Direct Force Measurements On A SubmergedBridge Model

Abstract

A measurement system to characterise the hydrodynamic forces due to the interaction between a free surface flow and a bridge deck model of rectangular cross section has been developed. This topic has not been explored exhaustively in literature and the long lasting experience acquired in wind tunnel tests served as a reference. In addition to the wind tunnel measuring techniques the actual experimental situation raises new problems, both for the characteristics of instrumentation and the definition of boundary conditions. Two possible solutions have been analysed to evaluate the dynamic forces exchanged between the flow and the bridge: distributed pressure taps and direct force measurements. A couple of ad hoc dynamometers using strain gage transducers has been built. The dynamometers are placed inside a PVC structure, simulating a section of the bridge deck. Setting up a suitable method to electrically insulate the strain gages proved to be a major task: tests were performed to investigate the reliability and the duration of different coatings under various conditions. Accurate measurements of flow rate, free surface levels, and velocity distributions are needed to give a complete description of the problem. The paper deals with the static behaviour of the bridge section and the checks for getting reliable results passing through a metrological confirmation of the instrumentation in the particular experimental conditions and a careful data managing. The whole system proved to be reliable and able to produce repeatable results. Transactions on the Built Environment vol 56, © 2001 WIT Press, www.witpress.com, ISSN 1743-3509