Structural Health Monitoring in the 21st century

Introduction

Structural integrity monitoring is a complex and exciting area of modern engineering practice. To ensure that the infrastructure of our cities – bridges, tunnels, buildings, dams – is safe, sustainable, and long-lasting, it requires the collaboration of many different disciplines. Civil engineers, geotechnical engineers, computer scientists, environmental engineers, electrical engineers, and many more disciplines play an active role in making the continuous monitoring of structures a reality.

This article aims to provide a comprehensive overview of what structural health monitoring means in practice and how this approach can help to continuously monitor and improve the state of the built environment. Although the subject is very complex, we have tried to summarise its most important aspects in a readable way to make it useful and relevant reading for all concerned – engineers, building/infrastructure operators, and investors.

Structural Health Monitoring

Structural Health Monitoring (SHM) is the continuous monitoring of the condition of various structures, such as bridges, tunnels, dams, buildings, and other infrastructure elements. SHM aims to detect potential structural failures and changing environmental conditions promptly and to use the data collected to inform engineering decisions and predict the need for maintenance. As a result of this process, major damage and accidents can be prevented and the useful life of structures can be extended. Ultimately, the aim is to optimize the cost to society, which includes preserving human life and safety, protecting natural and environmental assets, and minimizing direct material costs.

Definition of SHM: The continuous measurement, monitoring, or tracking of the status of a quantity, process, or system to detect changes and potential problems in time to make the necessary decisions to ensure proper and safe operation.

Structural Health Monitoring is key to supporting the safety and long-term sustainability of buildings. These systems can be installed during construction or during the operation of the building, facilitating full life-cycle monitoring. Monitoring during the construction phase allows real-time inspection of the structures under construction and visualisation of progress. This allows for the timely identification and rectification of possible construction and material defects. In the operational phase, sensors and data acquisition devices continuously monitor the load, vibrations, temperature changes or other environmental influences on the structural elements, allowing preventive maintenance and early detection of damage. The combination of these two approaches can significantly increase the safety and lifetime of buildings.

Key technologies and tools:

SHM systems are based on a variety of measuring instruments and related technologies. Together, these enable complex data collection and processing. Continuous and accurate monitoring of the condition of structures is essential for structural safety and sustainable operation. The most important tools for the efficient operation of SHM systems are:

Sensors: sensors are used to measure various structural and environmental properties. Examples of structural properties are natural frequency, displacement/deflection, tilt, magnitude of forces in the structure, crack size, and structural temperature. Environmental parameters include, for example, weather parameters, precipitation, wind and air temperature, groundwater level, and geological and geotechnical parameters. Sensors that measure these properties can detect deviations and changes at critical points in structures and their environment in time.

Data collection systems: data collectors collect raw data from sensors, which are stored or transmitted for analysis after varying degrees of on-site processing. Data collectors may be manual readouts or, in more modern systems, increasingly automated. Data loggers may be based on open hardware communication standards or specialized for a single manufacturer’s sensors. These systems usually include a sensor interface module that communicates with the sensors, a central processing unit, and a readout or communication module. The data loggers can be integrated into an industrial PC or even microcontroller-based target systems.

Data processing systems: the data collected is analyzed using specialized engineering and statistical software that evaluates the current state of the structure and, in many cases, predicts potential problems. Data processing systems can be fully integrated into the SHM process or provided by individual engineering software. Their common feature is that they produce information from the raw data that is interpretable by engineers. In modern systems, it is possible to compare different parameters and analyze their correlations, even in an automated way. In many cases, data processing starts at the field data collection and continues in a central system, depending on the available computing capacity and communication bandwidth.

Communication devices: these ensure the flow of data to the central system. Communication devices can be wired or wireless. In both cases, a standard communication protocol is mostly used. Wired systems are mostly Ethernet, EtherCat, ModBus, and CanBus. Wireless protocols are for example LoRA and LoRAWAN, WiFi, 4G/5G mobile networks, or even satellite data communication. Most of the time, the communication network includes one or more gateways that translate and transmit data between different standards with different ranges and bandwidths. Typical SHM communications include, for example, translation from on-site wired or short-range wireless networks to Internet wireless protocols.

