Want to know if the Golden Gate Bridge is holding up well? There might be an app for this.
A new study by MIT scientists shows that mobile phones placed in vehicles equipped with special software can collect useful structural integrity data when crossing bridges. In doing so, they could be a less expensive alternative to sensor arrays attached to the bridges themselves.
“The main finding is that information about the structural state of bridges can be extracted from accelerometer data collected by a smartphone,” says Carlo Ratti, director of the MIT Sensable City Laboratory and co-author of a new paper summarizing the results. of the studio. .
Part of the study was carried out on the Golden Gate Bridge itself. The study showed that mobile devices can collect the same information about bridge vibrations that stationary sensors collect. The researchers also calculated that, depending on the age of the highway bridge, mobile device monitoring can increase the useful life of the structure by 15 to 30 percent.
“These results show that massive, low-cost datasets collected by smartphones can play an important role in monitoring the health of existing transportation infrastructure,” the authors write in their new paper.
The journal Nature Communications Engineering published a study titled “A Crowdsourced Vital Signs Bridge Using Smartphones in Vehicles.”
The authors are Thomas J. Matarazzo, Associate Professor of Civil Engineering and Mechanical Engineering, US Military Academy at West Point; Daniel Condor, postdoctoral fellow at the Center for Advanced Sciences in Vienna; Sebastiano Milardo, Research Fellow at Senseable City Lab; Soheil S. Eshkevari, Senior Fellow at DiDi Labs and former member of the Senseable City Lab; Paolo Santi, Chief Scientist of the Senseable City Lab and Research Director of the Italian National Research Council; Shamim N. Pakzad, professor and chair of the Department of Civil and Environmental Engineering at Lehigh University; Marcus J. Buhler, Jerry McAfee Professor of Engineering, Professor of Civil and Environmental Engineering and Mechanical Engineering at MIT; and Ratty, who is also a Professor of Practice in the Department of Urban Studies and Planning at MIT.
Bridges naturally vibrate, and to study the underlying “modal frequencies” of these vibrations in many directions, engineers often place sensors, such as accelerometers, on the bridges themselves. Changes in modal frequencies over time can indicate changes in the structural integrity of the bridge.
To conduct the study, the researchers developed an Android mobile phone app to collect accelerometer data when the devices were placed on vehicles passing over the bridge. They were then able to see how well that data matched up with data recorded by sensors on the bridges themselves to see if the mobile phone method worked.
“In our work, we developed a methodology to extract modal vibration frequencies from noise data collected from smartphones,” says Santi. “As data from multiple trips across the bridge is recorded, the noise generated by the engine, suspension, and driving vibrations, [and] the asphalt tend to cancel out while the main dominant frequencies emerge.”
In the case of the Golden Gate Bridge, the researchers crossed the bridge 102 times with their devices turned on, and the team also used 72 trips by Uber drivers with their phones activated. The team then compared the data to data from a group of 240 sensors that were placed on the Golden Gate Bridge over three months.
As a result, the data from the phones matched the data from the bridge’s sensors; for 10 specific types of low-frequency vibrations, the engineers measured on the bridge and in five cases there was no discrepancy between the methods.
“We were able to show that many of these frequencies corresponded very closely to the main modal frequencies of the bridge,” says Santi.
However, only 1 percent of all bridges in the US are suspension bridges. About 41 percent are bridges with much smaller concrete spans. So the researchers also tested how well their method would work under these conditions.
To do this, they studied a bridge in Ciampino, Italy, comparing 280 car trips on the bridge with six sensors that were placed on the bridge over a seven-month period. In this case, the researchers were also encouraged by the results, although they found discrepancies of up to 2.3 Any relevant anchor
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