Not too hard, I think

Well, I wouldn't generally recommend the use of 18" radius curves, but if that's what you want or need, who am I to say you shouldn't?

The idea is fairly simple.  The girders themselves should be straight, and if you have multiple spans they should be centered beneath the curve.  The girders on the outside should be longer than those on the inside, unless the bridge is one or two spans at most.

You can use commercial girders and space them a little wider, or make your own if you're comfortable with scratchbuilding or kitbashing.

Sorry I can't be any more help, but hopefully that will at least get you started.

I believe this is a 24 or 26

It was bashed from Micro Engineering kits..

Interesting you post this......

I have an ME tall steel viaduct that I would like to build in a curved configuration. It's the 210 ft. long model and therein lies my problem. The instructions show trim amounts and span angles to build the 150 foot long one down to 18" radius. However they have blank spaces in those columns for the 210 ft. model until you get up to a 30" radius. My curves are 22" radius so I've been kind of puzzled if I could even uses this kit where I wanted at all. The geometry might be messed up for a such a long bridge on a tight curve.  I've been toying with the idea of just scratching a curved wooden trestle and using the ME somewhere else or keeping it stored for future use but that's time consuming and the layout is already overwhelming me with stuff I need and want to do.

18" R...ugh

Ken, I know what yer sayin'. Unfortunately, my situation won't allow for larger, as I limited to a 2' wide shelf. (Trust me, it's killing the trackplan too.) I do understand the segments have to be straight (curved bridge is a misnomer). I've never tried a scratchbuilt bridge before, so I plan to keep it as short as possible. It's a branch line passing over a small stream, just before it gets to a junction with the mainline.

Here is a deck girder bridge

Here is a deck girder bridge "set", on an old UP branchline in Eastern Oregon.

http://img.photobucket.com/albums/v143/Stottman/6b79fc10.jpg

http://img.photobucket.com/albums/v143/Stottman/3ddd893d.jpg

http://img.photobucket.com/albums/v143/Stottman/1d552276.jpg

http://img.photobucket.com/albums/v143/Stottman/e16afcd5.jpg

http://img.photobucket.com/albums/v143/Stottman/fb5c3285.jpg

I measured both girders of this bridge-

They are the same length. 

Basically, the piers are at an angle;The abutments also start at an angle. There are small gaps in between each bride. Naturally, the gap is larger on the outside of the curve, then on the inside.

don't do it....

Okay,

I have to chime in on this because I saw a very tight radius bridge at a train show recently. While the bridge was well done, I would have to say the unions would tell the railroad they are crazy to ask the crews to run over such a structure. 

We all know that 18" radius is rather unprototypical except maybe for a tight urban area. The bridge just looked dangerous. It was tall and spindly and it just over accented the tight radius.  It looked like even a SW1500 would launch off of it with any speed.

Well, due to the position of

Well, due to the position of the overheard light in the garage, I am forced to change the trackplan anyway, so this topic is now moot. Thanks for all the input.

TAG

Thumbs up

Nice photos, Stottman. Looks like the line that ran out to Burns and Hines.

Yes, thats it.    Makes a

Yes, thats it. 

Makes a nice hike now.