Hello everybody!
I need to build a rather long bridge, part of which will have a 32 1/2" radius curve. I'm looking at using 4 Micro Engineering 60' Viaduct Tower kits which are essentially two 30' deck girder sections put together. Can I install a 32 1/2" curve on those bridge sections or do I need to widen them?
Thanks as always,
Dave
I'm just a dude with a bad back having a lot of fun with model trains, and finally building a layout!
Here's what the M-E instructions show, Dave (if you haven't already studied them)
ME_curve by Edmund, on Flickr
I crudely penciled in the center line as it barely shows in the instruction photo.
I finally built my viaduct in a straight run but I did experiment with making it curved. I don't see a need to widen the girders. My bridge kits came with ME bridge ties which were wide enough to cover the tops of the girders if curved, but they were short (rail length) and would have been a pain to try to curve them and join them. Yes, I see ME makes a 36" length of bridge track
http://www.microengineering.com/products_ft.htm
They make a longer section of flex bridge track and I would go that route. You might have to epoxy the bridge ties to the girder since the ties are "slippery engineering plastic" Walthers Goo would probably work well, too.
I built my steel viaduct over twenty years ago. It was tedious but worth it. Very detailed.
Good Luck, Ed
Thanks Ed,
I have the ME instructions somewhere but I haven't found them yet. Doctorwayne was kind enough to send them to me a while ago.
Tedious is OK. I just modified about 40 Atlas and Peco turnouts to add jumpers between the point rails and the closure rails, and between the closure rails and the stock rails, as per Allan Gartner's recommendations. That was tedious, and I only have 30 or so more to do. Actually, I plan on running a seminar on how to modify the turnouts for anyone in the club who is interested. It will be interesting to see how many turnouts get destroyed in the process! I figure I will have to start with basic soldering techniques before the members actually start applying heat to the turnouts. Should be fun! I love teaching.
Dave,
My scratch/bash bridge has ME bridge track...1pc is 3ft. You have to add the code 70 rail to the ties and there are detail spikes that the track sits into. I would make My curve first held in place with metal pins to the radius desired and then glue the guard rail in place,,,that way it will hold the radius. Then you also have to glue the timbers in place. Each one is about roughly 3'' long. I used Zap-A-Gap Medium Ca for the rail and the wood ties, which are styrene. I rough-up both surfaces before applying CA. After it was all complete, I did not touch it for 24hrs. Everything dried extremely strong like it was one piece. I then air brushed the whole track with Floquil tie/rail brown. I'm sure You can do it on a curved section.
Images may be clicked on for larger view....
The bridge flex track also comes with two platforms used in a trestle with fire barrels, which are hollow made from Pewter. I used those for scrape metal in a shop area, Yellow drum....
Good Luck on what ever You decide!
Frank
Dave, the high bridge in the photo below is all Micro Engineering parts. A quick check shows the radius to be about 33"...
There are, as you can see, two spans using 50' girders, so your just slightly tighter curve should be easily do-able using the 30'-ers.
I used contact cement to affix the rails and guard rails to the ties.
Wayne
I have done this and it is easy as long as one side will not be seen as the rivits sometimes will not line up where they would normally be. I asembled the girder bridge and then chop sawed it with a hobby cutoff saw, you could also use a regular hobby saw but damage is more likely. Would include pic but photo hosting site is persona non grata.
I don't have a photo of the backside of the tall bridge (have one of the low bridge, though), but my method was to shorten the spans on the inside of the curve, usually at a vertical stiffener, and leave the ones on the normally-unseen side as-is. If you need to make a cut where the vertical stiffener at an end of the girder is removed, use a strip of styrene to fabricate a replacement on the end of the shortened span.
I built all of the bridges on the layout by cutting out the plywood strip of roadbed over the rivers, then turning them upside-down on the workbench and building the bridge and support piers, upside-down, atop the plywood. That ensured that the bridges all fit properly in place. All five major bridges on the layout are curved.
