#1
Hi guys, im trying to do my physics coursework (year 13 advancing physics ocr). Its on the tacoma narrows bridge collapse in 1940, if you dont know about it theres some pretty cool videos on youtube. Anyway i was wondering if anyone here could explain the aerodynamic instability of a bridge and airfoil flutter in fairly simple terms as most of what i have found is dissertation level and way over my head. Thanks for any help.
#2
pretty simple. They build a bridge high up in the air in where winds whipped in regularly at 30-40 mph. They also decided to make the bridge light using girders only 8 feet deep as apposed to the 25ft deep originally planned, making the structure much less rigid. The engineers dismissed that the bridge would be affected by the wind. AND the open truss construction created air convections under the road which led to resonant oscillations underneath the roadway that magnified the pitching of the bridge. In laymans turns it just means the aerodynamics acted like a really ****ty airplane wing- the air was moving over the bridge faster than it was under. But i said ****ty, so it wasn't uniform, which caused the thing to pitch up and down in oscillations. And the higher parts of the bridge rose, it made it more susceptible to this affect allowing wind to create even more lift under the bridge. These oscillations matched the resonant frequency of the bridge which magnified with every up and down motion. Its kinda hard to explain this part, but all objects have a frequency at which if they vibrate, each frequency magnifies itself. Its like pumping your legs when on a swing. If you match it right, it makes you go higher.

Mechanical engineer- Marquette
Last edited by DaveGilmour1189 at Mar 6, 2008,
#3
You're not gonna get a better layman's explanation than the guy above me....
I'm doing this coursework right now, and i'm doing the physics behind guitar electronics, tis gonna be a really easy one to do
Drive me home Jeeves
Last edited by GarlicBread at Mar 6, 2008,
#4
I was a former civil engineer. We did a class where we dissected some engineering disaster and i actually wrote a paper on this.