Structural health monitoring system for the new I-35W St Anthony Falls Bridge

The collapse of the I35W Bridge in Minneapolis shook the confidence of the public in the safety of the infrastructure that we use every day. The Design Build team realized the construction of the replacement bridge must help rebuild this confidence, by demonstrating that a safe, reliable bridge can be attained starting at construction and maintained throughout the projected 100-year life-span of the bridge. One of the central factors contributing to this is the design and installation of a comprehensive structural health monitoring system, which incorporates many different types of sensors measuring parameters related to the bridge performance and ageing behavior. This system continuously gathers data and allows through appropriate analysis to obtain actionable data on the bridge performance and health evolution. The data provided will be used for operational functions as well as for the management of ongoing bridge maintenance, complementing and targeting the information gathered with routine inspections. The main targets of the SHM system are to support the construction process, record the structural behavior of the bridge, and contribute to the bridge security. The design of the system was an integral part of the overall bridge design process allowing the SHM system to both receive and provide useful information about the bridge performance, behavior and expected lifetime evolution. Monitoring instruments on the new St Anthony Falls Bridge measure dynamic and static parameters to enable close behavioral monitoring during the bridge's life span. Hence this bridge will be considered to be one of the first 'smart' bridges of this scale to be built in the United States. The SHM system includes a range of sensors which are capable of measuring various parameters to enable the behavior and condition of the bridge to be monitored: vibrating wire strain gauges, thermistors, linear potentiometers, accelerometers, concrete corrosion and humidity sensors and SOFO long-gauge fiber optic deformation sensors. The sensors are located throughout both the northbound and southbound bridges, and are present in all spans. A denser instrumentation array is utilized for main span of the southbound bridge to validate load distribution and design methodology. In addition, it allows correlation and comparison between different methods of measuring. Finally, collected information may allow designers to refine specifications for future concrete box girder bridges.