The four main spans of the Huey P. Long Bridge extend nearly 2,400 feet over the Mississippi River in New Orleans, LA. This cantilevered steel through-truss bridge opened to traffic in 1935 and is owned and operated by the New Orleans Public Belt Railroad. The bridge currently carries dual rail lines between the trusses and two lanes of vehicular traffic cantilevered to the exterior of each truss. Based on the need to improve vehicular traffic flow and constraints due to uninterruptible rail traffic, the Louisiana Department of Transportation and Development decided to widen the bridge rather than replace it.
The main spans of the Huey P. Long Bridge consist of a three-span cantilevered truss with spans of 530 feet, 790 feet and 530 feet, and a through truss span of 530 feet. The roadway sits approximately 135 feet above the Mississippi River. The bridge widening entailed the addition of upstream and downstream trusses parallel to the existing trusses and will facilitate an increase in roadway width on each side of the bridge from 18 feet to 40 feet. This expansion will accommodate an additional traffic lane in each direction and the addition of dual shoulders in each direction.
A structural health monitoring system was included in the construction as a proactive measure to assess whether the anticipated amount of load is being transferred from the widening truss members to the existing truss.
CTLGroup designed a custom structural health monitoring system to satisfy the project requirements for strain gage monitoring. Two types of sensors and data collection systems were installed: static load strain gages and live load strain gages. The static system records measurements from vibrating wire strain gages and tilt meters. The dynamic system is a high speed system for recording measurements from the live load sensors. The structural health monitoring system consisted of a total 769 strain gages, 10 tilt meters, one wind gage (anemometer), 30 multiplexers, four data loggers and 32 wireless transmitters. The data measured by the strain gages, tilt meters and anemometer were collected via a system of hard wiring, radio transmitters, digital and analog hardware, computers and servers.
Data was collected at 10 minute intervals and was reported to a website with password-protected access. This allowed the contractor to monitor the effects of the widening construction process on the existing structural members.