Got another unusual one for my Forum friends: How did prototype railroads span rivers when the banks were at an angle to the track and they couldn't reshape the banks? I have a recycled section of benchwork from an old layout with a river in it. The river runs at an angle to the track and I am having a challenge bashing a girder bridge to fit the hole. As usual, any help that can be provided would be most welcomed.
I just Googled "skewed railroad bridges" and found lots of pictures.
Mike.
My You Tube
FRRYKid....How did prototype railroads span rivers when the banks were at an angle to the track and they couldn't reshape the banks?....
In some instances, they wouldn't necessarily "reshape the banks", but might create a concrete or masonry abutment on each side of the river, onto which the bridge could be built. The abutments might extend, on an angle, into the river, or one or both might be constructed fully back from the riverbank, but both at 90º to the track, necessitating a somewhat longer bridge than what would be required to merely span the river.
An alternative would be to build a skewed bridge, where the ends of the bridge deck and its support abutments are roughly parallel to the river's banks. Whether it's a truss-type bridge or a girder type, (either type with the trusses or girders above or below the bridge's deck) the supporting trusses or girders, along with the deck, will appear as a parallelogram when viewed from above.
I'm not sure if anyone offers a kit for a skewed bridge, but it shouldn't be too difficult to kitbash from a regular bridge that has sides long enough to span the river. Without going into an actual how-to, both bridge sides are placed on the abutments, parallel to one another, and crossing the river at the needed angle. The bridge's stock floor (or framing for it) is then placed between the two sides, and it will be readily apparent that the stock floor needs to be lengthened on one side at one end, and on the other side at the opposite end. Use either some left-over parts from the kit for this, or get some suitably-sized structural shapes from Evergreen (I-beams, H-columns, channel, etc.) to complete the construction.
Wayne
The larger the river or waterway, the more likely that the bridge abutment will be set back a good distance from the shore, making the exact angle of the crossing unimportant.
As in this bridge abutment here in Havre de Grace MD where the ex PRR crosses the Susquehanna River.
https://images.app.goo.gl/sbgHMvXMS5KGJe6eA
This bridge abutment is about 100' back from the shore line of the river, and you can see the road that crosses under the railroad bridge as well at this point.
Here is a shot of that bridge from the nearby shore:
https://images.app.goo.gl/8tJik1SidU5SEyQT8
I drive that road nearly every day.
Sheldon
You shape your own doing of what you're doing when you build a bridge on your model railroad.
I'm a custom Bridge maniac. No really, I love Bridges. I build them custom for my model railroading needs.
I like Bridges. I just have to make up with my paint
I was told by a civil engineer spanning this spot prototypically would be impossible. I never take no for an answer.
Don't know, just love Bridges
TF
doctorwayne An alternative would be to build a skewed bridge, where the ends of the bridge deck and its support abutments are roughly parallel to the river's banks. Whether it's a truss-type bridge or a girder type, (either type with the trusses or girders above or below the bridge's deck) the supporting trusses or girders, along with the deck, will appear as a parallelogram when viewed from above. I'm not sure if anyone offers a kit for a skewed bridge, but it shouldn't be too difficult to kitbash from a regular bridge that has sides long enough to span the river. Without going into an actual how-to, both bridge sides are placed on the abutments, parallel to one another, and crossing the river at the needed angle. The bridge's stock floor (or framing for it) is then placed between the two sides, and it will be readily apparent that the stock floor needs to be lengthened on one side at one end, and on the other side at the opposite end. Use either some left-over parts from the kit for this, or get some suitably-sized structural shapes from Evergreen (I-beams, H-columns, channel, etc.) to complete the construction. Wayne
The skewed bridge idea was what I was thinking. I am bashing with the sides from an M.E. 30' bridge kit. (They will be shortened by one panel to fit the river.) The instructions indicate that those bridges were always built as rectangles and not as parallelograms. I will have to go through my styrene and see what I have and what I need.
One thing with a skewed bridge is that while the ends are skewed, the interior crossmembers/floorbeams are usually at right angles. So vertical posts in truss bridges should be opposite each other except at the ends, and for plate girder bridges the same applies for the vertical stiffeners.
To avoid the complexity of the end panels on a skewed bridge, the railroads usually preferred to lengthen the bridge slightly so the abutments/piers were at right angles. But roads underneath, piers midstream, or an available second hand span would sometimes force the engineer's hand.
