Tobin Memorial Bridge Monitoring

In the next 18 months, the Massachusetts Port Authority’s (Massport) Tobin Memorial Bridge will be the state’s first bridge to have a wireless high-tech structural health monitoring system (SHM) in place to monitor stresses and strains in a real-time environment. In an effort to learn more about the behavior of the Tobin Bridge, Massport brought in an engineering consulting firm at a total project cost not to exceed $1 million. The firm will conduct structural modeling and analysis of forces and strains on the Tobin Bridge using a 3-D computer engineering model. Fay, Spofford & Thorndike (FST), located in Burlington, Mass., was chosen based on their overall qualifications and innovative approach. The firm’s knowledge base also is strengthened through an academic partnership with experts in the fields of structural engineering and computer analysis from Tufts University and the University of New Hampshire. A fourth member of the team, Geocomp of Boxborough, Mass., brings to the job worldwide expertise in placement and application of instrumentation. As a starting point, FST is working on the 3-D modeling, verification of results and recommendations for sensor and monitor placement on the Little Mystic truss and a six-span girder plate module on the Boston approach. These portions of the bridge were selected for their relatively simplified geometry in relation to the toll plaza and Big Mystic truss areas. A second phase for the Big Mystic truss also is under way. Further verification of the 3-D model results will be obtained by test loading of the Tobin Bridge once the sensors and monitors are installed. The test loading will consist of positioning fully loaded trucks along the bridge and recording the results. The test must be conducted when no other vehicle loading is on the portion of the span that is being tested. This will require that both decks of the Tobin Bridge be closed to traffic for a short period of time. The results of the test loading will help Massport engineers verify that the 3-D models are correctly predicting forces within the Tobin Bridge’s members and components. Once the verification process is complete, the models can then reliably be used to identify critical information points for sensor and monitor placement. These areas will include locations where elevated stress levels or unexpected deflections have been observed. At this writing, the initial 3-D models of the Tobin Bridge are still in development. Therefore, all key locations for sensor and monitor placement have not yet been finalized along with total project cost. [Roads and Bridges]