Low Girder Bridges

[port perran]

I have a low girder bridge across the Perran River (where it flows into the sea) which carries two tracks into Port Perran station.

Currently the track is ballasted across the bridge but I'm about to redevelop the station area. Would the track (in real life)normally be ballasted or would it just sit on sleepers across the base of the bridge ?
I think I've seen pictures of the latter option in goods yard situations (eg Hayle wharf) but I'm unsure of the situation in busier station locations.
Any ideas ?

[Newportnobby]

I can't be sure but I think I've seen examples of both ballasted and unballasted
However, the unballasted mostly had severe speed restrictions as, for example, in a goods yard

[lil chris]

There is a bridge on the railway going into Bury Lancs, still in use today, now by the tram. This bridge is known localy as the monkey bridge and that is ballsted across the top.It is a much large span than your bridge but there was also a smal girder bridege similar to yours on the line out of Bury Bolton st stn and that was ballasted too.

[EtchedPixels]

Depends on the bridge deck. It may be waterproofed and ballasted but it could equally be an open steel girder with a continuous line of tightly space sleepers. The latter style seems much more common outside the UK. They are usually the same arrangement as normal sleepers but closely packed and thicker.

Some bridges also have baulk sleepers laid along the bearing girders below the rails.

If you'd like some real ones, or a photo of that arrangement see
http://www.corbat-holding.ch/CMS/default.asp?ID=1858&Language=EN

Some bridges will also have additional guard rails between the main tracks, these are used to help prevent derailments pitching trains over the edge, particularly on bridges where there is little or no sidewall.

Great set of photos showing a mix of styles on the Royal Albert bridge

http://rmweb.co.uk/forum/viewtopic.php?f=7&t=34149

[Zunnan]

It depends entirely upon the construction of the bridge, but unballasted bridges don't necessarily come in for speed restrictions, certainly no more than other types. There are still a good number of timber decked girder bridges (unballasted) around to see on the network, but they're steadily being replaced nowdays. They're also far from simply being sleepers laid on the bridge cross girders and would actually be quite the challenge to model properly in N as you'd have to build your own track over the deck itself. You'd be aiming to make the bridge deck look like the Peco turntable deck, except that rather than inlaid rails you want the rails standing proud on longitudinal timbers with transoms and bolts making the track look more like a ladder laid on to the deck. Its the sort of thing that I like to tinker with, and have built quite a few in 00 but have yet to even attempt in N...maybe on my next layout, purely because I haven't done an N gauge timber decked girder yet

The way you've modelled the bridge with a stone infill would suggest that it has at some point been reinforced for some reason, so it would probably have a floorplate covering the reinforced bit and then be ballasted over the waterproofing. If you're remodelling the station, and remove the stone infill, it would still be quite a job to rebuild it as a timber decked girder, and I'm talking cutting and removing track kind of work. Personally, I'd either leave it as it is, or (and this is just me, as I'm a bit odd for building detail that isn't normally seen  ) open out the underside a little and build some deeper girders (Kestrel water tank sides are fantastic), then stick in a couple of strips of styrene to represent cross girders supporting a floorpate, but leave the track ballasted so there is no remodelling of trackwork needed.

A great source for all the finer detail for bridge building is 'Bridges for Modellers' by L. V. Wood (ISBN 0-86093-226-5), I always have it to hand when I'm building a bridge type that I haven't tackled before.

[lil chris]

Thanks for the information alan and zunnan, very imformative. I will be trying to model the bridge I mentioned ie the monkey bridge, the problem I am having is sourcing square section girders with a diagonal bar accross, I have bought a signal gantry kit it's 00 but looks about correct. I have been down to the bridge and measured it with a tape measure to get some idea, but I have mislaid my dimensions somewhere so I can check them.