John
cx500 One thing with a skewed bridge is that while the ends are skewed, the interior crossmembers/floorbeams are usually at right angles. So vertical posts in truss bridges should be opposite each other except at the ends, and for plate girder bridges the same applies for the vertical stiffeners.
Oops! I trimmed the panels thinking the angles would offset as well. Thankfully, I have a couple of already assembled bridges that I can raid the side panels from.
cx500 To avoid the complexity of the end panels on a skewed bridge, the railroads usually preferred to lengthen the bridge slightly so the abutments/piers were at right angles. John
To avoid the complexity of the end panels on a skewed bridge, the railroads usually preferred to lengthen the bridge slightly so the abutments/piers were at right angles.
Originally I was planning to have the abutment parallel the river. I will now change that idea as well.
Track fiddlerI was told by a civil engineer spanning this spot prototypically would be impossible.
regardless of the bridge design, there is a upper member that is in compression and a lower member that is in tension. any vertical members hold the upper and lower members in position
As you can imaging, the member is tension will be pulled straight. any deviation from being straight requires additional bracing preventing it from collapsing inward.
in the photo below, i count 8 tall I-beams to distribute the weight and cross bracing betwee the 2 outermost I-beams
i built a simple bridge using foam, a sheet of balse and packing tape with glass fibers. I put the packing tape on the bottom (tension) and the balsa on top (compression). The foam was very stiff in one direction and flappy in the other.
greg - Philadelphia & Reading / Reading
doctorwayne An alternative would be to build a skewed bridge, where the ends of the bridge deck and its support abutments are roughly parallel to the river's banks. Whether it's a truss-type bridge or a girder type, (either type with the trusses or girders above or below the bridge's deck) the supporting trusses or girders, along with the deck, will appear as a parallelogram when viewed from above.
An alternative would be to build a skewed bridge, where the ends of the bridge deck and its support abutments are roughly parallel to the river's banks.
Whether it's a truss-type bridge or a girder type, (either type with the trusses or girders above or below the bridge's deck) the supporting trusses or girders, along with the deck, will appear as a parallelogram when viewed from above.
I took an aerial photo of the PRR vertical lift bridge in Chicago using Google Images. I added red lines to facilitate viewing the angles of the bridge and towers. A pretty good example of a skewed bridge when it runs at an angle to the river below.
Rich
Alton Junction
Track fiddler I was told by a civil engineer spanning this spot prototypically would be impossible. I never take no for an answer.
I think you misunderstood what he said. Spanning that location is easy, I've seeen several locations like that.
Spanning that location with that bridge is "impossible", the bridge would be unstable.
If you substituted plate girders for the trusses, easy, peasy. Stable bridge and it will last 150 years. Through truss of that design would probably collapse with the first train.
Another technique is to build a large "deck" of steel supports, spanning both tracks, then run a track across the deck.
Dave H. Painted side goes up. My website : wnbranch.com
Hehe, yes technically. Truss bridges are never built in an angled fashion that I've ever seen. But this is model railroading! Building on a skew, however, happens all the time.
As another poster noted, the abutments are usually kept parallel with the river banks, although not always. Sometimes abutments will be placed at right angles to the direction of travel across the bridge, even if the bridge is on a skew. That's not as critical as the pier placement in -for example- a bridge crossing water. The smallest footprint for a pier in the water will be one where a pier is parallel to the flow the river. But you'd be surprised; I've seen bridges where the piers are not, or no longer are, parallel to the river flow, as in cases of bridges built long ago where the river course has meandered over the decades.
Fyi, I inspect bridge rehabs and new bridge construction for my job. While not on a skew, here is an old railroad bridge that was raised (for hydraulic reasons) a few years ago that I was the inspector on. (Note: I do not work for Stanley Consultants.)
https://www.stanleyconsultants.com/markets-we-serve/transportation/highways-and-bridges/des-moines-iconic-red-bridge-raised/
And he's another that I inspected when it was rehabbed in 2016:
https://www.desmoinesregister.com/story/news/local/des-moines/2016/11/10/fifth-street-pedestrian-bridge-set-open/93586410/
Andy
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Milwaukee native modeling the Milwaukee Road in 1950's Milwaukee.
https://www.flickr.com/photos/196857529@N03/
Correct. Plate girder bridges can be "curved" by means of multiple straight sections connected together with slight angles at each span.