Then see what this DU poster had to say.

This guy blames Reagan, Bush, Pawlenty and yes the VOTERS of Minnesota and America for voting in the GOP.

Here are some money quotes if you can’t read the whole thing:

Tim Pawlenty, GOPpie bushbuttkissing weasel that he is, certainly bears a share of the responsibility for the dead and injured

and

But Pawlenty isn’t by any means the only culprit or even the proximate cause of this disaster.

and

They include the first round of Kool-Aid brewers: the Reagan Misadministration. They include the Bush Crime Family and all of their cabal of cronies. And they include the voters of America and of Minnesota,

Please visit post #8 again. We have approximately doubled infrastructure spending per year on average over the last 8 years. I don’t know why this is getting on my nerves so much but there aren’t any leaders or media outlets REPORTING the facts about infrastructure spending.

But that isn’t important right now. What we all need to get to the bottom of is Bush, Cheney, and Rove’s dirty little figerprints on the collapse.

Wasn’t it nicknamed *Galloping Gurdy*,

Yup. People likened the effect to being on a roller coaster…you’d be driving across it, and see cars in the other direction suddenly dip out of sight, and then reappear as the road rose up again.

In layman’s terms, what exactly caused the Tacoma Narrows bridge to collapse?

I’m putting this together from my undergrad physics work too, so if Sev can spot any inaccuracies, I’ll yield to his expertise…my field’s chemistry, not physics.

Two factors: lightweight materials in construction and a roadway design that didn’t let wind pass through.

Look at the first part of the video above, and pay attention to the road. There’s just one solid bed there – no trusses underneath it to break up the wind and let it pass through.

So let’s say you’re on the bridge, and facing in the direction of the roadway, and the wind is coming from your left – across the road, not in the same direction. Since there’s nothing in the lightweight roadway to break up the wind, it will lift the left side up – basically, you’re getting aerodynamic lift, the same thing that makes planes fly – and the bridge begins to twist. You see that clearly in the video.

But the bridge is still a solid mass, and eventually the strain and stiffness build up enough so it starts rotating back. But it can’t just simply stop when it gets back to level – it keeps going. This is where the left side dips down and the right side goes up.

And the strain builds up again, this time in the other direction, so once again the rotation changes direction and the left side goes up, but this time with more help from the wind, which increases the amount of twisting. This is what Sev’s referring to by harmonic resonance. Think of when you were on a swing as a kid. If every time you came back, you got another push, you got higher and higher. Same principle.

Eventually the strain from the twisting got to be too much for the span and it broke apart.

Before anyone thinks the design was faulty, this wasn’t known at the time. It’s why bridge designs now go through wind tunnel tests.

Class dismissed. This will not be on your final, but the moonbattery will

What happened on Tacoma Narrows is that the bridge was not designed properly for the wind loading. A good summary is from Wikipedia:

Shortly after construction finished at the end of June (opened to traffic on July 1, 1940), it was discovered that the bridge would sway and buckle dangerously in relatively mild windy conditions for the area. This resonance was longitudinal, meaning the bridge buckled along its length, with the roadbed alternately raised and depressed in certain locations — one half of the central span would rise while the other lowered. Drivers would see cars approaching from the other direction disappear into valleys which were dynamically appearing and disappearing. From this behavior the bridge gained the nickname “Galloping Gertie” from a local humorist. However, the mass of the bridge was considered sufficient to keep it structurally sound.

The failure of the bridge occurred when a never-before-seen twisting mode occurred, from winds at a mild 40MPH. This is called a torsional, rather than longitudinal, mode (see also torque) whereby when the left side of the roadway went down, the right side would rise, and vice-versa, with the centerline of the road remaining still. Specifically, it was the second torsional mode, in which the midpoint of the bridge remained motionless while the two halves of the bridge twisted in opposite directions. A physics professor proved this point by walking along the center line, unaffected by the flapping of the roadway rising and falling to each side. This vibration was due to aeroelastic flutter. Flutter occurs when a torsional disturbance in the structure increases the angle of attack of the bridge (that is, the angle between the wind and the bridge). The structure responds by twisting further. Eventually, the angle of attack increases to the point of stall, and the bridge begins to twist in the opposite direction. In the case of the Tacoma Narrows Bridge, this mode was negatively damped (or had positive feedback), meaning it increased in amplitude with each cycle because the wind pumped in more energy than the flexing of the structure dissipated. Eventually, the amplitude of the motion increased beyond the strength of a vital part, in this case the suspender cables. Once several cables failed, the weight of the deck transferred to the adjacent cables which broke in turn until almost all of the central deck fell into the water below the span.

The bridge’s spectacular self-destruction is often used as an object lesson in the necessity to consider both aerodynamics and resonance effects in civil and structural engineering. However the effect that caused the destruction of the bridge should not be confused with forced resonance (as from the periodic motion induced by a group of soldiers marching in step across a bridge).[9] In the case of the Tacoma Narrows Bridge, there was no periodic disturbance. The wind was steady at 42 mph (67 km/h). The frequency of the destructive mode, 0.2 Hz, was neither a natural mode of the isolated structure nor the frequency of blunt-body vortex shedding of the bridge at that wind speed. The event can only be understood while considering the coupled aerodynamic and structural system which requires rigorous mathematical analysis to reveal all the degrees of freedom of the particular structure and the set of design loads imposed.

I remember the wind being 42 mph, whatever the bridge started oscillating in it, and the swings kept getting amplified to greater and greater displacements, like a car with bad shocks going over a bumpy road. It was used as a demonstration of damped, driven harmonic oscillation in class. Pretty good example, it sure stuck in everyone’s mind. The thing was obviously not designed properly for the wind loading over the sound.

See comment 8 Norma. As always, appropriations isn’t the issue. It isn’t with education, veterans benefits, the environment, health, infrastructure, Medicare, or ANYTHING. All categories of spending have gone up EVERY year for over 6 decades.

Knowing facts is what turned me from liberalism to conservatism in 1991. Ignorance is expensive. And it costs everyone else around us as well. It’s negligence continued….

That film was required viewing when I was an undergrad studying physics when we were going over harmonic oscillation. A more perfect example of resonance is hard to find.