The Federal Highway Administration’s (FHWA) Long-Term Bridge Performance (LTBP) Program is a major strategic initiative developed by the Office of Infrastructure Research and Development within FHWA, and designed to address the growing concern with aged and deteriorated infrastructure throughout the United States. As part of this flagship program, the FHWA launched an International Bridge Study (IBS) with the goal of establishing the worldwide “best practices” for the integration and application of technology to diagnose, perform prognosis, and design treatments to mitigate performance deficiencies for a given bridge. The general approach adopted for this study was to invite experts from around the world to demonstrate the ‘best practices’ associated with specific technologies on the same bridge. Intelligent Infrastructure Systems was contracted primarily to provide baseline structural responses from numerous types of loading, including static load testing as well as on-site coordination and support for the international research teams.
The selected bridge for the IBS study, built in 1983, was located in Wayne, NJ, approximately 25 minutes from Manhattan. The bridge sees nearly 100,000 vehicles a day, and was exhibiting substantial fatigue cracking, bearing deterioration, heavy vibration, and transverse deck cracking. After extensive review of the available documentation, an element-level finite element model was created, error-screened and used for sensitivity studies on seemingly uncertain parameters. Based on these results, a comprehensive static instrumentation plan including multiple modalities of response and amounting to more than 100 sensors was designed to provide situational awareness throughout the testing, to address the specific requirements of both direct and model-based data interpretation, and to fit within the specific project and bridge-related constraints. A custom distributed network of data acquisition systems was used to both reduce the amount of cabling required for such an extensive application, and to reduce the occurrence of cable-related difficulties. In conjunction with the distributed data acquisition system, a custom software program was developed for both reliable acquisition and immediate visualization of the data during the test. The software included a control interface which presented data through temporal and spatial variation, that latter of which facilitated direct interpretation of the data during the test. The loading occurred in three stages with various configurations of the trucks. The bridge was successfully loaded with over 420,000 lbs., showing substantial reserve stiffness, well beyond the prescribed original design requirement. It was determined through model-experiment correlation that the fatigue cracking was likely due to distortion stemming from differential displacements between the girders, and the excessive vibration, and not rebar corrosion, was the cause of the deck cracking.