Ultrasonic Measurement of Stress in Pin and Hanger Connections

摘要

Pin and hanger connections are used in bridges to suspend an interior span from211u001ethe outer spans. The connections can sometimes lock up due to corrosion. If 211u001elockup occurs the stresses in the connection are cycled due to thermal expansion 211u001eand contraction of the bridge; fatigue cracking and failure may occur. We 211u001econstructed an apparatus to simulate a locked-up pin and hanger connection. We 211u001eperformed proof of concept tests of a method to detect stresses in pin and hanger 211u001econnections. The method uses the stress-induced changes in sound velocity of 211u001eshear waves polarized parallel and perpendicular to the hanger axis. The 211u001ebirefringence is the normalized difference in these shear wave velocities. We 211u001emeasured the birefringence at opposite sides of the hangers, at midsection. We 211u001esimulated three scenarios: continuous monitoring of hanger status; intermittent 211u001emonitoring from a known initial state; measurement with no 'a priori' knowledge 211u001eof hanger status. Good agreement with strain gauge data was obtained for all 211u001ethree scenarios.