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A Review of Vibration-Based Scour Diagnosis Methods for Bridge Foundation, 2023 Zhang et al. Foundation scour poses a serious threat to bridge safety in the whole life cycle and leads to many bridge failure incidents. Recently, as an important subfield of bridge structural health monitoring, vibration-based scour diagnosis methods have garnered widespread attention, particularly due to their rapid and low-cost features, which overcomes the difficulties of complex equipment installation associated with the traditional approaches. Recent advances of this method within the last decade are reviewed in this paper. Firstly, the principle of scour diagnosis and vibration excitation methods are introduced. Then, existing qualitative and quantitative studies on scour diagnosis are reviewed, respectively. The former refers to identifying the scour location based on the bridge dynamic characteristics or dynamic response changes, and the latter refers to identifying scour depth based on model updating or machine learning methods. Based on the above review, some important but neglected issues are summarized and discussed in depth, and some challenges and future trends are proposed, including innovative excitation methods, mitigation of environmental conditions interference, soil–structure interaction prediction and application of machine learning techniques. PDF can be downloaded.
Wavelet-based operating deflection shapes for locating scour-related stiffness losses in multi-span bridges, 2023 O'Brien et al. Scour erosion poses a significant risk to bridge safety worldwide and affects the stiffness of the soil-foundation system, resulting in global changes in the dynamic behavior of the bridges. In this paper, a new approach to detect scour at multiple locations is proposed, using wavelet-based Operating Deflection Shape (ODS) amplitudes. A numerical model of a bridge with four simply supported spans resting on piers is used to test the approach. Scour is modelled as a reduction in vertical foundation stiffness under one or multiple bridge piers. A fleet of passing trucks, modelled as half-car vehicles, are used to excite the bridge to enable structural accelerations be calculated at each support. The approach is shown to be effective with acceleration measurements at each support location in a multi-span bridge. Using a fleet of passing vehicles, the temporal accelerations measured at each support are averaged and transformed into the frequency–spatial domain, in order to estimate the wavelet-based ODS for a given scour case. A damage indicator is postulated based on differences between the ODS of healthy and scoured bridge cases. The damage indicator enables visual identification of the location of scoured piers considering a range of natural frequencies of the system. PDF can be downloaded.
A review of bridge scour monitoring techniques and developments in vibration based scour monitoring for bridge foundations, 2023 Kazemian et al. Scour is the gradual erosion of the sediment around a bridge foundation and is one of the leading causes of bridge failure. This erosion is caused by turbulence and sediment transport mechanisms and worsens during high-water flow, such as flooding. A severely scoured bridge is a safety concern for commuters. Monitoring systems are sometimes used to provide indications of the scour extent. Most scour monitoring systems require underwater installation, which is inherently difficult to implement for existing structures. Data obtained from such systems may not necessarily be accurate due to factors such as site temperature fluctuations, or the presence of large debris in the channel causing faulty readings during times of high flooding. Inaccuracy in this data is a problem because it could display erroneous results, leading to a false sense of security. Researchers worldwide are exploring vibration-based techniques to monitor scour to overcome this challenge. These techniques can possibly monitor scour without any underwater installation and may be more efficient than the traditional underwater technologies currently implemented. This review piece aims to present a summary of the several types of scour monitoring techniques traditionally used to monitor scour of bridge structures and the advancement in technology for existing monitoring techniques based on the vibration characteristics of bridges. The importance of monitoring scour progression focused on vibration-based techniques will be discussed as well as providing a fair appraisal of these techniques. This review piece shows evidence through laboratory and field experiments that monitoring a structure based on vibrational changes due to scour is possible, and with the advances in technology over the most recent decade, it is now possible to design cost-effective and accurate scour monitoring systems for future field implemented structural health monitoring projects. This evidence is relevant to future researchers for the implementation of prospective bridge vibration-based systems. PDF can be donwloaded.
