For the past year, researchers at the University of
Minnesota have studied how the I-35W St. Anthony Falls Bridge, which spans the Mississippi River near downtown Minneapolis, is aging.
The researchers are monitoring nearly 500 sensors installed during construction of the bridge for strain, load distribution, vibrations, temperature, and the overall movement of the bridge.
As the bridge ages, the concrete naturally shortens due to a process called “shrinkage.” The concrete will also “creep,” meaning that it will continue to deform with time due to the permanent gravity and post-tensioning loads.
The research team is in the process of refining models to better predict the behavior of the bridge over time—data they plan to use as a baseline for detecting damage or potential problems in the structure. The award-winning bridge, which opened in 2008 after nearly 11 months of construction, is designed to last 100 years.
In conjunction with predicting the long-term structural behavior of the bridge, the research team has continued to monitor the sensors for behaviors related to temperature and time. This includes expansion joint movement, strains, and the dynamic modes of vibration.
The research team also is developing a unique prototype monitoring system that provides warnings to MnDOT Metro Maintenance personnel if problems arise in the expansion joints. They focused on the expansion joints first because those joints are easiest to incorporate into maintenance and inspection routines.
Once the monitoring framework for the expansion joint movement is finalized, the prototype also may be extended to evaluate other sensor data.
Read the full article in the November issue of Catalyst.