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rlcam

Here I go again/Photobucket

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Mark - this looks like a bridge down the coast at Batemans Bay N.S.W, not as big or as beautiful as the H 31 bridge but here is a brief description on how they work. pete

Truss Bridges

A beam, or girder, bridge is limited in span by the strength of its girders. This limitation is overcome by assembling a system of supporting members in triangles above the horizontal span girders to form trusses. Leonardo da Vinci sketched truss bridges, and the Italian architect Andrea Palladio probably built several. Two truss bridges were built in Switzerland about 1760. Truss-bridge construction, however, did not develop on a large scale until after 1840. In the United States the use of wooden trusses with iron tie-rods led to a combination cast- and wrought-iron construction about 1850 and, later, to steel trusses.

Opening Bridges

Where provision must be made for the passage of shipping under the bridge and where it is impracticable to build the bridge high enough for complete clearance, a movable span is constructed.

The oldest type is the 'bascule' bridge, on the principle of the drawbridge. The Clyde River bridge is of a less common type - the 'vertical lift'. A girder is lifted by counter-weighted cables suspended from the two towers.

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Mark, the bridge I operate is a lift span.The span between the two towers is what lifts up when a barge or big house boat needs through.We have to coordinate with the train traffic so we can keep both moving.It all runs electrically unless we have a power outage and then we have to use a diesel motor(located on the bridge) to raise it. The hwy.31 bridge used to be a lift bridge also until they replaced it several years ago,its just upriver from me.I sit in a small tower office on the south bank at the end of the bridge.I have to sit here most days watching people fish(sometimes I might bring a rod or two with me,if you know what I mean).

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Thanks Pete. I've always been facinated by the different bridges I've seen over the years. Both the designs, and the engineering behind them.

The idea of trusses, and how load is transfered, is something I use, but not every day, in wood framing.

I'm always amazed at the engineering of opening bridges on rivers, whether they are draw bridges, or pivot bridges. The point load on the pivots or hinges is enourmous, and the cable/pulley systems, along with the winches that do the lifting, are just facinating.

Someone posted pictures of a water wheel lock system that was built in Europe, to get boats down from one level to another. It is so cleverly balance that the muscle to move it is minimal. But the loads are enourmous. Clever people, for sure.

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The Falkirk wheel. Yes, I posted it, an awesome piece of modern engineering. But you have to respect the guys that built the old masters a hundred, even two hundred years ago. Their work looked good too.

This is where I fished every night after work when I was in Sweden. Alvsborg bridge, Goteborg.

IX8hCwaitpWuD8MNjer8Q-rSSGPv+bNf0215.jpg

Just look at that geometry!

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rlcam,

Does the section lift in one piece, or does it open in the middle?

Vodkaman,

I am really impressed by the old structures that people made hundreds of years ago. They had figured out the engineering without the math and formulas, from trial and error and experience.

I did some work on a windmill that some rich guy in Malibu had imported from Denmark. The whole thing was made out of wood. Amazing.

He had converted it into a guest house, complete with a tin bathtub that was actually in the shape of a person, with a small end for the head, and a larger section for the body. I guess, when you had to carry the water up four floors, it made sense to keep the shape as efficient as possible.

Kind of like lure building.

Spike-A-Pike,

What is a semidry?

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You would think that with todays mathematical and engineering knowledge, computer stress analysis and simulations, that designing bridges would be childs play.

Not so. Just a few years ago, a new bridge over the Thames, in London, had to be closed very shortly after the ceremonial opening. The bridge had a very slight sway. This caused the people to walk in step with the movement, also it is a natural instinct for humans to walk in step with each other. It just happened to be that the frequency of this step pace matched the resonent frequency of the bridge and the sway was dangerously magnified. How embarrassing for the designers!!!!

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