Field tests and numerical analysis of the effects of scour on a full-scale soil–foundation–structural system, 2022 Tubaldi et al. Scour is the prevailing cause of bridge failure worldwide, leading not only to traffic disruption, but also to social and economic losses and even to casualties. Many vibration-based monitoring techniques have been proposed for identifying the scour location and extent, based on the evaluation of the changes of the bridge modal properties due to scour. This study describes the experimental and numerical research carried out to investigate the effects of scour on the dynamic properties of structures with shallow foundations. Although these are the most vulnerable ones, they have received less attention compared to structures founded on pile foundations. To fill some existing knowledge gaps, field experiments were carried out on EuroProteas, a structural prototype with shallow foundation that was subjected to increasing levels of scour. The changes of the dynamic properties of the system are evaluated by postprocessing the ambient vibration recordings and by developing various models of the soil–foundation–structural system with different descriptions of the soil–structure interaction problem. The study results shed light on the effects of scour on systems with shallow foundations and on the accuracy of alternative modelling approaches. They are presented here to inform the development and validation of vibration-based techniques and modelling strategies for bridge scour identification. PDF can be downloaded.
Scour Repair of Bridges Through Vibration Monitoring and Related Challenges, 2022 Micu et al, Scour in railway bridges is often an important problem, especially for old bridges. In this regard, the assessment of full-scale bridges to establish scour repair adequacy or efficiency is an important question. Typically, scour weakens the bridge structure by modifying its boundary conditions. Such changes, when significant enough, can lead to changes in modal properties and in vibrations measurements with respect to the ideal baseline. On the other hand, a repair attempts to restore the release in boundary conditions. Consequently, a repair also changes the modal properties and the dynamic responses. This indicates that significant and consistent changes of bridges before and after repair can indicate the adequacy and efficiency of scour repair. This paper addresses this idea by carrying out a full-scale test on scour repair of a train bridge in Ireland. The bridge is monitored on two abutments with several wireless accelerometers while the bridge is operational. Both ambient and train passage events are considered in terms of collection of vibration data. While it is not possible to discern the difference between repaired and scour-damaged conditions, it is observed that time domain markers may be more consistent in indicating repair efficiency as compared to its frequency domain counterpart. This full-scale demonstration is expected to act as a full-scale example for vibration-based repair monitoring and performance criteria for future detection algorithms. The approach does not require the bridge to be closed down and can be relevant for other sensors as well. Would need to be requested.
The value of different monitoring systems in the management of scoured bridges, 2022 Giordano, Prendergast, Limongelli. Bridge scour is a leading cause of failure for bridges over waterways and is very difficult to detect accurately. Due to the large number of bridges on typical networks and the limited availability of financial resources within asset agencies, decision-makers must prioritize certain structures when it comes to management in the event of flooding. In response to the notable challenges associated with scour detection, methods that can monitor the actual performance of a scoured bridge have become popular in recent years, especially dynamic Structural Health Monitoring (SHM). One such approach relies on monitoring changes in the natural frequency of a bridge structure due to the occurrence of scour, which represents a change in the structural boundary conditions and therefore results in a change in modal behavior. A further reduction of the uncertainty involved in the problem can be obtained by monitoring the scour depth. The decision to install a monitoring system on a bridge must be balanced by the financial benefit of doing so, as limited resources often need to be carefully rationed. The Value of Information (VoI) from Bayesian decision analysis can be used to compute the benefit of installing a permanent monitoring system (scour or structural monitoring system). The VoI can be defined as the expected reduction in management cost related to informed decision-making, that is when the decision is aided by the newly acquired information. A case study is presented whereby different monitoring systems are considered to be installed on a typical bridge to support emergency management during a flood. A comparison of the relevant benefits, accounting for multiple flood events and scenarios, is carried out to identify the optimal monitoring strategy. PDF can be downloaded.
Quantifying the value of SHM information for bridges under flood-induced scour, 2022 Giordano, Prendergast, Limongelli. Bridge scour is a leading cause of failure for bridges over waterways and is notoriously difficult to detect with accuracy. Dynamic Structural Health Monitoring (SHM) of bridges for scour has gained traction in recent years as monitoring systems have improved and the reliability of measurements increased. Due to the large number of bridges on typical networks and the limited financial resources within asset management agencies, decision-makers must prioritize certain structures when it comes to management in the event of flooding. The decision to install a dynamic SHM system on a bridge must be balanced by the financial benefit of doing so, as limited resources often need to be carefully rationed. In this paper, a methodology is proposed to evaluate such benefit based on the Value of Information (VoI) from Bayesian decision analysis. A case study is presented whereby a dynamic SHM system is considered to be installed on a typical bridge with the aim to support emergency management operations during flooding. The proposed methodology allows computation of the financial benefit of installing a dynamic SHM system over a certain reference period, thus accounting for multiple flood events and scenarios. The various elements of the procedure are discussed in detail. Full-text.
