Hornby R8008 Grand Suspension Bridge - Based on any particular prototype?

[Nearholmer]

Reading the definition, anything within which the deck is hung from vertical cables is a suspension bridge, irrespective of how those cables are themselves supported, and irrespective of the rigidity of the deck. Which takes us back to Gisclard’s ‘rigid suspension bridges’.

 

if the cables supporting the deck are angled, it seems to be a ‘stayed’ bridge.

[BernardTPM]

And the Tri-ang bridge has both:

 

Part of the reason may have been to make the moulding stronger, looking at it. The suspension verticals at the tower end would have otherwise had very long, unsupported elements.

[jim.snowdon]

3 hours ago, phil-b259 said:

But how many of those are true suspension bridges?

From what I can tell all ‘suspension bridges’ used by trains are actually hybrid structures where stiff deep deck structures and cable stayed elements are used to remove significant amounts of the flexibility which would otherwise be present.

True, there aren't many, but I can point to -

The 25th April Bridge, Lisbon

Wufengshan Yangtze River Bridge, China,

Egongyan Rail Transit Bridge, China

 

All three are true suspension bridges.

 

[TravisM]

1 hour ago, jim.snowdon said:

True, there aren't many, but I can point to -

The 25th April Bridge, Lisbon

Wufengshan Yangtze River Bridge, China,

Egongyan Rail Transit Bridge, China

 

All three are true suspension bridges.

 

 

Those in China have been built recently and have probably been designed to reduce the vertical and lateral forces that affect suspension bridges.  I notice that the 25th April bridge and the Wufengshan Yangtze River bridge have the railway on a lower deck and therefore the whole bridge has been significantly strengthed to accept heavy rail and basically "bury" it within the structure.  The Egongyan Rail Transit bridge is from what I can see, was built to carry light rail and therefore not subjected to the heavy pounding of heavy rail.

Edited December 18, 2021 by jools1959
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[jim.snowdon]

8 hours ago, Nearholmer said:

Reading the definition, anything within which the deck is hung from vertical cables is a suspension bridge, irrespective of how those cables are themselves supported, and irrespective of the rigidity of the deck. Which takes us back to Gisclard’s ‘rigid suspension bridges’.

 

if the cables supporting the deck are angled, it seems to be a ‘stayed’ bridge.

I beg to differ. The characteristic feature of a suspension bridge is that the total weight of the bridge deck is carried by a pair of cables suspended between two piers. Break either of those two cables and the bridge fails.

 

In a cable stayed bridge, the weight of the deck is carried directly by the piers, with each stay carrying only a part of the load. Break one stay and the bridge does not fail.

 

There are some secondary characteristics that separate the two types of bridge. An obvious one is the basic structural element. For a suspension bridge, there can only be two piers, otherwise it becomes dynamically unstable. For a cable stayed bridge, the structural element is a single pier, and any number of single pier elements can be joined together to make a long bridge - the Millau bridge is a classic example.

 

[Nearholmer]

40 minutes ago, jim.snowdon said:

I beg to differ. The characteristic feature of a suspension bridge is that the total weight of the bridge deck is carried by a pair of cables suspended between two piers.

Well, I think you need to debate with others, not me, because it would appear that in definitional terms, the sort of bridge that you describe, which I think is what we’d all call to mind when the term is mentioned, is only a subset of the class ‘suspension bridges’.

Those terrifying things that consist of ropes strung across a gorge, with no piers, and with or without wobbly planks between the ropes, are also ‘suspension bridges’ apparently.

 

And, it seems that even in the kind you mention they still fall within the class if they have chains, rather than cables, between the piers. 
 

I admit to finding it all a bit confusing, because different definitions seem to be given in different sources, but one thing is for sure: the deck does not have to be highly flexible in order for a thing to qualify as a suspension bridge. Maybe the key word is ‘suspension’, hanging.

 

But surely, those bridges that consist of two beams crossing the void, with the deck hung from the beams don’t qualify, do they?

 

And, I do get that a ‘stayed bridge’ is a different thing, the load path is different.

 

 

 

 

 

Edited December 18, 2021 by Nearholmer

[Pacific231G]

7 hours ago, BernardTPM said:

And the Tri-ang bridge has both:

 

Part of the reason may have been to make the moulding stronger, looking at it. The suspension verticals at the tower end would have otherwise had very long, unsupported elements.

Interesting. Comparing thus with photos of the Rochers Noirs viaduct it appears that it would be entirely possible, with a bit of bashing, to turn this into a shorter span Gisclard suspension bridge that would be eminently suitable for a railway.

[Darius43]

Niagara Falls Railway Suspension Bridge

Designed by John Roebling no less.

 

Then you drive over to Suspension Bridge and divide your misery between the chances of smashing down two-hundred feet into the river below, and the chances of having a railway-train overhead smashing down onto you. Either possibility is discomforting taken by itself, but, mixed together, they amount in the aggregate to positive unhappiness.
Samuel Clemens

 

Cheers

 

Darius

[BernardTPM]

16 hours ago, Darius43 said:

Niagara Falls Railway Suspension Bridge

Designed by John Roebling no less.

...and with a combination of stay and suspension cables, so perhaps the Tri-ang effort is plausible.