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CAN YOU FEEL ME NOW?
OUR CELL PHONES MAY FIND another use much to society’s benefit: assessing the structural integrity of bridges. Good News Network, November 4, 2022, reports, “Using the Golden Gate Bridge in San Francisco as an example, researchers showed that smartphones can capture the same kind of information about bridge vibrations picked up by stationary sensors.”
Background. The primary reason for a cell phone accelerometer is almost a trivial one: It orients the display depending on how the cell phone is held.
On some devices, detection is keyed to special tracking such as a pedometer. Another application is fall-detection. Wikipedia notes, “Apple has included an accelerometer in every generation of iPhone, iPad, and iPod touch, as well as in every iPod nano since the 4th generation.”
“Vibration Analysis Using Mobile Devices (Smartphones or Tablets),” by A. Feldbusch et al., Procedia Engineering, Volume 199, 2017, offered specifics: “The characteristics of accelerometers installed in smartphones differ from professional acceleration sensors used in vibration analysis. High-precision sensors have a resolution up to 10-9 g and a measuring range usually below ± 1 g. For smartphone technology miniaturization plays an important role as well as robustness, low energy consumption and low price. This comes with limitations of accuracy. In recent smartphones so called MEMS-Accelerometers (Microelectromechanical systems) with a resolution from 0.1 to 15 mg and a measuring range of ± 4 g (and more) are installed.”
Structural Challenges. Good News reports, “There is a global need for infrastructure monitoring to improve the resilience and longevity of bridges, buildings, and other structures—it’s pretty much a guaranteed applause-grabber in political debates in America, because the need is so great.”
Its report continues, “The structural health of bridges is usually visually assessed by engineers on-site, which is often time consuming and infrequent, or measured using static sensors incorporated into the bridge, which are expensive. Measuring the vibrational frequencies of bridges has previously been used to identify bridge damage and deterioration, but the data to support this approach have been limited.”
MIT Research. “Crowdsourcing Bridge Dynamic Monitoring with Smartphone Vehicle Trips,” by Thomas J. Matarazo et al., Communications Engineering, November 3, 2022, describes this novel expansion of data collection. From Good News: “A team at MIT developed an Android-based app that collects data while travelling across a bridge which they compared with traditional bridge-based sensors.”
“As data from multiple trips over a bridge are recorded,” said Dr. Paulo Santa, one of the researchers, “noise generated by engine, suspension and traffic vibrations, [and] asphalt, tend to cancel out, while the underlying dominant frequencies emerge.”
Methodology. “In the case of the Golden Gate Bridge,” Good News reports, “the researchers drove over it 102 times with their devices running and they used 72 trips by Uber drivers with activated phones as well. They then compared the resulting data to what had been collected by 240 sensors that had been placed on the Golden Gate Bridge for three months.”
Good News writes, “Results showed that data from the phones converged with that from the bridge sensors. For 10 particular types of low-frequency vibrations the engineers measured, there was a close match, and in five cases there was no discrepancy between the methods at all.”
Suspension vs. Concrete Spans. “However,” Good News notes, “because most bridges are not suspension bridges the researchers decided to test their method on smaller and more common concrete span bridges. To do so, they studied a bridge in Ciampino, Italy, comparing 280 vehicle trips over the bridge to six sensors that had been placed on the bridge for seven months.”
“Here,” it was noted, “there was a 2.8% divergence between what was recorded with the stationary sensors and the smartphone data, while shorter trip numbers created more divergence, suggesting more trips would create less.”
Future Research. Good News writes, “Architecture Professor at MIT Carlo Ratti said there are ways to refine and expand the research, for example by accounting for the effects of the smartphone mount in the vehicle and the influence of the vehicle type on the data.”
“It might not reach the accuracy that one can get using fixed sensors installed on a bridge,” says Professor Ratti, “but it could become a very interesting early-warning system. Small anomalies could then suggest when to carry out further analyses.”
