Why Bridges Move...

...and other musings on thermal movement of large civil works.

Most people have a certain intuition about thermal expansion, but you may not have considered how engineers design to accommodate it on large civil structures. The video gives a quick overview on this important consideration that engineers must account for when designing infrastructure like pipelines, bridges, and even sidewalks.

Marxist Arrow by Twin Musicom is licensed under a Creative Commons Attribution License

Tonic and Energy by Elexive is licensed under a Creative Commons Attribution License

This video is sponsored by Blue Apron.

[DarthObscurity]

"It's a little hard to show on camera."

_Show's an excellent, clear visual of the bridge buckling side to side._

[Slushee]

I first learn about thermal expansion when I was pretty young: I was heating a glass of milk in the microwave but forgot to put the milk. When the microwave finished I realised i had forgotten the milk and I though: "I guess I'll put the milk now"
And as soon as the milk touched the glass it exploded.

[Travelinmatt]

I watched a show about building a large bridge. The bridge was being built from both sides and had to meet in the middle. When the last pieces were being bolted together in the middle they had to wait for the bridge to reach a certain temperature so the bolt holes would line up. You could see on camera that the bolt holes were slowly lining up as the bridge warmed up.

[gilbertos]

I love your videos. I love how you explain them. Not boring graphs and things that make sense. I'm not saying that graphs are bad but sometimes they are overused.

[TTMR]

In aircraft maintenance we have to take temperature into account when doing things such as setting control cable tension. As the expansion rates of the aluminum structure and steel cables is sufficiently different.

[Jaymac]

This channel is honestly making me consider switching from mechanical engineering to civil. I’ve started to find it so much more interesting, particularly traffic and transportation engineering and especially because it’ll be a stable market

[alecapristrudel]

Ah temperature, mortal enemy of all engineers.

[learn]

I studies two of years of civil engineering and we learned some of this or that, but the way you explain things make them look very easy to remember and learn.

[VeNoM]

Fun fact, in countries without much temperature fluctuation (like Philippines, or any tropical countries), they don't bother with expansion joints.
You will see whole stretches of highways with no cracks, just driving.

[cvc-gamingglitchrespositor]

A bridge is just a street that's high.

[StefanGotteswinter]

Great explanation, same principles take place in precision machine building.

[EricFortuneJr.]

You can also hear thermal expansion when you turn on your oven and the opposite (thermal contraction) when you shut your car off the exhaust manifolds make a clicking noise as it cools down. You can hear it in the plumbing when you turn the hot water or duct work when the heat comes on. Sometimes older homes pop and creak as temperatures change outside. I’ve always found this fascinating.

[Patricksworkshop]

in California, we also have to have room for systemic movement as well as thermal and take into consideration slow tectonic plate movement too. good info Grady

[randallleonard]

Hey Grady, great video. I know you were only addressing movement due to thermal expansion and contraction, but we also have to allow for rotational movement due to live load deflection. Moveable bearings allow for longitudinal and rotational movement while fixed bearings only allow rotational movement. I stumbled across your channel this week and I am enjoying it. Even after 36 years in the profession there are many areas of practice that I have rarely been involved with and your videos are great refreshers.

[johnalexander]

Might as well re-title the video, "I needed an excuse to buy a spot welder." We all know the truth.

[Chiaros]

I wish you went into a bit more detail on the specific techniques used to compensate for thermal expansion. Some of the contraptions in the photos you showed looked really interesting.

[megaboed]

The road expension zones on Bridgers make a really satisfying *Thunk* when you drive over them too.

[shivambansal]

Anti-clickbait.
The answer was in the thumbnail itself.
I love you.

[krtwood]

"That's a great smile, honey, but could you do it a little more to the left so I can see those cool expansion slots behind you." - Things you don't want to say on vacation.

[GuyNamedSean]

Every day’s a good day when there’s a Practical Engineering video.