Thanks everyone! I wanted to make sure the curve would fit before I started the detailed design of the bridges.
I'm finishing a 26"R viaduct and will be doing a 30"R next. I was really concerned about the curve but it was never a problem, other things were.
No towers, just bents, and used deck girder PLATES, not the full bridge KITS. Black foam spacers inside (can't see thru the ME bridge ties, or bottom). Also rough-cut the inner girders which are hard to see. Biggest challenge was mixing 50'L and 70'L girders to get different footer locations below the bridge. The 70'L girders are taller than the 50' so I had to add an I-beam under it.
Railings were hard to do but the outer walkway gave me overhang clearance for P cars. These railings are not prototypical, and the board gaps were for my wife's fear of heights, lol.
Terry
Nice work Terry! Thanks for sharing.
TBat55the curve .... was never a problem, other things were.
Would you mind mentioning specifically what other problems you had and how you solved them?
Thanks,
Getting it level (hope to get super-elevation) is my current challenge. It's so long that I'm having a tough time getting measurements. I'm using a Micro Mark digital level and a truck with a bubble level. Neither of those is working well - they show level at points along the way, but I can see it's not right. My next attempt will be a long carpenter level spanning each end with a metal bar pivoting from the middle. I'll move the bar along the rails to make sure everything is at the same elevation relative to the end points. Then I'll use the digital meter with a .020 shim (with the level set relative to sea level).
The bents are currently hanging since it was built upside down. I have a plaster mold for stone piers under the bents. I dropped a string "plumb bob" and had to adjust for where the piers ended up next to the dock. A 3D puzzle far worse than the bridge sections.
Also you can see I'm supporting it with clamped boards. The clamp is hard to adjust so I'm making a screw feed support (turn a bolt to raise and lower precisely).
TBat55I'm using a Micro Mark digital level and a truck with a bubble level. Neither of those is working well
Smart phones have level apps.
Henry
COB Potomac & Northern
Shenandoah Valley
Great idea. Never thought of it. Thanks.
TBat55Getting it level (hope to get super-elevation) is my current challenge.
Thanks for the heads up!
TBat55Getting it level (hope to get super-elevation) is my current challenge....
I think that only one of mine is level, while the other four are on grades. If you want superelevation, displace the base of the centre support (or as close to the centre of the entire span as you can get) towards the outside of the curve. The bridge and track will form their own vertical easements into and out of the curve and you need only support the piers accordingly.
Great tip. Thanks. I was having problems with the Micro Mark digital level (my fault not the tools) because I was setting zero on nearby tracks that I assumed where zero. Then I saw the note on the front of the tool "hold for SEA LEVEL" (can't believe I never saw it). That's the real datum to use, and with 0.020" superelevation it's important. I went back to other tracks and NONE were at zero.
hon30critter Thanks everyone! I wanted to make sure the curve would fit before I started the detailed design of the bridges. Dave
Dave, when I built the ME viaduct for the club layout, the base for the bridge section was actually run on spline, that I cut out and transfered the "footprint" to a piece of 1/4" plywood for use as a template for building. The track for bridge started staight and eased into a 42" superelevated curve. the template made mitering and fitting of the 30 and 50 foot sections quite easy. To get the angles and geometry right and easy to deal with, I transfered the template to cardboard to allow drawing out the mitered angles of all the bridge sections. Another hint for acurate bridge track bending, curve the track against the template, then minor changes can be done before gluing to girders.
Note: haven't posted in some time and need to retrieve photobucket pics or to another host site. Pics would be nice, drwayne has quite a few good ones to work from.
Modeling B&O- Chessie Bob K. www.ssmrc.org
Hi Bob:
We are doing basically the same thing with the sub roadbed except ours is 3/4" plywood with Homasote on top. However, I hadn't thought of transferring the bridge pattern to cardboard to help calculate the mitering angles. Thanks for that suggestion.
doctorwayne If you want superelevation, displace the base of the centre support (or as close to the centre of the entire span as you can get) towards the outside of the curve. The bridge and track will form their own vertical easements into and out of the curve and you need only support the piers accordingly.
