Strain Gauges

Strain is defined as the ratio between the length of an element before and after a force has been applied to it. In concrete strain can be seen in the change of concrete or reinforcing steel due to temperature, curing and forces applied during its use. These VW strain gauges can be set up individually or in concert to monitor the shrinkage/movement of concrete. Loggers can be monitored manually or remotely by GSM modem, perfect for remote projects There are a number of various methods as follows:

Surface mounted strain gauges
Embedded strain gauges & joint meters
Crack & 3d joint meters

Surface Mounted Strain Gauges

This strain gauge is designed for monitoring strain in steel structures or strain in concrete or masonry surfaces. These include built-in thermistor or RTD. The strain gauge is screwed onto mounting plates, which are welded, screwed, or bonded to the structure. Because there are a wide variety of surfaces to which the gauge can be attached, two types of mounting plates are available, one for steel and one for concrete.

Specifications

Range: 3,000 microstrain. User can set tension to maximize range for the application.
Resolution: 1 microstrain with VW Data Recorder.
Accuracy: ± 0.1% FS
Thermal Coefficient: 11ppm / °C.
Gauge Length: 140 mm (5.5")

Embeddable Strain Gauges

The embeddable strain gauges are ideal for measuring the internal strains in concrete, whether this is cause by shrinkage of the concrete itself, or the relative motion of the reinforcing. In reinforced or pre-stressed concrete, the strain gauge is usually tied to the reinforcing cage, as shown above. Some specifications require that the gauge be cast in a concrete briquette prior to installation. In mass concrete applications, the gauge may be installed either before or immediately after placement of the concrete.

Specifications

Range: 3,000 microstrain, set mid-range.
Resolution: 1 microstrain with VW Data Recorder.
Accuracy: ± 0.1% FS
Thermal Coefficient: 11ppm / °C.
Operating Temp: -20 °C to 80 °C.
Gauge Length: Standard gauge has gauge length of 140mm. Long-base gauge has gauge length of 250 mm. Gauges can be special ordered with gauge lengths from 50 to 250 mm.

Crack Meters

The VW Crackmeter is suitable for surface monitoring of movement at joints and cracks in concrete structures or rock. The Crackmeter can detect movements of 0.15 mm with a repeatability of ±0.3 mm. The VW Crackmeter is available in 60mm and 100 mm ranges. The crackmeter has a unique, twist-proof shaft that prevents accidental damage to the sensor during installation. Typical applications include:

Monitoring joints for unexpected movement to provide early warning of performance problems.
Monitor joints and cracks in structures that may be affected by nearby excavation and construction activities.
Monitor cracks in structures that experienced seismic activity.

Specifications

The VW Crackmeter includes a vibrating wire displacement sensor, two swivel mounts, and two groutable anchors. Signal cable, ordered separately, is connected to the sensor at the factory.

Range: 60 mm or 100 mm.
Resolution: 0.025% FS with VW Data Recorder.
Calibration Accuracy: ±0.1% FS.
Repeatability: ±0.5% FS.
Waterproof Rating: Waterproof Crackmeter is rated to 17 bar
Materials: Stainless steel, neoprene O-rings.
Nominal Length: 60 mm Crackmeter is 400 mm long; 100 mm Crackmeter is 530 mm long.
Sensor Type: Vibrating wire. A built-in thermistor or RTD provides temperature measurements.

Additional Information

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