Structural Health Monitoring of SEPTA's Crum Creek Viaduct
The Crum Creek Viaduct, constructed in 1897, has 17 spans and a total length of about 900 feet. The superstructure consists of four girders carrying two rail tracks, and the substructure consists of steel columns, forming four legged towers. The west tower is a single bent. After taking ownership of the Crum Creek Viaduct in early 1980s, SEPTA has repeatedly performed evaluations and assessments on the bridge due to its importance in the regional rail line system. The previous inspection reports had raised concerns about the fatigue life of the superstructure elements, and therefore SEPTA decided to employ advanced sensing and simulation techniques to provide a better understanding of the behavior of the structure, and to propose rehabilitation concepts to improve the performance and lifetime of the bridge.
During the preliminary investigation, the existing documents (photos, reports, and drawings) were reviewed and a 3D geometry replica finite element model of the bridge was created. Based on preliminary analysis results, an instrumentation plan (including both high-speed and vibrating wire gages) was developed. The idea was to capture the most critical responses of the bridge. As part of the preliminary data collection, interpretation and investigation, it was determined that the level of stress in most of the elements were reasonable. After a comprehensive geotechnical investigation was performed on the site and foundations of the structure, it was concluded that slope failure and foundation stability was a concern for this bridge. Therefore, it was recommended to the client that complete geotechnical testing, long-term monitoring, and fatigue analysis may be considered for the next phases of the project.