Field Tests and In-Service Monitoring of Newburgh-Beacon Bridge, New York

Field tests previously conducted on the Newburgh–Beacon Bridge in New York captured anomalous stress spikes in the critical hangers of the truss bridge. The very high magnitude spikes occurred sporadically, without warning and under various conditions. The cause and nature of the spikes were of great concern to the bridge owner, the New York State Bridge Authority. Originally, the spikes were thought to be due to some combination of wind, thermal effects, and an unlocking of stresses due to fabrication errors in the pin-and-hangers systems. A series of short- and long-term field tests were recently conducted on the bridge to help identify the cause of the spikes. Sections of the bridge were instrumented with strain gauges around two different pin-and-hanger members. One site was continuously monitored for over 3 months to obtain statistical data on the spikes. Through a series of different test setups, designed to debug the problem, the anomalous spikes were found to be caused by radio interference in the environment, which was being picked up by the strain gauge wires. The test setup, test program, and test results are described. The tests resolved a long-standing concern of the bridge authority and avoided costly and unnecessary retrofits.