate bearing capacity of the structure under different web damage conditions (e.g., web damaged region or damaged range) was studied by applying the displacement based lateral load on the flange of the U-shaped girder to simulate the damage caused by accidental train collision. The numerical results have shown that the damaged web greatly affects the ultimate bearing capacity of U-shaped girder, more severe bearing capacity descending occurs around the middle span rather than the beam ends. The damaged range (length) of the web has less influence on the falling amplitude of bearing capacity. It can be concluded that the major reason accounting for the bearing capacity decrease is that the original section is weakened by the web damage, and consequently results in the buckling of the damaged web and lead to the total failure of the structure. It is recommended that the lateral resistant design for the web should be taken into consideration to ensure the operation safety of the urban railway transportation.
U形梁因其在城市轨道交通系统中出色的适应性而被广泛应用。作为一种开口薄壁结构，U形梁与传统截面梁（如T形截面或箱形截面）的工作机制存在显著差异。薄壁腹板在U形梁的抗弯性能中起着重要作用。此外，行驶列车与梁之间可能发生严重碰撞，进而导致结构承载能力下降。本文通过开展足尺试验研究U形梁的极限承载能力和破坏机制，并建立精细化数值模型模拟损伤演化和破坏过程。结果表明，U形梁在竖向荷载作用下发生弯曲破坏。此外，通过在U形梁翼缘上施加基于位移的横向荷载来模拟列车意外碰撞造成的损伤，研究了不同腹板损伤条件（如腹板损伤区域或损伤范围）下结构的极限承载能力。数值结果表明，受损腹板对U形梁的极限承载能力有很大影响，跨中附近的承载能力下降比梁端更严重。腹板的损伤范围（长度）对承载能力下降幅度的影响较小。可以得出结论，承载能力下降的主要原因是腹板损伤削弱了原截面，并因此导致受损腹板屈曲，进而导致结构整体破坏。建议考虑腹板的抗侧设计以确保城市轨道交通运营安全。
