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.
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, [(-D] 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.
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.
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.
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.
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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