Richard. Thanks for sharing. Sounds like a great project you got ahead of you. Feel free to post a picture of your 4x6 HO layout if you wish.
To answer your question I did not have any problems with the foam Transformations from flat to grade. In fact the foam made its own easement doing so. When I started the grade I put one of these 2 1/2" engineering screws in on the flat then put my first 1/8" riser 8 inches away for the beginning easement. Then my risers are 6" on center 1/8" higher every 6" to achieve my 2% grade. I put one of these engineering screws on every other riser by hand with a screwdriver. They have backwards threads on the top so they push the foam tight into the glue. The process worked really well I suppose I could have took the screws out after the glue dried but I just left them in.
The bridge I need to build in this area is a combination of kitbashed and scratch built. The blueprints for all my bridges are written on my poster board cookie cutter paper cut-out. I can refer to and place over the foam when I’m ready to build another bridge.
I decided to get a jump on winter and start stenciling out the design for my forth bridge of my eight.
I like to mock up cardstock to get a view of what things will look like before I start the build.
The center rectangle will be a scratch-built bowstring truss Bridge. The parallelograms on either side will be kitbashed girder Bridges. The dotted line on the cork is how far I have to move the center line of the cork over to have outside radius clearance for my Bridge supports. I’m glad I used Alex plus caulk that was suggested before on this forum. It does release well if you change your mind.
This bridge is going to take a while but I have nothing to do a lot of the time in the winter and all day to do it.
The card stock mock-up for my next bridge was incorrect. I referenced my 4’x8’ cookie cutter poster board cut out. The correct one looks like this.
This is the rough draft of the next bridge I wish to build.
This is the stencil drawing I made with a few changes. I went with diagram A. I put it on quarter inch foam with a layer of wax paper over it. I then T-pin styrene (sandwich style) to the stencil drawing during the build.
My last bridge had 90 gusset plates. This new bridge would demand 190.
This isn’t happening. I cannot get myself to do that again. Two times as many, … I don’t think so!
I had to come up with a design for a bridge that requires no gusset plates and still remains somewhat prototypical.
A design good enough to satisfy my thinking. I’ll have to flip the (My bridge my rules card).
That design looks like this. It’s a deep well C channel on top that has 20 inches, plenty of room for rivets. It has two shallow well C channels on the bottom with plenty of room for rivets. The center is an H Channel.
The plan is to start building this bridge next Sunday.
Take care.
Track fiddler
Edit Please excuse me as I post from my phone. Its kind of tough to do and I always have to go back and make corrections.
I would like to comment about the bridge sketch shown just above. First of all, I totally understand the need to make compromises on a model railroad, and that sometimes visual “tricks” need to be employed. As a professional civil engineer, I would like to respectfully offer a couple comments regarding prototype truss bridge design:
Although you can conceivably build a “model” bridge that represents a chorded structure as you have shown, in real life a truss bridge is inherently a very rigid structure. During the days when these bridges were commonly built we did not have access to the computer programs of today that can analyze quickly all the (moving=live) load scenarios. They were designed often by graphical methods, where from a chart, for a given axle loading, certain “rules of thumb” were applied to arrive at the most economical members and configuration. In classical structural analysis, as employed for at least much of the 20th century, a truss can be analyzed by hand for a given, static (not moving) loading condition, but the analysis would have to be repeated a large number of times to find the worst condition for each member of the bridge, because the worst condition for each member would occur at different times, as the simulated load moved across the bridge.
In the prototype condition, steel truss bridges, especially a more complex one such as the one illustrated in your sketch are almost always built in a straight line, tangent condition. To put kinks, or chords, or horizontal curvature into a truss bridge itself (track positions on bridges were allowed to vary) is almost unheard of in real life. Your sketch implies varying member dimensions that may result in a “normal” appearance when viewed from the side, but these dimensions would produce torsional (twisting) stresses in real life in what is otherwise a very rigid, "fracture cr
One solution that is actually employed by current day engineers would be to construct a tangent span truss bridge extra wide and just allow the track to curve across the bridge. Then you can maintain the aesthetic look you are going for without having to shift your track alignment nearly as much.
This is commonly done on highway bridges today where the road is in a long horizontal curve but we do not want to build the bridge itself with a curve. Often the roadway shoulder will be constructed extra width on the bridge so that a relatively smooth curved path along the highway is maintained. Most motorists never even notice the slight adjustment to a wider bridge shoulder width.
