Swing Bridges

Outside the fence.
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steve howe
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Swing Bridges

Postby steve howe » Mon Dec 06, 2021 7:13 pm

Simple question really, on curved estuarine bridges where an opening section was required, would the track on the swing section always have to be straight?

Barnstaple.jpg


Steve
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Philip Hall
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Re: Swing Bridges

Postby Philip Hall » Mon Dec 06, 2021 8:04 pm

I don't know the answer to your question, Steve, but by way of being even more unhelpful I always thought that Barnstaple was just a viaduct. As there was (is) a masonry road bridge alongside there wouldn't have been much point in an opening.

Philip

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steve howe
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Re: Swing Bridges

Postby steve howe » Mon Dec 06, 2021 8:11 pm

You are quite right Phil, Barnstaple rail bridge was just a fixed bridge. I'm looking at something similar for Watermouth where the line describes a 180* curve over an estuary. It just occurred to me that a swing section might be needed (non - working!) to allow craft to move upriver. However I'm not out to make life unnecessarily difficult for myself!

Steve

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Noel
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Re: Swing Bridges

Postby Noel » Mon Dec 06, 2021 8:18 pm

steve howe wrote:Simple question really, on curved estuarine bridges where an opening section was required, would the track on the swing section always have to be straight?


I don't know, but I can't think of one off-hand that isn't. I suspect the issue is a need for symmetrical loadings on the central pivot and the impossibility of achieving this with a curved girder.
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Noel

Stephan.wintner
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Re: Swing Bridges

Postby Stephan.wintner » Mon Dec 06, 2021 9:25 pm

The load of the bridge alone could still be properly balanced about a pivot with curved rails.

The dynamic load of a train crossing is never truly balanced, but would be worse on a curve. And bridge structural members are always straight, for strength and stiffness reasons. That may explain why they are typically straight rails.

Stephan

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Jim Summers
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Re: Swing Bridges

Postby Jim Summers » Tue Dec 07, 2021 6:23 pm

The viaduct over the Tay at Perth might be useful, and in some ways is not unlike Barnstaple.
In this photo the swing bridge can be seen at the far end. It was manually operated.

Jim

Perth Tay Viaduct - CRA coll. .jpg
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stephenfreeman
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Re: Swing Bridges

Postby stephenfreeman » Sun Dec 12, 2021 4:20 pm

Not that it helps but Barmouth was straight too.

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Will L
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Re: Swing Bridges

Postby Will L » Sun Dec 12, 2021 4:58 pm

Interesting question. While having doodled around the subject a bit, I think it must be possible to design such a think. You'd have to add extra strength to allow for the differential loading, and the span would need to be longer for the same clear passageway through, as the curved deck would inevitable intrude into it a bit. On the whole I'm inclined to think the additional difficulties involved would mean that sticking in a short strait section would tend to be simpler and cheaper.


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