Understanding SHM Parts: Sensor Types for Structural Health Monitoring

Introduction

Structural Health Monitoring (SHM) plays a vital role in ensuring the safety, longevity, and efficiency of infrastructure, from bridges and tunnels to buildings and dams. This article delves into the core components of SHM, focusing specifically on sensor types, which are the backbone of any monitoring system.

What Is Structural Health Monitoring?

Structural health monitoring (or building movement monitoring) refers to the continuous observation and analysis of a structure’s physical behavior over time. This includes tracking displacements, deformations, stress, strain, and other dynamic changes. The goal is to detect anomalies early, assess structural integrity, and prevent potential failures. Whether it’s the subtle sway of a skyscraper or the stress distribution in a bridge, monitoring helps maintain safety and operational efficiency.

What Do We Need to Monitor Structural Health on a Construction Site?

While SHM systems can be complex, at their core, they rely on one critical element: data. Data is the lifeblood of any monitoring system, providing the necessary information to assess the health and performance of structures. This data doesn’t originate from a single source but rather from a multitude of channels, each contributing unique insights into the structural integrity.

Primarily, data comes from sensors installed directly on the structures. These sensors are the most typical and vital data sources in SHM systems. They capture physical changes such as strain, displacement, acceleration, and temperature variations, providing real-time, precise measurements essential for monitoring structural health.

However, the scope of data sources can extend beyond these embedded devices:

External Data Sources: Information such as weather data, including temperature, humidity, wind speed, and precipitation, can significantly influence structural conditions and help contextualize sensor readings.
Manual Measurements: Inputs from periodic inspections, including geodetic surveys conducted by specialists, provide additional layers of data for comprehensive analysis.
Third-Party Systems: Integration with external monitoring systems can supply relevant data, enhancing the overall picture of structural health.

By aggregating data from these diverse sources and processing them effectively, SHM systems can provide real-time insights into structural behavior. This holistic approach ensures that monitoring is not just about collecting numbers but understanding the dynamic environment in which these structures exist.

What Is a Monitoring Sensor?

A monitoring sensor in SHM is an electronic device designed to detect, measure, and record specific physical parameters of a structure. These sensors convert physical phenomena (like strain, temperature, or movement) into electrical signals, which are then processed to monitor the structure’s health. The precision and reliability of these sensors are critical for early detection of structural issues.

What Kind of Sensors Are Used for Measuring Data?

Various sensor types are utilized in SHM, each tailored to monitor specific aspects of a structure:

Strain Gauges: Measure strain on structural elements, helping to detect deformations and stress concentrations. They are often bonded to the surface of structural components to capture real-time stress variations under loads.
Accelerometers, vibration sensors: Track vibrations and dynamic movements, essential for seismic monitoring and dynamic load analysis. These sensors can detect even the slightest vibrations, which are critical for assessing structural responses during earthquakes or heavy traffic.
Displacement Sensors (LVDTs): Measure linear displacement to detect shifts or settlement in structures. They provide high accuracy in tracking small positional changes, making them ideal for monitoring bridges and tunnels.
Inclinometers: Monitor tilting or angular displacement, useful in slope stability and high-rise buildings. They are often deployed to detect subsidence, ground movement, or deformation in retaining walls.
Temperature Sensors: Record temperature fluctuations, as thermal changes can affect structural materials. These are essential in environments with extreme temperature variations, ensuring structural materials remain within safe limits.
Crack Meters: Detect and monitor the development of cracks over time. They help identify structural weaknesses early, enabling timely maintenance to prevent further damage.
Load Cells: Measure force or load applied to structural components. Common in bridges and cranes, they help monitor load distribution and structural capacity.
Fiber Optic Sensors: Offer high sensitivity for measuring strain, temperature, and pressure over long distances. They are immune to electromagnetic interference and ideal for harsh environments.
Humidity Sensors: Measure moisture levels, especially important for concrete structures, where excess humidity can lead to corrosion or material degradation.
Piezometers: Used to measure pore water pressure within soils or concrete, critical for dam and tunnel stability assessments. Piezometers can show water levels in wells too.

What Units/Values Do We Measure with the Sensors?

The data collected from SHM sensors are expressed in various units, depending on the parameter being measured:

Strain: Microstrain (με)
Displacement: Millimeters (mm) or micrometers (μm)
Acceleration: Meters per second squared (m/s²)
Tilt/Inclination: Degrees (°) or radians
Temperature: Degrees Celsius (°C) or Fahrenheit (°F)
Load/Force: Newtons (N) or kilonewtons (kN)
Crack Width: Millimeters (mm)
Moisture: Percentage (% relative humidity)
Water Level: Meters (m) or centimeters (cm)
Gas Concentration: Parts per million (ppm)
Torsion: Newton-meters (Nm) or degrees (°)
Frequency: Hertz (Hz)

These measurements provide insights into structural behavior, enabling early detection of potential issues.

Consulting with SHM experts and structural, geotechnical engineers ensures the selection of appropriate sensors tailored to specific project requirements or engineering challenge.

How Do We Know What Sensors We Need?

Choosing the right sensors for SHM depends on several factors:

Structural Type: Bridges, tunnels, and skyscrapers have different monitoring needs.
Monitoring Goals: Define whether the focus is on detecting movement, stress, vibration, or environmental effects.
Environmental Conditions: Harsh environments may require robust, weather-resistant sensors.
Accuracy Requirements: High-precision applications demand advanced sensor technologies like fiber optics.
Budget Constraints: Balancing cost with the need for comprehensive data collection.
Duration of Monitoring: Temporary construction monitoring versus permanent installation for long-term surveillance.

Consulting with SHM experts ensures the selection of appropriate sensors tailored to specific project requirements. Additionally, our team offers the opportunity to book demo sessions, where we showcase the system in action and answer any questions related to SHM, helping you gain a deeper understanding of its capabilities and applications.

Conclusion

Understanding the different types of sensors used in Structural Health Monitoring is crucial for maintaining the safety and durability of infrastructures. From strain gauges to fiber optic sensors, each type serves a unique purpose in capturing critical data. By leveraging the right combination of sensors, data acquisition systems, and analysis tools, SHM provides invaluable insights, helping engineers make informed decisions and ensure structural integrity for years to come.