I am building an elevated viaduct with double track 36" curve. In the area I have marked up on the photo I plan to run a 4 lane highway under. It has to be this height because I am using Walther's retaining wall to cover the gap as it goes around the curve to the left. In the backdrop the highway disappears via a tunnel portal (there's really like a foot and a half back there so plenty of room), so I don't want to obscure it with a truss bridge. This leaves a through plate girder bridge to provide clearance underneath for the highway. I've figured out the side obstacle clearance and track spacing using NMRA RP-7 tables. And I've added width to account for the curve. Most of the double track through plate kits I've seen are usually two singles stacked together, i.e. a third plate girder down the middle. So now I am adding even more track spacing and obstacle clearance so the 85 ft Superliner cars not only don't hit the sides, but they dont hit this center beam. Am I on the right track or do prototypes eliminate the center plate girder and beef up the height of the outer two?
Girders gain capacity through the height of the web. If you want to eliminate the center girder (and it isn't clear that you actually need, or want, one...), then from an engineering and materials standpoint, you'll need deeper webs. Fortunately, in our hobby, we allow ourselves license. We can fudge the 'engineering' and do what seems practical, and what looks good (that's usually important as well). If that means shrinking the girder depth a bit, so be it.
Remember, also, that span matters. Why not a combination bridge? Have a truss closest to the operator, but use a shorter girder span nearest the backdrop.
Welcome Chris, no photo showing, go the General Discussion forum, at the top, is a post from Steve O. on how to post pictures.
I think Selector has you covered on your question.
Mike.
My You Tube
Welcome to the forums, Chris.
Your first posts are moderated, so there may be a delay when you post things.
Please keep us up-to-date on your progress. Also, we all love pictures.
York1 John
Yeah, I knew I left that off. When I did the post, I thought I insert a button to add a photo. But I got busy typing, and hit Submit before I remembered I forgot to add the photo. Then since the moderator hadn't reviewed it yet, I wasn't able to edit it and it was getting late so I went to bed. My apologies for wasting everyones time without the photo posted. Thanks for the tip. I see the Insert icon here, maybe I'll try both.
Thanks, I actually have that book! Bought it many years ago and like a lot of 'em it sat on the shelf. Comin' in handy now, and it has lots of great details, but it doesn't say anything about whether the center plate girder can be removed.
Yes great answer by Selector, thanks all for the quick reply despite my unhelpfulness by not getting the photos up sooner!
Henry
COB Potomac & Northern
Shenandoah Valley
Thanks for the advice, I think I'll do that. Increase the web height a couple sizes from what is shown on the Central Valley/Walthers kit and call it good. Being an actual mechanical engineer by degree, I need to remember not to overthink my hobby too much! My 1-2 lb locomotive is probably not gonna collapse my bridge. Plus I'll put a support portal in between inbound/outbound lanes of the highway.