VW Rebar Strainmeter
Introduction  |  Spot-Weldable | Surface-Mount | Rebar Strainmeter | Embedment

Applications

Gage Technique's vibrating wire rebar strainmeter, commonly known as a "sister bar", is designed to measure strains in mass concrete. Typical applications include measuring strain in concrete piles, tunnel linings, mass concrete structures, diaphragm walls, and barettes.

Operation

The rebar strainmeter comprises of two lengths of ribbed rebar welded to a central gauge section. The central gauge section has a miniature stainless steel, hermetically sealed vibrating wire strain gauge element, fitted coincident with the longitudinal axis of the gauge. Incorporated within the gauge section are two orthogonally mounted coils for excitation and output of the vibrating wire strain gauge element. The coil units and cable connection are encapsulated within a proprietary rigid sub-sea grade polyurethane resin.

Sister bars are very long relative to their diameter and each rebar extension is in excess of fifty times the bar diameter to satisfy bond length requirements. To prevent bonding to the concrete, the central gauge portion is fitted with a polyolefin sleeve. As the overall length of the instrument is long, inclusion effects are minimal.

The rebar strainmeter is particularly applicable for strain measurements in mass concrete pours where placing of concrete is remote and uncontrolled such as typically occurs in diaphragm walls or deep piles, since the instruments are capable of withstanding impact from tremie pipes and large concrete flows.

For installation, the sister bars are simply tied by soft iron tie wire to an adjacent reinforcing bar. As the sister bars are of long length, they are readily able to maintain their orientation to the reinforcing cage.

Advantages

Reliable long term performance
Rugged, suitable for demanding environments
Can be embedded directly in the concrete
High accuracy
Insensitive to long cable lengths

Specification

Installation: Direct embedment.
Effective Gauge length: 50 mm ( nominal ).
Debonded length: 175 mm.
Overall length: 1.39 m.
Standard diameter: 15 mm.
Resolution: 0.5 microstrain.
Strain range: 2500 microstrain.
Coefficient of thermal expansion: 12 ppm /deg C.

For more information

Download the pdf datasheet for the rebar strainmeter.