Feasibility of vibration-based long-term bridge monitoring using I35W St. Anthony Falls Bridge

Principal Investigator:

Lauren Linderman, Assistant Professor, Civil, Environmental and Geo-Engineering

Co-Investigator

  • Carol Shield, Professor, Civil, Environmental and Geo-Engineering

Project Summary:

The overall approach for structural health monitoring (SHM) is the comparison of current performance to a known benchmark and to identify if differences are a function of damage. The dynamic properties of a structure, including the natural frequencies and mode shapes, form a fingerprint that can be used as a benchmark for comparison. One advantage of using modal analysis for SHM is that ambient vibration detected with relatively few sensors can be used to capture the behavior. However, correlating system behavior with damage outside of a laboratory environment can be challenging due to time-dependent and temperature effects, and data quality. In order to use vibration sensors effectively on bridges in Minnesota, it will be important to understand how temperature and potentially temperature gradients affect the natural frequencies and mode shapes. Minnesota offers the unique opportunity of using the acceleration data from the I-35W Saint Anthony Falls Bridge to evaluate the effectiveness of vibration-based techniques for long-term monitoring. A very cursory look at the accelerometer data from the 35W Bridge indicated that the natural frequencies have non-linear temperature dependence. During the proposed project, the existing accelerometer data along with newly collected data will be mined to look for trends in the natural frequencies and mode shapes with mean structure temperature and temperature gradient. The existing bridge monitoring system is likely able to detect problems with the bearings, but is not likely sensitive to issues within the concrete boxes themselves. An accelerometer-based monitoring system has the potential to augment the current monitoring system. Additionally, accelerometer based monitoring systems are easily installed post construction; hence methodologies developed within this project may be easily transferable to the monitoring of existing bridges in Minnesota

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