Some design professionals argue that we are “big boys (or girls)” now and should just sharpen our pencils to design more curved bridges. However, in actual practice today, horizontally curved bridges are still avoided wherever possible. Sure–with special training and really cool software engineers can design beautiful curved girder structures–but those more complex mathematical solution bridges all come at a price, that is not cheap, and they take considerably more effort to design and get approved (ie loss of time and money). So they only get used when there is no other “reasonable and prudent” alternative.
What’s really amazing is how well built early bridges are, despite all calculations having to be done by hand, before computerized finite element analysis came into commonplace. But today - there are at least TWO computer ‘games’ I know about that present yoou with an obstacle to cross and a limited set of material from which to build a bridge, and then it ‘tests’ your design with live load analysis! And they are FREE!
However, there is a difference between “free” and “acceptable to your local state DOT”.
By federal law, all public use bridges in the U.S. must be inspected every two years, and significant bridges, commonly interpreted as any river bridges, every single year, at least in the eastern U.S. The inspectors are looking for any cracks at all, difficult to see in steel bridges, which must then be photographed, measured, tested with dye penetrant to see how far they actually go, radiographed, etc. etc. Additionally, areas of section loss due to rust are measured after the loose rust is removed. Back in the office, the engineering staff is required to perform an updated structural analysis that takes into account any section loss of members due to rust. Then periodic “In Depth” bridge inspection and analysis reports are prepared and submitted to the local DOT or other governing/owning body. These reports detail all deficiencies and proposed corrective measures, along with cost to repair.
All this is done to prevent catastrophic bridge failures under traffic–and yet we cannot completely eliminate catastrophic failures–often they are a result of human error like a barge hitting a bridge pier.
Many of the existing truss bridges were conservatively designed, and are a
John. I would like to thank you for your reply. I appreciate you taking time out of your schedule dealing with real Bridges and sharing your knowledge relating to my model Bridge. Nice!
I am not at all offended or discouraged as I found your information very informative and interesting.
I’m kind of learning maybe having a carpenter design a steel truss bridge is kind of like giving a monkey a hand grenade. Lol. In my design I mixed a bowstring truss Bridge with a pratt truss Bridge. I’m sure you can see that. I guess cosmetically pleasing to the eye is not always practical in the real world is what I learned from you.
From what I gathered from your information my bridge design probably would work for a pedestrian or bike bridge over a highway, but certainly not at bridge for a locomotive coal drag.
What’s even funnier is if you look at my radius going over the sections of my bridge design in my stencil drawing. It’s way out of Center. I was completely dumbfounded and kept running back and forth from my workbench to the layout wondering why the mock-up was perfectly centered on my layout but not on my drawing.
I found the answer later it was a mistake of overlooking common sense. I separated my bridge sections by 5/8 in my stencil drawing. A total of an inch and a quarter which scales out to 30 feet in N scale. A Far Cry from a 1/8 inch mistake.
I think I will go back to the drawing board which is just fine, I enjoy drawing. I think I’m just going to put together three Pratt truss bridges.
Here’s a better view of the double Warren truss Bridge. I think this view will make a nice scene someday when it’s finished. Don’t you guys just love S curves.
I presume that you are going to put some sort of vertical support between the two spans and have just not got around to it yet, correct?
Yes.
I just figure it’ll be easier to put the scenery and ballast in first and Bridge supports later.
The series of girders that form a curved bridge somewhere in this thread will need a couple supports later as well.
Btw - My whole layout top is pink foam. I used Liquid Nails to glue down the track to the foam.
Another solution to the curved bridge:
Put a little space between the tracks below and put in pier(s) as able to fit. Then you can have 2 or 3 simple Pratt truss spans, or whatever you like.
I realized that mistake a while ago and still haven’t moved the cork. When I laid the cork under this future Bridge I didn’t reference my template and put the cork to close together.
I dug up one of my posts earlier in this thread when I had realized what I did wrong.
I think now I’m going to wait until I get the model bridge built. After that, while the bridge is still removable I’ll know exactly where to move the cork. I think that would be best. I would hate to have to move it twice.
Good sugestion. Railroads prefer simple straight spans. Long curved bridges would usually be made of a series straight spans with piers at each end of each span. They leave the fancy stuff to the Highway Dept.
I tried to be funny with the Stonehenge comment by inserting Spinal Tap’s “Stonehenge,” but it wouldn’t work. Even if it looks like Stonehenge, your risers and work are very well done.
Spinal tap… yeah yeah. I do somewhat remember that one now. Wasn’t that the one where the dude with the electric guitar was showing how the amp went up to 11 instead of 10 and that was way way better. Chuckle chuckle. I hope that was the one, I think I do remember that one now.
