Bridge Rails on a Grade


GandG_North

GandG_North

Member
Are there any prototypical examples of a bridge on a grade? In other words, a bridge deck that is not level. I have a spot on my layout where I'd like to lower one end of a bridge (really, a series of bridges connected end to end) to resolve a problem, but not sure a bridge in this condition would be a "normal" thing.
The problem I'm running into is that at the apex of a graded section of rail to where the grade levels out and connects to the bridge is such that it creates a hump that can cause a hang-up, plus it doesn't look natural when a train passes over, so I think I could resolve this by lowering the grade slightly.
 
All railroad tracks, except for in yards and the very odd place on the planet, are on a grade. Even if the grade is only 0.15%, the maximum grade that most companies permit in their switching yards, it's still a grade. Almost every bridge on the planet is on a grade, highway or rail, because that's what it takes to attain elevations from point to point. Of course there are many exceptions, but generally nothing is completely level or flat where we move on wheels.

The hump you describe, and I hope you won't take this personally, it's just an unfortunate truth for almost all of us, comes down to poor planning or poor construction, more likely a bit of both. I don't make perfect grades or transitions into and out of them, but I have gotten better over the years. Your solution, if I understand you correctly, it to redo the approaches on either side of the bridge, or build up the bridge deck or its supports so that the grade is considerably smoother. An alternative is to generate an 8" or longer transition vertical curve to the bridge deck. Use a surform file or a palm sander and generate a more gentle curve to the bridge deck, and adjust the footings/supports/abutment of the bridge to make the joint there smooth. There's simply nothing else for it.
 
Sounds like he wants to totally alleviate the hump by bringing the bridge end down and thus having a “straight” shot albeit on a slight grade…. Obviously this is done on roadways, not sure about rail bridges
 
You said it better than I did, Topherisme, and that's exactly what I'd like to do. It'll amount to about 1/4" over a section of bridges that span about 24"-30". I don't know if that'll even be noticeable, but I think it will be. So yes, I'm not sure this type of bridge would be built with one end lower than the other. 1/4" may be more like an 1/8".
Here's my hump. This is from my layout I started 40 years ago from a published Atlas track plan, the infamous Granite Gorge and Northern, just getting back to it and actually ran a loco through the loops for the very first time ever just a few days ago. This is the first time I've had this section of bridges installed. I've already sanded the cork roadbed down, and it has eliminated the hangups, but like I mentioned, it still is a little unsightly when a loco runs over it. I haven't run a train over it yet, just a loco. I'm working on rolling stock now, I hope to have a few cars ready to run today, after I work out changing the couplers. Still a noob.
I can't lower the other end, too much going on there. I'll have to shave the bridge pier down, no biggie. I intend in the future to build a more prototypical abutment. I've had that Atlas bridge pier for 40 years, it means a lot to me. haha
I need to improve my lighting skills, too.
And yeah, that's a piece of Atlas track sections, the brass pieces they used to sell as an assortment of short track sections. Maybe they still do. That rail stop to the left of the pier is brass rail. There's a few sections scattered through the layout, which I intend to replace with flex track.
Thanks for the help, guys and gals.
hump.JPG
 
In your case maybe dropping the bridge would be better than making the track leading in it any steeper, unless that wrecks your clearance for the ground track.

I was in the middle of suggesting raising the grade leading up to the bridge, but looks like it is already pretty steep. However, if you back up a ways and ad 1/8" or 1/16" shims for a few feet leading up to the bridge may be easier and look ok.

I was also adding that I don't use a level other than my eyeball. The legs of my table are all the same length so that starting point is going to be close enough for me. Others may be more particular but I like variation in elevation on the layout so that means there will be ups and downs.
 
I can't remember where I read this, but I swear some years ago I read that Southern Pacific's massive Benicia-Martinez Bridge, completed in 1930 in the northern part of San Francisco Bay, is on a slight grade. I don't know if it's humped in the middle or an overall grade, but the article describing it mentioned heavy freights back in the day sometimes needing helpers to cross the bridge.

As others have suggested, I would probably start by adjusting the approach end with shims or other adjustments if you can, but even if you do have to put the bridge itself on grade, I think it'll still look fine. I doubt you'll have visitors over looking at your layout and saying, "Hey wait a minute! Is your bridge ON A GRADE?"
 
Judging by the image you have provided, there is no way to achieve your aim. You'll have to make the bridge rise at approximately the same rate as the ramp end. At the far end, begin the curve downward from an at-grade abutment and joining of the far side tracks. IOW, you don't have a rubber bridge deck; so you cant get it to bend. The only recourse is to raise the far end of the bridge until the approach rails and the bridge deck are within 0.25% of each other. If this were a meet on a curve, a curve right up to the bridge deck, you'd have to meet it perfectly at grade.

...or, lower the ramp...by about 1.5%.
 
Bridges on a grade: this one is 2.2%, probably compensated.
https://flic.kr/p/oDa2x3
In 4 more turns, this helper set will cross another large trestle on a turn on a grade as they continue home to Helena.

One of my first big railfan adventures included this spot. 45,000 hp in the form of a collection of 14 SD45s, SD40-2s, SD45-2s lifting a 110 car grain train over the summit has been ringing in my ears for a long time. Not so much that you heard it as felt it.
 
This scene was on my third layout. I laid a straight edge across the cut-out ends of the roadbed, and then lifted the bridge up into place from below. When the deck met grade, I marked on the abutments where they had to be to hold the bridge deck at grade.

index.php


This is a prototype's bridge on the White Pass & Yukon Route in AK. It's not quite evident, but the grade is 3%.

index.php


On my second layout, a hand-made trestle o a 2% grade:

index.php
 
You must log in or register to reply here.



Back
Top