October 23, 2010

Haupt's Military Bridge W Trestles

 In looking at photos of many wooden trestles from the Civil War I have concluded the majority were built in the usual manner with the vertical posts under the rail stringers( See photo below). However, Haupt, in his book Military Bridges, expounds the virtues of the "W" trestle (see my earlier post here).  Yet, I had a hard time finding examples of Haupt's design in practice.

A USMRR trestle on the City point line built with
the usual design of vertical posts under the rail stringers.
In looking at photos from the Chatanooga area I finally spotted a couple of decent photos showing this type of trestle. The two photos below were taken on two different trestles on the Tennessee and Alabama Railroad in Maury County, TN. The USMRR rebuilt these bridges after the Confederates burned the originals.

Both bridges show similar construction techniques. They use finished lumber instead of raw logs. The ties are relatively thin boards and not normal thickness ties.

The bridges include a curious feature- sections of timber under the stringers where piers rest. The timber sections do not form a complete stringer and I wonder what purpose they serve. Since they appear on both bridges, I assume they are intentional design items and not field changes perhaps added to raise the grade to allow standard bents to be used in a slightly deeper location.  These extra pieces are not included in Haupt's drawing.

With all the variation in field installations, following a standard drawing is probably not the best way to get an accurate model. Ideally a modeler would follow a prototype example when building a model trestle. If you pick a spot where no photo documentation exists, like I did at Clairborne trestle, then following the standard drawing is a reasonable fall back approach, but just about anything could be possible.

The Culleaoka Trestle.  Note the details in the lower left showing the piers and bracing at the ground. Also
note that the piers are finished lumber and not raw logs. In spite of Haupt's text, this trestle
has X bracing on most of the visible bents.  
The Harris Trestle shows similar construction details as the Culleaoka Trestle above.  This bridge is
closer to Haupt's drawing, but it has the curious cut timbers between the
piers and stringers.

Military Bridges

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