Appendix E. No Stress-Strain Enclosure; Figure 12 - N Ostress Strain Enclosure - Geokon 4200 Series Instruction Manual

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APPENDIX E. NO STRESS-STRAIN ENCLOSURE.

Geokon's Model 4200-4 No Stress-Strain Enclosure is a double walled enclosure. The walls are
made of PVC and filled with Styrofoam. Figure 12 shows a typical 4200-4 installation.
The purpose of the no stress enclosure is to position a strain gage 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 Gage can be used to apply corrections for these
phenomena to the other strain gages in the mass concrete, allowing the strains due only to stress
changes to be quantified.
Installing the 4200-4:
1) Position the enclosure inside the mass concrete with the top open so that it can be easily
filled with concrete. (Often the 4200-4 will be placed next to a strain gage rosette.)
2) Mount the strain gage by wrapping two turns of wire around the gage and then feeding the
ends of the wire through the holes in the opposite sides of the enclosure.
3) Wrap the ends of the wire around the outside of the enclosure and tie together.
4) Use a tie wire tightening tool or similar device to tighten the wire.
5) Repeat this procedure, using another tie wire and the second set of holes in the enclosure.
6) Arrange the instrument cable so that it exits through the top of the enclosure.
7) When pouring concrete into the enclosure, remove aggregate that is too large. Be careful not
to disturb the gages during the filling process.
Figure 12 - No Stress Strain Enclosure