Description

DEMEC* strain gauge, setting-out and reference bars manufactured by WH Mayes & Son of Stroud, UK. Fitted wooden box.

The strain gauge
The strain gauge is a high-precision mechanical instrument used to measure strain or cracking across a structure. By taking manual readings between pre-established gauge points, it allows engineers and researchers to track structural deformation, cracking, and stress over time.
It is mounted on a steel bar with two hardened steel tips (conical points) set 2 in (50.8 mm) apart: one end of the bar is fixed while the other end is allowed to pivot and any movement of the pivot can be read on a dial and any strain calculated. It is used in conjunction with matching setting-out and reference bars which are contained in the same box.
Where there is suspected strain or cracking, two pre-drilled stainless steel discs are secured to the surface of a test area and a setting-out bar is used to set an exact initial distance. Subsequently, to determine if there has been any movement, the gauge’s two tips are placed into the pre-drilled discs on the reference bar to set the gauge to the initial set distance. The gauge can then be applied to the two discs set up on the test area and any difference in length can be read from the dial.

Setting-out and reference bars
The box contains a block which houses a setting-out (or spacer) bar and a reference bar for use with a DEMEC strain measuring gauge. Both bars are set to measure 2 in (50.8 mm). The setting bar has two hardened steel tips (conical points) which are used to locate two steel locating discs exactly 2 in apart across an area over which strain is to be measured. The reference bar has two pre-drilled stainless steel discs set 2 in (50.8 mm) apart and is used to set a strain gauge to 2 in prior to subsequent measurements.

This gauge was used in the Concrete Laboratory at Heriot-Watt University, Edinburgh, UK.

*DEMEC = demountable mechanical