Abstract
Field experiment on hydrodynamic forces exerted on a free-standing box-shaped structure partially submerged in inundation flow was conducted by using a metal frame setup on a natural riverbed wherein Froude number Fr ranged from 0.45 to 1.80. In result, following features were observed. Drag coefficient CD is significantly affected by both the Froude number and the blockage ratio in subcritical flows in the manner that higher CD is induced by smaller Fr as well as larger blockage, resulting in CD varying from 0.6 to 2.1. However, their effects are negligible in supercritical flows, resulting in nearly constant CD of 1.2±0.2, which may be attributed to reattachment of the separated flows on the side walls of the structure. Uplift coefficient Cupl is predominantly governed by Fr in a way of power law. With the elevation of Fr, the action point of uplift force shifts gradually to the upstream edge of the base of the structure, which develops a larger overturning moment.
