San Francisco’s Golden Gate Bridge or other bridges may have a smartphone app that can tell if they’re still standing, research suggests. Cell phones mounted in vehicles equipped with special software can collect useful structural integrity information as they travel over bridges, new research shows. This way, they can be a low-cost alternative to a bridge-mounted sensor package.
“The main finding is that information about the structural health of bridges can be derived from accelerometer data collected by smartphones,” said study co-author Carlo Ratti. The survey was conducted partially on the Golden Gate Bridge. A study involving researchers from the Massachusetts Institute of Technology (MIT) in the US has shown that mobile devices can capture the same type of bridge vibration data as stationary sensors.
According to the researchers’ estimates, depending on the age of the road bridge, mobile monitoring can increase the service life of the structure by 15 to 30 percent. “These results show that the massive and inexpensive data sets collected by smartphones can play a critical role in monitoring the health of existing transportation infrastructure,” the authors write in a new paper published in the journal Nature Communications Engineering.
Bridges naturally vibrate, and to study the important “modal frequencies” of those vibrations in multiple directions, engineers often place sensors, such as accelerometers, on the bridges themselves. Changes in modal frequency over time indicate changes in the structural integrity of the bridge.
To conduct the study, the researchers developed an Android-based mobile app to collect accelerometer data when the devices were placed on vehicles passing over the bridge. They could then see how well that data matched the data log through the sensors on the bridge to see if the mobile method was working.
“During our work, we developed a methodology to extract modal vibration frequencies from noisy data collected from smartphones,” said lead researcher Paolo Santi. “As the data from multiple trips over the bridge is recorded, the fundamental dominant frequencies emerge, while noise from the engine, suspension, traffic vibrations, (and) the asphalt tend to drop out.”
In the case of the Golden Gate Bridge, the researchers used the device to drive over the bridge 102 times, and the team took 72 rides with the activated phone by Uber drivers, the study said. The team then compared data from a group of 240 sensors placed on the Golden Gate Bridge over a three-month period.
The study combined data from cell phones with data from sensors on the bridge; Engineers on the bridge were in close agreement on 10 specific low-frequency vibration measurements, with no discrepancies between the methods in five cases. “We were able to show that most of these frequencies match the main frequency of the bridge,” Santi said.
However, only one percent of all bridges in the United States are suspension bridges. About 41 percent are much smaller concrete bridges. So the researchers looked at how well their method works in this situation. To do this, they compared the traffic of 280 vehicles on a bridge in the Italian city of Ciampino with six sensors placed on the bridge over a period of seven months.
The researchers were encouraged by the findings, although they found a 2.3 percent difference between the methods for specific modal frequencies across 280 trips, and a 5.5 percent difference on a smaller sample. This means that a larger volume of travel can provide more useful information. “Our initial results show that a small number of trips over a few weeks are sufficient to obtain useful information about bridge frequencies,” Santi said.
Taken as a whole, MIT professor Markus Bühler said, “Vibration signatures are a powerful tool for assessing the properties of large and complex systems, from the virulence of pathogens to the structural integrity of bridges. “Buhler said.
“This is a universal signal that is widespread in natural and built environments, and we are now beginning to explore it as a diagnostic and generative tool for engineering,” Buehler said. Ratti acknowledges that there are ways to refine and expand the research, including to account for the impact of smartphone mounts in vehicles and the impact of vehicle type on data.
“We still have work to do, but we believe our approach can easily be scaled up to the entire country,” Ratti said. “It may not reach the accuracy of using fixed sensors on bridges, but it could be a very interesting early warning system. Small anomalies can then suggest when to do further analysis,” Ratti said.
(with PTI input)
