# A question about this rippling concrete bridge video **URL:** \ **Category:** Factual Questions\ **Created:** [December 11, 2011, 3:14am UTC](https://boards.straightdope.com/t/a-question-about-this-rippling-concrete-bridge-video/605794 "2011-12-11T03:14:15Z")\ **Posts on this page:** 17\ **Page:** 1
**Author:** ![Leo\_Bloom](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/leo_bloom/32/10377_2.png) [@Leo\_Bloom](https://boards.straightdope.com/u/Leo_Bloom)\ **Post date:** [December 11, 2011, 3:14am UTC](https://boards.straightdope.com/t/a-question-about-this-rippling-concrete-bridge-video/605794/1 "2011-12-11T03:14:15Z")
In this [fun video](http://www.youtube.com/watch?v=IwAtUH4bkl4&feature=youtube_gdata_player), the length of the bridge shows waves traveling (I think in only one direction). What allows a solid material like concrete to deform in such a smooth manner and then for it to return to its original form? Or are some sort of strain relievers placed up and down, sort of like mini -hinges? \*By-the-by, the sound of the wind in the vid sounds extraordinarily like some of the compositions of Ligeti used in Kubrick’s 2001, when the monolith is touched and where that guy begins his trip to Jupiter and Beyond. But the tones are all _sung_ in those compositions! ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [December 11, 2011, 3:20am UTC](https://boards.straightdope.com/t/a-question-about-this-rippling-concrete-bridge-video/605794/2 "2011-12-11T03:20:20Z")
Everything is flexible, at some scale. And the force restoring the bridge to its original shape (and beyond, to distortions in the other direction) is gravity: The bridge’s normal position is that which puts its center of mass as low as possible, subject to the constraint from the cables. ---
**Author:** ![2gigch1](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/2gigch1/32/3313_2.png) [@2gigch1](https://boards.straightdope.com/u/2gigch1)\ **Post date:** [December 11, 2011, 3:29am UTC](https://boards.straightdope.com/t/a-question-about-this-rippling-concrete-bridge-video/605794/3 "2011-12-11T03:29:57Z")
As a professional videographer I would like to point out that long shots (zoomed in compressed video) tends to exaggerate movements to look far more dramatic than it actually is. Yes the bridge is moving, but it is deforming over a much longer distance than is readily evident. ---
**Author:** ![qazwart](https://avatars.discourse-cdn.com/v4/letter/q/5fc32e/32.png) [@qazwart](https://boards.straightdope.com/u/qazwart)\ **Post date:** [December 11, 2011, 3:38am UTC](https://boards.straightdope.com/t/a-question-about-this-rippling-concrete-bridge-video/605794/4 "2011-12-11T03:38:20Z")
For a while, I thought you were talking about[Galloping Gertie](http://www.youtube.com/watch?v=j-zczJXSxnw) ---
**Author:** ![Projammer](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/projammer/32/559_2.png) [@Projammer](https://boards.straightdope.com/u/Projammer)\ **Post date:** [December 11, 2011, 3:42am UTC](https://boards.straightdope.com/t/a-question-about-this-rippling-concrete-bridge-video/605794/5 "2011-12-11T03:42:32Z")
A not so fun video. [Tacoma bridge](http://www.youtube.com/watch?v=j-zczJXSxnw) Make sure to check out about 2:45 on. ETA: Curse you qazwart! ---
**Author:** ![Elendil\_s\_Heir](https://avatars.discourse-cdn.com/v4/letter/e/7cd45c/32.png) [@Elendil\_s\_Heir](https://boards.straightdope.com/u/Elendil_s_Heir)\ **Post date:** [December 11, 2011, 5:50am UTC](https://boards.straightdope.com/t/a-question-about-this-rippling-concrete-bridge-video/605794/6 "2011-12-11T05:50:41Z")
The Millennium Bridge in London had similar problems, now fixed, apparently: > **[Millennium Bridge, London](https://en.wikipedia.org/wiki/Millennium_Bridge_(London))** > > The Millennium Bridge, officially known as the London Millennium Footbridge, is a steel suspension bridge for pedestrians crossing the River Thames in London, England, linking Bankside with the City of London. It is owned and maintained by Bridge House Estates, a charitable trust overseen by the City of London Corporation. Construction began in 1998, and it initially opened on 10 June 2000. > Londoners nicknamed it the "Wobbly Bridge" after pedestrians experienced an alarming swaying motion on ... [![](https://img.youtube.com/vi/eAXVa__XWZ8/hqdefault.jpg "Millennium Bridge") ](https://www.youtube.com/watch?v=eAXVa__XWZ8) ---
