New HO layout in design - planning to use at least 2 of Atlas’s bridges - Warren Truss (length = 9 inches) and curved cord (length = 18 inches).
Can anyone advise as to whether these bridges are strong enough to support trains on their own at these spans or is some type of additional support under the bridge roadbed necessary to support trains crossing these bridges?
You should have no trouble using a properly constructed Atlas bridge supported at the ends as intended. I bet these scale out to be as strong as their steel prototypes.
I’ve got both of these bridges, and they work fine. The 18-inch chord bridge has provision for a support in the center, but it’s not really necessary.
Like all Atlas bridges, they are designed to sit perfectly on Atlas bridge piers. However, they work just fine on any other support, too, as long as you fasten them down to limit motion.
Edit - I just put a tape measure at the center point of my Atlas chord bridge and ran 3 locomotives on to it. No noticeable deflection.
Is Atlas going to be there when you have to pick your broken bloodied engineer and fireman out of the creekbed two scale miles downstream?
Is Atlas going to tell their wives and children that daddy’s not coming home ever again?
Get in there and design yourself a truss.
Walk high steel with your piece of a W90 I-beam on your shoulder, your life in the hands everyone else toting a piece of that beam with the winter wind polishing the ice on the three inch stringer under your Wal-Mart workboots.
Inspect every bolt, every weld, every pour on every pier yourself, and make sure every ex-con on the jobsite knows you can outwork them, outfight them, outdrink them, and that the penalty for sloppy work and cut corners is the road home.
It’s the only way to be sure.
I used the Atlas 18" curved chord bridge with a 9" truss bridge on either side of it. Of course you have to put supports where the big bridge and short bridges meet, but otherwise it’s quite strong.
I have to disagree about the strength of the bridges… Or at least qualify the claim. I have a couple of the code 83 Warren Truss bridges on my layout. Problem is that the bridge deck is so thin and flimsy, that if you roll a heavy loco over it, it bends ever-so-slightly under the weight. I have a Bowser 4-8-4, which weighs a ton, and when I run it over the bridge, the lead trucks pop off the track every single time on the “uphill” climb out of the sag. That being said, any diesel can handle it, but heavy, long-wheelbase steamers will give you problems.
Dan:
I had Warren Truss bridges on the last layout I built. Even though I was using Code 100 rail, I didn’t trust the strength of the bridge to withstand my accidently bumping against it. I installed them with brass 1/4" square tubing running underneath the bridges as stringers. Paint them black and no one will notice them. These structures handle a Bowser lead casting PRR T-1 with no problem.
I have both of theses bridges. The 9" WT is no problem. In fact, in my experience all of the 9" variety are very stable. I have also had no issues with the 18" curved chord bridge either. Mine only has supports at the ends though sometimes I think it might be more ethethically pleasing if there were a bridge pier in the middle…then the feeling passes… Structurally it’s not necessary.
To span the same distance for automobile traffic I glued together two 9" plate girder bridges. So far it hasn’t colapsed! Then again is carries no weight. Those HO Scale vehicles are pretty light weight!
Trevor