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US bridge with built in smart technology able to test for structural defects

MnDOT is analysing vibration data from the I-35W St. Anthony Falls Bridge to create oversights that could detect structural defects during the early stages and enable engineers to improve designs for bridges.

Assistant Professor Laura Linderman of the  Department of Civil, Environmental and Geo-Engineering at the University of Minnesota said that the I-35W St. Anthony Falls Bridge was ideal for studying the environmental effects on new bridges in areas where the weather tends to be extreme.

Principal Benjamin Jilk at the MnDOT Bridge Office said that the project helped MnDOT get closer its goal of combining bridge monitoring systems with visual oversight to detect issues before they require costly correction and compromise public safety.

The I-35W St. Anthony Falls Bridge was built nine years ago to incorporate a ‘smart’ structural defects electronic monitoring system. It includes over 500 sensors that provide ongoing data on how the concrete changes shape in response to traffic, temperature changes, and wind. They can detect problems before they get out of hand and improve future bridge designs.

This smart bridge system features accelerometers, which transmit data on bridge response to stimuli such as structural damage. This allows damage to be detected anywhere on the bridge instead of at specific locations that contain measuring devices.

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It can, however, be challenging to detect damage when vibration is hidden by a normal structural response to traffic, temperature changes, wind, and other factors. When a bridge girder cracks, it can create a vibration similar to that created by a beam length change due to temperature variations.

As a result, MnDOT has been carrying out a succession of projects using St. Anthony Falls Bridge data to create a method of differentiating potentially dangerous signals from background noise attributable to normal causes.

The current structural defects technology strove to establish a way of analysing accelerometer data to demonstrate how the bridge vibrates due to natural conditions like wind and traffic, and use this information as a baseline for detecting anomalies that could signal structural damage.

Substantial amounts of data have been collected from the bridge since it was built. To create a vibration fingerprint for it, researchers reviewed the frequencies and modes of its vibration waves in data collected between April 2010 and July 2015. They also examined how frequencies changed due to temperature variations between its segments. The researchers concluded that the ratio of RMS to peak signal amplitude in the vibrations was a firm indicator that the data should be analysed.

MnDOT confirmed that it will continue to collect data as the bridge ages to acquire additional insight into its behavior. This will allow them to determine how anomalies in vibration data relate to signs of structural issues such as cracking. MnDOT ultimately hopes to use this monitoring system in tandem with visual inspection to detect problems in bridge structure and come up with better bridge designs.

Researchers are presently working on a follow-up project to determine the effects of temperature on the bridge’s vertical displacements, with the results intended for use in monitoring the bridge’s foundations, connections, and stiffness.

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