How Sensors Keep Bridges From Collapsing (and other structures too)

Infrastructure Instrumentation to save lives and make cool graphs!

It turns out that plenty of types of infrastructure, especially those that have serious implications for public safety, are equipped with instruments to track their performance over time and even save lives by providing an early warning if something is going wrong. Engineers keep an eye on strain, vibrations, temperature, pressure, tilt, flow rate, and more to make sure that structures behave like they were designed and to keep people safe from disaster.

Practical Engineering is a YouTube channel about infrastructure and the human-made world around us. It is hosted, written, and produced by Grady Hillhouse. We have new videos posted regularly, so please subscribe for updates. If you enjoyed the video, hit that ‘like’ button, give us a comment, or watch another of our videos!

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DISCLAIMER
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This is not engineering advice. Everything here is for informational and entertainment purposes only. Contact an engineer licensed to practice in your area if you need professional advice or services. All non-licensed clips used for fair use commentary, criticism, and educational purposes.

SPECIAL THANKS
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This video is sponsored by Henson.
Stock video and imagery provided by Getty Images, Shutterstock, Pond5, and Videoblocks.
Tonic and Energy by Elexive is licensed under a Creative Commons Attribution License
Hosted/Written/Produced by Grady Hillhouse
Edited by Wesley Crump
Script Edited by Ralph Crewe
Production Assistance from Josh Lorenz
Graphics by Nebula Studios

[EBuff]

In Calvin & Hobbes, Calvin asked his dad about bridge weight limit signs. His dad's explanation was that they build the bridge and then drive heavier and heavier trucks over it until it collapses. Then they rebuild it and put up the appropriate sign!

[matthewcocke]

I work at Geokon! I have been a fan of this channel since before I began my engineering degree, and I never would have guessed I would see the devices I work on every day to pop up on this channel! Thanks so much for trusting our equipment!

[evan-edstrom]

I live in Seattle. A few years ago, there was concern about the integrity of the West Seattle Bridge. They shut it down and did an extensive overhaul. Prior to re-opening, they tested it. The engineers put numerous sensors on the bridge, and drove 12 loaded 80, 000lb trucks onto the bridge and measured the bridge's response using the sensors.

[Campfire_Bandit]

As a US state bridge engineer, I love these videos! I share these around the office all the time, it's incredible how useful these simple breakdowns of common engineering principles are.

[chrisoconnor]

I am a mining engineer specializing in rock mechanics. Instrumentation is important but much more challenging in a deep underground mine as the material is dis-continuous, heterogeneous, anisotropic, non-linear, and subject to plastic deformation. Point sensors can provide mis-leading information as they become highly dependant on local conditions, most of which cannot be accurately defined. We also use Geokon for most of our instrumentation.
Our best tool is often the micro seismic system from dozens or even hundreds of sensors collectively working together to collect and compile rock noise data due to fracturing. Despite being a “remote” sensing approach, there is a lot of detailed local understanding of performance and conditions that can be extracted.

[paulhaynes]

Much as I like civil engineering, I never thought anyone could make strain gauges interesting! Yet another excellent episode. Thanks.

[ChristianAkacro]

Wow Grady! I'm a longtime subscriber and viewer of your content. I also happen to be the Producer of Poly Bridge 1 & 2. So glad to see you 'break down' and give the game a try!

[DrDrumminKY]

i really enjoy your videos. My wife is a civil engineer that deals mainly with storm water mgmt and stream restoration. After watching your videos, i can actually have conversations with her about her work and understand (albeit at a rudimentary level) what shes saying. Thanks so much for these and please keep them coming! I've got a lot more learning to do.

[rayoflight]

In the sector of telecommunications, we use an instrument called TDR (time domain reflectometer) which sends an electric pulse in a wire and check the returns from that pulse, to measure at what distance from the test equipment the fault is located.
This test equipment is similar in principle to the sensor you showed in the video, but the frequency is higher and the domain is different (time instead of frequency) but the methodologies are similar.
This is a very nice video - I begun my formal studies - a lifetime ago - specialising in "Transducers"; the devices have now been revolutionised because of the MEM technology, but the principles and the designs stayed the same.
Thank you for the great video,
Greetings,
Anthony

[Halfwayparticular]

I used to work at Geokon as an electrical engineer. It was a wonderful place to work with exceptional leadership. Seeing the scope trace of the excitation and subsequent ringing brings back a lot of memories. Really glad you featured their stuff.

[Dr_le_Quack]

Its something that I am very grateful for in the field of electronics is that we can very easily monitor the performance of out systems (well, most of the time). I think its something that us electronic engineers often take for granted in comparison to the other fields of engineering.

[pitcheung]

I worked in a watermains flowmeter project: we install lots of flowmeter and pressure logger at the watermains, to monitoring the initial pressure and Flowrate of each watermains, and send those data to server for inspection everyday.

