The Rebar Strain Gauge is designed to measure strain in concrete piles, mass concrete structures, diaphragm and slurry walls, caissons and cast in place concrete piles. 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. Rebar Strain Gauges are welded into the re-enforcing cage and should 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.

The Rebar and Sisterbar Strain Gauge 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 Rebar strain gauge operates on the established Vibrating Wire principle. With the gauge embedded within concrete, deformation of the concrete mass causes the two pieces of rebar to move relative to one another, thus altering the tension in the steel wire and its natural frequency. As the gauge is attached directly to the structure then an externally housed electromagnetic excitation coil, sealed within a PVC housing situated at the mid-point of the gauge tube, is used to excite the strained wire. Connected by tough 4-core, screened cable, the coil is activated by an electrical pulse from a vibrating wire readout unit, which then measures the resulting frequency of vibration. Using a gauge factor, the measured frequency may be converted directly