I'm trying to build a bridge accross a double loop and a spur that runs to the coal yard, the height is 4.5 to 5" above the lower track because of the grade loops.I'm wondering what is the maximum height a plate girder bridge could like the one I'm attaching below and how far in between supports would be acceptable. I borrewed the picture from one of our members and thank him for that.
brige elevation
- Thread starter belg
- Start date
The record length is one that passes over a blvd. in Chicago at about a 45 degree angle. It's the USA's longest plate girder bridge at 150'.
Belg, as Robin notes, the NMRA info will help. It is actually the A.R.E.A. prototype engineering standard.
Keep in mind that the prototype RR engineers generally used as many support towers as feasible, in order to cut down on depth of girders, and therefore contain material cost without sacrificing strength.Towers were a lot cheaper than extra-deep girder assemblies.
For example, on a 30 foot span, ( for E70 loading ), they only needed a girder depth of 5'9", but for a 110 foot span, they needed a girder depth of 10 feet !
The prototype freely mixed different sizes and kinds of bridges to cross odd spans, much more so than we tend to do on our model railroads. So they would throw in a short through-girder in a series of deck girder spans, just to provide a specific situational clearance.
It was also common to see two or even several different tower designs in the same structure.
good luck & regards
Mike
Keep in mind that the prototype RR engineers generally used as many support towers as feasible, in order to cut down on depth of girders, and therefore contain material cost without sacrificing strength.Towers were a lot cheaper than extra-deep girder assemblies.
For example, on a 30 foot span, ( for E70 loading ), they only needed a girder depth of 5'9", but for a 110 foot span, they needed a girder depth of 10 feet !
The prototype freely mixed different sizes and kinds of bridges to cross odd spans, much more so than we tend to do on our model railroads. So they would throw in a short through-girder in a series of deck girder spans, just to provide a specific situational clearance.
It was also common to see two or even several different tower designs in the same structure.
good luck & regards
Mike
I read once that one design goal for a bridge is that the cost should be split 50-50 between the supports and the bridge. That would make an interesting study. Even more interesting to apply it to your modelling.
your welcome for that shot, as for that bridge i have removed it from the layout do to a 2nd track on the main line on that part. but it got a new home on the southern end of the layout as the branch line runs out of the mountans and joins the main line