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110%er [5776]
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Question for a construction engineer (prefer Clemson grad)
Jan 12, 2014, 6:23 PM
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regarding the design of a football stadium. Each time I watch the video of the 1940 Tacoma Narrows Bridge collapse and hear the discussion of elementary forced resonance with the wind providing an external periodic frequency that matched the bridge's natural structural frequency, albeit the actual cause of failure was aeroelastic flutter, I always wonder if the jumping and dancing by football fans during certain songs during a football game (or perhaps some advanced form of the wave) could ever create a similar "beat frequency" stadium collapse. Any thoughts?
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110%er [5912]
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Re: Question for a construction engineer (prefer Clemson grad)
Jan 12, 2014, 6:28 PM
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White people have no rhythm. (I "M KIDDING!!!)
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Orange Blooded [2245]
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Re: Question for a construction engineer (prefer Clemson grad)
Jan 12, 2014, 6:29 PM
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When 80,000 sing along with national anthem and everyone one hits that high note, then Jericho will come tumbling down again. 
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Orange Blooded [4139]
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yes, and it is part of design criteria
Jan 12, 2014, 6:30 PM
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if you are interested, google a hotel balcony failure. Big lawsuit. FWIW, I am an '85 Building Science grad 
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All-In [49613]
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Or "Rockin' at the Tea Dance" ....
Jan 12, 2014, 6:36 PM
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...by the Rainmakers
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Orange Blooded [4139]
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btw the tacoma bridge vid is pretty crazy, huh?***
Jan 12, 2014, 6:32 PM
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110%er [5776]
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Yes***
Jan 12, 2014, 6:33 PM
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CU Guru [1346]
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Boy you wonder about odd things on a Sunday. But
Jan 12, 2014, 6:35 PM
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my guess is people can't stay in unison in large enough numbers to make a situation like the wind did for the bridge. Energy and frequency are key. A stadium full of people probably creates a very random frequency and not very high or focused energy. It's spread out all over the place.
Also, maybe large stadiums are built from a bunch of isolated pieces. Not that they aren't connected, just isolated at many points of connection exactly to prevent this kind of thing.
Engineer but not a seismic expert........
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110%er [5776]
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Sort of assumed the "isolated" construction aspect, but I
Jan 12, 2014, 6:43 PM
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thought the rhythmic beat of the music driving the jumping might negate the randomness.
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CU Guru [1346]
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Hmmm. A combo of inebriated and sober fans who
Jan 12, 2014, 7:17 PM
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are able to stay in sync for minutes or even tens of seconds.....dunno...seems pretty difficult. But I would expect the design of stadiums includes a lot of....okay getting more technical.....damping around any natural frequencies. That's part of what the isolation accomplishes too. Just guessing.
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CU Guru [1679]
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Re: Question for a construction engineer (prefer Clemson grad)
Jan 12, 2014, 6:37 PM
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1970 Building Construction grad here. I have often wondered the same thing. Let's just say that I wouldn't want to be in the upper deck when everybody is jumping up and down to the same beat. Or underneath it either.
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CU Guru [1760]
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First post on tigernet
Jan 12, 2014, 6:38 PM
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That reminds me that Clemson actually is an engineering school. That was refreshing for some reason.
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Rookie [16]
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Re: First post on tigernet
Jan 12, 2014, 6:49 PM
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Remember that they had to reinforce the Willy Brice because there was too much movement in the upper deck and actually banned the playing of a song that got everyone dancing. BSCE '76.
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CU Medallion [56713]
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Coots would say "if it ain't swayin we ain't playin"***
Jan 12, 2014, 7:06 PM
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Standout [344]
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Re: Coots would say "if it ain't swayin we ain't playin"***
Jan 13, 2014, 9:16 AM
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When I was a teenager, my uncle--a big coot fan--took my brother (now a coot grad) and me to the '86 Nebraska game at the roach. The lower portion of the upper deck in the SE corner of the stadium was very visibly waving at one point.
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Head Coach [757]
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The roach is famous for that.....someone really screwed up
Jan 14, 2014, 1:46 AM
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when calculating natural frequencies at that hole.
