bridge help needed

[jeffers_mz]

I'm really looking forward to seeing the layout with scenery too, but I've told my kids to expect up to two years before it starts looking finished. That probably will happen within 6 months, three from now since we're al;ready 3 months into the project, but this way I have more time than really needed in case something takes longer.

The trak plan does look busy, even more so since I've added more track since then, but with the foam on and roughcut, more than half the trackplan is under mountains and it really doesn't look so crowded. The mountains are all removable for access, but so far, the track is holding up well and the only derailments are when the operator forgets to throw a turnout. You know how those operators are.

I like that gorge you're doing in your layout, it looks good with steep sides. It limits your bridging options a little bit, but with all the suggestions in this thread, I think you can span it in a way that will carry the trains and look good too, you just have to choose which option and execute it.

As for the drawing, that's just a quick and dirty Photoshop sketch. If you zoom in you'll see that the corners aren't perfect and some lines are a little long or short. Not blueprint quality by any means, but then I get about $100 a page for those. This sketch definitely isn't to scale, for instance, all the bent members are usually about the same size timbers, 12" by 12" or 12" by 14" inch in real life. Stringers go maybe 7" by 14" built up to 14" by 14" or even thicker, and the batter baords were nominally 7" by 14" timbers.

I didn't put the guards on the drawing, but roughly tie sized material is usually run alongside the rails, with joints placed over the bents, to keep the trains on the bridge if they happen to de-rail.

Another option is to run some laterals from each sill back to the embankment horizontally, so the bent can't fold sideways (in the elevation drawing) at the sill plates. Most old pictures I've seen use one lateral per each vertical bent member, four in your case. If the ends of those aren't anchored in the embankment, another option is to use an X brace in the space between the first two bents to fix the laterals in space, but that's for longer trestles with at least three bents.

By the way, "bents" can be an ambiguous term. Most times it refers to a full trestle assembly, ut some guys call an angled member a bent, so keep that in mind if reading something that doesn't seem to make sense. The top piece of a truss is the "top chord" and the bottom is, well, the bottom chord. Verticals are vertical, and if you don't call the angled pieces bents, then they are called braces.

Looks like you're well on the way to bridging that gorge, keep us posted how it comes along.

[wickman]

Thanks Jeffers
I really look forward to seeing your layout with scenery ... looks very cool and busy.
As for mine well funney u mention the truss under the curve bridge I've thought of making the long legs like that down into the gorge but I didn't feel that moving the rock walls inward much more than they already are would do any justice but as u hit the post button I was in middle of making a copy of the double curve and I'm gonna maybe try to make like a lower level and truss as u call it between so it looks like a full deck bridge with the upper and lower main beams matching the curved part then filling in between perhaps as you drew the pic. Ah yes and I can see that you can draw as well as you type LOL
As for the truss bridge once I cut back the banks so it fits I will put little ledges for it to rest on same as on the curve bridge,[:)]

[jeffers_mz]

The truss bridge you have looks fine just like it is, except for it needs abutments after you get the terrain finished there.

To support the curved bridge under the double track main, you might do something like this:



I don't have many pictures of my layout, since I've been spending all my time working on it and not much taking pictures, but I have a few of them uploaded, you can see them here:

http://photobucket.com/albums/y138/jeffers_mz/misc/

The track plan has changed somewhat since that diagram was uploaded. The grade (red) at far left has been replaced by a pair of spurs on the lower level, which I use to store trains while they are in "Durango" (under the mountain). On the top edge of the diagram, I've added a pair of eight foot tracks to be used as staging for now. In the future, they might be the interchange feeders to connect to other modules, a real Durango, plus other rail lines in the area, the Silverton Northern, and the Silverton, Gladstone, and Northerly, and maybe the Silverton Northern's branchline into Cunningham Gulch.

I'll put up more pictures as time goes by, probably a lot of them when the terrain and scenery is done and all I have to worry about is building all the structures.

[wickman]

Ok I'm quickly realizing you have some very very good input but to tell you the truth I'm completely lost when it comes to bridge lingual [:)] Can you draw as well as you can type cause I'd really like to see your best suggestions drawn onto the 2 bridges I posted pleaaaaaaaaaaaaaaaaaaaaasssssssssssssssseeeeeeeeee [:)]
her's a couple better pics

Also do you have a layout I can take a peek at sounds real intersting

[jeffers_mz]

I type really fast, three fingers just clicking away. When you've had airline VP's breathing down your neck, wanting your computers back online so the fleet can get back into the air and offset some of the formidable interest charges they're carrying, speed typing is a necessity. What takes the most time here is trying to find the right words to convey what really should be done with elevations and plan view drawings.

