ON THE EFFECTS OF CIRCULAR BOLT PATTERNS ON THE ...

strain gauge from potential damage during installation and testing, as well as reducing the risk of static
arching. Figure 3-7(d) shows the instrumented bolt with wiring and coating.
The strain variation on the opposite surfaces of the bolt due to the curvature reduces the accuracy of the
data obtained from the strain gauges. To eliminate this error, two strain gauges were installed
symmetrically on opposite sides of the bolt shank. The alignment of the two strain gauges was arrenged
to be perpendicular to the T-Stub stems or beam flanges during tightening of the bolts. Thus, the
maximum and minimum strain at the body of the bolt-shank was measured. The reported axial force in
the bolt was calculated by taking the average of the two strain gauges’ measured values.
3.2.3.1.4 Verification
In spite of precautions taken during the installation of the strain gauges, some of the strain gauges failed
during preliminary testing. These failures were due to inadequate bond between the strain gauge and the
bolt and/or damage to the wiring during the installation or the testing procedure. To ensure adequate
bond between the strain gauge and the bolt, each bolt was tested individually using the test setup shown
in
Figure 3-8 and Figure 3-9. Each bolt was pulled monotonically up to 50% of its yield strength, and the
forces obtained from the strain gauge were compared with the reading from the load cell. This procedure
ensures the proper bond between the strain gauge and the bolt, and verifies the functionality of the strain
gauges during the test.
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