**Author:** ![Snarky\_Kong](https://avatars.discourse-cdn.com/v4/letter/s/a183cd/32.png) [@Snarky\_Kong](https://boards.straightdope.com/u/Snarky_Kong)\ **Post date:** [December 11, 2011, 6:08am UTC](https://boards.straightdope.com/t/a-question-about-this-rippling-concrete-bridge-video/605794/7 "2011-12-11T06:08:35Z")
That’s not a concrete bridge, it’s a steel suspension bridge. If I saw a concrete bridge do that, I’d stay away. Well, I’d probably stay away in any case. But, like **Chronos** said, it’s just the natural elasticity of the material. Concrete also cracks a lot. You wouldn’t be able to see them from a distance, but they’re there, and allow sharper deflections. ---
**Author:** ![Leo\_Bloom](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/leo_bloom/32/10377_2.png) [@Leo\_Bloom](https://boards.straightdope.com/u/Leo_Bloom)\ **Post date:** [December 11, 2011, 7:35am UTC](https://boards.straightdope.com/t/a-question-about-this-rippling-concrete-bridge-video/605794/8 "2011-12-11T07:35:31Z")
Thanks for the answers and cites. I saw the Tacoma bridge video before, but forgot its name, and only thought about structure resonance modes. **2gigchi1** , your point is well taken. ---
**Author:** ![Leo\_Bloom](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/leo_bloom/32/10377_2.png) [@Leo\_Bloom](https://boards.straightdope.com/u/Leo_Bloom)\ **Post date:** [December 11, 2011, 7:42am UTC](https://boards.straightdope.com/t/a-question-about-this-rippling-concrete-bridge-video/605794/9 "2011-12-11T07:42:05Z")
Just re-watched the Tacoma film. My gosh. ---
**Author:** ![mnemosyne](https://avatars.discourse-cdn.com/v4/letter/m/c4cdca/32.png) [@mnemosyne](https://boards.straightdope.com/u/mnemosyne)\ **Post date:** [December 11, 2011, 7:49am UTC](https://boards.straightdope.com/t/a-question-about-this-rippling-concrete-bridge-video/605794/10 "2011-12-11T07:49:17Z")
I am not a civil engineer, but I know that bridges aren’t built as fixed, rigid structures; they are designed to bend, flex and move a certain amount based upon anticipated/modelled conditions. For a simple span, one end of the bridge may be fixed, but the other is on “rollers”, allowing it to move back and forth along its length a certain amount. A fully rigid/stiff bridge would break rather rapidly. I’m not sure how suspension bridges are built, but it looks to me like this bridge is bending at the joints between segments of concrete/steel/span - the concrete itself isn’t rippling. It’s more like the joints in a toy snake like [this one](http://www.toyandgift.co.uk/acatalog/jointed%20snake.jpg). The suspension design allows for more freedom of movement, I think. ---
**Author:** ![Leo\_Bloom](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/leo_bloom/32/10377_2.png) [@Leo\_Bloom](https://boards.straightdope.com/u/Leo_Bloom)\ **Post date:** [December 11, 2011, 11:14pm UTC](https://boards.straightdope.com/t/a-question-about-this-rippling-concrete-bridge-video/605794/11 "2011-12-11T23:14:31Z")
That’s what I was trying to get in my OP “mini-hinges…” ---
**Author:** ![jasg](https://avatars.discourse-cdn.com/v4/letter/j/f0a364/32.png) [@jasg](https://boards.straightdope.com/u/jasg)\ **Post date:** [December 12, 2011, 2:03am UTC](https://boards.straightdope.com/t/a-question-about-this-rippling-concrete-bridge-video/605794/12 "2011-12-12T02:03:23Z")
> [@Leo\_Bloom](#): > > Just re-watched the Tacoma film. My gosh. My dad still talks about the Strength of Materials course he was taking at that time. The next day, the classroom bulletin board had a newspaper picture of the bridge with a caption that said “Damn that decimal point!” (only funny if you have used a slide rule) ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [December 12, 2011, 2:27am UTC](https://boards.straightdope.com/t/a-question-about-this-rippling-concrete-bridge-video/605794/13 "2011-12-12T02:27:11Z")
