bridge on an incline

[bogp40]

This ME viaduct is on a 1.25%, it curves into a 54" superelevated radius.

The slope is barely noticable. The easment into the radius and superelevation may mask some slope.

[dante]

A couple of days ago, I happened to drive over a highway truss bridge that slopes slightly.  The verticals are perpendicular to the sloped roadway (and the bottom chord of the trusses); they are not plumb.

[twhite]

My Deer Creek Viaduct is a rather long (5-1/2') combination of two Microscale Tall Viaduct kits on a 34" curve and also on a 2% descending grade.  The bents have been shaved both top and bottom to keep them vertical, while allowing the girders supporting the track to keep the descending grade constant.  This is pretty typical of steel viaducts built in the west on railroads such as the ex-SP Donner Pass line and the ex-WP Feather River line, where the ruling grade is fairly constant.   I also have a double-truss on an ascending 2% grade.  In that case, I just laid the two truss bridges from abutment to abutment, without worrying about the grade 'distorting' the bridge beams. 

Tom  

[ShadowNix]

Having the bridge on an incline is fine as LONG as you have a mild (< 1.5% grade) slope in my opinion.  Below is the bridge I have on an ~1 % grade.  

As stated by others earlier, you have to keep the supports vertical... this means "shimming" the supports so the bridge sits properly... for me, I used different sizes of styren I beams on top of the ME supports...dunno if you can see these on my pic's... it looks fine in person... Good luck.  Just think it through and it should be fine.

Brian

[bsteel4065]

Same thing applies. You would still keep all your trestle uprights true. 

[cacole]

It's unlikely that a narrow guage logging railroad would use a steel bridge -- they would cut trees and make a trestle.

[dante]

In the case of a deck truss, you could set the bottom chord level, the verticals plumb and slope only the top cord carrying the deck.

[bsteel4065]

Hi elcercao

All buildings and bridges and civil engineering works must be built with verticals that are true. The incline of the track bed of the bridge would slope but the vertical supports must still be true and 90 degrees to the horizontal. If the grade is great and the structure itself does not have sufficient height clearance, then the sturcture must be designed in steps to accomodate the train. Even so, the vertical uprights would still have to be at 90 deg to a true horizontal. 

It's the same as brick walls up a hill. The wall gets to a point at which it is too low to be effective and then steps up. Odd looking? If the incline is that severe, yes possibly. Not look right? If the verticals are correct then that's the way it would look in reality.

Hope that helps!

Cheers

Barry

[60YOKID]

I have a Walthers double track bridge near the top of a 2% grade and it looks fine.  I just installed it to the same grade as the track and the easement is another 12 inches up the hill.  Real life bridges are sometimes made of standard girder sections and the like, and are sometimes installed out of plumb. 

I remember well, a large highway bridge over the Mississippi river at Dubuque, Ia where several sections were on a grade.  Very dicey in the winter when ice was often found on the steel open mesh deck!  That bridge looked crooked...and it was! 

[Andrew Falconer]

Both Steel and Wood Bridges would most likely be built on an incline if there is no other solution, from what I am reading. I might need to do that with an ATLAS steel girder bridge. It was not intentional, but one side ended over 1/4" higher than the other.

Andrew

 

[jeffers_mz]

The vertical members of the truss would look very strange to me if they were 3 degrees out of plumb, and you'd have some very strange mechanics going on in there, deck members under tension or compression when they are designed mainly for bending moment etc.

You're either going to have to rebuild the truss from scratch to get the vertical members (kingposts) back plumb or else try another type of bridge. A scratchbuilt trestle is the "one size fits all" answer, and a plate girder which isn't so deep that the vertical stiffeners on the web are noticably out of plumb would probably work too.

[mlehman]

Bridges on inclines? Sure, the Rio Grande and other Colorado roads all had 'em.

Since it is a logging line and narrow gauge, a wooden trestle makes perfect sense. While trestles saw far less use after 1920, they still existed and were installed as replacements for earlier bridges where appropriate and economical. This is particularly so for bridges that were not particularly tall. The Camas Prairie (see: http://www.wwvrailway.com/camas.htm) is one exception to this rule, but I'm sure there are others. I would agree that tall trestles were far less common after 1920, but they certainly did exist, even on heavier, standrad gauge lines.

