The Delaware River Joint Toll Bridge Commission (DRJTBC) owns and operates 20 bridges over the Delaware River between New Jersey and Pennsylvania. Among the oldest structures in its jurisdiction are the New Hope-Lambertville Toll-Supported Bridge, and the Rivertonâ€“Belvidere Toll-Supported Bridge. Both of these through trusses are more than 100 years old, and are currently posted for 4 tons and 8 tons, respectively. These bridges were selected by DRJTBC to be used in a Bridge Monitoring System Study with the goal of enabling the Commission to improve safety and maintainability of its aging bridges. Additionally, the installed system was studied for its use as a detection, enforcement and early-warning tool for overweight or oversize vehicles.
To assist DRJTBC in these goals Intelligent Infrastructure Systems developed a work plan aimed at both structural health monitoring (SHM) and overweight vehicle detection. Both of these goals required a thorough understanding of the behavior of each bridge. Following the Structural Identification (St-Id) framework, Intelligent Infrastructure Systems designed an instrumentation plan capable of meeting the two objectives laid out by DRJTBC: (1) update load ratings of all critical elements and (2) identify feasibility of using a SHM system for real-time assessment of overweight vehicles. A controlled load test was conducted on each structure to initialize the monitoring portion of the program, and Finite Element (FE) models were calibrated to the measured structural responses.
Using the information gained by the St-Id process, a short-term monitoring study was carried out to assess performance under vehicle and environmental loadings, and to assess the ability of the system to identify overweight vehicles. During a month of monitoring, the SHM system identified several significant vehicle crossing events, which the Commissionâ€™s Electronic Surveillance/Detection System (ESS) confirmed to be oversized vehicles. The system was then used to determine if these crossings changed the behavior of the structure, which could be indicated by some nonlinearity induced by the vehicle.