> [@](#): > > The next day, the classroom bulletin board had a newspaper picture of the bridge with a caption that said “Damn that decimal point!” (only funny if you have used a slide rule) Believe me, I’ve seen students make decimal-point errors all too often, using electronic calculators. ---
**Author:** ![Yorikke](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/yorikke/32/4335_2.png) [@Yorikke](https://boards.straightdope.com/u/Yorikke)\ **Post date:** [December 12, 2011, 2:45am UTC](https://boards.straightdope.com/t/a-question-about-this-rippling-concrete-bridge-video/605794/14 "2011-12-12T02:45:21Z")
> [@Projammer](#): > > A not so fun video. [Tacoma bridge](http://www.youtube.com/watch?v=j-zczJXSxnw) > > Make sure to check out about 2:45 on. > > ETA: Curse you qazwart! That was an amazing video. Joe ---
**Author:** ![md2000](https://avatars.discourse-cdn.com/v4/letter/m/73ab20/32.png) [@md2000](https://boards.straightdope.com/u/md2000)\ **Post date:** [December 12, 2011, 7:24pm UTC](https://boards.straightdope.com/t/a-question-about-this-rippling-concrete-bridge-video/605794/15 "2011-12-12T19:24:16Z")
> [@mnemosyne](#): > > I am not a civil engineer, but I know that bridges aren’t built as fixed, rigid structures; they are designed to bend, flex and move a certain amount based upon anticipated/modelled conditions. For a simple span, one end of the bridge may be fixed, but the other is on “rollers”, allowing it to move back and forth along its length a certain amount. A fully rigid/stiff bridge would break rather rapidly. > > I’m not sure how suspension bridges are built, but it looks to me like this bridge is bending at the joints between segments of concrete/steel/span - the concrete itself isn’t rippling. It’s more like the joints in a toy snake like [this one](http://www.toyandgift.co.uk/acatalog/jointed%20snake.jpg). The suspension design allows for more freedom of movement, I think. Yes, if you watch the video closely, it seems there are solid segments (about 4 suspension wires apart?) and the flexing is happening at the joints between the segments. In a long shot it looks like a smooth ripple, but it is segments. So the bridge was built to take this. (I hope) ---
**Author:** ![Tangent](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tangent/32/3098_2.png) [@Tangent](https://boards.straightdope.com/u/Tangent)\ **Post date:** [December 13, 2011, 7:54am UTC](https://boards.straightdope.com/t/a-question-about-this-rippling-concrete-bridge-video/605794/16 "2011-12-13T07:54:32Z")
[Check out this oscillating Russian bridge](http://www.youtube.com/watch?v=k9bynDA9fSc). Very cool! ---
**Author:** ![Blakeyrat](https://avatars.discourse-cdn.com/v4/letter/b/ecd19e/32.png) [@Blakeyrat](https://boards.straightdope.com/u/Blakeyrat)\ **Post date:** [December 13, 2011, 8:15pm UTC](https://boards.straightdope.com/t/a-question-about-this-rippling-concrete-bridge-video/605794/17 "2011-12-13T20:15:42Z")
> [@jasg](#): > > My dad still talks about the Strength of Materials course he was taking at that time. The next day, the classroom bulletin board had a newspaper picture of the bridge with a caption that said “Damn that decimal point!” (only funny if you have used a slide rule) As a resident nearby, in our defense, the original Tacoma Narrows bridge was built before bridge wind-tunnel tests were standard, and before the conceptual framework for avoiding resonance in large construction projects was in-place. And I’ll note that the replacement bridge, with only minor changes to the design (it uses the same towers, in fact) is still standing tall and proud. So there.