The fatigue crack characteristics and wheel load stresses of steel box girder diaphragms in an existing bridge
Li Chuanxi1 Chen Zhuoyi1 Zhou Aiguo2 Cao Shuidong1 Ke Lu1
1. Key Laboratory of the Ministry of Education, Changsha University of Science & Technology, Changsha 410114, China；
2. Foshan Road & Bridge Construction Co., Ltd., Foshan 528303, China
Abstract：The cracks in the diaphragm arc incision are common fatigue diseases of orthotropic steel deck. Due to the limitations of research methods, there is no general recognition for the fatigue mechanism of the diaphragm as yet. Thus, the characteristics of diaphragm fatigue cracks of two existing bridges was given and examined in this paper. The FEA analysis and stress test of a variety of vertical and horizontal moving load conditions for the crack-free diaphragm was conducted，and corresponding results and the laws were given. The research indicates that: (1) The cracking of diaphragm usually initials near the arcing point of far away from the U rib, the surface on both sides of the crack dislocated out of plane. (2) The stress of arcing point far away from the U rib under the wheel load is always compressive, and the absolute value is maximum. The stress on the arc incision near the diaphragm-U rib junction is tensile stress. (3) The stress caused by the out of plane bending is relatively small, especially on the crack potential initiation around the arc incision, where the stress difference between the two surfaces is almost 0. (4) The direction of compressive stress is almost perpendicular to the cracks. (5) For the background project with 16mm-thick roof and 10mm-thick U rib, the stress of U rib near the diaphragm is less than 22MPa, which almost introduce no fatigue risk. (6) The maximum absolute stress on the arc incision emerges when the location of the wheels are one U rib spacing from the diaphragm. The longitudinal loading position for maximum absolute value of the farer is just above the diaphragm.