Visualization and analysis systems: visualization software enables technical staff to view graphs and reports representing the status of structures, which contributes to fast and efficient decision-making. Modern visualizers allow the comparison of data series and the combined analysis of several parameters. Some software is completely general-purpose, allowing the expert in the field to define complex analyses tailored to his own needs. The other part of the software focuses on full automation and the customized system runs automatically the calculations defined during the projects. The output of the visualizations can be a table, map, or graph displayed on the screen, or a data file ready for further analysis. Automated analysis systems are capable of generating and sending pre-defined reports to stakeholders. Customized notifications, which can be defined based on complex criteria, provide immediate information to engineers, investors, managers, or other stakeholders affected by the impact. This is useful when immediate intervention, further consultation or evaluation is needed. Modern SHM shortens the time it takes to get interpreted information to the right stakeholder. It can ensure that a stakeholder receives information with the right data content at the right time. Notifications can be related to the status of the system (e.g. measurement outage) or the value of a structural parameter exceeding a tolerance (e.g. larger than expected displacement).

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A prominent feature of modern SHM systems is their ability to integrate different technologies and tools into a complex system that supports the safe operation and sustainability of structures with real-time data. This ability to continuously monitor and respond immediately is essential for the effective management of infrastructure elements.

It's like a smartwatch but for buildings

SHM technology compares well with smartwatches. Just as a smartwatch constantly monitors your body’s physiological parameters, such as heart rate, step rate, or sleep quality, SHM systems monitor the “health” of your built environment similarly. Smartwatch data, presented in an easy-to-understand format, can help users make better decisions about their health and lifestyle, while SHM data can be vital for engineers and maintenance professionals to detect potential problems and prevent structural damage in time. Ease of access and interpretation is also key here.

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For example, when a smartwatch alerts a user to an elevated heart rate or unusual physical activity, SHM systems can also send signals to engineering teams when atypical vibrations, movements, or other parameter changes are detected on a bridge, building, or other structure. The analogy also holds in the sense that by analyzing data from smartwatches worn by very many people, we can draw new conclusions about human health. The data generated from monitoring structures is not only interpretable in itself, but also provides relevant input for interventions on other structures or future design decisions. This parallel helps us to better understand, the critical role that these monitoring systems play in modern infrastructure, just as smartwatches play in everyday health maintenance.

SHM Industry

The structural health monitoring (SHM) industry is estimated to be a $2 billion industry and has shown significant annual growth of around 10% in recent years as more and more infrastructure projects and maintenance around the world are concerned with ensuring the long-term stability and safety of structures. Advances in SHM technologies have enabled improvements in the efficiency and reliability of monitoring processes in many areas, from bridges to tunnels to civil engineering projects. This is underpinned by the spread of digitalization technologies used by SHM and their significant cost reduction.

Economic Growth

Several factors are driving the growth of the SHM industry:

Increasing investment in infrastructure: global economic growth and urbanization processes are generating an increasing number of new construction projects, all of which integrate SHM systems as an essential part of their design. In addition, the structures built in the developed world are aging and there is a great need to extend their lifetime. The high cost of a highly skilled engineering workforce is also driving toward automation processes.

Increasingly stringent safety regulations: the tightening of regulations governing the safety of structures is encouraging companies to adopt more advanced SHM systems.

Advances in technology: the development of IoT, artificial intelligence, Big Data, and cloud-based technologies has opened up new possibilities for SHM systems, improving the speed and accuracy of data collection at ever-lower costs.

The horizontal aspect of sustainability: on the one hand, life extension is a natural option for society to reduce CO2 emissions, and on the other hand, lower material consumption of structures can be supported by “closer” monitoring. The automation of measurement tasks reduces direct emissions from the work.

Key actors and partnerships

Key players in the industry include technology companies, engineering service companies, research institutes, and universities working together to develop and deploy the latest SHM technologies. Partnerships such as academic and industry collaborations facilitate the rapid market introduction of new technologies.

In the EU, a good example of such cooperation is the Danube Interreg project GeoNetSee, a project on automated forecasting and monitoring of funnel clouds involving 14 academic, governmental, and business organizations from 8 countries.

