Measurement, control and interpretation
Structural health monitoring observes over time how a building or a structure behaves, and compares each measurement with a declared reference condition. NHAZCA combines sensors installed on the asset with remote observation techniques and returns interpreted measurement series: structural health monitoring services operated as a continuous service, not as a one-off survey.
On-structure sensors
InSAR for buildings
PhotoMonitoring™
Crack monitoring
The definition
Structural health monitoring is the systematic, repeated observation of how a structure behaves — displacement, rotation, strain, crack opening, vibration — in order to recognise change against a stated reference condition and support the decisions of the party responsible for the asset. It is not a single investigation: it is a comparable time series read inside a technical model of the structure.
01
Every programme starts from a declared baseline. Without a reference, a measurement describes neither a trend nor an anomaly.
02
Measurement geometry, acquisition cadence and quality checks stay constant over time, otherwise the comparison loses meaning.
03
Data is referred back to the expected behaviour of the asset. Measurement describes what happened; the decision stays with the owner.
Structural health monitoring services measure and document. They do not replace structural verification, statutory inspection or the safety assessments that remain with the designer or the asset owner.
The methodological framework
The most cited definition describes structural health monitoring as the process of implementing a damage identification strategy for civil, mechanical and aerospace engineering structures, by observing their response over time (Farrar & Worden, 2007).
In the technical literature the discipline is normally abbreviated to SHM: structural health monitoring and SHM are the same object, one written in full and one as an acronym. The abbreviation is common in journals and course material, while the extended form is the one used when scoping a service.
The literature orders damage identification into progressive levels. Each level requires more information than the previous one, and stating which level a structural monitoring system is designed to reach is part of scoping structural health monitoring services — not an afterthought.
Recognise that the observed behaviour departs from the reference condition.
Identify where the change appears, within the spatial coverage the measurements actually provide.
Estimate the extent and nature of the change, supported by structural verification and modelling.
The most demanding level: it requires modelling and specialist judgement, and is not an automatic output of monitoring.
The building blocks
A structural health monitoring system is the set of instruments, acquisition and analysis through which the behaviour of a structure is observed repeatedly and compared with a declared reference condition. It is built in four layers: sensing, acquisition and transmission, data management with quality control, and engineering interpretation.
The four layers are not interchangeable, and a weakness in any one of them limits the whole. A dense sensor network feeding a series with gaps produces less usable information than a sparser network with continuous, validated acquisition.
01
Instruments installed on the asset measure a physical quantity at the point where they sit: tilt, strain, crack opening, acceleration, temperature. Coverage depends on how many points there are and where they are placed, not on how sensitive each one is.
02
Readings are collected at a stated cadence and transferred from the asset. Cadence, power supply and connectivity are design choices: they decide whether a phenomenon that develops in hours is visible at all.
03
Series are stored, referenced to the baseline and checked before use. Gaps, outliers, instrument drift and environmental effects are identified and declared, because an uncorrected series is not a shorter series: it is a misleading one.
04
Validated series are read inside a technical model of the structure, with the observed quantity, the measurement geometry and the validity limits stated alongside the result. This is where measurement becomes a usable input for a decision.
| Layer | What it does | What it returns | What limits it |
|---|---|---|---|
| Sensing | Measures a physical quantity at the point of installation | Raw readings from each instrumented point | Spatial coverage: an instrumented point describes the point, not the structure |
| Acquisition and transmission | Collects readings at a stated cadence and moves them off the asset | A time series per measurement point | Cadence, power supply and connectivity; a phenomenon faster than the cadence is invisible |
| Data management and quality control | Stores, references to the baseline and checks the series before use | Validated series, with gaps and anomalies declared | Instrument drift, interruptions and environmental effects must be separated from real change |
| Engineering interpretation | Reads the validated series inside a technical model of the structure | Trends, items requiring attention and stated validity limits | Interpretation describes what has been observed; it does not forecast future behaviour |
A remote technique can replace the first two layers, but never the last two: satellite or ground-based observation removes the need to install instruments, not the need to validate and interpret.