Similar crowdsourced early-warning is already evolving in response to even more dramatic vibrations—earthquakes. ds
© Dennis Simanaitis, SimanaitisSays.com, 2022
Simanaitis Says 
Interesting idea of using cell phones as a proxy for dedicated vibration sensors. Even if slightly off on accuracy the apps could flag possible concerns that could then be explored in more detail/accuracy with dedicated sensors.
Structural dynamics was an area of interest in my career, and under the definition of an expert as “the person who is least confused” I was often tapped in the office for expertise in areas such as equipment foundation vibrations, structural vibrations, and blast resistance.
While we never had enough work to enable me to become a true expert in these areas, I did develop some skills that were useful over the years to tackle simple problems, or at least to discuss problems intelligently with more dedicated experts.
Near the end of my career one of our clients had a problem with a large blower (providing combustion air to a large furnace). I did an assessment of the expected vibrations using tools that we used for pump/compressor foundation design and determined an expected amplitude of vibration. I mentioned these numbers in a weekly client meeting, and the client’s very cooperative rotating equipment SME said that she could instrument the machine and get me actual readings. Two days later I had readings that confirmed my estimates, giving me the information that I needed to develop a remedial foundation design that would have improved the performance of the equipment, without having to remove the machine.
Another time we were adding some fixed piping to a large heater/furnace (I dealt with more than just furnaces in my career, despite both my examples) to facilitate maintenance cleaning of the heater tubing. The original drawings were hand drafted, but we were creating CAD drawings, using both the original drawings and laser scan survey data. At one point my draftsman called me over and said “this doesn’t look good”, whereupon he revealed the significant bulge in the furnace that the survey data showed. After spending quite a while trying to determine what happened, a casual conversation with a plant operator revealed that about a dozen years before when they were trying to restart the burners after a maintenance shutdown it had taken a while to restart, but a lot of gas had already been injected, so that when they finally got ignition they actually had an explosion inside the heater.
Using my blast resistant design experience I was able to determine that the significant permanent lateral deformation of the exterior columns (in the order of 12”) had been preceded by a much larger dynamic deflection resulting in a permanent reduction in structural capacity. The reason that the structure had probably survived was that the plate work of the heater acted as part of the structural resisting system, although it was not considered in the original design calculations (just was well that the furnace wasn’t designed by Colin Chapman as he probably would have utilized the plate to optimize the design).
I was concerned that the heavy manifolds and valving that we were adding up top might overload the compromised furnace, and convinced the client that we would add the vertical drop pipes on the side ‘now’, but that all the heavy stuff up top should only be installed at maintenance time after the heater had been drained of all fluids to compensate for their weight.
Fun stuff.
A fascinating career, Sabre.
Thanks, although much of it was pretty mundane. I actually retired a year sooner than I had originally planned because I got tired of the politics.
This article sounds something like the earthquake early warning stuff with Shakealert developed. They found that they could use the accelerometers in phones as rudimentary seismographs, and were able to process the data to automatically remove the effect of picking up the phone and moving it around. Google now uses it to flag earthquakes in places where there aren’t many real seismographs, for warning others that shaking is coming. Cool stuff! Thanks!
Reminds me of the time I was down in Martinez, CA, doing an inspection on a fluid Coker at the Tesoro refinery. Fluid Cokers are tall process vessels that vibrate a lot. I remarked to my client project manager that if we had an earthquake while we were up on the platform about 2/3 of the way up the 100 ft. tall vessel that we’d probably never know it because the operational vibration amplitudes are so large and random, that seismic amplitudes would probably be indistinguishable.
So the question is: did anybody feel the 2014 Napa M6 quake in Martinez at the refinery? I understand it did some minor damage in Crockett, but most of the damage was in Napa itself. And an early version of the shake alert software functioned as designed, with firehouse doors opening automatically a second or 2 before the S waves arrived. https://en.wikipedia.org/wiki/2014_South_Napa_earthquake
Good question, but I was down there in the early 2000s (can’t remember exactly which year now, and my only direct contact was that project manager who planned to retire after the end of the project. We had exchanged personal contact information, planning to keep in touch. Sadly we received notice from our client that he had passed away from a sudden heart attack during his last week there. It hit a lot of us in the office really hard because we had really enjoyed working with this guy (which is pretty rare in our business).