Your truss bridge doesn't really lend itself to a trestle bent, nor does it need one. It's good just like it stands. Unless the bent was directly under a vertical truss member, (which would put it off center and probably look unbalanced from the side) it either wouldn't carry any weight, or else would just bend the bottom chord of the truss up without helping the structure of the bridge carry the train.


To me, a truss is a very cool thing. Looking at yours, the right end is anchored in solid rock. For the top of the first angled member to change position, the member itself would have to get shorter, and a stout beam is always strongest in compression. From there the vertical member hangs the weight of the first section of deck, for the deck to sag, the vertical member would have to get longer, and stout timbers are second strongest in tension. That first vertical also carries the bottom of the second angled member, and the process continues, truss panel by truss panel, all the way to the center of the bridge. As long as that truss remains flat in the vertical plane, is not allowed to deflect sideways under lateral loads, it is almost impossible for it to fail. Odds are the attachment points would fail first, not the truss members themselves.

On the curved bridge, another option that would look nice would be to install a trestle bent under the two quarter point crossmembers, instead of the center one. Then between them, you could build a two panel truss to span the deep portion of the chasm. The truss section wouldn't need to be more than two inches high to look right, just a bottom chord, a vertical under the center crossmember, and two angled members up from the first horizontal of the trestle bents below the deck level, four pieces of timber per side, a total of eight more pieces cut to fit. If you're real ambitious, two more pieces would form an X brace under the center cross members to keep your truss panels honest in the vertical plane. At that point, you'd have a good looking, prototypically legal (designwise, anyway, but I bet you could find a real world example if you looked long enough), easy to build bridge and kill all the birds with a single stone.

Just one more option, there are as many ways to bridge a gap as there are railroaders and designers. Keep us posted if you will, I'd like to see how this progresses. No rush, I know how priorities work here on my layout, the bridge will be done when it's done.

(My only "trestle" is currently supported by a four inch wide by five inch tall piece of one by six, no bents visible at all. I need to get on that bridge guy, but he's known to be an unreliable sort, the kind who'd rather play with his trains than meet deadlines.)

:-)

[wickman]

Obviously you took time to do the little right up and I sure appreciate it . I do model in what I call my basement model room world and not the rivet counting world which is a relief LOL . I do intend to put a tressel bent under the double rail bridge and the truss bridge in back ...I still have to cut away some of the incline from both sides and fit the bridge .
ty for the input [:)]
Lynn

[jeffers_mz]

First off, there's real world bridges, and then there's model train bridges. In the real world, the vibration and large live loads a train imposes on a bridge demand vertical support along the entire load bearing length. Between much lighter model trains, and an economy of scale mismatch in materials used, a much lighter bridge will carry the load. For illustration, look at the vertical cross section of your truss bridge versus the vertical cross section carrying the bridge in question. My eyeball says the truss uses 5 vertical inches to support a single track, while three eigths of an inch supports the two track main.

Still, I think you can get away with what you have now, with the addition of either a trestle bent under the middle, or diagonal braces from the middle crossmember back down to the canyon walls. In other words, you probably won't have to call out the derrick to fish your locomotives out of the gorge. I also think it will look decent too.

However, if you have rivet counting tendencies, you may not be happy with a non-prototypical approach later on down the road. For a realworld trestle, the crossmembers would run either perpendicular to the track, meaning that each was at a slightly different angle, or else they would run perpendicular to a line drawn from the center of each abutment, in which case the cross members would all be parallel to each other at about 35 degrees counterclock to what you have now. Center to center spacing on the cross members generally ran about 15 feet.

From there, there are two options. One, each cross member would have a vertical trestle bent under it, or two, each cross member would have the vertical member (kingpost) of a truss section underneath it. You can combine the two approaches with a center trestle bent and two trusses, or even other combinations.

On top of the cross members, there are usually a pair (sometimes up to four) of timbers laid on edge to carry the weight between crossmembers called stringers. In a curved bridge, these could be straight from crossmember to crossmember, or they can be built up to match the curve of the rails. There is one stringer for each end of the ties that support the rails, but they usuallysit inward from the tie ends so that the weight from the train is transmitted down through the rails, then the ties to the stringers, directly underneath, or as nearly directly underneath as a straight stringer under a curved rail permits. A very nice look is to use two seperate sets of ties, each set perpendicular to the tangent, you can use a piece of curved sectional track to get the change in angle for the ties right. That would require four stringers, wich is the minimumused anyway, even if the ties span under both sets of rails.

