1.Introduction

geokon vibrating wire embedment strain gauges are designed for direct embedment in concrete. This can be accomplished by attaching the gauge to rebar or tensioning cables and then casting the gauge into a concrete briquette, which is subsequently cast into the structure, or grouting the gauge into boreholes in the concrete.

Strains are measured using the vibrating wire principle. A length of steel wire is tensioned between two end blocks that are firmly in contact with the mass concrete. Deformations in the concrete will cause the two end blocks to move in relation to each other, altering the tension in the steel wire. This change in tension is measured as a change in the resonant frequency of vibration of the wire.

Two coils, one with a magnet insert, the other with a pole piece insert, are located close to the vibrating wire. In use, a pulse of varying frequency (swept frequency) is applied to the coils causing the wire to vibrate primarily at its resonant frequency.

Portable readouts and dataloggers are available from geokon. These models, when used in conjunction with vibrating wire strain gauges, will provide the necessary voltage pulses to pluck the wire. During vibration, a sinusoidal signal is induced in the coils and transmitted to the readout box where it is conditioned and displayed.

This manual contains installation instructions, readout and data reduction procedures, and troubleshooting guidelines.

Note: Do not rotate or pull on the gauge end blocks, because this will alter the readings and may cause permanent damage.

 

Figure 1: On-site Installation Photo