Seok,

Dave has made my point, from the software side. You can do anything you want with the software input, and eventually get a report that satisfies all the design criteria. But then you have to build what you have modeled. That's not always so easy.

The flaw in your plan is that, by imposing a displacement on a rigid support, you are in effect assuming that you have a "smart" rigid support that readjusts itself between the sustained and operating load cases. We have such "smart" supports, that readjust themselves as displacements are imposed, but they're called spring supports. And your avowed goal is to avoid using a spring support.

The problem with rigid supports on piping near pumps is that pump nozzles have thermal growth associated with them, while rigid supports generally are "cold" since they have very little surface contact area with the hot pipe compared to their surface contact area with air. Yes, I know the heat transfer coefficients are miles apart to, but in general they are not considered to be "hot." And they would often expand in the opposite direction from your desires anyway. Most pump nozzles are in the bottom half of the casing, and most pumps are supported so that the shaft centerline remains at a relatively constant elevation. Most rigid supports, if they expanded, would causer the pipe to rise.

There are things you can do analytically. The rigid support usually bears on the bottom of the pipe. It's possible to use Roark (or other general solid mechanics texts or procedures) to estimate a stiffness for the pipe that considers its tendency to ovalize under such a load, but in general (1) the pipe is awfully stiff, and (2) this calculation is highly dependent on the actual wall thickness [try running the calc with nominal wall thickness, then with wall thickness +12.5% and -12.5% and you'll see what I mean].

Usually the best practical solution is to move the rigid support far enough away from the pump nozzle so that the displacement of the pump relative to the support point becomes "insignificant." It's up to you, as the anaalyst, to define "insignificant." Then, to minimize the forces on the pump nozzle, you probably want to reconfigure the geometry of the piping system so that the first support, at its new location, has "sufficient" weight of pipe on the side away from the pump so that the net vertical force on the pump is minimized in both load cases. Again, "sufficient" is your call. That's what we get paid the big bucks for! (LOL)

This is not as difficult as I have made it sound. Usually, if the first pipe support is 4-6 pipe diameters away, the relatively small thermal displacements of the pump nozzle become bearable. And pipe is rigid enough that most of the time, it's not necessary to jump through hoops to balance off the weight loads on the inboard (pump) and outboard (pipe) side of the first support. And usually, models are linear enough that you can predict what the final geometry needs to be as soon as you do two or three runs and one of them is remotely close to being acceptable.