Outlook for the future

The future of the SHM industry is characterized by a shift towards complex and integrated systems and the development of automated and self-service solutions. Future developments will address issues of sustainability and energy saving, as well as increasing the efficiency of monitoring systems.

The ever-expanding field of SHM offers opportunities for technological innovation and for improving global infrastructures where safety, reliability, and economy are key considerations.

The problem and the solution

The development and application of structural health monitoring systems can present several problems and challenges that can significantly affect the effectiveness of monitoring processes. Data collection, data recording processes, and on-site accessibility can present technical and logistical constraints. Environmental factors, such as extreme weather conditions or physical impacts, can further complicate the accurate operation of measuring instruments. These factors pose complex challenges in accurately and reliably monitoring the condition of structures, which is essential for early fault detection and the success of preventive maintenance strategies.

Common problems and challenges in monitoring structures

Data collection: Traditional “manual” methods, such as data collection using geodetic measuring stations, are time-consuming, occur at fixed intervals, require large amounts of human resources, and are limited in the collection of data useful for determining the health of the structure.

Measurement site accessibility: Some measurement sites are difficult or impossible to access during construction, when there is active work in the area, or due to the nature of the structure, for example at high altitudes. Thus, the data for the structure will not be complete.

Data recording: Manual data capture is prone to errors and does not provide a continuous flow of data for decision-making processes. It also slows down project implementation and the optimization of maintenance processes. More sophisticated, on-site digital readout recording also requires human intervention and different software for different sensors, which complicates subsequent processing.

Environmental factors: Environmental factors, such as strong winds or heavy rainfall, can significantly affect the feasibility of geodetic measurements, for example. This technical limitation can prevent accurate data collection, which can be particularly problematic in situations where the safety of structures depends on continuous and accurate monitoring.

Lack of early fault detection: Because periodic measurements are hampered by environmental factors, small changes in structures often remain hidden until they become a more serious problem, increasing risks and repair costs.

How SHM provides solutions to these problems

The design of modern SHM systems represents a significant improvement over traditional methods. These systems offer intelligent solutions to the challenges posed by the problems listed above, optimizing the safety and long-term sustainability of structures. Below we will show how SHM provides concrete solutions to problems in the areas of data collection, site accessibility, data recording, environmental factors, and early failure detection.

Early error detection

A key advantage of modern systems is their ability to detect errors early. These systems continuously analyze the condition of structures, allowing potential problems to be identified long before they become serious or have a detrimental effect. This early diagnostics significantly reduces the risk of unexpected failures, allowing proactive maintenance measures to be implemented promptly, resulting in significant cost savings. Early detection of failures also allows infrastructure owners, who manage thousands of bridges, tunnels, or buildings, to determine optimal maintenance priorities. This activity is known collectively as predictive maintenance.

Forecasting

Forecasting is one of the key functions of SHM systems that helps to understand the future evolution of the state of structures. By analyzing the data collected, the systems can identify trends and make predictions, which allows the expected behavior of structures to be predicted. This allows engineers and maintenance teams to react promptly, preventing major repairs and longer downtime, thus significantly increasing operational safety and reducing maintenance costs. A big leap in predictive technologies is expected soon when sufficient data samples will be available to support engineering in this way.

Automatization

Automation is an essential element of SHM systems that significantly improves the efficiency of monitoring processes. From data collection to data analysis and reporting, automated systems reduce the need for human intervention, thus minimizing inaccuracies due to human error. In addition, automation allows for continuous, real-time data processing and monitoring, ensuring that the status of structures can be monitored at all times and immediate intervention can be taken when necessary.

Remote monitoring

Remote monitoring allows structural health monitoring systems to monitor and assess the condition of structures in real-time, regardless of their physical location. This feature is critical for structures in hard-to-reach or remote locations where regular site inspections are logistically difficult or costly. The continuous flow of data ensures that technical teams can respond immediately to any potential problems, reducing the risk of catastrophic events and improving the long-term safety of structures. Remote monitoring provides managers of a large number of infrastructure elements with an overview of the processes on all structures from a single interface.

