Hydrodynamic Forces On A Submerged Bridge

Abstract

We consider the problem of the hydrodynamic interactions between an open channel flow and a bridge deck. The relationship between drag and lift coefficients and characteristic state variables of the flow is of interest for a proper estimation of mean dynamic forces exerted by the flow on the structure. The recent survey of Ballio et al. [ l ] showed that the problem has not been extensively studied in the past, even though the knowledge of hydrodynamic forces plays a major role in assessing the vulnerability of a bridge structure. Most theoretical and experimental work in the literature is concerned with obstacles in an infinite uniform flow field and only a few consider interactions between free surface stream and man-made structures. We analyse the problem by means of dimensional analysis and perform a series of experimental measurements of time-varying forces acting on a bridge deck in a laboratory flume. The bridge structure was modelled by a rectangular cross section box. A pair of ad hoc dynamometers were placed inside the hollow structure and connected to an automatic acquisition system. Measurements of forces were taken for fully submerged structure. Experiments are compared with theoretical values obtained upon application of the momentum equation in the direction of flow, under some simplifying assumptions.