Re: What Do Truss Rods Indicate?

Anthony Thompson <thompson@...>

Dennis Storzek wrote:
Since the couplers have traditionally been mounted below the neutral axis of the sills in North American wood car framing practice, buff (compressive) forces tend to make the cars hump up in the center, putting the truss rods in compression. Since one of the first things budding engineers learn (or should) is that you can't push a rope, the truss rods are worthless in resisting buffing forces.
Draft (tensile) forces, maybe, since they did tie the end sills together, but the draft gear weren't attached to the end sills, but rather to the draft sills, which were bolted and keyed to the center sills. I suppose that transferred some of the force to the end sills, and thus to the truss rods, but the common failure mode was the draft attachments ripping out from between the sills.
I agree. And it's well documented that with the introduction of knuckle couplers, air brakes and thus much longer trains, wood center sills DID fail, often in compression (buff(, which helped overcome the conservatism of old-line mechanical officers who thought you could do most everything with wood. Steel center sills became virtual standards long before all-steel freight cars did.

Tony Thompson Editor, Signature Press, Berkeley, CA
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