Notifications

The notification function is a key element of the system, allowing an immediate response in case of problems. The system automatically generates alerts and reports, either at intervals or when monitored data show deviations from normal operating parameters. This allows the technical teams to react quickly before serious damage to the structure occurs. Rapid response significantly increases the safety of structures and reduces unplanned maintenance costs.

SHM as a system

Components and principles of the SHM system

Process

The data collection process of the SHM system starts with the measuring devices (sensors) that record data from the structures. These data are first sent to a local data collection unit, which transmits them to the central data processor via the communication network. Here, the data is processed, analysed and visualised, allowing users to easily interpret it. As part of the process, automatically generated reports and alerts are generated to warn of potential problems, ensuring that structures are managed quickly and efficiently.

[illustration of the process]

Components

A system designed for structural health monitoring (SHM) consists of a number of key components that work together to ensure continuous and effective monitoring of structures. The essential elements of monitoring include:

Sensors: Various types of sensors (e.g. accelerometers, tilt sensors, temperature sensors) measure physical characteristics such as motion, pressure, temperature, etc.

Data loggers: These devices receive and store, and in some cases pre-process, data from sensors.

Communication systems: They ensure the transmission of data from the site to the central processing units.

Data processing and analysis software: Data are analysed, evaluated and visualised to help assess the condition of the structure.

User interface: Enables engineers, managers and other stakeholders to access, interpret and respond quickly to data.

Alarm and reporting systems: generates automatic alerts and reports based on detected data, alerting to potential problems or required actions.

Together, these components form the SHM system, which enables continuous and detailed monitoring of the condition of structures.

Stakeholders

There are two main actors in SHM systems: the monitoring service provider and the customer.

The service provider: they design and, in most cases, install the system based on the customer’s needs and their own professional experience. Their tasks include installing sensors and data loggers, setting up the communication network and configuring the data processing and visualisation software. They are also responsible for the ongoing operation, maintenance and support of the system.

The contracting company (the customer): they use the system to monitor the status of the structures. Based on the data and alerts they receive, they are able to take timely interventions, carry out maintenance work and ensure the long-term safety and reliability of the structures. They are responsible for evaluating the system data and taking the necessary decisions.

The cooperation between these two actors ensures that the SHM system works effectively and contributes to the continuous improvement and maintenance of the condition of the structures.

In addition to these two actors, the investors, designers, constructors and operators of engineering structures also contribute significantly to the successful operation of the system. In recent trends, the community and environment affected by the structure are also included as stakeholders in the SHM system. In the latest SHM platforms, different users can access information at different levels and get a picture of the situation at their level.

Investors: they can define the need for safe construction and operation, and require a monitoring system. They can use their technical inspection powers to use monitoring data.

Engineer designers: whether from their own experience or from the investor’s demand, they formulate the engineering question to which the subsequent monitoring must respond. They commission a monitoring specialist to select sensors and design the monitoring system. They use the data from the developed platform as part of a design workshop.

Contractors: order the monitoring system during construction, provide the necessary boundary conditions for operation. During the construction activity, they use and reconcile the data for further progress.

Operators: Order the monitoring system during operation, provide the necessary boundary conditions for operation. During their operational activities, they use and agree data to plan maintenance activities.

Affected community, environment: Community representatives and relevant authorities may have access to the system to receive reports and notifications concerning them and to make informed enquiries about the processes.

The process of data collection, -analysis and -evaluation

The SHM system works by accurately and continuously collecting data from various sensors such as accelerometers, inclinometers or GNSS systems. This data is often received in large quantities, so efficient processing and analysis is essential. The aim of the data flow is to continuously assess the current state of the infrastructure and to identify potential problems in time before they become serious.

User interface

One of the most important elements of SHM systems is the user interface, which allows quick and intuitive access to data. The interface should be transparent and easy to use, and provide multiple levels of information so that not only engineers but also other stakeholders, such as city managers or project managers, can use the system in a meaningful way.

Interactive maps, graphs, and 3D models allow problem areas to be visually identified, while users can easily navigate between different structures. Features such as real-time notifications or access tailored to different roles further enhance the usability of the SHM system.

