charliealphabravo
Structural
Well, not exactly "news" but video of an instructive sign failure I found while trolling the yous-tube. At the very end you can see the guy catches a panel dropping off the tube frame.
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Failure of highway sign in Calgary
- Thread starter charliealphabravo
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That video was featured on the CTV news tonight. I believe it is an example of vortex shedding, although I am a bit surprised that the rectangular sign did not act as a 'spoiler'.
I have seen similar effects in the Edmonton area, but the exact explanation for it is beyond my ability to explain.
BA
I have seen similar effects in the Edmonton area, but the exact explanation for it is beyond my ability to explain.
BA
Can't believe everyone kept driving!
I am sure it reminds most of us of the Tacoma Bridge failure, which Wiki explains it as:
The bridge's collapse had a lasting effect on science and engineering. In many physics textbooks, the event is presented as an example of elementary forced resonance with the wind providing an external periodic frequency that matched the natural structural frequency, though its actual cause of failure was aeroelastic flutter.[1] Its failure also boosted research in the field of bridge aerodynamics-aeroelastics, the study of which has influenced the designs of all the world's great long-span bridges built since 1940.
I am sure it reminds most of us of the Tacoma Bridge failure, which Wiki explains it as:
The bridge's collapse had a lasting effect on science and engineering. In many physics textbooks, the event is presented as an example of elementary forced resonance with the wind providing an external periodic frequency that matched the natural structural frequency, though its actual cause of failure was aeroelastic flutter.[1] Its failure also boosted research in the field of bridge aerodynamics-aeroelastics, the study of which has influenced the designs of all the world's great long-span bridges built since 1940.
MikeHalloran
Mechanical
A sign-sized horizontal panel might have damped the response at that frequency. In the mode shown, the signs just acted as additional 'mass per unit length', reducing the resonant frequency below that of the naked tube.
I think the difficulty of predicting such resonant responses, let alone building in defenses against them, is the primary reason why highway-spanning signs are (in the regions I frequent) more commonly supported by three-tube or four-tube trusses with a _lot_ of diagonal tube bracing.
Mike Halloran
Pembroke Pines, FL, USA
I think the difficulty of predicting such resonant responses, let alone building in defenses against them, is the primary reason why highway-spanning signs are (in the regions I frequent) more commonly supported by three-tube or four-tube trusses with a _lot_ of diagonal tube bracing.
Mike Halloran
Pembroke Pines, FL, USA
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charliealphabravo
Structural
i think it would act more like a stable airfoil if it were shaped differently. i'm guessing the wind was perpendicular to the face. as a flat surface the wind just spills off the sign face causing a vertical force and the frame exerts a restoring force. without any damping the oscillation amplifies.
maybe someone in aerospace will chime in
maybe someone in aerospace will chime in
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