When laying the sub roadbed in a “Long tall bridge area” does one leave a narrow plywood base support, to be hidden by the plate girders.
Just trying to prevent problems latter on and have bought a bridge book, but there wasnt much about the structural support.
Going to build two. One is the WP Keddy Wye 26 to 28 inch long. The other a more modern tall truss, thirty two inches long, with concreat supports. It will have a highway on top of it, as like the Highway 70 bridge over Lake Oroville. The train on this bridge comes out of a tunnel(helix), through the enclosed bridge and into another tunnel.
As long as any bridge, viaduct or span is ballast filled it is best to use the subroadbed.
Depending on the length of individual spans/ supports, you can use 1/4, 3/8 or 1/2" plywood. I would not recommend 3/4" unless you are planning large spans with stone or concrete arches- the thicker materials are too much to add plate girders to. I find that quality birch, luan or other cabinet grades of ply are the most stable and usually use 3/8 or 1/2". Depending on the material used for supports, many times the plywood can be glued and screwed directly. Glue your chioce of roadbed and lay track.
If planning a see thru girder steel or wood then it becomes a new ballgame. Walther’s steel viaduct or kitbashing w/ Microenginering giders topped with Central Valley bridge ties is one way for steel. The combinations you can come up with are endless, even going to wood trestle w/ bents and bracing, if it fits the period that you model.
Bob K.
I actually kit bash but is more like scratch building my bridges…I use plastruct beams and evergreen strip styrene to form the bridge supports and hand lay the ties and rails across the tops of the bridge…the only part that is a kit are the deck girder sections which i modify with a razor saw from N scale Atlas deck girder bridge kits…the bridges come out great and are sturdy enough so that the subroadbed is not needed…Kalmbach publications has a book titled “Bridges and Trestles” that explains how to build any kind of bridge known to railroading…it is worth purchasing because the bridges the book will show you how to build will come out a bit more prototype than the ones with the plywood subroad bed built around them…here is a picture of one of the bridges http://community.webshots.com/photo/137793353/185723777qospgM chuck[:D]