Scottech are experts in the field of technology and data acquisition, but are not structural engineers. The following is a brief overview of the technology available to allow us to work in partnership with suitably qualified engineers to design the most suitable system for your application. Every structure is different so we invite you to discuss your specific requirements with us.

Types of applications we can monitor include:

• Long term monitoring of bridges for the effects of temperature, traffic loading or changes in construction materials on strain and displacement
• Dynamic monitoring of bridges for displacement, strain and acceleration during individual traffic events
• Monitoring the load on structures (and piles) during critical construction stages
• Dynamic and long term monitoring of structures such as dams, bridges and stadiums for public safety
• Monitoring the performance of new construction materials or methods
• Ground water pressure for mining, building or other applications requiring excavation
• Seismic monitoring for modal analysis of buildings before and after earthquakes

Accelerometers & Seismic Recorders

Scottech support the GeoSIG range of seismic monitoring equipment from Switzerland.

Accelerometers are the key sensors used for measuring seismic events. The AC-7x accelerometer from GeoSIG is based on MEMS technology which allows for the development of very small, accurate fast-response sensors. The AC-7x can be purchased as triaxial, biaxial or uniaxial.

The GMS recorder incorporates accelerometers and other sensors, with 24-bit processing to provide the following functionality:

• Data processed in real time for calculations of Peak Ground Acceleration (PGA), Peak Ground Displacement (PGD) and Response Spectrum (RSA) at various frequencies
• Triggered by seismic (or other) event(s)
• Ethernet or optional 2.4GHz WiFi
• Real Time Clock synchronization
• Use with GeoDAS communications software

Typical configurations and costs

Structural sensors (strain gauges, crack meters, tilt sensors)

Structural sensors measure very small movement changes in a structure. It is important to determine if you are interested in fast response (dynamic) changes or long-term changes as this will affect your choice of technology.

For long-term monitoring, Scottech recommend the Geokon range of vibrating wire sensors. Vibrating wire sensors are very accurate, precise and can support very long cable runs without signal degradation. They cannot however be used for sub-second sampling due to the time the measurement takes. The types of measurements that can be achieved include:

• Strain measurement - different models suitable for embedding in concrete, welding to steel structures, bonding to concrete, attaching to steel cable or rebar. Measure down to 1µs (micro-strain) (1x10-6 meters per meter of deformation)
• Crack meters - measure movement across surface cracks or joints. Measurement precision down to 3 x 10-3 mm dimensional change across the crack. For measuring lengths up to 100mm.
• Tilt meters - measure tilt in a single, or dual directions. Measurement precision down to ±10 arc seconds (±0.005mm/m).
• Load cells - typically installed during construction, these output a direct reading in N. Measurement precision down to 2kN

Signal processing for these sensors is done using a Campbell Scientific datalogger, using multiplexers if required, to measure up to 256 sensors. In a large network of sensors such as this, the majority of cost is generally in the sensors and cabling.

Typical configurations and costs

For dynamic monitoring, the sensors used have very fast response times, and use a different measurement principle. They may include a combination of LVDT Displacement sensors, accelerometers and Foil Strain gauges with a high speed datalogger.
Dataloggers for these applications also need to :

• be able to high resolution to measure very small changes
• have a large memory capacity and/or remote telemetry to avoid data loss
• the ability to apply calibration factors or other algorithms to provide the data of most use

Campbell Scientific dataloggers are able to manage these requirements with measurements typically in the range of 10 to 1000 per second. This dynamic type of measurement is usually associated with a live load test, like driving a truck or train moving over a bridge or similar. This type of measurement can get very expensive very quickly, due to the recording requirements.