Assessment of bridge natural frequency as an indicator of scour using centrifuge modelling
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ORIGINAL PAPER
Assessment of bridge natural frequency as an indicator of scour using centrifuge modelling Kasun D. Kariyawasam1 · Campbell R. Middleton1 · Gopal Madabhushi1 · Stuart K. Haigh1 · James P. Talbot1 Received: 10 January 2020 / Revised: 15 June 2020 / Accepted: 1 July 2020 © The Author(s) 2020
Abstract One of the most prevalent causes of bridge failure around the world is “scour”—the gradual erosion of soil around a bridge foundation due to fast-flowing water. A reliable technique for monitoring scour would help bridge engineers take timely countermeasures to safeguard against failure. Although vibration-based techniques for monitoring structural damage have had limited success, primarily due to insufficient sensitivity, these have tended to focus on the detection of local damage. High natural frequency sensitivity has recently been reported for scour damage. Previous experiments to investigate this have been limited as a result of the cost of full-scale testing and the fact that scaled-down soil-structure models tested outside a centrifuge do not adequately simulate full-scale behaviour. This paper describes the development of what is believed to be the first-ever centrifuge-testing programme to establish the sensitivity of bridge natural frequency to scour. A 1/60 scale model of a two-span integral bridge with 15 m spans was tested at varying levels of scour. For the fundamental mode of vibration, these tests found up to a 40% variation in natural frequency for 30% loss of embedment. Models of three other types of foundation, which represent a shallow pad foundation, a deep pile bent and a deep monopile, were also tested in the centrifuge at different scour levels. The shallow foundation model showed lower frequency sensitivity to scour than the deep foundation models. Another important finding is that the frequency sensitivity to “global scour” is slightly higher than the sensitivity to “local scour”, for all foundation types. The level of frequency sensitivity (3.1–44% per scour depth equivalent to 30% of embedment of scour) detected in this experiment demonstrates the potential for using natural frequency as an indicator of both local and global scour of bridges, particularly those with deep foundations. Keywords Vibration-based scour monitoring · Bridge scour · Natural frequency · Centrifuge modelling · Integral bridge
1 Introduction Bridge scour refers to the removal of soil from around structural foundations located in a river or coastal region as a result of the erosive action of water [1]. Scour around a * Kasun D. Kariyawasam [email protected] Campbell R. Middleton [email protected] Gopal Madabhushi [email protected] Stuart K. Haigh [email protected] James P. Talbot [email protected] 1
Department of Engineering, University of Cambridge, Cambridge, UK
bridge foundation leads to a reduction in bridge stiffness and stability because of the loss of embedment, which can even lead to bridge failure. According to historical bridge failure surveys, more than 50% of bridge failures have primarily be
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