I ran it in Sunday photo fun and now I’m not sure.
My friend, who owns the bridge, writes:
Dave … I would need to defer to Atlas! Its advertising for its bridge
says it based its bridge’s design on a reproduction on a Missouri
Pacific Railroad prototype.
Is the jury still out? According to multiple references I checked, the
Warren truss has no vertical support members. Here is one excerpt: “The
Warren truss is a more common and simple truss bridge than the above 3.
The Warren is a pattern of repeating triangles. It has no vertical
supports as the other bridges and is therefore lighter.”
However, another engineering source depicted a Warren truss bridge that
incorporates vertical supports, and it sure looks like the Atlas design.
Why not punt this up to Atlas, forwarding your link and mine, to seek
resolution? I’m surprised a question has not been raised before this!
It’s a Warren Truss bridge. They sell the same design in HO and N and call it a Warren Truss. The vertical bracing isn’t an issue, the direction of the angled bracing is. Warren Truss is easy to spot as the angles look like … W’s
The only thing I can think of is the specific model goes over a body of water called Pratt or the actual engineer that designed the bridge was named Pratt.
FWIW, Atlas neither knows nor cares. I have been in contact with several of their people, and none could identify it or even work up the gumption to try. Thye rely on their own catalog, and anything beyond that is as foggy as a graveyard on Halloween. In a reply to my inquiry about the origins, an Atlas rep wrote:
“The documents that the bridge was based on only had Missouri Pacific bridge noted.”
I suspect that someone dug up an old set of engineering plans while simply looking for any RR bridge that sould be used. They did a great job of engineering the model from those plan (as you can see by comparing with the prototype pics)! But no one at Atlas is a bridge engineer or knows a Pratt (/\//) from a Warren (///) from some of the more exotic (such as whipple or Pennsylvania), and someone in development at Atlas misread an identification chart somewhere. As Chuck notes, it’s the angles that count.
Thanks for sharing your bridge thoughts and facts. The topic is rather interesting. Too often, modelers just choose a simple girder design or an old fashioned trestle. Nothing wrong with those but there are other options as well out there.
These bridges all started out wood in 19th century but in latter part of that century, iron and then steel replaced the wood, though each type of bridge can still be found in some part of the world today!
As to warren trusses, this is a double portal warren truss bridge. Look at the top cord of the center truss and you will see that it is significantly larger than the top cords on the exterior trusses. It is designed to carry twice the load.
The Atlas double track bridge to be prototypically correct, should have much larger exterior trusses than its single track counterpart. From my observations, the double track Atlas bridge is just the single track Atlas bridge, widened.