Advances in vibration-based scour monitoring for bridge foundations, 2021 Lan et al. Scouring around bridge foundations is one of the main factors causing structural amage of bridges. Traditional scour monitoring techniques generally require a large number of sensing devices set up underwater, which is difficult to be implemented for actual bridges. To address this issue, scour monitoring technology based on structural vibrations is paid attention gradually, because this technique can work well with less equipment and can be free from the influence of the submerged environment. This study presents a systematic summary and analysis of the selection of scour indicators, sensor deployment principles and other related research involved in scour monitoring technology based on structural vibration. On this basis, the research status of the bridge scour monitoring method based on vehicle excitation is further summarized. Finally, the prospects for the application of vibration-based bridge foundation scour monitoring technology are presented, discussing the technologies that are currently missing and urgently needed for this monitoring method and the challenges faced today. Full-text.
Laboratory investigation of a bridge scour monitoring method using decentralized modal analysis, 2021 Khan et al. Scour is a significant issue for bridges worldwide that influences the global stiffness of bridge structures and hence alters the dynamic behavior of these systems. For the first time, this paper presents a new approach to detect bridge scour at shallow pad foundations, using a decentralized modal analysis approach through re-deployable accelerometers to extract modal information. A numerical model of a bridge with four simply supported spans on piers is created to test the approach. Scour is modelled as a reduction in foundation stiffness under a given pier. A passing half-car vehicle model is simulated to excite the bridge in phases of measurement to obtain segments of the mode shape using output-only modal analysis. Two points of the bridge are used to obtain modal amplitudesin each phase, which are combined to estimate the global mode shape. A damage indicator is postulated based on fitting curves to the mode shapes, using maximum likelihood, which can locate scour damage. The root mean square (RMS) difference between the healthy and scoured mode shape curves exhibits an almost linear increase with increasing foundation stiffness loss under scour. Experimental tests have been carried out on a scaled model bridge to validate the approach presented in this paper. Full-text.
Vibration-based method for structural health monitoring of a bridge pier subjected to environmental loads, 2021. Belmokhtar et al. This paper proposes a method for structural monitoring using operational modal analysis (OMA). Frequency domain decomposition (FDD) of the output-only system is developed to define new modal parameters to be monitored. Parameters from OMA make it possible to characterize the structure using experimental modal analysis EMA). The method is applied to a bridge pier subjected to scour. Indeed, a prestressed concrete, motorway bridge on A71 in France has been equipped with sensors to follow in real time the vibrational behavior and external events such as temperature, hydraulic flow velocity and scour depth. This measuring chain is connected to a central acquisition system. Collected data are post-processed in the frequency domain combining a standard method for modal parameter estimation and statistic methods using averaging and Principal Component Analysis (PCA). A fully automated method is developed by correlating operational modal parameters with data of external event. Finally, an assessment of the evolution of the structural health condition of the bridge in real time is carried out. Would need to be requested.
Mitigating effects of temperature variations through probabilistic-based machine learning for vibration-based bridge scour detection, 2020 Zheng et al. This paper presents a novel approach to mitigating the effect of temperature variations on the bridges’ dynamic modal properties for more reliably detecting scour damage around bridge piles based on the vibration-based measurements. The novelty of the presented approach lies in its ability to reasonably remove the impacts on the modal properties of bridges, particularly caused by changes in material properties and structural boundary conditions due to temperature variations without explicitly modeling these complex effects. The main idea is to adopt the probabilistic-based machine learning method, Gaussian Process Model, to learn the correlation between the changes of modal properties of a monitored bridge and the corresponding temperature variations from in situ sensor measurements, and probabilistically infer the bridge scour based on the modified vibration measurements, which have mitigated the identified impacts of temperature variations, by applying Bayesian inference through the Transitional Markov Chain Monte Carlo simulation. The proposed approach and its applicability are presented and validated through the numerical simulation of a prototype bridge, demonstrating its potential for practical application for mitigating effects of temperature variations or other environmental impacts for vibration-based Structural Health Monitoring. The limitation of the presented study and future research needs are also discussed. Would need to be requested.
