Girder Bridge in Planning

[Peaky 556]

Hi all,
I may have said already that my garden has a rather overgrown, but attractive in a sort of 'natural, wildlife' way, pond.  As I now have permission to start my garden railway in a small way (ie innoccuous and somewhere well away from visitors, wife's plants etc) I have the first length planned alongside the duck enclosure.  As my wife well knows this will be the thin end of the wedge and it will soon progress across the driveway, down the side of the garage and workshop, through the summerhouse (yes, this will be the undercover operations centre!) and thence across said pond.  I don't know why the railway should cross the pond, but it seems to have a fatal attraction, as with a rabid Aussie and a pint of lager.  Maybe one of you can throw some light on it?

In anticipation of 'getting away' with the project thus far, I would like to progress some concepts for the bridge design, so as to have some more things to dream about whilst at work.  I quote Andrew Foster below from another topic, and am intruiged by this metal section mentioned below:

One of my friends likes to annoy me by showing off his outdoor railway bridges made from the 'top hat' galvanised steel posts used for small road signs. They are very stiff, you can make long spans, and they don't cost much.  Two of them side by side with a wood deck would give a fine double track structure. 

Andrew

Can Andrew or anyone throw any light on what section type and size we are talking about, where it might be available (short of digging up signposts by moonlight) and in what lengths?  The best I have come up with so far is 25mm square hollow section mild steel in about 3mm wall thickness; very very substantial but a bit OTT in terms of weight and strength. 

Regards, Tim 

[454]

Tim

Question:

1) Total length of span between terra firma required?

2) Height above mean water level to allow navigation on pond, herons, ducks, leaping trout etc?

I think my 1 metre span King Truss girder design might be inadequate for your application.

Cheers
Dave
454

[Peaky 556]

Span is about 17'.  Height above water will be around 2 1/2 to 3 feet, to give a nice working height in the summerhouse right next door.  I worked up a girder design when I thought of going the G1 route, and I estimated it would take my weight at mid-span no trouble!  Surprised me!  Material was the 25mm SHS steel.
Tim

[454]

Suspension bridge Tim, with the end piers on terra firm.

I think with a pond to use dry terra firma at each end for the supports saves the bother of having to deal with water immersed support columns on the pond floor unless of course you really do like building bridges over water.

Do I understand that with it taking your weight in the middle you will be walking over it?
In that case probably a suspension bridge might not be suitable.

Visit a Japonese water garden centre they might have a nice one for you to walk on. Trouble is the grades at either end might be a bit challenging for the trains.

Seen a great design on a French garden railway that looks the part & probably quite easy to make.

Will try & find the link again.

Dave
454

[454]

Tim,

Do a search for "Chemin de Fer de villare en IIm" OK so it's G scale but that does not matter, same principle applies.
This is a garden to be admired by the way. Several views should give lots of ideas on construction.

Cheers
Dave
454

[454]

Apologies folks, that title may not Google very well as it is on a French website.

Try Googling "Railway Garden Blayais" instead, there are at least 2 lovely garden railways albeit in G45 displaying some quite impressive bridge structures in metal over quite wide voids. Just work your way down the list & you will find links to Chemin de fer de Villare & Chemin de few de Bories.

Both these are worth looking at.

Dave
454

[Peaky 556]

No I do not want to muck around with foundations in the water; supports on dry land with a girder structure between is the target.  If steamers come I will need to ensure a drip tray catches any oil to avoid it damaging the pond environment.
Walking on it is not planned, but good to know it might be strong enough for the occasional retrieval activity!
I can't get on those French websites from work, will try one evening.
My book "Bridges Explained" states that suspension bridges are not suitable for railways, I think because of the way they sway around or the concentrated load.  They are normally arched to a small degree too.  Does anyone know of a railway-carrying suspension bridge in real life?
Tim
PS Apologies to Peter regarding comments about Aussies, no connection or offence intended!

[454]

Tim, in real life maybe unsuitable, but this is model world. The vapeur park at le Bouveret has a 7 1/4 railway with I believe a suspension bridge. I'm sure that a model bridge will not sway around & it can be modelled flat. Does not need miles of knitted cable & anchored in concrete either. Remember this is model world not real life.

The other super design is a flat platform with a steel arch underneath. Prototype by Mr Eiffel the Viaduct de Garabit.
Look that up on either Google or Wikipedia. Very spectacular, even better in gauge 3.