Reporting

Reporting is one of the most important outputs of SHM systems, presenting the collected data in a summary form. The system can generate reports on a regular or ad-hoc basis, including current status, trends, and possible warnings.

The format of the reports can be customized, be it simple SMS or PDF documents or more complex analysis results that can be integrated into other systems. This data is key for decision makers to take timely maintenance or emergency actions.

Safety measures

The security of SHM systems is essential, as the protection and integrity of data directly affect infrastructure operations and decisions. The system must protect against attacks and data leaks, provided by multiple layers of security protocols, such as encrypted data transfers and authentication processes.

Data stored in the system must be backed up regularly to be restored in the event of any failure. Software updates and regular audits (such as penetration tests) also help to maintain security and ensure that SHM systems always use the latest security technologies.

Application areas, examples

Application areas

Bridges

Constant monitoring of the condition of bridges is essential for road safety. Structural integrity monitoring systems measure the deformation and stress of structural elements of bridges. These data can predict potential structural failures or material fatigue.

Problems that can occur on bridges: bearing pad failures, dilatation issues, corrosion, thermal expansion

Measuring possibilities: vibration, dynamic displacement, inclination, force, stress measurement, slow displacement, deformation, bearing pad displacement, crack width, icing, scour, structural moisture, structural temperature, dilatation movement, ambient temperature, wind, precipitation, groundwater level, traffic

Tunnels

For tunnels, building health monitoring systems are used to continuously monitor structural integrity. Sensors can detect earth movements, structural deformations and water seepage. Real-time data collection helps prevent serious accidents and structural damage. Data analysis allows for more accurate maintenance and repair plans within the bridge.

Problems that can occur in tunnels: ground deformation, inclination, displacement (extensometer), problems due to changes in groundwater level

Measurement possibilities: inclination, force, stress measurement, air quality, slow displacement, deformation, crack width, structural moisture, ambient temperature, ground water level, traffic, pressure, displacement

Dams

Continuous monitoring of the condition of dams is key to water safety. Building health monitoring systems can measure dam deformation, displacement and water pressure. This data can help prevent dam breaches or severe structural damage.

Problems that can occur in dams: slope, displacement, cracks, pressure

Measuring possibilities: inclination, force, tension measurement, structural moisture, ambient temperature, bottom water level

Buildings

Monitoring the structural health of buildings is essential for safe use. Sensors can be used to measure the movement, deformation and material condition of buildings. The data can provide building owners with timely information on maintenance work needed.

Problems that can occur in buildings: tilt, subsidence, structural dampness, cracks in load-bearing structures

Measurement possibilities: vibration, dynamic displacement, inclination, force, stress measurement, air quality, slow displacement, subsidence, crack width, structural moisture, structural temperature, ambient temperature, wind, precipitation, ground water level

Monuments

Monitoring the structural integrity of monuments is a priority for their long-term preservation and safe visitation. Using sensors and advanced technical solutions, structural movements, cracks, signs of material fatigue and environmental effects such as temperature or humidity fluctuations can be measured. The data collected will allow maintainers to intervene in time to prevent damage while minimising damage to the original structure. This allows monuments not only to preserve their aesthetic and cultural value, but also to continue to serve their community or tourist functions safely.

Problems that can occur with monuments: tilt, subsidence/erosion, wetting of walls, cracks in load-bearing structures

Measuring possibilities: vibration, dynamic displacement, inclination, force, stress measurement, air quality, slow displacement, subsidence, crack width, structural moisture, structural temperature, ambient temperature, wind, precipitation, ground water level

Silos

Continuous monitoring of the condition of silos is important to ensure the safe storage of stored materials. Building health monitoring systems can be used to measure the deformation, displacement and internal pressure of silos. The data allows timely maintenance and repair work to be carried out, preventing structural failures.

Problems that can occur in silos: corrosion, material fatigue, tilt, subsidence

Measuring possibilities: inclination, force, stress measurement, air quality, slow displacement, subsidence, crack width, structural moisture, structural temperature, ambient temperature, precipitation, pressure, ground water level

Monitoring systems provide real-time data that can be used immediately for decision-making. The use of these systems increases the lifetime of various infrastructure structures and buildings and reduces maintenance costs. Data analysis can be used to make more accurate predictions about the future condition of the above-mentioned structures and the interventions needed, which not only allows cost efficiency but also increases the safety of human lives.