Evaluating the benefit of structural health monitoring for improving bridge resilience against scour. Deliverable D1–Report on critical review of alternative techniques for bridge scour monitoring, 2020 Tubaldi et al. This report presents the critical review of the various monitoring techniques available in the literature or deployed in bridges across UK and in particular in Scotland. The considered techniques include visual inspections carried out by divers, techniques providing a direct measurement of the scour at a location (such as smart probes), and techniques measuring the effects of scour (e.g. satellites monitoring bridge settlements due to scour or dynamic identification techniques looking at changes of bridge dynamic properties). The report also shows a comparison among the techniques based on their different features, such as cost and ease of installation, capability to provide continuous measurements, accuracy, distribution of information they provide, and contribution to the four dimensions of critical infrastructure resilience (robustness, redundancy, resourcefulness, rapidity). Full-text
Experimental demonstration of a mode shape-based scour-monitoring method for multispan bridges with shallow foundations, 2020 Malekjafarian et al. This paper experimentally investigates a vibration-based scour monitoring approach applicable to bridges with multiple simply supported spans on shallow foundations. A monitoring strategy based on the relative changes in pier-mode shape amplitudes due to scour is postulated. The first global mode shape of a bridge structure with multiple spans is extracted from acceleration measurements using an output-only approach, frequency domain decomposition (FDD). The relative changes of the pier-mode shape amplitudes under scour are then tracked. Here, each pier-mode shape value is compared with the mean values of the remaining piers in a process that creates a mean-normalized mode shape (MNMS). The approach is demonstrated on a scaled model of a bridge with four spans, supported on sprung foundations, where scour is simulated by the replacement of springs, with springs of lower stiffness corresponding to a reduction in foundation stiffness. It is shown that at a given “scoured” pier, significant increases in the MNMS value occur, suggesting that the location of the scour can be identified. The magnitude of the MNMS at a given pier also increases with an increase in stiffness loss due to scour. In practice, the approach would work best by carrying out a visual inspection of the bridge to establish the initial health condition at the time of sensor installation. After this initial process, the bridge can be monitored remotely for scour on an ongoing basis. Can be downloaded from ODOT computers.
Using rocking frequencies of bridge piers for scour monitoring, 2020 Boujia et al. In this study, scour-based vibrations of bridge piers are investigated using a bridge model in a water flume: first, the eigenmode corresponding to the measured frequencies of pier-like structures is identified. Secondly, the effect of the pier-deck interaction is studied. Finally, a theoretical model is proposed to characterize the pier vibration, and identify its input parameters. To this end, experimental campaigns were conducted and a laboratory scale model pier was tested in two configurations: single piers and two piers in bridge configuration. The experimental results enable the identification of the modal shape and indicate that the deck decreases significantly the pier's frequency. Parallely, a theoretical model was proposed to model the pier, where the soil was modeled with both lateral springs along the pier and a rotational spring at the base. These springs stiffness were then identified using a 3D-finite element model. These results, obtained with the theoretical and numerical models, are in good agreement with the experimental results with the bridge pier in the two tested configurations. Moreover the obtained theoretical, numerical and experimental results were compared to experimental data found in the literature, for further validation. Full-text
A New Method for Detecting the Onset of Scour and Managing Scour Critical Bridges, 2019 Orsak. This project explores monitoring railroad bridges using a hybrid sensor that measures acceleration, tilt, and temperature. The objective of the research is to detect scour and changing soil conditions at an early stage before railroad operations are affected. The sensors were installed on six railroad bridges and have been in operation since 2013. An overview of the data is presented including recommendations for continued monitoring. A methodology has been created for how to analyze the data and send alerts if changing conditions are detected. Scour conditions are not known to have occurred on any of the bridges, but the data collected can provide insight into the structural response of bridge piers PDF can be downloaded.
Field deployment of an ambient vibration-based scour monitoring system at Baildon Bridge, UK, 2019 Kariyawasam et al. Most of the limitations with the current techniques could potentially be avoided by an indirect technique, vibration-based scour monitoring, which correlates the change in support condition due to increased scour depth with a resulting shift of certain natural frequencies of the bridge (Prendergast et al., 2013). This technique has been widely adopted on railway bridges in Japan, where the impact of iron balls is used as a source of impulsive excitation (Masui and Suzuki, 2009; Shinoda et al., 2008). However, to the authors knowledge, this technique has not been widely adopted in other countries, perhaps in part due to the practicalities of the excitation method. With the recent advances in high-sensitivity accelerometers (Zhu et al., 2018), it is possible to obtain the natural frequencies of bridges using low-level ambient vibration due to sources such as traffic or wind (Brownjohn et al., 2017; Rehman et al., 2016). PDF can be downloaded.
