Re: Photo: Wrecked Freight Cars (Undated)


Dennis Storzek
 

On Sun, Jun 20, 2021 at 10:07 AM, Bob Chaparro wrote:
http://digitalcollections.uwyo.edu/luna/servlet/detail/uwydbuwy~23~23~992579~208256?qvq=q:wreck&mi=123&trs=184
Coming in late here, but this photo is an excellent example of the problems with early steel roofs, and why they were so slow to be adopted. Looking at the wrecked cars in the pile, only one has a steel roof. The cars with the double board roofs are mostly intact, while the one steel roof is completely destroyed; all of the seams between panels have split open. Admittedly, the car has likely endured extreme racking, but wood framed house cars ( and the early steel framed cars with less than optimal stiffness in the roof structure) where known to rack in normal service, termed "weaving" in the trade press of the day. Because of this the sheets of the early steel roofs would loosen from the car, and leak. The initial solution to this problem was to add heavy metal clasps to the edge of the roof, the theory being that this allowed larger screws into the eave, to better hold the sheets in place. The car in the photo has these, two per panel. However, as the photo illustrates, this really was not effective because it didn't address the basic problem.

The next stage of improvement, about WWI, was the "flexible" or "pivoted" metal roof, examples from all three major roof vendors illustrated HERE.
This separated the metal panel from the roof eave with a slip joint, and provided wide wood battens to clamp down the edges of the sheets without restraining their lateral movement. The wood battens were then covered with wide metal seam caps designed to keep the water out of the joints.

The next stage of development, in the twenties, eliminated the wood sheathing and integrated the seam caps with the supporting carlines, while still providing the flexibility required. The Hutchins Dry Lading and Viking roofs are examples., The problem wasn't truely solved until the carbuilders and railroads decided to allow enough material in the roof structure to actually prevent weaving, with the flat riveted roofs as used on the X29 and early ARA steel cars, which were a precursor to the Murphy "Solid Steel" roof.

Dennis Storzek


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