Hi Wayne,
I have a question regarding your method for superelevation. Are the piers/towers actually built on a slight angle or are they straight up and down? Sorry, I'm not quite getting the picture in my mind.
Well, I did mine with the piers at a slight angle - I don't know if it's prototypical or not, but chose that method mainly because it worked so well where the track is on risers.For the riser-supported track, I had all of the risers clamped to the benchwork crossmembers, with a pencil line on each denoting the proper height to keep the rise of the grade constant. I then selected the riser closest to the middle of the curve, and after placing a locomotive on the curve, carefully removed all of the clamps. I then lifted that centre riser to approximately its proper height, and pushed its bottom end towards the outside of the curve. When the angle of superelevation "looked right" on the locomotive, I aligned the inside end of the pencil line on the riser with the top of its joist, and re-clamped it in place.
Because all of the other risers were not fixed to the benchwork, the 3/4" plywood roadbed (about 2" wide) flexed torsionally when that centre riser's bottom end was pushed out, but the amount of cant decreased as the distance from the centre riser increased , automatically creating easements into and out of the superelevation. All that was left to do was to lift each riser, in-turn and without changing its newly created angle of deflection, until the inside end of its pencil line was was even with the top of the joist to which it was to be fastened. It's actually easier to do than it is to explain.
doctorwayneIt's actually easier to do than it is to explain.
I think you explained it pretty well! I'm not sure if I want to tilt the piers and towers. I'm worried about them looking 'crooked'. I seem to notice these things more than some folks. Apparently you aren't experiencing that feeling. I will take your input to the Layout Committee and no doubt we will experiment with your approach, but I'm personally leaning (pardon the pun) towards just shimming the track itself. Shimming the ties could create its own problems because the ties won't be sitting tight on the bridges.
What to do? What to do?
Thanks for your input.
I can't seem to find any info on how the real railroads accomplish superelevation on curved bridges which are not ballasted. Ones with ballasted decks use the ballast profile to accomplish it, as they do on such curves located on solid ground.To my instincts, tilting the bridge supports seems like it would better distribute the forces generated by the passing train, but my only connection with engineering is running model trains.On a model railroad, we don't really need to consider such things, but shimming the outer rail is, I think, not the best solution because it doesn't allow an easy and unvarying spiral into and out of the superelevation: where does the superelevation begin and end and where is its peak? I'm not claiming that my method is prototypical (it came to me while I was installing the roadbed when the layout was built....no sitting down with pencil and paper or some non-understandable computer programme, simply a "Say, what if...".).My grades on the curves to which I refer are fairly steep, about 2.8%, and while there's a 45mph speed limit for upbound trains, none but light locomotives or ones with abnormally-short trains can attain such a speed.Downbound trains are restricted to 20 and 25mph for freight and passenger respectively, but I seldom run them that fast.
The superelevation, therefore, is more or less unnoticeable unless you're aware that it exists - in that case, you can see the train and its cars transitioning into and out of it, but it's nothing like running slot cars.
hon30critter Hi Bob: We are doing basically the same thing with the sub roadbed except ours is 3/4" plywood with Homasote on top. However, I hadn't thought of transferring the bridge pattern to cardboard to help calculate the mitering angles. Thanks for that suggestion. Dave
Dave, also for track bending, I cut another piece of plywood to the inside of the arc (tie width) and used this to bend the bridge track. perfect sweeping curve with no kinks or messing with final shape. Pliobond worked best for me to attach.
