Application
Spot-weldable strain gauges are used with strain gauge sensors and a vibrating wire indicator or data logger to monitor strain in steel members. Typical applications include:
- Monitoring structural members of buildings and bridges during and after construction.
- Determining load changes on ground anchors and other post-tensioned support systems.
- Monitoring load in strutting systems for deep excavations.
- Measuring strain in tunnel linings and supports.
- Monitoring areas of concentrated stress in pipelines.
- Monitoring distribution of load in pile tests.
Operation
The strain gauge, with its tensioned wire inside, is welded to the structural member, so that an increase in tensile strain increases tension in the wire, and a decrease in tensile strain decreases tension in the wire. A strain gauge sensor is mounted on top of the strain gauge.
On flat surfaces, the sensor is typically held in place by weld-down straps. On reinforcing and tieback bars, the sensor is often secured by cable-ties and tape.
The strain gauge sensor uses an electromagnet to pluck the strain gauge and then returns a frequency signal to the readout or data logger, where it is converted to units of microstrain or period. The VW strain gauge sensor also incorporates a temperature sensor, which supplies data for temperature compensation.
Advantages
Very Low Profile: The vibrating wire element is positioned only 0.96 mm (0.038 inch) above the measured member. This patented, low-profile design reduces errors caused by bending of the structural member.
Pre-Tensioned Wire: Slope Indicator's weldable strain gauges are delivered pre-tensioned, ready for spot welding. Pre-tensioned gauges eliminate the time-consuming, process of tensioning the vibrating wire element in the field. Gauges can be ordered in three tension ranges to match virtually any application.
Full-Length Welding Flange: The full length welding flange allows reliable coupling of the gauge to the structural member and prevents misalignment of the end points of the gauge, a common problem with other strain gauges.
Stainless Steel Construction: The welding flange and the protective tube that seals the vibrating wire are constructed from stainless steel for corrosion resistance. The wire itself is steel, selected to match the thermal characteristics of structural steel.
