Published in the paper ‘Dynamic Monitoring of Crowdsourcing Bridges with Smartphone Trips’, the results of this study could turn out to be a less expensive alternative to sensors built attached to the bridges themselves.
“The core finding is that information about the structural health of the bridges can be extracted from accelerometer data collected by smartphones,” said Carlo Ratti, director of the Sensor City Laboratory. said MIT variable and co-author of a new paper summarizing the study’s findings.
The study was carried out in part on the Golden Gate Bridge itself. It shows that mobile devices can capture the same kind of information about bridge vibrations that stationary sensors compile. The researchers also estimate that, depending on the age of a road bridge, mobile device monitoring can add 15 to 30 percent to a structure’s lifespan.
“These results suggest that the huge and inexpensive data sets collected by smartphones can play an important role in monitoring the health of existing transport infrastructure,” he said. the authors write in their new paper.
Image files are for illustrative purposes only
The study was published in the journal Nature Communications Engineering.
The authors are Thomas J. Matarazzo, assistant professor of civil and mechanical engineering at the United States Military Academy at West Point; Daniel Kondor, postdoctoral fellow at the Center for Complex Sciences in Vienna; Sebastiano Milardo, a researcher at Senseable City Lab; Soheil S. Eshkevari, senior research scientist at DiDi Labs and former member of Senseable City Lab; Paolo Santi, principal research scientist at Senseable City Lab and research director at the Italian National Research Council; Shamim N. Pakzad, professor and chair of the Department of Civil and Environmental Engineering at Lehigh University; Markus J. Buehler, Jerry McAfee Professor of Engineering and professor of civil and environmental engineering and mechanical engineering at MIT; and Ratti, who are also professors of practice in MIT’s Department of Urban Studies and Planning.
Bridges vibrate naturally, and to study the essential ‘modal frequencies’ of those vibrations in multiple directions, engineers often place sensors, such as accelerometers, on the trees themselves. bridge. Changes in modal frequency over time may indicate changes in the structural integrity of the bridge.
To conduct the study, the researchers developed an Android-based mobile phone application that collects accelerometer data when the device is placed in vehicles crossing the bridge. They can then see how those data match the data records of the sensors on the bridge themselves, to see if the cell phone method works.
“In our work, we designed a method to extract vibrational frequencies from noisy data collected from smartphones,” adds Santi, “When data from multiple trips over the bridge is recorded, the noise generated by the engine, suspension and traffic vibrations, [and] bitumen, tends to cancel out, while the underlying dominant frequencies appear.”
In the case of the Golden Gate Bridge, the researchers drove across the bridge 102 times while their devices were running, and the team also used 72 Uber drivers’ trips with the phone activated. The team then compared the data obtained with data from a group of 240 sensors that had been placed on the Golden Gate Bridge for three months.
As a result, the data from the phone converges with the data from the bridge’s sensors; for 10 specific types of low-frequency vibrations that the engineers measured on the bridge, there was a strong match and in 5 cases there was no difference between the methods.
“We were able to show that many of these frequencies correspond very precisely to the salient modal frequencies of the bridge,” says Santi.
However, only 1 percent of all bridges in the US are suspension bridges. About 41 percent are much smaller concrete span bridges. So the researchers also tested how well their method would work in that context.
To do so, they studied a bridge in Ciampino, Italy, comparing 280 vehicles across the bridge with six sensors that had been placed on the bridge for seven months. Here, the researchers were also encouraged by these findings, although they did find differences of up to 2.3% between methods for certain modal frequencies across all 280 trips. away and a difference of 5.5% for a smaller sample. That suggests larger trip volumes can yield more useful data.
“Our initial results suggest that only one [modest amount] of trips over a period of several weeks is sufficient to obtain useful information on bridge modal frequencies,” says Santi.
Looking at the method as a whole, Buehler comments: “Vibrational signatures are emerging as a powerful tool for assessing the properties of large and complex systems, from the viral character of pathogens to structural integrity of bridges as shown in this study.It is a universal signal found widely in natural and man-made environments that we are just beginning to explore as a diagnostic and generating tool. out in engineering.”
As Ratti admits, there are ways to refine and expand the study, including calculating the impact of having a smartphone in a vehicle, the effect of the vehicle type on the data, etc.
“We still have a lot of work to do, but we believe our approach can be scaled up easily — to the level of an entire country,” says Ratti. “It may not be as accurate as one can get using fixed sensors installed on the bridge, but it could turn out to be a very interesting early warning system. Then, minor anomalies may suggest when to conduct further analyses.”
First published date: December 5, 2022, 18:21 PM IST
