The orthotropic steel deck is sensitive to fatigue, and a number of cracks have been found in existing bridges. Based on the long-span Guangzhou Mingzhu Bay steel arched bridge, this paper focus on the cracking process, fatigue mechanism, and fatigue performance evaluation of an orthotropic steel bridge deck under traffic load. A finite element model of a three-U-rib and three-span bridge deck was first established to investigate the stress state and the most unfavorable wheel loading position under the longitudinal wheel load. Then, four full-scale single-U-rib specimens were fabricated with high-strength lower alloy structural steel Q370qD in compliance with construction standards. High-cycle loading was subsequently implemented according to the Specification for Design of Highway steel bridge (JTG D64-2015), and the crack initiation, propagation process, and fatigue failure modes were studied. The results showed the stress at structural concern points is larger than in other locations, which was located around 35 mm from the welding seam of the U-rib and the lower end of the diaphragm plate. The Mingzhu Bay steel bridge deck meets the fatigue design requirements. However, the bottom of the welding seam between the U-rib and diaphragm plate is a dangerous fatigue position, and attention should be paid to the welding quality at this position during construction.
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