Figure 17: No Stress Strain Enclosure - Geokon 4200 Series Instruction Manual

26 | NO STRESS STRAIN ENCLOSURE | GEOKON
APPENDIX E. NO STRESS STRAIN ENCLOSURE
's Model 4200-4 No Stress Strain Enclosure is made of double PVC
GEOKON
walls and is filled with polystyrene foam. The figure below shows a standard
4200-4 installation.
Instrument Cable
Wire Tie

FIGURE 17: No Stress Strain Enclosure

The purpose of the no stress enclosure is to position a strain gauge so that it is
not subject to changes in strain in the mass concrete surrounding it, yet still
remains subject to changes in strain caused by the fluctuation of moisture
content, temperature, and alkali/aggregate reaction. The data gleaned from the
No Stress Strain Gauge can be used to apply corrections for these phenomena
to the other strain gauges in the mass concrete, allowing the user to quantify
only those strains that result from stress changes.
INSTALLING THE 4200-4 ENCLOSURE
1. Position the enclosure inside the concrete mass with the top open so that it
can be easily filled with concrete. (Often the 4200-4 will be placed next to a
strain gauge rosette.)
2. Mount the strain gauge by wrapping two turns of tie wire around the gauge
and then feeding the ends of the wire through the holes in the opposite
sides of the enclosure.
3. Wrap the ends of the tie wire around the outside of the enclosure and tie
together.
4. Use a tie wire tightening tool or similar device to tighten the wire.
Concrete
Coil Assembly
4200
Enclosure Wall
Polystyrene Foam
Wire Tie