Campbell Scientific ST350 Strain Transducer for Structural Testing - Manual (Page 37)

Appendix A. Special Instructions for using ST350
IMPORTANT: Once the extensions have been installed, the transducers are
much more susceptible to damage during handling due to the large extension
“lever”. To minimize possible damage, place the transducer/extension
assemblies in a plastic five-gallon bucket with the extension ends down. This
will allow for many assemblies to be carried at once and still be relatively
protected.
FIGURE A-6. Example of Ceiling Mounting
It may be noted during testing that there is significantly drift due to ambient
temperature changes once the extensions are installed. This is due to the
relatively low thermal inertia of the transducer/extension assembly compared
to that of the concrete structure. The best solution is to run the tests on a day
when the temperature is remaining constant. This is not always possible,
therefore, the drift can be minimized, particularly for assemblies that receive
direct sunlight (on top of the deck, on the parapet, etc.), by covering the gage
and extension with an insulating material. Often, a temporary cover of foam or
cloth attached with duct tape can protect them from wind and direct sunlight.
Alternatively, CSI can provide custom gage covers that can be mounted
temporarily.
After the test has been completed, extreme care must be taken in removing the
securing nuts from the tabs, as often tabs will have a tendency to “twist off” at
the glue line, particularly if the concrete is slightly rough. Do not attempt to
remove the extension from the transducer while the assembly is still mounted
to the structure. Also, before the assemblies are removed, double-check that
the gage length used for each transducer is recorded. If this is not done, the
data will be useless!
Back off the securing nut between the transducer and extension by holding the
extension only. If the tabs are still attached to the transducer or extension after
removal from the structure, use vice grips to hold the bottom of the tab while
the securing nut on top is removed. Again, never use the transducer as a lever!
To reduce the strain data, remember that the recorded strains have been
“amplified” by the integer multiple of the gage length. For example, if the
longest possible gage length is used (24 in, 58.8cm) this is eight times the
standard gage length. Therefore, the data will need to be divided by eight to
arrive at the correct “averaged” strain. In addition, a factor of 1.1 will need to
be applied to the output to account for the extension effect. The BDI WinGRF
Software has a feature to easily handle this operation.
A-5