Field assessment of ambient vibration-based bridge scour detection, 2019 Kariyawasam et al. Scour is the main cause of bridge failure in the United States and around the world. It involves the loss of soil from around bridge foundations due to fast flowing water. Monitoring bridge scour is challenging as it occurs underwater. A scour monitoring technique that uses accelerometers on the bridge piers and deck to provide real-time measurements of ambient vibration, from which scour-induced changes in the natural frequencies of the bridge may be monitored, has recently emerged. However, field validation of this method is difficult as scour is hard to predict – a monitoring system would need to be installed on a candidate bridge with no guarantee that natural scouring would occur within the trial monitoring period. Previous research on vibration-based scour monitoring has therefore been limited to laboratory-based experiments and numerical simulations. This paper presents a field study in which a bridge with preexisting scour was monitored throughout a repair program, which involved the controlled raising of the riverbed level (i.e. scour in reverse). Ambient vibration due to vehicle traffic over the bridge was monitored before, during and after the repair, using eight high-sensitivity accelerometers and a remote data acquisition system. The riverbed profile was measured with sonar scanning before and after the repair. Numerical modeling predicted a 3-5% change in the first two natural frequencies of the bridge due to the scour repair. However, the actual frequencies measured on site, derived using operational modal analysis (in this case, Frequency Domain Decomposition), showed a high degree of variation. Alternative structural response parameters (mean power spectral density at the modal peaks and the modal amplitude) were found to capture the change in behavior resulting from scour. The opportunities for using these alternative parameters as a measure of scour, and the challenges involved in using operational modal analysis for scour monitoring on a real bridge, are discussed in detail. Full-text.
Drive-by scour monitoring of railway bridges using a wavelet-based approach, 2019 Fitzgerald et al. This paper numerically investigates the feasibility of using bogie acceleration measurements from a passing train to detect the presence of bridge scour. The Continuous Wavelet Transform is used to process the simulated acceleration measurements for a number of train passages over a scoured bridge, with scour represented as a local reduction in stiffness at a given pier. Average Wavelet coefficients are calculated for a batch of train runs passing over the same bridge. A scour indicator is developed as the difference in average coefficients between batches from thehealthy bridge and when it is damaged by scour. The method is assessed using a blind test, whereby one author simulated trains passing over the bridge in various states of health. The remaining authors were provided only with the train accelerations and had to predict the state of scour without any prior knowledge. This scour indicator performed quite well in the blind test for normal vehicle operating conditions. Full-text.
Scour damage detection and structural health monitoring of a laboratory-scaled bridge using a vibration energy harvesting device, 2019 Fitzgerald et al. A vibration-based bridge scour detection procedure using a cantilever-based piezoelectric energy harvesting device (EHD) is proposed here. This has an advantage over an accelerometer-based method in that potentially, the requirement for a power source can be negated with the only power requirement being the storage and/or transmission of the data. Ideally, this source of power could be fulfilled by the EHD itself, although much research is currently being done to explore this. The open-circuit EHD voltage is used here to detect bridge frequency shifts arising due to scour. Using one EHD attached to the central bridge pier, both scour at the pier of installation and scour at another bridge pier can be detected from the EHD voltage generated during the bridge free-vibration stage, while the harvester is attached to a healthy pier. The method would work best with an initial modal analysis of the bridge structure in order to identify frequencies that may be sensitive to scour. Frequency components corresponding to harmonic loading and electrical interference arising from experiments are removed using the filter bank property of singular spectrum analysis (SSA). These frequencies can then be monitored by using harvested voltage from the energy harvesting device and successfully utilised towards structural health monitoring of a model bridge affected by scour. PDF can be downloaded.
Effect of scour on the natural frequency responses of bridge piers: development of a scour depth sensor, 2019 Boujia et al. Local scour is the removal of soil around bridge foundations under the erosive action of flowing water. This hydraulic risk has raised awareness of the need for developing continuous monitoring techniques to estimate scour depth around bridge piers and abutments. One of the emerging techniques is based on monitoring the vibration frequency of either bridge piers or a driven sensor in the riverbed. The sensor proposed in this study falls into the second category. Some unresolved issues are investigated: the effect of the geometry and material of the sensor, the effect of the embedded length and the effect of soil type. To this end, extensive laboratory tests are performed using rods of different materials, with various geometries and lengths. These tests are conducted in both dry sand and a soft clayey soil. Since the sensor will be placed in the riverbed, it is crucial to evaluate the effect of immersed conditions on its response. A numerical 3D finite-element model was developed and compared against experimental data. This model was then used to compute the 'wet' frequencies of the sensor. Finally, based on both the experimental and numerical results, an equivalent cantilever model is proposed to correlate the variation of the frequency of the sensor to the scour depth. PDF can be downloaded.