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CU Medallion [61465]
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Legend [18539]
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Fans jumping cannot create enough force to cause flutter.***
Jan 12, 2014, 7:05 PM
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In addition the stadium is not suspended by cables. The force of the fans jumping is projected downward thru concrete pillars which do not have flexibility necessary for the occurrence of flutter.
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CU Guru [1899]
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Re: force to cause flutter.***
Jan 12, 2014, 7:21 PM
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It depends on the ratio of wow to flutter, which is in direct correlation to the output of your woofer, to the harmonic distortion of your tweeter. Sometimes additional area is required to spread your load to prevent uneven settlement which puts undue stress on some of your structural members.
GO TIGERS!!!
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110%er [5776]
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Sorry, but I must report your abusive response to Crump***
Jan 12, 2014, 7:29 PM
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CU Guru [1734]
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Re: Question for a construction engineer (prefer Clemson grad)
Jan 12, 2014, 7:18 PM
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short answer: Yes, it is very much a concern at clemson. This is actually why they stopped playing zombie nation at the games. However the benefit of a stadium is the spans and structural elements are very different from a bridge, especially a cable stay. The main concern in stadium is the columns crushing in compression, as opposed to a cable suspension bridge which is more failure of the cable or flexural bending in the spans
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110%er [5776]
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Zombie Nation is the song that made me think about this
Jan 12, 2014, 7:26 PM
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Did they really quit playing it?
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Oculus Spirit [81628]
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CU Medallion [61465]
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Praise the Lord!***
Jan 14, 2014, 8:28 AM
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All-In [27366]
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Yes, which is why it's good they don't make 'suspension
Jan 12, 2014, 7:28 PM
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stands.'
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110%er [5776]
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Question regarded "beat frequency" not flutter or suspension***
Jan 14, 2014, 12:30 AM
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Orange Blooded [4816]
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From Clemson grad, Structural Engineer...
Jan 12, 2014, 11:23 PM
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...the short answer is yes, a crowd can create a harmonic resonance that could cause damage and possibly collapse of a structure that was very flimsy (low mass), but it is extremely unlikely for a concrete stadium like at Clemson.
This was studied by a Clemson grad student in 2009 after complaints were received by the University about excessive movement in the South Stands during the playing of Zombie nation. The conclusion is that because the beat of that tune came close to the natural period of the structure, the crowd did experience vibration (movement) in the structure that exceeded the comfort threshold for the typical human, but in no way came close to the amount of movement that could be accommodated by the structure or even begin to exhibit damage (cracking).
They may have stopped playing the song to calm the fears of the fans, but the structure is safe.
Incidentally, this only occurs in the south stands because they were built using thinner post-tensioned members, where the North stands were built with traditionally reinforced (mild steel) members.
So, relax and bounce away...
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All-In [40872]
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When did you graduate?
Jan 13, 2014, 4:49 AM
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I see 1988 on your profile. I was a structures guy in grad school in 1988. BSCE in 87 MSCE in 89.
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Rock Defender [50]
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Re: From Clemson grad, Structural Engineer...
Jan 13, 2014, 9:51 AM
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vfral1 is exactly right. Most of the other answers on here pertaining to force and energy are incorrect. At resonance frequency you don't need much force at all to cause a violent response.
-Professor who teaches Mechanical Vibrations
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Orange Blooded [2457]
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Re: Question for a construction engineer (prefer Clemson grad)
Jan 12, 2014, 11:28 PM
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If Camp Randall hasn't come down during Jump Around, then we are fine
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Legend [19910]
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All-In [25381]
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Many probably don't know that bamboo was used instead
Jan 13, 2014, 6:07 AM
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of rebar to reinforce the concrete in the original construction.
One other special ingredient was provided by no less than the "Legend," Frank Howard, himself: a spit of chaw.
And that's why older Tigers still alive, who were students when the stadium was built, wear flip-flops, carry along a pouch of Red Man and always greet each other with an "Ah so...Want a chaw?" when at games. A nice commemoration, I think.................
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