Isolating the location of scour-induced stiffness loss in bridges using local modal behaviour

Abstract

Detecting scour by analysing bridge vibrations is receiving an increasing amount of attention in the literature. Others have considered changes in natural frequency to indicate the presence of scour damage; however, little work has been reported on identifying the location of a scour hole based on vibration measurements. In this paper, a numerical study is carried out using a bespoke vehiclebridge-soil dynamic interaction model to examine how the first six vibration modes (Eigen frequencies) of a typical integral bridge are affected by scour at different locations. It is found that depending on the location of the scour hole, some modes are much more affected than others in terms of frequency changes. In fact, a clear pattern emerges as to which modes are affected by which scour location. Using this knowledge, the location of a scour hole can potentially be detected on a real bridge. However, recognising that it is not possible to undertake an eigenvalue analysis on an actual bridge, an analysis is performed by collecting acceleration signals from various points on the structure. The bridge is loaded by a realistic vehicle model, incorporating vehicle-bridge interaction effects, which leads to the generation of discrete acceleration signals at various 'sensor' locations on the bridge. In this paper, it is found that it is possible to detect the location of a scour hole using a relatively small number of 'sensors'. However, to achieve this, careful signal processing is necessary and advice on a number of pertinent issues is provided.

Structural Health Monitoring for Performance Assessment of Bridges under Flooding and Seismic Actions

“…Such scour fragility functions should be calibrated via soil-structure models in order to capture the global behaviour of the soil-structure system. 6,[24][25][26]…”

“…Methods based on frequency changes can be reliably applied to detect damage, 6,24,53 although they are usually unable to provide adequate information about the location of the damage (however, for a recent study related to scour damage localisation, see Ref. [26]). More effective methods for detecting the location of seismic-induced damage include those based on the analysis of changes in modal 52 or operational [54][55][56][57][58] shapes or their derivatives.…”

Recent Development and Remaining Challenges In Determining Unique Bridge Scour Performance Indicators

“…Most of these methods involve measuring the dynamic response of a bridge or bridge element using an accelerometer or otherwise, and observing how modal properties change when the foundation stiffness is compromised by scour. A variety of authors have investigated various aspects of the potential applicability of these approaches, in (Briaud et al , 2011;Chen, et al, 2014;Elsaid & Seracino, 2014;Foti & Sabia, 2010;Klinga & Alipour, 2015;Prendergast, et al 2013Prendergast, et al , 2016Prendergast, et al and 2017.…”

“…One of the more pressing and less investigated problems with vibration-based scour monitoring is where to place sensors to ensure the desired modal characteristics of the structure under investigation are detected. A recent study by Prendergast et al (2017) postulated that various sub-structural bridge elements (piers, abutment, and piles) act locally when affected by scour. This implies that a mode of vibration 1 8/ 1 3 ( 3) local to the pier, is only affected by scour at the pier (and other elements are unaffected).…”

“…Sensor locations to locate the scour holes on the two-span integral bridge(Prendergast, Gavin, & Hester, 2017) …”