In a perfect world, there would be a vertical trestle member or a vertical truss member directly under each stringer at each crossmember, you want to carry that load all the way to to bedrock if possible, but in real life, many trestles did not put a vertical member under each stringer, they splayed them instead, hoping for more lateral stability against side loads. This they achieved, at the expense of vertical support under the greatest loads. You get lateral stability from the outside members of the trestle bents anyway, put verticals under the stringers in the interior of each bent and you get the best of all worlds.

On Max-X last night, they showed video of a late model diesel sitting on un-supported rails which were steadily being washed out by floodwaters underneath. Eventually the rails could no longer support the loco and into the drink it went. If you decide to go with what you have, you don't have to worry about that. I'm interested to see which way you go and how it turns out, because I have a similar length of curved bridge yet to build under a two track main, and I'm not sure I want to put in the time it will take to build a prototype bridge there either. The rails aren't very high above the water level, any trestle built there is not likely to look impressive or be a focal point, and if there's an easier way to get across the creek and you invent it, I might just want to borrow your solution.

[wickman]

Well here'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



Lynn

[Susquehanna And Rimouski]

I tried water once, and it leaked. You've really got to use a waterproofing resin (like for a concrete foundation!) all around. There's a massive layout in Sharttlesville Pennsylvania (O Gauge) called ROADSIDE AMERICA with a large river running through it, with a large waterfall and goldfish in the water.

From what I could tell, the "River" looked like galvanized metal coated in some kind of tar sealant, but I could be wrong. Roadside America was begun in the 30's and finished in the 50's or 60's, so you know they didn't use plexiglass.

If you use real water, I think the best thing you can do is have that as separate from your structures as possible. A friend several years ago integrated a 29 gallon fishtank in a living room layout with the trains going over the front of the tank, and the rest was like a lake in the layout. You could sit and look at the fish and watch the trains go over it but there was one serious problem for this shortlived configuration ---

When the trains were turned on, the fish went ballistic. Once they got used to it, or went deaf, the chemicals from the water effected everything around them.

Back to the drawing board......

S&R.

[wickman]

I have thought of real water and would probalby pretty straight forward to make but it not in the near future plans I have a bunch of campbell kits and dpm kits coming as well as a fsm 170 sawmill ...that'll keep me busy for a while . Real water may come in down the road ...way down the road
Lynn

[Susquehanna And Rimouski]

Have you thought of getting a pump and running real water, rather than a resin project? All you have to do is keep it clear up with a little Javex now and then![:)]

S&R

[wickman]

The main line is down permanent just needs to be ballast, the layout is actually a walk around I can reach without a prob from all angles there will be 7 bridges total including one vehicle bridge across the gorge and one trin bridge will probably end up being a 2 short bridges joined. I just have a few spurs to add in my main concern right now is to get the bridges assembed for the gorge get the waterfall and river put into the gorge and paint the rocks then I can run the trains again its been since November since running anything.I got the new hill layed down I will paint it after gorge is complete as well .
Lynn

[Susquehanna And Rimouski]

I can't say I like it, I LOVE IT. Saw your CP Rail gear and you shouldn't have any problem, but from my own previous, disasterous experience, try and give yourself a good 7 Cm of straight going into the curved bridges on both sides.

During construction I always have my longest (auto parts cars), highest (double stack) and most finicky cars (a Roco 6 axle flat) on hand to test clearances and joints. If these cars can clear new work, I'm home free.

I notice you're gluing the cork right down on the plywood. In my region, I use and am a major advocate of using HOMASOTE. With Homasote, one can firmly lay down track, test for a period ( a year to make sure temperature and humidity changes aren't going to hose you!) before doing permanent gluing and landscaping around it.

You've got a good sized layout against the wall. Can you reach all the way back without a stretch? How many other bridges are you putting in?

S&R.

[wickman]

that 18" on the gorge curve is the smallest radius I have most others are 22" My era is old but not new ... I don't follow any rules for a certain era .[:)] If you chk out this link it'll give you a better idea http://www.trains.com/community/forum/topic.asp?TOPIC_ID=54510
Lynn

[Susquehanna And Rimouski]

I ditched 18" radius after I bought a Mallet. My present layout has a minimum of 22" and a maximum of 36". I strongly recommend that if space is not an issue, that you try and go for 22" or larger, which with Flex is possible to make anything fit. You will be glad you did in the longrun.

What era are you modelling, or do you have a collection spanning the last century?

S&R[

[wickman]

Well I belive the raduis on the corners crssing the gorge are 18" could be a bit larger . You can see the difference between the 2 where I traced along the rail ties on the styrene template


I have tested this track for months and have never ever had a problem with these 2 curves even without a bridge supporting them all I had was the cork roadbed under them.[:)] But I'm willing to listen to your ideas .[:D]

[Susquehanna And Rimouski]

Era is a factor in not only the type of bridge you want, but the length of equipment which is going to run on it.

