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Heavy rain in July 2020 washed away 17 bridges in Kumamoto Prefecture, Japan. This paper calculated the hydrodynamic force acting on one of the bridges washed away during the flood. One-dimensional analysis of riverbed variation was conducted based on the water level observed upstream of the bridge. The results showed that the drag exceeded the estimated strength of the bridge bearings based on the design criteria at the time of construction. The maximum drag was less than the bearing strength specified in the current design standard of the 2017 specifications for highway bridges. If the truss was completely blocked by debris, the maximum drag was about twice that of the case without blockage.
FUJISAWA et al. (Sat,) studied this question.