Kato curved bridge

[Kabutoni]

 

Old Cobden railway bridge, New Zealand. Has since been replaced with a concrete one.

Edited December 12, 2016 by cteno4
Coprighted image removed

[velotrain]

Yes - found it via an image search, as I suspect you did.  The image is from 1969.  It's lost the S-curve, and the town is called Greymouth. 

I'm not actually seeing rails on it, so wonder if the line is still active?

There was clearly once a railway along the river, but it looks like it's gone now.

 

 

 

 

 

[Eurostar25]

Certainly is in use however the line was replaced by a curved concrete bridge that is shown in the Google maps photos, the branch line now connects with the mainline and runs across the hills to Christchurch rather than heading into greymouth's yard. The photo with the Dc loco and coal train on it is probably from just prior to the bridge being replaced in 2004. It had a 10km/hr limit across it and was certainly never designed for the 56T coal cars or the 80T loco...

[kvp]

You keep mentioning the "width in the center". Do you actually know of any "curved" (superstructure and/or rails) railway bridge where the width is not consistent over the entire length of at least that section - if not the whole bridge? Sound engineering would seem to dictate that the structural width should remain a constant, and this is true on masonry viaducts, as well as steel bridges of all designs. It even appears to be true on this quite unusual S-curve wooden bridge - which is undoubtedly located in a country with minimal standards for governmental inspection of infrastructure.

Actually the idea is that a bridge composed of several sections, including ones that have curved rails on them may have different loading gauges as the loading gauge is usually widened in curves. This means the bridge builders may choose narrower superstructures for bridges that have straight rails, while using the widened loading gauge for the ones having curves. Since in this case the straight sections were built much earlier than the new curved sections, having very similar superstructure width is interesting. This might be a result of model railway engineering, where straight viaduct sections usually have the same width as curved ones, so they fill the maximal allowed loading gauge based on the track to track distances. This is not required as the trains would fit in a narrower space, but gets away with having no transition pieces between straight and cuved sections and allows most curves to start right next to the bridge. In real life the differences are not as huge as for a model, since real life curves are relatively large and the loading gauge widening is very little. The whole idea is more visible for trams and other elevated railways run on viaducts with relatively sharp curves. In this case, the superstructure of the straight bridge would be narrower if the extended walkway was not added, while the curved bridge doesn't have (and honestly doesn't really need) an extended walkway. Still the two widths are essentially the same, but result from two different design points. On the other hand, the main beams formed from the two plates are differnt, but for reasons i wrote above. In real life, these load bearing components would be the same and the superstructure would be slightly different in width. I think Kato choose this curve radius as this was the smallest that could work with the older straight sections without transition pieces while allowing most longer rolling stock to pass without hitting the railings on the end of the straight sections. For smaller curves, new straight sections would be needed, that lack the narrower end railings.