Campbell Scientific ST350 Strain Transducer for Structural Testing User Manual
Page 34
Appendix A. Special Instructions for using ST350
very heavy, we recommend that the gain level for the STS be set to 500. It
should be noted that in most cases, the live-load strain magnitudes recorded by
BDI on reinforced concrete structures have been less than 100
με.
TABLE A-2. Maximum Strain Ranges
Multiple of
Original
Length
Actual Gage
Length w/
Extension
Maximum
Strain
Range
Approx. Conc.
Stress for
f’’
c
= 3,000 psi
Approx. Conc.
Stress for
f’’
c
= 4,000 psi
Approx. Conc.
Stress for
f’’
c
= 5,000 psi
Approx.
Steel
Re-bar
Stress
1
3 in (76.2 mm)
±1000 με.
3.1 ksi
3.6 ksi
4.0 ksi
30 ksi
2
6 in (152.4 mm)
±500 με.
1.6 ksi
1.8 ksi
2.0 ksi
15 ksi
3
9 in (228.6 mm)
±330 με.
1.0 ksi
1.2 ksi
1.3 ksi
9.9 ksi
4
12 in (304.8 mm)
±250 με.
780 psi
900 psi
1.0 ksi
7.5 ksi
5
15 in (381.0 mm)
±200 με.
625 psi
720 psi
800 psi
6.0 ksi
6
18 in (457.2 mm)
±160 με.
500 psi
575 psi
650 psi
4.8 ksi
7
21 in (533.4 mm)
±140 με.
440 psi
500 psi
560 psi
4.2 ksi
8
24 in (609.6 mm)
±125 με.
390 psi
450 psi
500 psi
3.8 ksi
A.2 Attaching the Concrete Extension to a Strain
Transducer
Once a gage length has been determined, there are three possible scenarios for
mounting the transducer/extension assemblies to the structure:
1. Adhesive/tabs on both ends. If conditions are dry, the concrete surfaces
relatively smooth, and testing will not last more than a day, the
tab/adhesive system will usually work fine as described below.
2. Adhesive/tab on transducer end and a masonry anchor on the extension
end. This is the preferred method of BDI. Again, if conditions are dry,
then the adhesive/tab system on one end will be sufficient for a couple of
day’s worth of testing, as long as the other end is securely mounted with a
mechanical anchor. It is highly recommended to use masonry screws such
as 1/4-20x3.25” concrete studs or another type of masonry anchor (readily
available at most hardware stores) to install transducer/extension assembly
due to the additional weight of the extension.
3. Anchor/masonry anchor on both ends. Use this approach only when the
structure is wet and/or very rough.
In either of the above scenarios, the steps below should be followed for
mounting the extensions to the transducers. The extension jig is used to
ensure that the transducer is aligned properly with the extension. If using
the anchor mounting on both ends, then omit the mounting tabs described
below.
A-2