Wednesday, February 9, 2011

Howe Truss

Photo curtesy
The W&A was known for having many railroad bridges along its 138 mile line. Over Chickamauga Creek alone there were about 12 crossings. Many of these were covered bridges, two of which we have modeled on the "North Branch". If you follow our yahoo site, American Civil War Railroads Historical Society, you may have read references to my layout as the North Brnach. LeBron Matthews operates his version of the W&A and is reffered to as the "South Branch" since he lives in GA.

Period photos, especially along the Tennessee River and Chickamauga Creek, show remains of bridges and some that were rebuilt. Although slight alterations may have existed, I am more interested in the reamins as they are more likely to be most prototypical.

The Howe Truss pictured above, which crosses Chickamauga Creek, is my template for a  bridge I chose to model.

Researching bridge construction was done through photographs primarily. One find was that bridges were made with 30' timber lengths. I estimated (guesstimated) that these bridge sections, in general, were approximately 90'. This offered the opportunity for a bridge model long enough for that dramatic and more authentic appearance. The model below was built to accomodate three 90' sections spanning 270 scale feet.

At this stage the bridge is completed, abutments have been placed and we are now contouring the river's landscape. Brian Kammerer has been working on the backdrop and has included Lookout Mountain, a most prominent land feature distinguishing the Chattanooga area. I will be sure to include photos of Lookout Mtn. in a future posting.

The following photos are described below the picture.

This section on the W&A is positioned just on the outskirt of Chattanooga. The bridge is constructed with mostly bass and spruce with some balsa. Piers will be a styrofoam core wrapped with a new Chooch product, Flex Wall. I was considering carving the foam but this product is dead on for the actual stone.   
Here you can see an error in my modeling of the bridge cross ties. Looking at the period photo these initially appeard to be planks. A thanks to Bernie Kempinski, and my realization on how shadows can be deceiving, I have replaced the planks with standard beams, I believe 8"x8". The pier is this photo is from ARC or AIM (?). I believe someone on our yahoo site mentions this manufacturer in one of his notes as to who manufactures HO piers.

One of the many questions regarding bridge construction was how did engineers join bridge sections. One of my 'senior advisors' and construction engineers, Christopher, while helping me view photos, saw what appears to be a long brace connecting these 90' sections. The piers of course would be placed just below these braces and the section joints.

Stay tuned for more posts as we reach completion.

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