Evaluation of the hydrodynamic forces on an isolated building induced by a dam-break flow

Climate change is increasing the frequency and intensity of floods, exacerbating damage to buildings. In Belgium, current building standards do not account for flood risks. To address this issue, Buildwise initiated the FLOOD project to develop strategies for building flood-resilient structures. This study focuses on flow forces, encompassing both hydrostatic and hydrodynamic components. This research aims to analyze how flow forces can be computed based on water depths and velocities and to evaluate the ability of a 2D numerical model to accurately estimate these forces. To this end, laboratory experiments were conducted, simulating a dam-break flow impacting a rectangular obstacle. Force measurements revealed two distinct phases: an initial impact phase followed by a quasi-static phase. The experimental tests were then reproduced numerically using Watlab, a software developed at UCLouvain that solves the 2D shallow water equations on an unstructured mesh using a finite volume scheme. Flow forces were estimated using a physically based method, where the force is computed as the sum of the hydrostatic component and the momentum flux over a refined mesh incorporating the obstacle, and a drag-based approach, where the force is estimated as proportional to the momentum flux over a coarser mesh that excludes the obstacle. The results demonstrate that the 2D numerical model accurately reproduces the measured water depths and velocities. Furthermore, empirical formulas from the literature yield flow force estimates consistent with experimental measurements. Finally, both numerical approaches provide force predictions in good agreement with the measured values, validating their applicability for assessing hydrodynamic loads on flood-exposed structures.