Re: Case of the Missing Truss Rods - Revisited

Posted by Todd Hackett on
URL: http://c-sng-discussion-forum.254.s1.nabble.com/Case-of-the-Missing-Truss-Rods-Revisited-tp6387p6414.html

Jim Courtney wrote

I'm a baby doctor not an engineer, but if the 27 foot UP cars had no truss rods, only two long tension rods running parallel to the center sills, the purpose of the tension rods would have to be to hold the end beams solidly against the various floor sills while under tension, while being pulled in a train (i.e. to keep the ends from being pulled off the car).  

The needle beams (without truss rods) would serve the same function as the strap bolsters, but in the middle of the car -- to keep the various floor sills parallel during compression, while being pushed in a train (i.e. to keep the sides from bowing out when pushed). Only truss rods would prevent longitudinal sag under load from above....

Dr. McCoy, the strap bolsters had lateral rods that served to distribute the weight of the car from all sills to the truck (they sloped up from the side sills and over the bolster to support the side sills) to lift the side sills while the strap and blocking took the inward loads and helped distribute load to the intermediate sills:


Needle beams that did not have support (i.e. didn't sit on trucks and weren't supported by truss rods) wouldn't serve that purpose. To keep the sills parallel and a the correct spacing, they could have used boards similar to needle beams, but it would be more effective to use blocking between the sills mortised into the sills for compression loads (similar to the ones above the strap bolster), and lateral rods running along them (with washers and bolts countersunk into the side sills - no need for sloping rods because no vertical support) to take tensile loads. While I am an engineer, it doesn't mean I understand how they built these things, and they clearly did have the beams.

A few more photos to ponder:



The truss rods are clearly visible in the next car in the train (and the two after it):


At Robinson:


At Buffalo:


Near Fairplay (not a 27-foot car, but I don't see truss rods):


Again, the next car in the train (same photo) has clearly visible truss rods: