Re: Wood underframes and truss rods - a few questions

Hi,

Wood is a good compression material but not so good in tension.

The plans for the 14' and 17' 4-wheel cars of the early D&RG, show iron rods for tension. The 4-wheeled flat cars had queen posts and the 4-wheeled box cars did not - just straight tension rods. For short 4-wheeled equipment, the queen post was apparently optional.

When pulling a train, the closer to the locomotive the car is, the more the loading of the tension/truss rods. This is also why there are iron tension rods inside the walls of wood box cars - to take the tension loads.

As one additional thought, the rebar (reinforcing bars) in concrete is for the tension loads. Concrete is like wood in that it will not take much of a tension load.

Doug vV