Project Overview

Bridge engineers added “helper” strands on this 1924 suspension bridge to counter load shedding by the main suspension cables. GEO-Instruments installed special strain gauges on the helper strands and anchors. These would be used to monitor the performance of the helper strands and to detect any further load shedding of the main cables.

The Strain Gauges

Specifications called for bonded strain gauges on the strands and the saddle anchors holding the strands. The strand gauges were designed specifically for seven-wire strands. Redundant layers of moisture protection, physical protection, and sealing were applied to help the gauges withstand the harsh weather conditions of the Northeast.

Temperature Corrections

Two “no-stress” gages were installed to provide data for temperature corrections. Any changes in strain in these gauges would be due solely to changes in temperature.

Data Collection

All of the strain gauges were wired to a central location and provided bridge engineers with real time data during the loading and lock-off of the helper strands.

Over the long term, the monitoring system will provide valuable data for evaluating the overall structural health of the bridge.

Bear Mountain Bridge

Bridge engineers installed helper strands on this suspension bridge after learning that the main suspension cables were shedding load.

Bear Mountain Strand Gauges

GEO-Instruments designed special strain gauges to monitor the performance of the helper strands. The gauges were protected by multiple layers of weather-proofing.

suspension-bridge-helper-cable

The strain gauges provided real time data during the loading and lock-off of the helper strands and are now assisting with the long-term monitoring of the bridge.