What is measured
Structural health monitoring measures physical quantities, each with its own unit, its own instruments and its own limits. Scoping a programme means choosing which quantities matter for the decision to be supported, and stating for each one how it will be measured and how often.
| Quantity | Unit | Typical technique | What conditions the measurement |
|---|---|---|---|
| Displacement | millimetres (mm), or millimetres per year (mm/yr) as a velocity | Satellite InSAR, ground-based radar interferometry, topographic and GNSS methods | Measurement geometry: a remote technique observes the component along its own line of sight |
| Rotation and tilt | degrees, or millimetres per metre (mm/m) | Tiltmeters installed on the structural element | Describes the instrumented element; temperature affects the instrument as well as the structure |
| Strain | microstrain, dimensionless | Strain gauges bonded to the element | Requires a sound bond and a temperature reference to separate thermal from mechanical strain |
| Crack opening | millimetres (mm) | Crack gauges, extensometers, multi-temporal image comparison | Seasonal opening and closing is normal: a single reading without a series says little |
| Vibration | hertz (Hz) for frequency, metres per second squared (m/s²) for acceleration | Accelerometers, radar in dynamic configuration | Excitation conditions and ambient noise are part of the result and must be declared |
| Temperature | degrees Celsius (°C) | Temperature sensors alongside the other instruments | Rarely the objective in itself: it is the variable that makes the other series readable |
The same quantity can be measured by more than one technique, and the choice is not a matter of preference: it follows from access to the asset, from the required coverage and from the cadence the phenomenon demands.
Environmental conditions are not noise to be removed and forgotten. Temperature, humidity, wind and site activity act on the structure and on the instruments at the same time, and a series read without them can turn a seasonal cycle into an alarm.
The NHAZCA approach
An instrument is useful only if it measures the required quantity with adequate geometry, sensitivity and cadence. Scoping structural health monitoring services therefore starts from the expected behaviour of the asset and the decisions it must support, and only then selects the configuration. Interpretation runs alongside acquisition instead of arriving at the end as an attachment.
L’interpretazione accompagna l’acquisizione: non arriva alla fine come un allegato. Quando il programma è un monitoraggio strutturale continuo, la stessa configurazione deve reggere per tutta la durata prevista: cambiarla a metà interrompe la confrontabilità della serie.
The service lifecycle, from an agreed basis to technical handover.
Complementary techniques
On the structure and from a distance, a structural monitoring programme observes different quantities. The techniques are not interchangeable: each keeps its own measurement geometry, resolution, cadence and sensitivity to environmental conditions. Combining them is worthwhile when it adds information, not for catalogue completeness.
Tiltmeters, extensometers, crack gauges, accelerometers and temperature sensors measure at the point where they are installed. Crack monitoring is the most direct case: a gauge bonded across a crack reads its opening against a fixed origin, and the value only becomes information once there is a series. Spatial coverage depends on how many points there are and where they sit.
Processing satellite radar series can reconstruct displacement of structures and buildings, including over past periods, with nothing installed on site. It needs stable radar targets, and the observed component remains the one along the satellite line of sight.
Explore NHAZCA InSAR
A radar operated from a fixed position observes a façade or a front and returns displacement maps and time series. In real-aperture configuration it can also follow the dynamic behaviour of the asset. Signal coherence and viewing geometry govern how readable the result is.
Multi-temporal images and point clouds support digital image correlation, crack-pattern review and geometric comparison. Lighting, vegetation, site activity and registration must be separated from actual deformation. Results are delivered through the IRIS platform.
Explore PhotoMonitoring™
Where the behaviour of the asset depends on the foundation soil or on nearby works, the programme is designed together with geotechnical monitoring: the superstructure and the ground–structure interaction are two distinct readings of the same problem.