While some watermain have non-stop flow data even at mid-night(which normally nobody use water) we realize that there is some leakage after that flowmeter, thus we could carryout a faster inspection/repair/exchange activity of those leakage pipe.(We don't need to checkthe water supply zone entirely)

Sensors is really good

[matthewwalburn]

I use a lot of these sensors for my work! I work for a fracture mechanics research lab where we often get representative pieces of piplines and other infrastructure that were made decades ago (without good data kept on it and often old impure steel) and test how it cracks to see if the rest of the line is still safe to run for awhile. Often times you can detect cracks with a pipeline inspection tool (called a PIG), but quite often smaller cracks things are missed and even then they often don’t know what material the pipe is after a few decades. So research is always being done to asses the likelihood of a leak.
There’s also tons of effort being put into studying how converting our gas lines to hydrogen would work (hydrogen “embrittles” steel) in an effort to switch our infrastructure to cleaner energy.

Crack growth is super facinating and suprisingly very complex to predict. But it also can be measured directly by measuring the resistance change across a crack as it grows (from the steel left getting thinner and thinner) it’s quite hard to interpret this data, but one of the more useful “sensors” we use because you can watch a crack grow with a very high accuracy without having to break open the material

Sometimes it’s so geometry dependent that a small scale sample changes the results too much. So sometimes we do full scale tests (like purposely putting a flaw in a pipe and then cycling pressure) because small scale samples just don’t tell the whole story. Often this is compared to finite element analysis models to try and improve those tools. And the data from these large scale tests can be quite complex to analyze with so many channels and sensors. We did a pretty complicated test last year with easily over 100 channels (strain gauges, string pots track 3D position, linear displacement transducers, resistance measurements, thermocouples, etc.) and the test took a few months to set up.

If you haven’t done one already, an episode on failure analysis would probably be a fun topic, although I’ll admit a very broad and complex one

[joeyager]

Not exactly the same thing, but this happened when I was working for a large elevator company as a young draftsman about 50 years ago. The R&D Group was tasked with redesigning the escalator frame to try to reduce the number of welds to make the fabrication less expensive as the current fabrication required "weld all around". The goal was to produce a frame with a minimum of welds as determined by the engineer's calculations. The new frame would be set up a series of strain gauges and loaded up to test the structural integrity and add welds as required.

This was all preCAD so I spent about a three weeks learning and adding weld symbols to the weldment detail drawings and having the engineers check it and make some changes as required.

It turns out that the contracted fabricator's welders weren't certified so not understanding the weld symbols, they just welded all around, just to be safe! Needless to say it pretty much doomed the project and a series of lawsuits followed. I wound up leaving the company about a month later for what turned out to be a very interesting 36.5 years at a local machine design and fabrication company.

[J-Bibble]

Great video. I was the engineer of record for a number of state owned dams. We routinely used piezometers, inclinometers, crack meters and other instruments to measure performance of earth dams and their concrete components. I used to enjoy observing trends in the data that correspond to things like changes in reservoir elevation. You start to learn how the infrastructure performs under different conditions, allowing you to spot potential issues.

[ThatsPety]

I don't know man, something about this video is just so magical. Your demeanor, the experiments, graphs, games, information, everything about it just comes together so beautifully. It's like the perfect culmination of everything you've been doing and improving on with your channel.

Practical engineering at its finest, and I mean that in more ways than one

[CatsT.M]

1:35
About the bridge shown here: that is the Tacoma Narrows Bridge, luckily when it collapsed no one died but inside the car shown in this video there was a dog that several people attempted to save but were unable to. The driver, Leonard Coatsworth, was bringing the dog back to his daughter, after the collapse he said "I believe that right at this minute what appalls me most is that within a few hours I must tell my daughter that her dog is dead, when I might have saved him." (even though I have read and heard this quote several times it still feels terrible)

[phoenixbloomfield]

I worked for a summer installing monitoring equipment for a wetland restoration company. We put finely perforated PVC pipes in the ground 1-2M deep. Next we put two small pressure sensors into the pipe: one was dangled at the very bottom, and the other was above the ground on the top to gather atmospheric pressure data. They took a reading once an hour for a year and then the data was downloaded. By knowing the density of water and the atmospheric pressure above that water we could generate a very nice plot of how the water table was fluctuating at that well. By installing 6 wells or so in strategic points at each site we could get a pretty good map of where the water was going underground through that wetland area, how much water was being absorbed into the ground, and (when correlated with weather data) how upstream conditions affect the wetland water table and how long the wetland held water (slowing it down from all rushing downstream at once) after a rain storm.

[rayoflight]

The engineering sector lives and thrives on the use of sensors. There are some incredible type of sensors (e.g., a silicon diode used as temperature sensor - instead of an NTC or a termocouple, or an hot wire used as airflow meter - instead of a turbine connected to a micro-alternator).
A comprehensive video of most types of sensors used in the world around us - from an automobile to an electric power plant to traffic lights), I believe, would be greatly popular here on YouTube.
Best Wishes,
Anthony

[nax]

I work for HensonRazor, and i must say, its been a delight having one of our products featured on this channel, we used to have a joke in the shop where we used to go round saying which youtube channel we wished we started, most said things like H3 or Mr beast, but there was one guy who said leisics or practical engineering, so this definately came as a surprise when marketing managed to make this sponsorship happen. much love grady.