bridge help needed

Discussion in 'HO Scale Model Trains' started by wickman, Feb 9, 2006.

  1. wickman

    wickman Member

    Ok here it is just trying to narrow things down a bit for a double rail bridge over the gorge. As you can see on the styrene template I made up there are 2 rails outlined or actually the edges of the ties are outlines , then the lines outside of that are the min clearance according to the nmra guage except for the upper rail in the pic where the edge of the styrene is actually the limit. You can see I marked the distance from edge of gorge to other side which would be 13 inches across bottom from side to side and 10-5/8 inches on top side to side I would need a widest width of a bit more than 5-1/2 inches if I were to make a straight beamed bridge ( truss type ) or even with low sides because of the clearances needed which is one big bridge. There is 1/4" clearance between the 2 rail clearances on the inside curves making it impossible for 2 single curve bridges. So I'm thinking that any type of bridge that shows the top is out of the question and I'm leaning toward a below bridge or like a deck bridge. So I'm looking for all options and suggestions and pictures would be great.


    here's the template I traced by placing the properly cut sized styrene under the tracks and tracing along the ties


    this is the below type deck bridge which may be constructed in a couple seperate bridges

    this is the truss type of bridge whether with overhead or just sides that would take quite a bit of room because of the straight beeams needed from one side of the gorge to the other
  2. pgandw

    pgandw Active Member

    Just a guess - I'm an electrical engineer, not a civil - but given the situation in the real world, one option I would consider would be to put a support in the middle of the gorge if at possible so I could use 2 short narrower bridges instead of one large nearly square one. A wood or steel trestle is the ultimate extension of that thinking (you would have 2 trestles, 1 for each track). Each curved trestle is made up of multiple short straight sections tied together at an angle to make up the curve. The prototype engineers would consider protecting the trestle supports in the gorge with engineering of the water flow, and protective berms and dams if they felt the water flow was too strong for the trestle supports.

    Another real world option would be to examine the cost of straightening the track over the gorge - perhaps even at the cost of much sharper curves on either side.

    The prototype also preferred under track bridge structures - easier and cheaper to build and maintain - where clearance underneath was not an issue. This favors your preference where the width wouldn't be quite so visible.

    Hope this helps.

    yours in bridging
  3. Russ Bellinis

    Russ Bellinis Active Member

    You could use a piece of luan door skin or styrene under the track, with ballast or long bridge ties. the main thing is to hide the piece that you put under the track. If you are modelling modern (after WW2), you could use Micro Engineering steel trestle bents to support it. I didn't see the dimensions of the gorge. How long a span is it.
  4. wickman

    wickman Member

    :) The specs are on the styrene template the gorge width is 8 and 1/4 inch side to side which would be the width I would use if it was a straight bridge but becauce of the curve I would need to use 13 inches at the closer rail and 10 and 5/8 or so inches for the outside edge of the upper rail
    I have also considered a stone arch using a chunk of roam and cementing rocks on the sides ...just trying to pick some brains before I decide. I may just go as simple as a simple deck bridge comsisting of 3 timbers going from one side of the gorge to the other then 4 timbers ontop of those going parrel to the gorge and then putting boards for the top for the rails to run over and finshish with a single 5-6 leg bend reching from under the bridge to the gorge river at the bottom. I was thinking of using 3/16 timber but I'm statring to think it may look too heavy and bulky.
    kinda like this crude drawup
  5. Doc Holliday

    Doc Holliday Member

    Here's a couple of pics of how I handled a similar situation. I only had one track, but needed to locate a turnout within the bridge span. Like you, I traced the tie outline and then used Atlas plate girders on the outside edge of a piece of cardboard used to form the bridge deck. I cut some of the plate girders in half and reglued them to follow the curved outline of the track.
  6. wickman

    wickman Member

    thanks thats very interesting and good input
  7. jim currie

    jim currie Active Member

    you could build the bridge on a angle and also you could run a gauntlet track across so a single track bridge could be used.would add a lot of operational challange :)
  8. b28_82

    b28_82 Member

    How about a Concrete Bridge with ballast across it?
  9. wickman

    wickman Member

    That sounds kinda along the same line as a simple arch bridge started from foam board ...if we're on the same page LOL:)
  10. wickman

    wickman Member

    Well her's a little something I came up with over the weekend
    I just painted in the planks in red . Not sure if I'm going to keep this or not right now it just needs a 7.5" 5 leg tressel bent the planks that are in red and a guard rail. I'm still thinking about the low arch bridge.

    If anyone has some ideas as to how to complete the deck and cares to edit the pic and repost I'd appreciate it
    I'm always open for idea's.


    Here's the campbell bridge completed just needs to be fitted and stained

  11. viperman

    viperman Active Member

    Has there been any progress on this bridge build?
  12. doctorwayne

    doctorwayne Active Member

    The best solution for bridging this gap if you leave the tracks on a curve is either a stone or concrete arch bridge. Because of the curve, any bridge must have its supporting structure below the track level, in order to maintain side clearance for the trains. The bridge that you show in your last photograph should be supported under each of the members that run parallel to the sides of the gorge: because of the rocky nature of the gorge, not the best place to drive piles or to create a level area for bent foundations.
    Cut a suitable piece of plywood, 1/2" or 3/4", to use as the bridge deck. Cut it so the edges parallel the tracks. You can use 1/2" extruded blue or pink foam for the sides, carved with stone detail (there's a thread somewhere on how to do this - if the bridge is only viewed from one side, you can leave the unseen side plain). Allow the sides to extend a bit above the deck, enough to retain the track ballast, but not so high as to interfere with passing trains. If the bridge cannot be viewed from below, close in the bottom of the arch with anything; cardboard, sheet styrene, etc., just to keep the sides of the arch where they should be. If it will be visible, you may be able to find a suitable material that you can put stone detail onto, then curve into place.
    If I were doing this bridge, I'd use .060" sheet styrene to make a "concrete" arch, again using plywood for the bridge deck. You can even use the styrene in layers, with cutouts in the outermost layer to give some visual relief to the structure. It's easy to curve to make the underside of the arch, and because it's easy to cut, form, and glue, it shouldn't take very long to bridge this gap. You can paint it to look like concrete, or scribe lines in it to make it look like cut stone.
    You could also make forms from sheet styrene, then pour the bridge from hydrocal, although this would require more work.
    In my opinion, an arched bridge of either stone or concrete is the best choice for this location, and the easiest way to build one is with sheet styrene, around a plywood deck.


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