I'm analyzing an existing system for fatigue, and part of my system is a sway brace that's diagonally attached to the piping system. For simplicity, let's say it's at a 45 degree angle in the X-Y plane.

I've read the Application Guide for modeling sway braces, but this appears to only be for a brace acting in 1 direction. Is that correct?

I currently have all of the inputs I would need to model the brace, but I'm curious if I would need to include X, X2, Y, and Y2 restraints for my problem. Would this be the correct way to model the brace? Also, would I need to break my spring rate, loadings, and movement into X and Y components for the input?

One other thing I'm a little confused about. My brace is about 20 feet long, so I'd like to account for its inherent flexibility. It appears that the modeling technique in the Application Guide would not account for the brace's flexibility. Is that correct?

You don't need to model two different restraints. Instead apply direction cosines, like this:

X(.7071, .7071, 0.0)

You can do this for the X2 also. Note that if you specify direction cosines the restraint is orientated according to the cosines, and the alpha-label (X in the example above) is ignored except for labeling purposes.

You are correct, the modeling technique does not account for the length of the sway brace. You can model the brace as pipe, with the X and X2 restraints at the midpoint. If you decide to do this, test things out on a very small model so that you understand both the modeling and the behavior.

If your pipe is at an extremely arbitrary angle, it'll be easier to orient it first in one of the primary axes (x,y,z), with the support oriented in one of the primary axes, and then use the rotate tool to place it into the direction that suits your needs.

The command is under Global>Rotate, and also appears on the right side of the screen in default setup.