Cheers
Dave
454

[cabbage]

Tim,

I know these are not what you are looking for but they may be a source of inspiration

http://www.cabbagepatchrailway.co.uk/trestle.html

regards

ralph

[Andy B]

Span is about 17'.  Height above water will be around 2 1/2 to 3 feet......

I asked my dad (a civil engineer) for any possible prototype bridges that might have had that kind of span (17ft in G3 = 382ft in full size), on which to base your design should you want something reasonably close to scale - his reply:

"Huge span!  Probably has to be a truss girder or lattice girder.  Usually those sizes of span were only used where there were navigation or other constraints underneath.  So that big headrooms and proportionate height to span ratios are typical.  Typical span/girder-depth ratios are of the order of 1/10, so anticipate a bridge 0.5m deep – plus headroom.


King Edward VII – Newcastle – 300ft spans – 'deck' bridge with 27ft deep truss girders under deck.

Connel Ferry – Actual span 524ft – Through cantilever (think Forth) – (but perhaps might not scale down very well for 382ft)

Nottingham (GC over MR station) – only 170ft span though

Tay (Dundee) – main spans 254ft – 'Through' girders

Spey viaduct – 350ft span – Through girder – possibly a good model – (twin hogback/bowstring girders)

Severn (Sharpness) – 324ft main spans – Through girder - (twin hogback/bowstring girders)

Monkwearmouth – 318ft span - Through girder – possibly a good model chunky girders and fewer spidery trusses - (twin hogback/bowstring girders)

Wylam – 240ft span – Wrought iron arches and deck suspended  - a little short; but elegant and could scale up

Runcorn – 305ft spans – Lattice girder through bridge – Very typical (but may be difficult/fiddly to model well)

Oykel – 280ft – lattice girder deck bridge

Victoria bridge (Arley) – Severn Valley – 200ft span - cast iron arch supporting wrought iron deck

Weston Mill (Plymouth) – I have not searched for the spans of the 1903 rebuild – lattice girder through spans – appear to be about 220ft each

Saltash – 455ft – composite action arch-cum-suspension bridge of wrought iron girder deck, supported by iron bar 'cables' propped apart by overhead arched tubes (of w.i. plates)

Spey (Orton) – 230ft – through bridge with tall thin wrought iron box edge girders

Wye (Chepstow) – 300ft – suspension bridge of wrought iron girder deck, supported by iron bar 'cables' propped apart by overhead tubes (of w.i. plates)

Conway – 400ft – tubular box of wrought iron strip plates

I hope that helps; it probably is almost exhaustive of big single spans."

I expect you'll find pictures of all of them on the web somewhere - but if not let me know and I'll see if he has a picture of any you are particularly interested in.

Andy

[Peaky 556]

Wow, that's a fantastic response from all.  I have plenty to look through now.  Andy please thank your Dad very much.  Would he care to throw up a design for me!!! That French Garabit viaduct is pretty amazing, but I couldn't reproduce the detail in that with welded bits of box section! 
Thanks very much again, aren't bridges fascinating?
Tim

[Andy B]

Would he care to throw up a design for me!!!

I'm sure he'd offer some further advice once you've narrowed down your basic design choice.
Some of them would be ideal candidates for a set of laser cut steel parts - such as the ex-GCR bridge over Nottingham MR station, and especially Monkwearmouth.
I think the latter would make a very attractive garden feature - there's even a plan of it here: http://www.rmweb.co.uk/community/uploads/monthly_11_2012/post-8688-0-75594600-1353284908.jpg.

As an aside - here's a thread on building a big girder bridge in plasticard, in a smaller scale - http://www.rmweb.co.uk/community/index.php?/topic/53995-points-bridge-hagg-bank-wylam-northumberland/

Andy

[Peaky 556]

Thanks Andy, will review the bridges you suggested.
Have viewed the plastikard bridge thread - absolutely rivetting (not a pun), but don't read unless you like being made to feel inadequate.
Tim

[Peaky 556]

Correction, the span is only about 4.1m.  That should help with proportions.  Following suggestions from all, I now favour the cast iron arch design of the Arley bridge over the Severn, carrying the SVR.  I have lots of pics of this, but so far no plan/drawing.  Never mind I will adapt the design to suit materials readily available, and my lack of intricate welding skills!  Keeping the weight down to something two people can lift will be a major challenge!
Thanks all
Tim

[cabbage]

Tim,

You could make it out of wood and make it look like metal... This is a couple of shots of the bridge on the original Cabbage Patch Railway -it was 3m long.





It was strong enough to take my weight...

regards

ralph