Infrastructure Technology Institute
In early 2012, the ITI REG and several civil engineering students took part in a collaborative research project with Metro North Railroad (MNR) near New York City. MNR, the second-largest commuter railroad in the nation, carries over 270,000 passengers every weekday from five surrounding counties and Connecticut to Grand Central Terminal in Manhattan. Operating six rail lines over 765 track-miles with 121 stations and over a thousand rail cars, the amount of critical infrastructure for which MNR is responsible is staggering.1
In addition to the tracks, embankments, stations, tunnels, cars, communication systems, power systems, and railroad bridges that one might expect such a large railroad operator to maintain, MNR is also responsible for several bridges that carry local automobile and pedestrian traffic over its tracks. One such bridge, the one carrying Fulton Avenue over the MNR New Haven line in Mount Vernon, New York, is over a century old and requires special attention from MNR forces to ensure its safe operation.
The Fulton Avenue Bridge, a steel eye-bar through-truss structure with an asphalt-overlaid wooden deck, carries two lanes of traffic, two sidewalks, and several local utility lines over four active tracks and a power substation. The bridge also provides access to two staircases to the platforms of the Mount Vernon East rail station. Routine inspections of the bridge by MNR’s engineers have resulted in several repairs and improvements, including re-decking and installation of steel cables to bolster critical tension members supporting the deck, that have allowed the bridge to continue operating for the past hundred-plus years.
To supplement its inspection and engineering analysis activities and to gain more insight into the performance of the retrofits, MNR enlisted the ITI REG to design and install an autonomous remote structural health monitoring system on the bridge. The system, comprising a high-speed data logger, nineteen strain gages, five accelerometers, two thermocouples, an ambient environmental condition sensor, two high-definition cameras, an encrypted cellular uplink, and support electronics, monitors and records the condition of the bridge at all times, automatically publishing this data to a password-protected Web every night. Should a large vehicle cross the bridge (in violation of the posted three-ton load restriction), the system will automatically record high-frequency data from all of the sensors along with digital images of the vehicle as it crosses. It will then alert MNR engineers so they can evaluate the structural effect of the illegal crossing.
The system was installed during Northwestern’s spring break in March by ITI REG staff members and two undergraduate students who traded a more traditional collegiate spring break experience for a week of working long hours on the railroad – sometimes in the very early morning, the only time some portions of the tracks could be taken out of service to allow for access to certain bridge components. Using the automated Web display, MNR engineers will be able to track any changes in performance of the bridge between inspections, providing more information to guide the choice between repairing and replacing the structure.