Vibration-Based Identification for the Presence of Scouring of Cable-Stayed Bridges, 2018 Xiong et al. This study applies structural dynamics monitoring to identify the presence of bridge scouring through tracing the changes of vibration characteristics induced by scour. Four scour-indicating dynamic features, i.e., the frequency change ratio, modal assurance criterion, mode shape curvature, and flexibility-based deflection, are applied as the scour indicators. Based upon the study of a cable-stayed bridge, each scour indicator is calculated and its corresponding relationship with scour depth is obtained. The feasibilities and effects of using each indicator are comprehensively examined. After comparison, the flexibility-based deflection is finally recommended as a sensitive and practical indicator to identify the presence of the scouring. When applied in practice, the deflection can first be extracted from the ambient vibration measurement; then the scour depth can be back-deduced based on the preobtained relationship between the deflection and scour depth. For the specific cable-stayed bridge investigated in this study, the pylon-based deflection indicator can identify the scour presence more effectively and distinguishably. The scour location can also be known because the scoured pylon or pier shows many obvious deflection changes compared with those without scour effects. This study demonstrates that tracing the change of vibration responses can both qualitatively and quantitatively identify the scour of cable-stayed bridges. This vibration-based technique does not require any underwater devices or operations, which could be integrated into a routine assessment task for bridges. PDF can be downloaded from ODOT computer.
Structural health monitoring for performance assessment of bridges under flooding and seismic actions, 2018 Prendergast et al. Bridges can be subjected to damaging environmental actions due to flooding and seismic hazards. Flood actions that result in scour are a leading cause of bridge failure, while seismic actions that induce lateral forces may lead to high ductility demand that exceeds pier capacity. When combined, seismic actions and scour can lead to effects that depend on the governing scour condition affecting a bridge. Loss of stiffness under scour can reduce the ductility capacity of a bridge but can also lead to an increase in flexibility that may reduce seismic inertial forces. Conversely, increased flexibility can lead to deck collapse due to support loss, so there exists some uncertainty about the combined effect of both phenomena. A necessary step towards the performance assessment of bridges under flooding and seismic actions is to calibrate numerical models that can reproduce structural responses under different actions. A further step is verifying the achievement of performance goals defined by codes. Structural health monitoring (SHM) techniques allow the computation of performance parameters that are useful for calibrating numerical models and performing direct checks of performance goal compliance. In this paper, various strategies employed to monitor bridge health against scour and seismic actions are discussed, with a particular focus on vibration-based damage identification methods. Full-text.
Recent development and remaining challenges in determining unique bridge scour performance indicators, 2018 Prendergast et al. There have been significant developments in the area of vibration based bridge scour monitoring in recent years. Traditional scour monitoring using either visual assessment or diving inspections are now recognised to be very unreliable and highly subjective. There has been a concerted effort to move towards reliable systems capable of either direct measurement of scour or indirect measurement, based on monitoring the response of the structure to damage. The developments have unearthed new challenges and problems. This paper describes some recent developments in the field. In addition, remaining challenges that act as a barrier to the successful wide-scale deployment of the methodologies are discussed. In particular, it addresses issues related to how to measure key performance indicators (such as the vibration response of the structure) and the potential of these approaches in real-world applications. PDF can be downloaded.
