Vibration-based monitoring of civil infrastructure: challenges and successes

Smart Materials and Structures, 2001

This paper discusses two very relevant practical issues in the application of vibration-based health monitoring to civil engineering structures: the excitation source and the effect of temperature. The idea of vibration-based damage detection is to measure dynamic characteristics such as eigenfrequencies, damping ratios and mode shapes on a regular basis. The state, and eventually degradation, of the structure is reflected in the evolution of these characteristics. Unfortunately, it is not only the health of a structure that influences its measurable dynamics, but also the applied excitation and the changing temperature are important factors and may erode the damage detection potential. In the first part, the results of different excitation types are compared: band-limited noise generated by shakers, an impact from a drop weight and ambient sources such as wind and traffic. In the second part, the undeniable effect of temperature on measured eigenfrequencies is demonstrated and a methodology is proposed to distinguish these temperature effects from real damage events. The method could be validated on a unique data set from a bridge that was artificially damaged after a one-year monitoring period.

Advances in Structural Engineering, 2012

Considerable amount of research has been carried out in the area of Structural Heath Monitoring (SHM) of civil engineering structures using changes in modal parameters such as natural frequencies and mode shapes. These modal parameters depend on the mass and stiffness distributions in the structure and hence any subsequent changes in these distributions will result in a change of the modal parameters . Sensor systems including accelerometers, GPS (Global Position System), FBG (Fiber Bragg Grating) sensors are normally used to extract modal parameters of structures which can be used to assess the health and performance of structures . Bridges comprise a small number of discontinuous structural components while buildings comprise a much larger number of continuous geometrically complex structural components. It is hence obvious that measuring vibration characteristics of buildings require a

Studia Geotechnica et Mechanica, 2023

The paper concerns the wide range of strategies used to protect structures against man-made dynamic excitation. The most popular approaches applied worldwide are compared, and the main differences and similarities are summarized. The literature studies are supported by the results of the measurements performed on different types of real structures, which are sensitive and insensitive to the dynamic load. To make the conclusions more general, various types of excitation forces are examined (long-term and shortterm excitations, traffic load, and loads resulting from geotechnical works). The main issue raised in the paper is the problem of unequivocal and accurate assessment of the potential structure damage, based on the different legislations. It can be seen that the application of different codes can even result in opposite conclusions about the safety of the structure.

For the last two decade, there has been a growing interest to use the vibrationbased Structural Health Monitoring (SHM) as a global assessment method for existing infrastructures. This technique provides a tool for assessing inaccessible structure areas. The vibration-based technique includes different approaches which can be classified as linear or nonlinear. The former one is faced by various obstacles preventing it from going beyond research topics in civil engineering fields. Accompanied with the linear, the nonlinear method overcomes some of these disadvantages, for which the existence of a datum for the intact structure is a necessity. This datum is usually not available for existing infrastructure as mostly all the codes do not enforce collecting the structure dynamic response just after construction as a datum for future monitoring. However, the need of a reference can be eliminated in the nonlinear approach by detecting special features occurring only due to the nonlinear structure behaviour in the presence of damages. The aim of this paper is to highlight some of these features such as sub-harmonic and supper-harmonic components, which could be used as indicators for existence of degradation. Firstly, an analytical investigation is carried out in which a concrete post with breathing crack is modelled using MATLAB. Secondly, the system stiffness is determined based on the breathing crack situation either it is opened, partially opened, or fully closed. Then the system dynamic response is determined for different level of deterioration illustrating the corresponding nonlinear features.

A peculiar aspect in Structural Health Monitoring is concerning the monitoring of vibrations in urban environments that may affect the integrity and conservation of architectural heritage buildings. The paper reviews the main issues on the subject and takes into consideration the problem of measuring and interpreting vibrations in buildings. The use of numerical models is also discussed and a practical case study is finally presented.

