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DEMEC Mechanical Strain Gauge

DEMEC Mechanical Strain Gauge

Demountable Mechanical Strain Gauge developed at the BCCA - British Cement and Concrete Association


The demountable mechanical strain gauge ( DEMEC ) was developed at the Cement and Concrete Association to enable strain measurements to be made at different parts of a structure using a single instrument.

The DEMEC consists of a standard or a digital dial gauge attached to an Invar bar.
A fixed conical point is mounted at one end of the bar, and a moving conical point is mounted on a knife edge pivot at the opposite end. The pivoting movement of this second conical point is measured by the dial gauge.

A setting out bar is used to position pre-drilled stainless steel discs which are attached to the structure using a suitable adhesive.

Each time a reading has to be taken, the conical points of the gauge are inserted into the holes in the discs and the reading on the dial gauge noted. In this way, strain changes in the structure are converted into a change in the reading on the dial gauge.

The gauge has been designed so that only minor temperature corrections are required for changes in ambient temperature, and an Invar reference bar is provided for this purpose.

Although originally designed for use on concrete structures, the gauge is just as useful on any type of structure. In the case of steel structures, the locating holes can be drilled directly into the steel if required.

To simplify analysing the results, a software programme which will run on any MSDOS computer is available. This gives user friendly instructions on how to enter the data and then calculates the strain changes

DEMEC strain gauges - specification

Microstrains represented by one division on the dial gauge, or one increment on the digital indicator.

Gauge length Dial version microstrains Digital version microstrains
50 mm 20 -
100 mm 16 8
150 mm 10.7 5.3
200 mm 8 4
250 mm 6.4 3.2
300 mm 5.6 2.8
400 mm 4 2
500 mm 3.2 1.6

Each division is visually sub-dividable on the dial version of the DEMEC.


A variety of methods of locating the DEMEC points are available.

Specification (addendum):
200mm Dial 1 div = 8 x 10 to power of minus 6 2.6kg 300 x 200 x 110mm
50mm Dial 1 div = 20 x 10 to the power of minus 6 1.2kg 260 x 120 x 115mm
200mm Digital 1 div = 4 x 10 to the power of minus 6 2.6kg

Each instrument, together with reference bar, setting out bar and user instructions is supplied in a purpose made wooden box