You may want to try sanding or cutting a bevel to match your grade at the top of each abutment. You want everything in your subroadbed and roadbed to conform to the grade and avoid "stair-steps" so to speak.

I have bridges in grades on both narrow gauge and standard parts of my layout. They all work well, but do take some fitting to get right. The standard gauge one took the most work. Fortunately, I use standard L-girder construction. Eventually, I loosened the riser at one end of the bridge and let it down just enough to take the hump out of it at that end of the bridge. As long as each abutment has a riser that you can adjust, you should eventually be able to get it looking and operating well.
Mike Lehman
Urbana, IL

[selector]

The load vectors are more than 95% down, toward the centre of the Earth, unless you are talking about a grade above 15%, or thereabouts. So one abuttment higher than the other is not only correct, but necessary and sufficient for the purpose. The few
%age points of downhill vector loading at the top of the lower abuttment will be negligible, and the tons of rock and dirt behind that abuttment will easily support your 130 tons of train inside of the space of concern.

[elcercao]

Thank you very much for your answers, but I am afraid my question was too broad.

I had placed a deck truss bridge over a wash, but on the incline it did not look 'real'. And the reason is that the abutments are vertical, although to keep with the 3% incline in the track, one of them is higher that the other. Therefore as I set the bridge in the abutments it keeps the same incline of the track, and one end of the bridge is lower than the other putting a lot more of weight and stress on one end. It does not look right, I am sure this type of bridge would not be choosen for this spot.

In my travels and book research I doon't recall ever seeing a bridge on an incline.

Having thoght about it, I assume this has to do with enegeneering force considerations, and as it is obvious, I am no structural engineer.

This then leads to my questions:

- Are any type of prototypical bridges ever built on an incline?

-From reviewing old "logging railroad " data I think that a trestle might be the only type bridge capable of functioning satistactory on an incline - but I have not been capable to find a specific stratement or example on this situation.

[dgwinup]

When you say "it doesn't look right", what do you mean by that? Does the bridge appear to be out of scale in relation to the scenery? Is the bridge tilted at an odd angle? Are the abutment piers plumb-bob straight or are they perpendicular to the base of the bridge?

Yes to any of those questions could be what doesn't "look" right, especially the last one. Remember, in the real world, things are built with supports that are straight up-and-down. If your bridge model was built with the piers attached, the piers will not be straight up-and-down, they will be tilted to match the angle of the bridge and will "not look right".

A bridge that looks out of scale may actually be out of scale, with heavier girders than you would see on a comparably sized real bridge. Short of re-building it, you could try carefully removing some of the bracing to "lighten" the look of the bridge.

If the bridge appears to be at an odd angle, re-grading the incline may improve the looks. Most bridges are built fairly level. One that is built on an incline may look wrong.

Sometimes, it's hard to describe what "doesn't look right". Everything looks fine until all the parts come together on the layout, then it looks wrong. Maybe posting a picture in your next post would give us some clues as to what may need to be done.

Hope this helps.

Darrell, quiet...for now

[selector]

There is no reason not to put a bridge on a grade if the tracks rise on a grade.. the real railroads do that as they need to. However, you say it doesn't "look right", and I am guessing that your grade is probably more at odds with your ideal than is the bridge that follows it. The bridge only parallels the grade that you put it on, so I think your grade probably needs rethinking more than the bridge.

Depending on the era, a trestle, especially a wooden one, would not have been built after about 1920 or so. Steel trestles and girder bridges were the norm thereafter.

How long, in scale feet, is this logging road bridge to be? Perhaps build retaining wall type abuttments at either end, out of scale 10" X10" creosoted lumber, and use one bent in the middle if the span is across a washout or creek less than 15' across.

[elcercao]

For my HOn3 logging layout I had built a deck truss bridge, but it is on an incline and does not look right. Is a wooden trestle my only other "prototipical' option?
Thanks
Lourdes