Reports on geodesy, 2011

Traditional visual inspection tools, which are typically carried out annually, can only detect obvious damages like disruption, cracks or rust on the surface of bridges. Advanced non-destructive and destructive inspection tools are usually applied when visual inspection can't provide sufficient information. Besides these techniques engineering surveyors can conduct geometric deformation analysis that provides additional information for damage detection of structures. The implementation of appropriate methods for data acquisition and analysis to detect changes to the material, geometric and dynamic characteristics of structures is summarised under the term Structural Health Monitoring (SHM). The essential idea of SHM is to determine a normal behaviour of undamaged structures and to obtain qualitative conclusions from changes of this behaviour related to the current health status. Information about changes within the dynamic characteristics of structures can be detected by applying accelerometers, which are a component of Ambient Vibration Methods (AVM) as an integral part of SHM. Analysis of acceleration measurements can derive natural frequencies that depend on weight, material, stress and strain as well as the geometry of the object. Hence this data can be used to derive additional information about the capacity and condition of a structure. In this paper we present a measurement system based on low-cost accelerometers that nevertheless performs measurements with high accuracy. This autonomously operatable device features a memory card slot, an internal battery, a waterproof housing and temperature resistant components. Additionally real time data transfer can be obtained via wireless LAN or USB connection to a computer. All necessary steps of data acquisition, processing and interpretation of vibration monitoring will be presented on a practical example.

In order to evaluate the usefulness of approaches based on modal parameters tracking for structural health monitoring of bridges, in September of 2007, a dynamic monitoring system was installed in a concrete arch bridge at the city of Porto, in Portugal. The implementation of algorithms to perform the continuous on-line identification of modal parameters based on structural responses to ambient excitation (automated Operational Modal Analysis) has permitted to create a very complete database with the time evolution of the bridge modal characteristics during more than 2 years. This paper describes the strategy that was followed to minimize the effects of environmental and operational factors on the bridge natural frequencies, enabling, in a subsequent stage, the identification of structural anomalies. Alternative static and dynamic regression models are tested and complemented by a Principal Components Analysis. Afterwards, the identification of damages is tried with control charts. At the end, it is demonstrated that the adopted processing methodology permits the detection of realistic damage scenarios, associated with frequency shifts around 0.2%, which were simulated with a numerical model.

2023

Vibration sensing systems play a critical role in ensuring the safety and longevity of modern structures, contributing to the advancement of intelligent and sustainable infrastructure. This research focuses on the design and implementation of a vibration-detecting system utilising accelerometers and velocity transducers for continuous monitoring and structural health assessment. The study emphasizes the importance of structural health monitoring for enhancing safety, reducing maintenance costs, extending the lifespan of vital structures, and increasing resistance to harsh situations. The developed vibration sensing system strategically deploys accelerometers and velocity transducers to convert mechanical vibrations into electrical impulses, enabling real-time monitoring and comprehensive structural health analysis. Integrating this system into smart infrastructure projects enables data-driven decisionmaking, resource-optimised performance, and improved energy efficiency. These sensors improve the monitoring of structural safety evaluations during events such as earthquakes, severe winds, and imbalanced operations of equipment, thereby protecting lives and property. In addition, constant monitoring facilitates the early detection of damages or irregularities, allowing for swift responses and efficient resource allocation for preventive maintenance. This research underscores the pivotal role of vibrationdetecting systems in advancing intelligent and sustainable infrastructure, ultimately leading to safer and more durable buildings and environments. These technologies contribute to the creation of robust and environmentally friendly structures by providing realtime data insights to engineers that will in turn guide the policymakers in ensuring a sustainable future for the built environment.

Shock and Vibration

Bridge Maintenance, Safety and Management, 2012

This paper presents an innovative software for continuous dynamic monitoring of civil infrastructures. The followed approach is based in the continuous on-line automatic identification of the structure modal parameters, using its response under operation and adopting state-of-the-art identification algorithms. Therefore, the monitoring software, called DynaMo, includes routines for data and results management, algorithms for operational modal analysis, statistical tools for elimination of environmental and operational factors on the identified modal parameters and also statistical tools for automatic identification of abnormal frequency values that might be associated with the occurrence of damages. The utility and efficiency of DynaMo is illustrated with an application on a large span concrete arch bridge that is being monitored since 2007.