Displacement Monitoring of I35W Bridge with Current VibrationBased System

Project summary:

Since the opening of the I-35W Saint Anthony Falls Bridge in 2008, more than 500 sensors have been collecting data to better understand the behavior of post-tensioned concrete box girder structures. Recent research in the accelerometers installed on the bridge indicated they can be effectively used in a vibration-based structural health monitoring system, but previous studies have shown that natural frequency alone may not be sufficient to determine the performance of the structure. Vertical displacements were believed to be a simpler performance measure since direct comparisons can be made with design calculations and maintenance guidelines. To avoid the shortcomings of conventional displacement measurement options, this study focused on using the currently installed accelerometers to estimate the vertical displacements of the southbound bridge. The proposed technique utilized up-to-date modal parameters within a dual Kalman filter to estimate the vertical displacements of the structure from noisy acceleration measurements. When applied to the I-35W Saint Anthony Falls Bridge, researchers found that the dual Kalman filter approach captures only dynamic displacements due to relatively slow loading (e.g., traffic loading and thermal loading) and the corresponding low-frequency static displacements are likely too small for GPS measurements due to the high stiffness of the structure.