Structural Health Monitoring and Nondestructive Evaluation of the Merrimack River and Washington Street Bridges

The Merrimack River and Washington Street Bridges are comprised of three bridges with twelve spans (five trusses, four deck girders and three through girder spans) for a total length of 1,042 ft. After serving as a vital rail infrastructure link for passengers and freight for over 85 years, the bridge structures have deteriorated with various major structural deficiencies. Phase I (rehabilitation design) for these bridges included field inspections, load ratings, controlled live load testing and fatigue monitoring. Also, remaining life analyses were performed to assess the current condition of the bridges. Controlled live load testing was chosen as a reliable and proven nondestructive evaluation (NDE) method to accurately assess the performance of the structure under live loads and the results were used to calibrate structural models for the load rating. Additionally, the bridges were monitored for fatigue performance. This structural health monitoring was used in conjunction with the historical load data to evaluate the remaining fatigue life of the bridges. NDE and fatigue monitoring established that the majority of the bridge members still have a satisfactory remaining life. Presented herein are the initial ratings and the NDE procedures that were used to assess the structural capacity and the remaining fatigue life of the bridges.

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