Vibrating Wire Sisterbar/Rebar Strain Gauge
The Vibrating Wire Rebar and Sister Bar Strain Gauges measure strain in concrete and consist of a coil assembly and a Vibrating Wire element with rebar extensions at each end. Rebar Strain Gauges are welded into the reinforcing cage and must be matched to the size and grade of the rebar forming the cage.
Sister Bars are installed alongside existing lengths of rebar within the cage. Both types of strain gauge are extremely robust, reliable and waterproof. The gauges can be read individually or remotely/ automatically as part of a data collection system. A factory ﬁtted, four-core screened cable connects the coil to the readout unit. The Rebar Strain Gauge operates on the established Vibrating Wire principle.
- Located within rebar cage
- Individually calibrated
- Integral thermistor
- Over 30 years of expertise in the design and manufacture of Vibrating Wire instrument technology
- Accurate, repeatable readings over long cable lengths
- Long working life, long term stability and reliability
- Suitable for remote reading and data logging
- Unaﬀected by bending
The Rebar and Sister Bar Strain Gauges consist of a sealed element containing the wire, which is de-bonded from the concrete by a plastic coating. This is attached to two lengths of rebar, one at either end, which in turn are used to transfer strain from the structure to be monitored to the gauge. These rebar extensions are long enough to ensure full transfer of the strain within the concrete to the strain gauge.
The sensor can be read with any commercially available Vibrating Wire readout and the integrated thermistor allows for temperature data to be recorded, aiding the evaluation of thermally induced strains. As with all Vibrating Wire instruments, the use of a frequency based signal allows for long cable runs (in excess of 1,000m) between the instrument and the readout point or data logger.
The Rebar Strain Gauge is used to measure strain in concrete piles, mass concrete structures, diaphragm and slurry walls, caissons and for casting in place concrete piles.
Typical applications include:
- Diaphragm and slurry walls
- Monitoring of strain due to load
- Bridges and dams
- Monitoring strain and load during construction and service life
- Piles and mass concrete
- Monitoring strains in reinforcing bars during construction, pile testing and service life.
The Rebar Strain Gauge is installed by welding the gauge into the rebar cage at a location within the structure suitable to accurately pass loads from the cured concrete into the gauge. Sister Bars (of 12mm diameter) are installed alongside existing lengths of rebar within the cage.
Rebar Strain Gauges and Sister Bars are usually installed in pairs within the structure on either side of the neutral axis, so that bending movements can be separated from axial loads.
Cables from gauges are run in a convenient way to a readout or data logging point. Care must be taken to ensure no damage occurs during pour.