×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Failure of highway sign in Calgary

Failure of highway sign in Calgary

RE: Failure of highway sign in Calgary

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

RE: Failure of highway sign in Calgary

What you are seeing is the frame vibrating at resonnance caused by the wind frequency (Wind speed or strength not related).

This is called Areodynamic Resonnance !

RE: Failure of highway sign in Calgary

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.

RE: Failure of highway sign in Calgary

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

RE: Failure of highway sign in Calgary

(OP)
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 :)

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources