Hello All
As I'm laying the foundation for my trackwork I have come across 2 sections that will require a curved bridge. I've looked around and haven't found anything that seems to fit so I think I'll try to build my own.
Layout is HO.
The first section is about 18 inches across and 3 1/2 inches High. The radius is 30 inches. 2 tracks will pass under the bridge leaving room for a support in the center.
The second section is 27 inch radius and about a foot wide:
Has anyone here done something similar and/or have ideas on the best way to go.
Also is there a source for girders material that can be shaped to a curve?
Thanks
Springfield PA
Here's one way two levels of track can cross at shallow angles:
http://www.bing.com/maps/?v=2&cp=qrzrzs8t8m04&scene=55543088&lvl=2&sty=b
Dave
Just be glad you don't have to press "2" for English.
http://www.youtube.com/watch?v=zQ_ALEdDUB8
http://www.youtube.com/watch?v=6hqFS1GZL4s
http://s73.photobucket.com/user/steemtrayn/media/MovingcoalontheDCM.mp4.html?sort=3&o=27
Thanks.
That is basically a tunnel. I think my setup is too shallow since it's one track deep. I do see a curved bridge in the lower right of the same view. That would work for me if I could find Girders long enough.
most if not all free standing steel bridges were really a series of short straight sections with slightly angled ends. stone arch and poured concrete structures along with pile trestles were sometimes built with a curve all the way through but i never saw steel structural members curved.
grizlump
HamltnblueI do see a curved bridge in the lower right of the same view.
That bridge is not curved. The girders that form the bridge are straight. The track curves as it passes over the bridge.
Having a couple of flat sections for the 18 inch or large flat section would still require girders that I can use to scratch build. I don't mind though doing curved steel for this short an area.
On page 50 of this link there is a steel bridge that is curved on the top of the pic.
I like the stone bridge idea but with the short height I'm limited on the arches.
http://books.google.com/books?id=7EPYtBGAPDwC&pg=PA50&lpg=PA50&dq=curved+railroad+bridges&source=bl&ots=BlWANcSz8p&sig=eq6j7bFBOo_shZu5qRnp1QAnAYY&hl=en&ei=9QM6TKf2EIa0lQfO7-3SBw&sa=X&oi=book_result&ct=result&resnum=9&ved=0CDcQ6AEwCA#v=onepage&q=curved%20railroad%20bridges&f=false
What the prototype would have done is bring the embankments up as close to the lower level tracks as clearance (and vertical concrete walls) would allow, and then bridge the remaining slot(s) with the shortest, least expensive span that would do the job. They also wouldn't have hesitated to put a two foot thick pier between lower level tracks - its cost would have been made up in the reduced amount of steel in the spans.
For short spans, the preferred structure is steel - deck girders if the below-track clearance allows, otherwise through girders. The concrete structures seen in the map link are also fairly common - many such were built during the steel shortages of WWI and WWII. Far from being, "Tunnels," they're only a couple of feet thick - comparable to the floor system of a through girder. They also have the advantage of avoiding bridge ties, guard rails and all that extra carpentry and ironmongery required by open decks. On a cost basis alone, the ballasted solid deck trumps open decks every time - and railroads are nothing if not cost conscious.
Of course, if it was MY prototype railroad, the bridge of choice would have been a steel girder - painted oxide red (It's a Japanese thing...)
Chuck (Modeling Central Japan in September, 1964)
"On page 50 of this link there is a steel bridge that is curved on the top of the pic."
the first paragraph of the article states that such bridges do not exist in the real world. what the heck?, i have done a lot of things on my model railroad that are not quite "Kosher". you can too if you want.
Looks like what I need is the sides only of a plate girder bridge, other than the 9 inch one offered by atlas, so that I can make a wider version to accommodate curved track.
Even a wide warren truss bridge would help with the shorter span.
HamltnblueLooks like what I need is the sides only of a plate girder bridge, other than the 9 inch one offered by atlas, so that I can make a wider version to accommodate curved track.
I'm wrestling with a similar problem. Anyway, MicroEngineering makes an 85 foot plate girder. Here's a link to a picture on the Walthers website, complete with ruler so that you can compare it to your space: http://www.walthers.com/exec/productinfo/255-80180
For my particulat situation I've sort of resigned myself to the fact that I'll probably need to construct a flyover concrete structure such as the one shown in one of the first posts to this thread.
Thanks. That might help on the 2nd section.
I just ordered a set of bridge decks and Trestle Bents from Scenery express. I've used them a few times and never knew they had bridge parts. It's hidden in their tunnels and portals section. Hopefully I can do the job with these. Oh and I've never heard of a Bent before surfing and studying for an idea.
http://www.sceneryexpress.com/products.asp?dept=1098
Here's my curvy bridge. But the angle of the lower line isn't that shallow. On the real WM, Keystone Viaduct was a good example for you.
The crossing of the B&O was at a very shallow angle, so the WM built a massive through truss to make the span and still maintain clearances for itself. The bridge was built to accommodate double track, but only ever carried one.
You can see the curvature of the left hand track. The bridge is now part of the Allegheny Passage Rail Trail.
Stupid Chessie.
Route of the Alpha Jets www.wmrywesternlines.net
What was your source for girders in the first pic? It won't apply to this application but I'm curious still.
Curved bridges are as rare as hens' teeth in the 1:1 world. That's because of the load on the bridge not staying within the rectangle of support when a train passes over it.:
The curved bridge creates a twisting force and will soon fail.
This is what prototypes do:
Then they put supports at each joint - this is how curved trestles are made.
I, on the other hand, took some "modelers' license" and built this:
All of the curved pieces are laminated from thin strips of wood, then I built the bridge as if it were straight. I tell people that the engineer who designed it is a CSU grad and that passenger trains have to stop and let the passengers walk across, then the train picks them up on the other side.
Phil, I'm not a rocket scientist; they are my students.
Do it "right" and prototypcal by making the bridge out of straight sections. If the bridge must be curved, make masonry bridge.
Mark (and that's not my layout)
Thanks Mark. I'm going to give the straight decks a shot. I ordered two 12 inch pre made decks. I'll have to cut them down. They might be in tomorrow
Many/most bridges had guard rails, particularly if the bridge was long or on a curve.
Mark
That's something I'll have to learn how to do next. I'll have to add them to the Atlas Flex Track.
Oh and by the way, that hand laid tracks looks great.
I have something similar I'm still banging my head over. I have three tracks to cross and there is a slight curve in the track I need a bridge for. I felt like a bride trying on Wedding Dresses. Every bridge I considered was a "well maybe". And then an experienced modeler and RR buff said to me, "if you have a spot where just about any bridge looks goofy. Make it a combination Railroad/ highway or railroad something else bridge and then it is OK if it looks a little out of place because those combination bridges often require a double take as they are often one of a kind". Just something I thought I'd throw in to the mix.
Brent
"All of the world's problems are the result of the difference between how we think and how the world works."
The following bridge is made up of ME 40' spans set straight but angld at the ends to form a curve. Taller than you want but hopefully gives you an idea. You could also use the BLMA bridge segments to form a modern cement bridge. You can use them straight or cut them to the required angle.
John
Well I got the first bridge installed before a sudden power failure. Pitch black. Luckily my wife was near a flashlight. It was time to call it a night anyhow. First bridge is wooden at this point and the second was taken from another post but still in process.
The bridge girders I used are by Micro Engineering. ME also offers "bridge track" which has longer ties that are spaced more closely together. The N scale track that I use also includes to two strips of code 40 rail to make the guard rails.
Looks Good. I like those telegraph poles as well.
I got my wood bridge parts from Scenic express. I found them on their site by accident since they don't advertise them very well.
markpierce Do it "right" and prototypcal by making the bridge out of straight sections. If the bridge must be curved, make masonry bridge. Mark (and that's not my layout)
It would have been tempting but I had to have max clearance for trains passing under. The limitations of the layout size only gives me 3 inches to work with.
Mark offers a great example of a model that matches prototype practice, and good engineering. The problem for me was that there was no space to put the supports that would go at the junction of each bridge section. I think the original poster has a similar challenge. I think he and I both needed maximum clearance under the bridge as well.
I pondered it for some time and finally decided that it was a reasonable compromise to make a curved bridge. It was also an interesting challenge to make it appear credible. I take so much pride in my bridge that I don't wait for visitors to comment on it - I just tell them how I created this model of a nearly impossible curved truss bridge. Most folks reply that they'd have never guessed that there was anything wrong; some even try to think of 1:1 curved bridges they have seen, because they had never noticed that practically all railroad bridges are straight (Interesting how building models helps us to see details we otherwise might not have noticed).
By the way, if you watch for them, it's not that uncommon to see that other modelers have taken similar engineering liberties. Even John Allen built a slight curve into one of his truss bridges. From my standpoint, if we achieve credibility we have accomplished our objective - dead-on accuracy is not THAT important.
it sounds like you have your act together. form must follow function.
the prototype doesn't curve as sharply as our model track does; a 16 degree curve on the prototype is quite sharp but scales to 48" radius in HO. there is a curved RR bridge on an ex-GN branch north of wenatchee at pateros which uses a pony truss and a through truss; both spans are widened to accomodate the curve which i would estimate is 4 degrees. in this location, deck trusses would have been partially submerged by a new dam. -big duke
I know you already have some plans from previous posts. Whenever I need a curved bridge I go with the wooden trestle.
However, European model companies make curved steel bridges: http://www.rocousa.com/DETAIL.ASP?PRODUCT_ID=VO2547
This one they call a ramp but it can be used on a level grade:
http://www.rocousa.com/DETAIL.ASP?PRODUCT_ID=FA120475
As someone already mentioned, IF a railroad was to build a curved bridge today it would be made of concrete.
Good luck.
shayfan84325The problem for me was that there was no space to put the supports that would go at the junction of each bridge section. I think the original poster has a similar challenge.
I don't know enough about US practice to point to a prototype example, but at least in Japan, this problem is solved by putting piers on either side of the lower track, then putting a beam across those piers, and using that beam as a bridge pier. This is also useful for shallow angles, or even when the upper track is running parallel to and directly above the lower track.
Unfortunately, this does somewhat reduce clearance under the track, as you have the depth of the support beam as well as the thickness of the bridge deck. In the model, you can compromise by making both the deck and the beam thinner than they'd have to be in real life. (I dunno if this has ever been done in real life, but you could also theoretically make the piers really tall and run the beam over the upper track, with the track bridge suspended from the beam.)