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