Reliable performance indicators for bridge scour assessments, 2018. Gavin, Prendergast. There has been significant progress made in the area of vibration-based bridge scour monitoring in recent years. Traditional scour monitoring using visual-type inspections relied on divers investigating the condition of bridge foundations and manually locating and measuring scour holes. This is now considered very unreliable and highly subjective, and increasingly is no longer being used as the main inspection strategy. There has been a concerted effort to move towards more reliable systems capable of either direct measurement of scour holes themselves using automated instrumentation placed near / around bridge foundations, or indirect measurement of the issues scour induce, based on monitoring the response of the structure to this damage. The developments are becoming more advanced all the time, but are now giving rise to questions about appropriate indicators needed to assess scour severity. This paper describes some recent developments in the field, and identifies potentially reliable scour indicators going forward. Specific topics addressed relate to how to measure key performance indicators (in thisrespect, identified as for example, the vibration response of the structure under scour) and the accuracy with which these may be relied upon in real world applications. Full-text
Scour depth estimation in a balanced cantilever bridge with deteriorated central hinges based on natural frequencies: field measurements, methodology for estimation and verification, 2018 Choudhury, Matsumoto, Amin. A scheme based on field measurements of vibrations is proposed for estimating the scour depths of a multi-span balanced cantilever bridge resting on foundations embedded in soft soil. Field measurements of ambient vibrations using velocitysensors indicated elongated periods of vibration in the transverse direction at the pier tops due to scour underneath. Themodal properties were identified using the Eigensystem Realization Algorithm. The unknown spring constants of thecentral hinges were determined to represent the deteriorated performance of the bridge superstructure under no-scour benchmark conditions from a finite element model incorporating soft soil conditions. A single set of spring constantscompatible with the measured natural frequencies was thus identified for the transverse movement of the central hinges.The strong dependence of the transverse bending mode of the pier and weak dependence of the longitudinal bending modeof the pier on scour phenomena were clearly observed. The observed relationships between the scour depth and naturalfrequency were sensitive to soft soil conditions in both modes. The estimated spring constants representing soft soil were used to assess the unknown scour depths in the pier foundations suffering from scour. Independent bathymetric surveysverified the general applicability of the proposed scheme for estimating the scour depths around bridges of this type within reasonable limits. Full-text
Bridge scour monitoring technique using the vibratory response of rods embedded in the riverbed, 2018. Boujia et al. Local scour is a major risk threatening the stability and sustainability of bridges across rivers and in coastal areas. The main purpose of this paper is to propose a monitoring technique based on the dynamic response of rods embedded in the riverbed. First, extensive laboratory tests are conducted to investigate the effect of scour on the vibratory response of different rods in sand and in saturated clay soil. Secondly, a numerical finite element model is developed and validated with these laboratory tests. This model is then used to assess the effect of the added mass of water on the sensor. Finally, based on the numerical and experimental results, a simplified analytical cantilever model is proposed to correlate the dynamic response of the rods to the current scour depth. Full-text
The effect of local scour of a single pier on the vibration parameters of a multi-span bridge under seismic excitation, 2018' Anzlin. Some preliminary results of a numerical investigation carried out on the finite element model of a bridge under flood and seismic actions are reported in this paper. The numerical model of a multi-span bridge is subjected to a seismic base input considering several defined scour conditions. Scour has been mod-elled as the incremental increase in length of one of the piers and the effect of scour on the seismic response is investigated. The studies showed, that the effect of scour is to increase the peak displacement of the pier (at deck level), with a corresponding increase in the peak acceleration at the same level. The shear force at the base of the scoured column drastically decreases with scour; however this results in a redistributed higher shear being experienced by adjacent columns. Full-text.
A review of bridge scour: mechanism, estimation, monitoring and countermeasures, 2017 Wang, Yu, Liang. Scour of sediments around bridge foundations by the stream is the most significant contributing factor for bridge failures. The scour failures tend to occur without prior warning and have led to fatalities and economic loss every year. A significant amount of work has been conducted on bridge scour. Such efforts can be broadly classified into two major categories, namely science driven and engineering driven. The science-driven research focuses on understanding the scour mechanism and aims to explain the cause of scour due to different factors. Meanwhile, engineering-driven research focuses on the estimation, monitoring and countermeasures of bridge scour. This paper presents a comprehensive and up-to-date literature review of bridge scour research and practice. Firstly, a brief introduction is given which includes recent cases of failures caused by bridge scour. Then, both scientific and technical research on bridge scour is reviewed, which are categorized into four aspects: macroscopic and microscopic mechanism, scour depth prediction carried out by experimental and field data, direct and remote monitoring methods and active and passive countermeasures. Finally, a summary is provided covering both experimental and computational methods for scour research. Discussion is also provided on emerging ideas to investigate bridge scour from both science and engineering perspectives. Would need to be requested.
Isolating the location of scour-induced stiffness loss in bridges using local modal behaviour, 2017 Prendergast, Gavin, Hester. 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 vehicle–bridge–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. PDF can be downloaded.