Technical selection
In structural health monitoring services, configuration follows the technical requirement, not the instrument that happens to be available.
| Requirement | Possible technique | Output | Limitation to consider |
|---|---|---|---|
| Slow change in the attitude of a building | Satellite InSAR | Velocity and time series for radar points on the building | Line-of-sight component only; stable radar targets required |
| Local rotation and crack opening | Tiltmeters, crack gauges, extensometers | High-rate point time series | An instrumented point does not describe the whole structure |
| Dynamic behaviour | Accelerometers or radar in dynamic configuration | Oscillation frequencies and amplitudes | Excitation conditions and ambient noise affect the measurement |
| Displacement field over a façade or a front | Ground-based radar interferometry | Displacement maps and time series | Line of sight, signal coherence and instrument position |
| Crack pattern and visible change | PhotoMonitoring™ and laser scanning | Thematic maps, geometric comparison and control points | Separating deformation from lighting, vegetation and site activity |
| Behaviour driven by the foundation soil | Coordinated geotechnical instrumentation | Subsurface profiles and pore water pressure | Requires a coordinated ground monitoring plan |
The handover
The value of structural health monitoring services is not the volume of data acquired, but a technical picture that makes trend, quality and limits visible.
Objectives, configuration, baseline, cadence, roles and exclusions agreed before installation.
How the measured quantities evolve at the observed points and over the observed periods, with the measurement geometry stated.
Coverage, continuity, interruptions and environmental conditions that influence the data.
Comparisons, items requiring attention and validity limits, without over-reading the measurement.
Applications
The method is the same; what changes is the observed object, the installation constraints and the type of decision to be supported. Structural monitoring is scoped asset by asset.
Building structural health monitoring follows the attitude, rotation and crack pattern of residential, office, industrial and school buildings in service or affected by nearby works. Satellite InSAR can reconstruct behaviour even before the programme starts.
On protected assets the priority is minimal intrusion: remote techniques and discreet sensors reduce the impact on the fabric. Design is coordinated with conservation requirements and the responsible authorities.
During excavation, strengthening, demolition and underpinning, a reference condition is needed before works begin and continuity of measurement is needed through the critical phases.
Where the behaviour originates in the foundation soil or in an adjacent slope, the structural reading is integrated with geotechnical monitoring, which owns the ground and the ground–structure interaction.
Bridges, viaducts, dams and tunnels apply the same method, but with their own operational, regulatory and management constraints. The dedicated pages cover how the service is scoped for each asset.
Across several structures at once, satellite observation helps set priorities and decide where dedicated measurement is worth adding. The asset-management layer is described in SGAM.
From method to practice
At the Colosseum Archaeological Park NHAZCA designed an integrated environmental and structural monitoring system, static and dynamic, for the conservation of the Flavian Amphitheatre. For the Venice heritage authority, satellite monitoring and ground-based radar interferometry were applied to the bell towers of the historic centre and its lagoon.
Every result stays tied to its site, observation period and configuration: published cases show the method, they do not replace the design of a new programme of structural health monitoring services.
Further reading
Sources for the scope and limitations of the techniques described above.
Philosophical Transactions of the Royal Society A: the reference definition of structural health monitoring as a damage-identification process.
Review of how monitoring is applied to civil structures and of the practical limits of real implementations.
General framework for monitoring by field instrumentation of ground, geotechnical works and structures interacting with the ground.
International scientific committee on the analysis and structural restoration of architectural heritage.
Ground and structure motion products derived from Sentinel-1 InSAR processing.
FAQ
Structural health monitoring is the repeated, systematic observation of how a structure behaves — displacement, rotation, strain, crack opening, vibration — read against a stated reference condition. It is a continuous reading of measurable quantities rather than a visual judgement or a single survey, and it exists to support the decisions of whoever is responsible for the asset.