hon30critter Dave, I found it easier in my case to build the bridge girders flat/ level and would superelevate by shimming the tiesat the girder contact points with styrene. My bridge started straight then eased into the superelevated 42" curve. Also to tilt/ twist the base girder would make it difficult to fit miters, they would by all accounts be slight compound miters if doing so. Fitted small shims to the appropriate ease into superelevatio, then sanded down styrene to fit, glue on girder, painted black then glued down the bridge track. doctorwayne If you want superelevation, displace the base of the centre support (or as close to the centre of the entire span as you can get) towards the outside of the curve. The bridge and track will form their own vertical easements into and out of the curve and you need only support the piers accordingly. Hi Wayne, I have a question regarding your method for superelevation. Are the piers/towers actually built on a slight angle or are they straight up and down? Sorry, I'm not quite getting the picture in my mind. Dave
Dave, I found it easier in my case to build the bridge girders flat/ level and would superelevate by shimming the tiesat the girder contact points with styrene. My bridge started straight then eased into the superelevated 42" curve. Also to tilt/ twist the base girder would make it difficult to fit miters, they would by all accounts be slight compound miters if doing so. Fitted small shims to the appropriate ease into superelevatio, then sanded down styrene to fit, glue on girder, painted black then glued down the bridge track.
doctorwayne If you want superelevation, displace the base of the centre support (or as close to the centre of the entire span as you can get) towards the outside of the curve. The bridge and track will form their own vertical easements into and out of the curve and you need only support the piers accordingly. Hi Wayne, I have a question regarding your method for superelevation. Are the piers/towers actually built on a slight angle or are they straight up and down? Sorry, I'm not quite getting the picture in my mind. Dave
Hi again Bob. Thanks for the pictures.
I'm afraid I'm still being a bit thick in the head. Did you put the shims under the girders so that the girders have the superelevation and the track fits 'flat' on the slightly angled girders? That's how I'm reading it.
hon30critter...Did you put the shims under the girders so that the girders have the superelevation and the track fits 'flat' on the slightly angled girders? That's how I'm reading it....
I interpreted it as the shims being between the top of the girders and the bottom of the outer ends of the ties.
doctorwayneI interpreted it as the shims being between the top of the girders and the bottom of the outer ends of the ties. Wayne
OK, after re-reading Bob's post I understand, finally, that the ties are shimmed, not the girders.
Thanks Wayne,
hon30critter doctorwayne I interpreted it as the shims being between the top of the girders and the bottom of the outer ends of the ties. Wayne OK, after re-reading Bob's post I understand, finally, that the ties are shimmed, not the girders. Thanks Wayne, Dave
doctorwayne I interpreted it as the shims being between the top of the girders and the bottom of the outer ends of the ties. Wayne
Yes that is exactly where I shimmed for the superelevation. My case was tricky though as it eased from straight to the curve. played with small wedges/ shims and clamps until satisfied, then filled in with styrene glued to top of girder just under outboard tie end.
one other note, to anchor the bridge, I allowed the bridge rails to extend past the bridge and on the abutment. Have wood ties/ spline on one end and made spiking easy. The other end is Walther/ Shinohara so replace a few ties with wood to allow spiking to anchor bridge. I anchor all bridges in this fashion, the extended ties and guard rails allow for a rather secure method, but removal is simplifies if nec.
If you're using individual shims (rather than strips of styrene) under the outer ends of the ties, you can use the same "from-the-centre-method" similar to what I used for deflecting the bottom of the risers: if all of the curve is on the bridge, or if it extends past one or both ends of the bridge, determine the mid-point of the total curve and add a shim of suitable thickness there to give you the effect you're seeking. Because the rail, without a train atop it, is fairly stiff, it will decrease in height as the distance from that first shim increases, and should do so at a fairly constant rate. Pick a frequency, perhaps every fifth tie, or whatever seems practical, to add shims suited to the gap that's showing at those points. With strip styrene available in .010" increments of thickness, you can then maintain the easement into- and out of- the superelevation that's been naturally created by the flex track and that single, centred, shim.
Thanks Bob and Wayne!
The fog in my brain is clearing! I'm looking forward to the challenge.
I'm going to try to recruit a couple of guys to help build the towers and the girders. One member has already expressed an interest.
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