Bridge scour monitoring: challenges and opportunities, 2017 Farooq, Banthia, Azhari. Scour and related hydraulic causes have been identified as the reason for almost 60% of over-water bridge failures in the United States. Hundreds of millions of dollars have been spent in direct repair costs. With increased frequency of flooding due to erratic rainfall patterns, scour-related damage to bridges is expected to increase. In the last few decades, several periodic and real-time scour monitoring systems have been developed. This state-of-the-art review introduces various contact and non-contact methods of bridge scour monitoring along with their strengths and limitations. Next, the challenges in installation and performance of some of the scour monitoring techniques in field applications are discussed. Indirect methods of monitoring bridge scour based on ambient and forced vibration analysis of the structure are also reviewed. Finally, the paper also provides some thoughts on novel methods of conditions assessment hitherto not tried for scour monitoring.

Critical insights for advanced bridge scour detection using the natural frequency, 2017 Bao et al. Scour around bridge foundations is regarded as one of the predominant causes of bridge failures. The concept of vibration-based real-time bridge scour detection has been explored in recent years by investigating the change in the natural frequency spectrum of a bridge or a bridge component with respect to the scour depth. Despite the progress, significant issues still remain unsolved in the application of this concept. This paper investigates three unsolved issues in the current framework of scour detection using the natural frequency spectrum: the physical meaning of the measured predominant natural frequency, the location of sensor installation, and the influence of the shape of scour holes, which are easily neglected but critical to the further implementations of the natural frequency spectrum-based bridge scour detection. Firstly, in-depth discussions of these three major issues were made separately by numerically modeling the scour progression of a typical and documented laboratory test. Laboratory tests were then performed to validate the conclusions made in the discussions. It was found that for an eigenproblem of the system with soil-structure interaction, the physical meaning of the natural frequency obtained from modal analysis can be understood by comparing the modal natural frequency with the natural frequency calculated from the dynamic response of the test component in that system. The results also verified that the obtained predominant natural frequency of the pier body greatly varies with the location of the pier body where a sensor is mounted for signal pickup. The shape of the scour hole affects the predominant natural frequency of the pier, causing difficulties in practical measurements. To address such a problem, a new criterion was proposed to identify the depth of unsymmetrical scour holes for the first time, which is of practical significance to advance the natural frequency spectrum-based scour detection framework. Full-text.
Vibration‐based bridge scour detection: a review, 2017 Bao, Liu. Scour around bridge foundations is regarded as one of the predominant causes of bridge failures. Traditional methods primarily employ underwater instruments to detect bridge scour depths, which thus have difficulties in instrument installations and operations. The concept of scour detection derived from vibration‐based damage detection has been explored in recent years to address such difficulties by investigating the natural frequency spectrum of a bridge or a bridge component. This paper presents a comprehensive review of existing studies on scour detection using the natural frequency spectrum of a bridge or a bridge component. Underlying mechanisms, laboratory and field tests, numerical studies, and data processing schemes are reviewed to summarize the state of the art, which are absent but urgently needed. Updates on recently developed scour monitoring sensors are also provided to complement the introduction. Based on the review, in‐depth discussions in existing studies are made regarding a few controversial and unsolved issues to shed light on future research, highlighting issues such as the soil–structure interaction, locations of the sensor installation, and the influence of shapes of scour holes. Full-text.
Determining the Presence of Scour around Bridge Foundations Using Vehicle-Induced Vibrations, 2016 Prendergast, Hester, Gavin. Bridge scour is the number one cause of failure in bridges located over waterways. Scour leads to rapid losses in foundation stiffness and can cause sudden collapse. Previous research on bridge health monitoring has used changes in natural frequency to identify damage in bridge beams. The possibility of using a similar approach to identifying scour is investigated in this paper. To assess if this approach is feasible, it is necessary to establish how scour affects the natural frequency of a bridge, and if it is possible to measure changes in frequency using the bridge dynamic response to a passing vehicle. To address these questions, a novel vehicle–bridge–soil interaction (VBSI) model was developed. By carrying out a modal study in this model, it is shown that for a wide range of possible soil states, there is a clear reduction in the natural frequency of the first mode of the bridge with scour. Moreover, it is shown that the response signals on the bridge from vehicular loading are sufficient to allow these changes in frequency to be detected. Full-text.

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Monitoring Bridge Scour using Vibration - Based Methods

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