Scour depth evaluation of highway bridge piers using vibration measurements and finite element model updating

Abstract

Scour of piers is one of the major causes of the bridge collapse. Most studies related to scoured bridges focus on the mechanics of bridge scour and detecting or monitoring changes in bridge characteristics caused by scour, but less on the quantitative sour evaluation. This paper proposes a novel method using measured vibration responses and finite element model updating technique to address the quantitative evaluation of existing scour depth, including general scour depth and local scour depth for the common pile foundation in short and medium-span highway bridges. The pile-soil interaction is simulated by the rotational and translational spring elements in horizontal directions. Indices including the residual of natural frequencies and frequency response functions are adopted in the objective function that is iteratively minimized. The longitudinal (i.e. the direction along the bridge axis) response excited by impulse force on bridge pier is proved to be more sensitive to the bridge scour than the transverse (i.e. the direction perpendicular to the bridge axis in the horizontal plane) response, so it is adopted in the numerical analysis. A field test was performed on a typical bridge to validate the proposed method. Test result shows the scour depth of piers can be quantitatively evaluated by the proposed method, which avoids the detailed underwater inspection and continuous vibration monitoring of the piers.