You're in Canada, and there's LOTS of old timber bridges still on CN and CP tracks, so you can get away with just about anything in wood. However, my first misgiving is that you want to build this on a curve, and that's just asking for trouble from the start.

If you're running AHM/Rivarossi length passenger cars, a maintained distance of 2-1/2 inches between the track centers on 22" radius will clear them as well as 85' auto parts cars. But if you're running equipment like this, you MUST go with the girderwork beneath the deck for clearance. Also, it would appear from your pictures that the tracks are coming closer together on the right side, which can be a major problem without proper spacing.

We've all had the problem of putting a beautiful bridge in and the first train goes WHAM into it for the wrong reason. It's easily avoidable.

Clearance is a messy issue that one must be generous with to avoid problems. With a bridge on a curve, if the approach isn't straight enough, longer carriages will crash into the corner of the structure.

Remember the adage about "Don't raise the bridge, lower the river"? Were I you, to save a lot of grief, I would construct a double track bridge that works properly FIRST, then work the terrain around it.

I hope this helps. What is the radius you're working with?

S&R.

[wickman]

QUOTE: Originally posted by Robert Knapp

The bridge to be built is skewed and needs to be quite wide. Top timbers do seem out of the question, the bridge would look out of proportion. If you don't mind building the skewed timber bridge, timbers can anchor into the abutments, it should work and look great. Did you consider spanning the gorge with a skewed stone arch? Foam, 1/4" ply and sheet stone castings. This would be a simple solution, subroadbed/ roadbed can be continued and run a ballasted deck. Save the wooden truss bridge for a different spot, preferably not on a curve.
Bob K.

Yes Bob 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

Lynn

[jeffers_mz]

Flipping either of the bridges over without modification would go against prototype practice. The first bent member of a truss that uses tension members (wire rope) should angle up from a pier to the top chord, with the cable supporting the bottom chord. You can support a load by pulling on a rope., but not by pushing on one, except in specialized circumstances.

I like the trusses under the deck on a curved bridge, because the stringers can be closer together, allowing the crossmembers that stiffen a pair of trusses to be shorter, using less material and holding more rigid than the wider deck you need to allow clearance with above deck designs.

In a straight section of track, the plane of each truss's maximum resistence to deflection would like to be directly under or above the maximum load, in this case the rails, but when you use chords (straight trusses or beams) to approximate an arcing section of rail, you need a stouter stringers or trusses, located to "catch" as much of each track's vertical loading as you can.

The longer the span between piers, the stouter the truss needs to be, since it will be further out from under the max load at each end and in the middle of each arc.

[bogp40]

The bridge to be built is skewed and needs to be quite wide. Top timbers do seem out of the question, the bridge would look out of proportion. If you don't mind building the skewed timber bridge, timbers can anchor into the abutments, it should work and look great. Did you consider spanning the gorge with a skewed stone arch? Foam, 1/4" ply and sheet stone castings. This would be a simple solution, subroadbed/ roadbed can be continued and run a ballasted deck. Save the wooden truss bridge for a different spot, preferably not on a curve.
Bob K.

[pcarrell]

QUOTE: Originally posted by wickman

QUOTE: Originally posted by pcarrell

Maybe this would help give you some ideas;

http://pghbridges.com/basics.htm

It's not real specific like a "how to" or anything, but it might spark an idea.

thanks that link definatley helps
I came across this link as well
http://www.gardentexture.com/bk.htm
Lynn

That's kind of like a 3D effect of my link! Cool!

[wickman]

QUOTE: Originally posted by pcarrell

Maybe this would help give you some ideas;

http://pghbridges.com/basics.htm

It's not real specific like a "how to" or anything, but it might spark an idea.

thanks that link definatley helps
I came across this link as well
http://www.gardentexture.com/bk.htm
Lynn

[pcarrell]

Maybe this would help give you some ideas;

http://pghbridges.com/basics.htm

It's not real specific like a "how to" or anything, but it might spark an idea.

[wickman]

QUOTE: Originally posted by nfmisso

Depends on your era. In modern times, a ballasted concrete deck type, earlier, either of your lower pictures, with the bottom one turned upside down.

A bridge/trestle for each track is more likely on a curve.

Well era is definately not real modern but not real old either. I never even thought of tunning the bottom pic bridge upside down ty good input
Lynn

[nfmisso]

Depends on your era. In modern times, a ballasted concrete deck type, earlier, either of your lower pictures, with the bottom one turned upside down.

A bridge/trestle for each track is more likely on a curve.

[wickman]

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

TY
Lynn