Chapter 13 Vibration-Based Scour Monitoring: Prototype Design, Laboratory Experiments and Field Deployment Sez Atamturktur and Abdul Khan Abstract Scouring is caused by the removal of bed material surrounding the piers and abutments and can rapidly compromise the integrity of a bridge structure and cause catastrophic failure. Such failures, which occur most frequently during peak flow periods, such as flooding, are a hindrance to emergency personnel trying to enter affected areas and to individuals trying to evacuate. As a countermeasure to mitigate the effects of the bed degradation, this article presents a vibration-based scour monitoring technique. This novel approach exploits the differences between the measured lowfrequency ambient excitations of a thin, flexible plate located in the flow and the same plate located in the sediment. The underlying principle is that a flexible plate excited by the turbulent flow vibrates at significantly higher amplitude compared to an identical plate placed within sediment. Laboratory and field results obtained at various flow conditions indicate that the vibration-based scour monitoring concept is able to supply reliable information regarding both scour and refill processes. This article details the underlying monitoring concept, the design and optimization of sensors, the evaluation of sensitivity of the developed sensors to environmental conditions, and their long-term field deployment. Keywords Scour monitoring • Riverbed detection • Pier protection from scour • Structural health monitoring • VTP sensors 13.1 Introduction Riverbed scouring entails the abrasion of the material surrounding the bridge piers and abutments by high velocity flows typically during flood events and hurricanes. Scouring has a negative effect on the foundation support of the bridge abutments and piers, and can ultimately lead to bridge failure risking public safety. Bridges are essential for the evacuation and relief efforts during a flood or hurricane event; thus, scour induced bridge failure causes losses beyond those associated with the replacement bridge. Scour monitoring using portable or permanently installed instrumentation is listed as a viable option for prevention of scour induced bridge failure in the Federal Highway Administration’s Highway Engineering Circular #23 [1]. The primary advantage of scour monitoring over other countermeasures (such as riprap and/or armor installation as well as channel and bank control measures) is its low cost and rapid deployment potential. Since early 1990s, significant efforts have been dedicated to the development and investigation of scour monitoring systems. Some prominent examples of existing monitoring systems include sonar fathometers, the time domain reflectometry (TDR) and magnetic sliding collar. These monitoring techniques, however, are sensitive to environmental and/or flow conditions, such as temperature, salinity, turbidity, air entrainment and debris. Such sensitivity hinders the effectiveness of these existing monitoring sensors and makes the development of a sensing technique that exhibits robustness against such environmental and flow conditions necessary. The concept behind our novel approach is simple: several dynamic sensors mounted on thin, flexible plates (referred to as VTPs) distributed along the length of a pier or abutment reveal the difference in the vibration levels of sensors that are in the river and subjected to the natural turbulence of the river flow and those that are in the sediment and not exposed to the turbulence [2]. A number of VTPs placed in a sealed pipe that is driven into the riverbed near the abutment or pier of interest measure the time history of the vibration levels. The proposed scour monitoring method yields point measurements, hence, the steel pipe must be buried near the bridge pier or abutment at the location where the riverbed measurements are desired. Once the vibration levels are monitored in the time domain, various metrics (such as root-mean-square) can be used to reduce the high dimensionality of the collected time-history data and extract information regarding the changes in S. Atamturktur ( ) •A. Khan Glenn Department of Civil Engineering, Clemson University, South Carolina, USA e-mail: sez@clemson.edu © The Society for Experimental Mechanics, Inc. 2015 C. Niezrecki (ed.), Structural Health Monitoring and Damage Detection, Volume 7, Conference Proceedings of the Society for Experimental Mechanics Series, DOI 10.1007/978-3-319-15230-1_13 137
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