WASH AWAY OF TRUSS BRIDGE DUE TO FLASH FLOOD DURING HEAVY RAIN IN JULY 2020

Abstract

 Heavy rain in July 2020 washed away 17 bridges in Kumamoto Prefecture. This paper calculated the hydrodynamic force acting on the Nishize bridge in Hitoyoshi City 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 smaller than the bearing strength specified in the seismic design standard of the 2017 Specifications for Highway Bridges. If the truss cross-section was completely blocked by driftwood, the maximum drag was about twice that of the case without blockage.