A question about the Iowa floods.

[hedgehog]

There was a report of a railroad bridge that was swept away. In an attempt to save the bridge, the railroad had parked 40 rail cars full of stones across it. My question is, how was loading (overloading?) the bridge supposed to protect it?

[HereSince1628]

1. It helps prevent vibration which can shake the bridge apart.

The water pounds on the structures, flotsom like tree trunks crashes into the structures all these things vibrate and shake the bridge.

[HereSince1628]

2. Here in Wisconsin they parked sand filled trucks on the interstate

while it was closed for the same reason

[hedgehog]

3. Okay, that sounds halfway reasonable. I guess it's akin to the

old rule about having marching units break step on a bridge. I would like to see an analysis of this theory. In this case, I suspect it may be one of those concepts that's a myth. I would think the side loading from all the water running over the bridge would be a magnitude greater than any vibrations from impact.







(Off-topic, but my husband was wondering if the high school band had been instructed to break step when marching over the bridge in the Memeorial Day Parade. I asked him, "what are you worried about? Have you ever seeen these kids marching in step?" He agreed, "Point taken.")

[HereSince1628]

4. I think its a matter of more mass meaning more inertia to movement getting started

Saving bridges is something civil engineers have been working at for a while. I think this one may be more than myth behind it. But I understand how recent years have left everyone skeptical about authority.

[hedgehog]

I'm thinking that if the bridge is already fully loaded, how well is it

going to withstand the additional stress of high water?


Besides which, how do bridges fail in these situations? I can think of several cases in which a creek rose past the bridge supports and washed them out.

[HereSince1628]

12. I am not a civil engineer. But loading refers to the weight on the bridge

The super-structure is made to deal with anticipated wind and probable forces of water from regular floods in its life. The water in Iowa (and elsewhere) is smacking the sides of bridge superstuctures with forces of unprecedented floods.

The bridges here in Wisconsin where I watched this done have supports only at the ends, and the ends and approaches weren't in danger of been washed out.

Remember the vector force of the train cars' weight was down. The vector force of the water slamming the bridge is sideways.

[hedgehog]

5. I'm thinking that if the bridge is already fully loaded, how well is it

going to withstand the additional stress of high water?


Besides which, how do bridges fail in these situations? I can think of several cases in which a creek rose past the bridge supports and washed them out.

[countryjake]

11. The method has been used to save bridges for probably a hundred years...

by railroad companies. If the flood is too bad, weighing a bridge down becomes fruitless, which was the case in Cedar Rapids.

Hell, back in the old days, they used the much heavier locomotives, but that practice was abandoned after too many engines were lost in riverbeds.

Our county lost a train trestle as cars loaded with rock were en route to be parked on it, to save it. That was almost twenty years ago, but the method is still used during extremely high flood danger.

[hedgehog]

14. My dad says the theory is that the bridge will be lifted by the water

and the extra weight is meant to counteract that. He agrees that it smacks of urban myth. It's true that water will lift a concrete tank out of the ground, but that's because most of the volume is less dense than water. A bridge deck is pretty dense.

[bullwinkle428]

6. There's also a dual railroad bridge in Cedar Rapids, and they

put rail cars on both sets of tracks. That one has held up to the onrushing water, and has even had several houseboats and little cabins get loose and float up against it without budging!

[hedgehog]

8. But are the rail cars helping or hurting? If the bridge holds, people will

say the rail cars helped. If it fails, they'll say the water was just too high.

[jwirr]

7. Flood waters loaded with junk washed down the river rush at a bridge and if strong enough

it pushes through. The train was trying to make the bridge stronger than the waters.

[hedgehog]

9. Now see, that seems counter-intuitive to me. The rail cars are turning the bridge into a dam!

Bridges are designed to be loaded vertically and to resist wind load and dampen vibration.

[CODemocrat]

10. River Front..

Property comes with a price....

"Get It"?

[Sal Minella]

13. How does this unpleasant post have anything to do with the physics of loading

cars onto a railroad bridge during a flood?