Plate girder bridges

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steve howe
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Plate girder bridges

Postby steve howe » Sun Jun 22, 2014 3:36 pm

Can anyone advise on the maximum span between supports of a plate girder bridge carrying a road? I am using the Wills plates to make a view-stopper across the end of the scene, but am pondering the best places to put the supporting walls (or columns)

Steve

Alan Turner
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Re: Plate girder bridges

Postby Alan Turner » Sun Jun 22, 2014 4:14 pm

Work on a span to depth ratio of 12 to 15.

regards

Alan

Terry Bendall
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Re: Plate girder bridges

Postby Terry Bendall » Mon Jun 23, 2014 5:52 am

You can see what I did here.

http://www.scalefour.org/shows/S4North2 ... t_4232.jpg


Terry Bendall

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Noel
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Re: Plate girder bridges

Postby Noel » Mon Jun 23, 2014 10:28 am

Alan, has a decimal point slipped, please? A 12:15 ratio would produce a girder deeper than its width. Or did you mean between 12:1 and 15:1?

Noel
Regards
Noel

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Mark Tatlow
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Re: Plate girder bridges

Postby Mark Tatlow » Mon Jun 23, 2014 10:47 am

Steve,

Alan's reply does mean a depth of beam to span in the range of 1:12 - 1:15.

Actually, I would say this is a tad long and the more sensible depth to span range would be 1:10 - 1:12 but the actual depth to span ration will depend on a number of factors such as loads, thickness of plates and presence of stiffening places - so either of our answers would work.

A couple of observations on the Wills vari-girder kit:

    The top flange plate is way too thick. It is a bit of effort but you will get a much more realistic bridge if you create one with a rivet tool out of brass. If you don't fancy this try and sand it thinner.

    At the bearing ends at either end of the span there would typically be a reduced width plate (say 60% of the adjacent panel).

    A more common design of girder would have stiffening plates between each panel. These can be formed easily with 20 thou plasticard and transform how the bridge looks - if you take a look at mine on Portchullin you will see what I mean (pictures are in various places here, on RMweb or find "A Day's Trainspotting at Portchullin on Youtube).

    Make sure you have resolved how the girder lands onto the abutments; lots of modellers don't and to anyone that understands structures they are immediately impossible structurally speaking!
Mark Tatlow

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Russ Elliott
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Re: Plate girder bridges

Postby Russ Elliott » Mon Jun 23, 2014 11:33 am

I agree with Mark. Railway engineers tended to be conservative in their girder bridge design, even though the bridge in question is for a road overbridge rather than a railway one, and I would say a height to length ratio would not exceed 1:12, and would typically in earlier times be probably less than 1:10.

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steve howe
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Re: Plate girder bridges

Postby steve howe » Mon Jun 23, 2014 6:39 pm

;)
Make sure you have resolved how the girder lands onto the abutments; lots of modellers don't and to anyone that understands structures they are immediately impossible structurally speaking!


Thanks for that guys, very useful information, I had built the small bridge before Mark posted his comments on the end plates and the top stiffeners, the examples I have seen sit between stone piers with the girders resting on substantial padstones, so that's what I did

DSC_0166.JPG


I will elaborate a bit more in the next post on the SGW. The capstones to the piers are not fixed so still a bit cock-eyed but I hope the general arrangement is acceptable ;)

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steve howe
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Re: Plate girder bridges

Postby steve howe » Thu May 21, 2015 10:41 am

On a slightly different tack:

I am looking at ways of constructing a lengthy curved iron bridge to carry a single track line over an estuary on our group Watermouth project. The bridge will end up about 4' long and I'm using the Taw bridge at Barnstaple as inspiration and reference, although the model itself will be adapted to suit both the location and the means of production. There are several issues to overcome: we have enough components to hand to make the stanchions, these are trickier than they look because rather than being radially arranged (i.e all pointing towards a central point) they are arranged parallel to the current, presumably to minimise the restriction to the tidal flow. This means the stanchions get wider towards the ends of the bridge and narrower as they approach the centre....
barnstaple bridge.jpg


However the real tricky issue is the side girders as I can't find a suitable ready made source of plates of the appropriate depth and length. This leaves three options as far as I can see:
1. make the spans from Plastruct section with applied detail, inevitably this will mean loss of rivet detail and possible inconsistencies in pattern;
2. as above but cover with aluminium foil overlays with the rivet detail empossed on; or,
3. get the sides etched which will probably require a three-part etch for each side member and some tricky soldering
_4615965_orig.jpg


Any thoughts or observations gratefully received!

Steve

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martinm
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Re: Plate girder bridges

Postby martinm » Thu May 21, 2015 12:56 pm

Steve,

You could have a word wth Mike Edge, Judith Edge Kits, I saw that they were doing "a kit for the basic 50ft span overhead structure and a number of other special parts for the station girders." for the LOR.

It doesn't look dissimilar to the one you show, so might help you.

regards,

martin

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Ian Everett
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Re: Plate girder bridges

Postby Ian Everett » Thu May 21, 2015 6:23 pm

I was surprised to see that the Masokits catalogue which John has just loaded - http://traders.scalefour.org/masokits/ - lists a bridge girder kit as item 8.05. This gives a 42' X 6' girder.

Mike, with typical honesty, says it will probably drive you bananas! But the rivets are ready-etched, so don't need punching.

Ian


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