Wireless Truss Monitoring
Design and installation of a real-time wireless monitoring system to measure truss tilt and distortion during lifts
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The Challenge
- New trusses built on shore, transported to barges, and lifted into place
- Perceived challenge was distortion and sweeping of the truss, any titling of the truss could initiate buckling
The Huey P. Long Bridge in Jefferson Parish, Louisiana, is a four-span steel truss bridge that carries a two-track railroad line over the Mississippi River. Two lanes of US 90 are on each side of the central tracks owned by the New Orleans Public Belt Railroad. Three different pairs of 2,700 ton trusses were built on shore, transported on barges, and simultaneously lifted 13 ft. and set in place during a weekend closure of the bridge and day closure of the navigation channel.
The biggest concern to HNTB was out-of-plane distortion, primarily ‘sweeping’ of the truss. Since the 528 ft. long truss would be lifted at the end points, any tilting of the truss could initiate buckling. Therefore, the two most important parameters to measure were tilt and out-of-plane deflection of the truss.
The Solution
A real-time remote monitoring system was designed and installed to measure truss distortions to monitor for possible overstressing or buckling of the truss during the transport, lift, and setting operation. All sensors were hard-wired to a data logger and transmitted to a laptop with multiple display panels under the bridge deck. Data was continuously transmitted, and updated approximately every 2 seconds. Data was under constant review by the design engineers and decisions made for controlling lift were based on real-time truss tilt/deflection measurements. To aid in the review of data, graphical representation of truss tilt and deformation was developed.
For each truss, a ‘birds eye’ view of the truss was displayed on separate screens to show ‘sweeping’ of the truss during the lifting and skidding operation.
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