Building structural health monitoring applies the same method to buildings in service: attitude, rotation, crack opening and, where relevant, vibration are observed over time on residential, office, industrial and school buildings, including those affected by nearby works. Satellite InSAR can reconstruct how a building has behaved even over periods before the programme starts.
In practice they describe the same activity. Structural health monitoring is the term used in the international technical literature for the methodological framework; structural monitoring is the everyday wording for the same observation of behaviour over time.
It depends on the requirement. It may include displacement, rotation, crack opening, strain, oscillation and temperature. For each quantity the scope must state measurement geometry, cadence and limitation: without them a structural monitoring system cannot be compared over time.
Sensors are chosen from the quantity to be observed: tiltmeters for rotation and tilt, strain gauges for strain, crack gauges and extensometers for crack opening, accelerometers for vibration, and temperature sensors for the environmental reference. No sensor describes the whole structure: it describes the point where it is installed, and coverage depends on how many points are instrumented and where they sit.
Sensors are chosen from the quantity to be observed: tiltmeters for rotation and tilt, strain gauges for strain, crack gauges and extensometers for crack opening, accelerometers for vibration, and temperature sensors for the environmental reference. No sensor describes the whole structure: it describes the point where it is installed, and coverage depends on how many points are instrumented and where they sit.
Partly. Satellite InSAR measures displacement of structures and buildings with nothing installed, including over past periods, but it needs stable radar targets and observes only the line-of-sight component. It does not replace sensors where high acquisition rates or local quantities are required.
No single standard covers structural health monitoring end to end. What the programme must deliver is set in a monitoring basis agreed before installation: objectives, quantities, measurement geometry, cadence, roles and exclusions. Reference documents on monitoring by field instrumentation and on architectural heritage are listed in the references above, while structural verification, statutory inspection and safety assessment remain governed by the framework that applies to the asset. Monitoring measures and documents; it does not certify compliance.
SHM is the standard abbreviation of structural health monitoring: the two forms name the same object, one written in full and one as an acronym. The abbreviation prevails in journals and course material, while the extended form is the one used when scoping a service, because it says what is observed and on what.
No. Monitoring supplies measurements and technical interpretation; structural verification, statutory inspection and safety assessment remain with the designer, the checker or the asset owner. Thresholds and operational response must be assigned explicitly.
When the observed behaviour may originate in the foundation soil, in a nearby excavation or in an adjacent slope. The programme is then coordinated with geotechnical monitoring, which observes the ground and the ground–structure interaction, while this page stays on the superstructure.
A structural health monitoring system is designed from the behaviour to be observed and the decision to be supported, not from an instrument catalogue. The design states quantities, measurement points and geometry, cadence and baseline, and it covers four layers: sensing, acquisition and transmission, data management with quality control, and engineering interpretation. A weakness in any one layer limits the whole system, however dense the sensor network is.
Crack monitoring measures the distance between the two sides of a crack and how it changes over time, in millimetres, with a gauge bonded across the crack; the overall crack pattern is also followed with multi-temporal images and geometric comparison. A single reading says little: what is needed is a series, the same measurement geometry at every repetition, and the temperature recorded alongside the data, because thermal movement opens and closes a crack as well.
Cost follows the scope: objectives, type of asset, access, techniques, number of measurement points, cadence, duration and expected deliverables. Without these elements a figure would not be technically meaningful. Share your brief for a scoped estimate.
Why NHAZCA
We do not sell a sensor catalogue: we design, acquire, validate and interpret the measurement over time.
Satellite and ground-based InSAR and PhotoMonitoring™ observe the asset where installation is difficult or inappropriate.
The method comes from a university research background and stays anchored to the technical literature on structural monitoring.
Geometry, quality, environmental conditions and temporal validity stay visible in every deliverable.
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Preliminary assessment
Share your objectives, context and constraints: the first step is agreeing which quantities to observe, with which techniques and with which limits.
