Deformations and displacements
Changes in shape and position of structural elements over time.
Technical guide · Pillar page
Structural monitoring and SHM: systems, sensors and data interpretation
Observing the behaviour of structures and infrastructures over time, turning measurements, changes and vibrations into information useful for decision-making.
Structural monitoring is not a single test technique: it is an organised system for observing the behaviour of a structure over time, through sensors, acquisition, processing and interpretation. Unlike a single diagnostic survey, which captures a condition, monitoring builds a time series.
«A diagnostic campaign captures a condition. Monitoring builds a time series and makes it possible to observe the evolution, changes and response of the structure.»
Why monitor a structure
Many management questions cannot be answered by a single inspection: is a crack stable or evolving? How does a deck respond to traffic? How does the behaviour of a historic building change over time?
Structural monitoring (SHM — Structural Health Monitoring) answers these questions by observing significant quantities continuously or repeatedly, and turning measurements into interpretable information.
- Verify the evolution of an observed phenomenon
- Check the structure's response to loads and operating conditions
- Support maintenance and management decisions
- Characterise the dynamic behaviour of the structure
Structure
Quantity to observe
Sensors
Acquisition
Analysis
Interpretation
Decision
What can be monitored
The quantities to observe are chosen according to the question: it is not everything that is monitored, but what is significant for the decision.
Cracks
Opening and evolution of cracks, with strain gauges and crack gauges.
Tilts and rotations
Rotations of elements and supports, checked with clinometers and inclinometers.
Vibrations and dynamic response
Accelerations, natural frequencies and mode shapes of the structure.
Environmental parameters
When relevant, environmental quantities useful for correctly interpreting the structural data.
Other structural quantities
Further parameters defined according to the specific monitoring question.
Static and dynamic monitoring
The choice between static and dynamic observation depends on the diagnostic and management question: they follow different phenomena and use different sensors.
Static
Slow evolution over time
Follows slowly evolving phenomena: deformations, displacements, rotations, crack opening. Uses sensors such as clinometers, strain gauges and crack gauges, with measurements taken over time.
DeformationsDisplacementsRotationsCracks
Dynamic
Response to vibrations
Observes how the structure vibrates: accelerations, natural frequencies and mode shapes. Uses accelerometers and enables identification of the structure's dynamic response.
VibrationsAccelerationsNatural frequenciesMode shapes
From sensor to data: how a monitoring system is built
An effective monitoring system starts from the question, not from the available instrumentation.
01
Defining the objective
The management or diagnostic question that monitoring must answer.
02
Choosing the quantities
Identifying the parameters that are truly significant for the objective.
03
Choosing the sensors
Sensors consistent with the quantities, the structure and the operating conditions.
04
Installation
Installation and configuration of the acquisition system.
05
Data acquisition and management
Collection and control of measurements over time.
06
Processing and interpretation
Analysis of time series and technical reading of results.
07
Reporting
Reports, deliverables and attention thresholds defined with the client.
Dynamic identification
Modal analysis and dynamic identification
Every structure vibrates in a characteristic way: natural frequencies and mode shapes describe its dynamic behaviour. Modal analysis makes it possible to identify them from measured vibrations, even under operating conditions (OMA — Operational Modal Analysis, with techniques such as OMA-SSI).
The identified parameters can be compared with a numerical model (FEM) to calibrate it, or tracked over time to observe changes in dynamic behaviour.
- Natural frequencies of the structure
- Mode shapes and damping
- Dynamic identification under operating conditions (OMA-SSI)
- Comparison and calibration with numerical models, when relevant
Cases and applications
Real examples of different questions that monitoring can answer, from documented Novatest Engineering experiences.
Monitoring from the construction phase
Sensor integrated into the reinforcement before casting: tracking the stress state of the element from the construction stage onward.
Monitoring rotations and displacements
Clinometer and data logger to track rotations and displacements of the structure over time.
Crack evolution
Electronic strain/crack gauge used to verify whether a crack is stable or evolving.
Dynamic response of a deck
Operational modal analysis (OMA-SSI) with Artemis: identification of frequencies and mode shapes of a bridge deck.
Calibration of a numerical model
FEM modal analysis with Midas on a historic tower: comparison between measured frequencies and numerical model.
Non-destructive testing
Point-in-time knowledge
NDT surveys provide information on materials, internal geometry and anomalies at a given moment: they are a snapshot of the condition of the structure.
Structural monitoring · SHM
Evolution over time
Monitoring observes behaviour over time: time series of significant quantities, to track the evolution and response of the structure.
Diagnostics and monitoring are not the same thing, but they can be used together when the question requires it.
A diagnostic survey can prompt monitoring; monitoring data can direct new targeted surveys.
Cluster deep dives
Deep dives on structural monitoring
Dedicated guides to the main areas of structural monitoring.
Modal analysis and dynamic identification
Natural frequencies, mode shapes and dynamic response of structures.
Static monitoring
Deformations, displacements, rotations and crack evolution over time.
Dynamic monitoring
Vibrations, accelerations and identification of the dynamic response.
Sensor networks and SHM
Design of the sensor system, acquisition and data management.
The Novatest Engineering approach
Novatest designs and manages end-to-end structural monitoring systems, from initial consultation to data interpretation: every system starts from the client's management question.
01
Management question
What needs to be known, and why.
02
Defining the quantities
The parameters that are significant for answering the question.
03
System design
Sensors, acquisition and configuration consistent with the structure.
04
Installation and acquisition
Field installation and collection of measurements.
05
Processing
Analysis of time series and dynamic parameters.
06
Interpretation
Technical reading of results in the context of the structure.
07
Decision support
Reports, deliverables and support in management choices.
Frequently asked questions
- What is the difference between structural monitoring and non-destructive testing?
- Non-destructive testing (NDT) consists of targeted surveys that capture the condition of an element at a given moment: internal geometry, materials, anomalies. Structural monitoring instead observes the evolution over time of quantities such as deformations, displacements, cracks and vibrations, building a time series of the structure's behaviour.
- What does SHM mean?
- SHM stands for Structural Health Monitoring: an organised system of sensors, data acquisition, processing and interpretation that makes it possible to follow the condition and behaviour of a structure over time, supporting management and maintenance decisions.
- Which quantities can be monitored?
- Depending on the diagnostic and management question: deformations and displacements, crack opening and evolution, tilts and rotations, vibrations and dynamic response, and, when relevant, environmental parameters. Choosing the quantities is the first step in designing the monitoring system.
- What is the difference between static and dynamic monitoring?
- Static monitoring follows slow phenomena: deformations, displacements, rotations, crack evolution. Dynamic monitoring observes the structure's response to vibrations: accelerations, natural frequencies and mode shapes. The choice depends on the question monitoring must answer.
- What is modal analysis used for?
- Modal analysis makes it possible to identify the natural frequencies and mode shapes of a structure, that is, its characteristic way of vibrating. It is used to characterise dynamic behaviour, assess changes over time and calibrate numerical calculation models when relevant.
Do you need to monitor a structure or infrastructure over time?
Designing a monitoring system starts from the question it must answer. Novatest's technicians can support you in defining the most effective quantities, sensors and acquisition strategy.