Examples

International example: the Golden Gate Bridge

There are many examples of building health monitoring in the world, including the well-known Golden Gate Bridge. Structural monitoring of the Golden Gate Bridge, in particular health monitoring of the building, is key to maintaining the long-term stability and safety of this iconic bridge. The bridge spans between San Francisco and Marin County and is one of the most iconic structures in the world. Over the years, a number of advanced technologies have been introduced to ensure that the bridge’s condition is constantly monitored, especially as the structure ages and is exposed to heavy traffic and the elements.

The Structural Health Monitoring (SHM) systems used on the bridge collect real-time data from different parts of the bridge. A variety of sensors are installed to collect data, including accelerometers, strain gauges and temperature sensors. Accelerometers measure the motion and vibration of the bridge, while strain gauges detect stresses and deformations within the structure. Temperature sensors monitor temperature changes, as the bridge material can expand or contract due to temperature fluctuations. In addition, wind sensors are used to measure wind direction and force, as the bridge is exposed to significant wind loads on the Pacific coast.

Steel structures such as the Golden Gate Bridge are at risk of corrosion, especially from salty sea air. Corrosion monitoring is a priority and various corrosion sensors are installed on the bridge to detect signs of corrosion in time. Regular painting and maintenance of the bridge is also essential to prevent deterioration of the steel structures.

Since California is an earthquake-prone area, monitoring the seismic stability of the Golden Gate Bridge is also critical. The bridge’s foundations and main structural elements have been strengthened to withstand seismic effects, and seismic sensors have been installed on the bridge’s structural elements to measure earthquake-induced movements. These sensors are crucial for rapid response after an earthquake and for assessing the condition of the bridge.

The Golden Gate Bridge pays particular attention to the effects of wind and vibration. Wind resonance can cause serious structural damage in the long term, so wind sensors and vibration meters on the bridge continuously monitor the level of fluctuations. In 2020, aerodynamic modifications were made to the bridge to reduce wind resistance and structural sway.

The data collected through the continuous monitoring of the bridge is analysed by engineers and technicians to determine when maintenance or renovation work is needed. A proactive maintenance approach allows bridge operators to intervene in time before serious structural damage occurs, thus extending the life of the bridge.

Domestic example: the Kettős-Körös Bridge

Built in Hungary in the 1970s, the Köröstarcsa Kettős-Körös bridge faces significant structural challenges, including corrosion of the pre-stressed cables in the bridge box. Inspection was previously limited to periodic geodetic movement testing and detailed main inspections every five years. In recognition of the risks associated with ageing infrastructure and in line with the recommendations of the last main inspection, Magyar Közút, in collaboration with SURVIOT, has developed a modern, continuous structural health monitoring system.

SURVIOT installed three triaxial accelerometers and three wireless structural thermometers at critical points on the bridge. These sensors provide real-time data on vibrations, natural frequencies and temperature changes, and the information is transmitted to a central data acquisition system for cloud-based processing and analysis. The initial results confirm the safety of the bridge, with no signs of critical degradation in the cable trays. This early result underlines the potential of advanced monitoring to mitigate risks and enable preventive maintenance.

Future plans include adding additional sensors to the monitoring system, such as displacement sensors and strain gauges, and integrating traffic data to better understand the impact of load. The portability of the SURVIOT system will facilitate cost-effective installation on similar bridges in the region. This project is a good example of how modern technology can extend the life of critical infrastructure and increase safety through proactive, data-driven decision making.

Summary

Structural health monitoring (SHM) is essentially like a smartwatch for the built environment: it reveals hidden problems and provides a comprehensive picture of the condition of structures. With SHM, operators not only know the current condition but also have the opportunity to react to problems on time, increasing safety and reducing costs.

SURVIOT is committed to creating safe and smart cities. Our mission is to contribute to modern urban development with innovative solutions that guarantee the long-term reliability and sustainability of infrastructure elements.