I need to analyze several piping systems that cross a structural expansion joint and is in a seismic region (I am specifically required to perform a static seismic analysis).

When the building is one structure, I have no problem applying the Uniform Load to the entire system and including the appropriate displacements at the restraints (C-nodes) and building the appropriate load cases for the building moving together. However, the Uniform loads are limited to 3 vectors and I have a single vector assigned to each direction (I use Z for vertical):

UX1=0.171 (positive East)
UY1=0
UZ1=0

UX2=0
UY2=0.171 (positive North)
UZ2=0

UX3=0
UY3=0
UZ3=0.046 (positive vertical)

I have a structural expansion joint running east-west and I would like to segregate the uniform loads and displacements to each half (north and south) so I can analyze a whole piping system and represent building/seismic movements independently (through load cases). Obviously, I want to make sure my piping is supported properly and expansion loops designed properly for the worst cases when each half is going to be moving in opposite directions (compression/tension AND twisting). I would need to be able to add more Uniform Load vectors to accomplish this.

Has anyone come across this before? This "idea" should be able to be applied to piping between buildings, between buildings and highlines, and between highline sections at air gaps.

I appreciate any/all help.

Thanks,
Pat

One possible solution can be:

-define the accelerations as you specified for the part that is in one building:
UX1=0.171 (positive East)
UY1=0
UZ1=0

UX2=0
UY2=0.171 (positive North)
UZ2=0

UX3=0
UY3=0
UZ3=0.046 (positive vertical)

then, for the part that is in the other buildind change as follows:

UX1=-0.171
UY1=0
UZ1=0

UX2=0
UY2=-0.171
UZ2=0

UX3=0
UY3=0
UZ3=-0.046

Then you will have U1 or -U1 in load cases, that will change the sign.

I already use U1 and -U1 in the load cases to represent movement as a whole in the opposite direction. I had thought about this approach, but it gets complicated when I consider movement in all directions instead of limited extreme cases.

For the example you gave, I would be limited to the following combinations:

(Using addition of the Uniform Load in the load case)
Group 1 - North, East, and Up
Group 2 - South, West, and Down
>stretches north-south pipe runs
>twists north-south pipe runs one direction

(using subtraction of the Uniform load in the load case)
Group 1 - South, West, and Down
Group 2 - North, East, and Up
>compresses north-south pipe runs
>twists north-south pipe runs the other direction

This won't allow me to analyze for uniform movement of the whole building unless I copy the file and adjust all the displacements. I know this might sound like overkill, but I don't know where to draw the line. This building has another expansion joint running North-South and we may end up with piping from one system in all four "quadrants" of the building that could move independently.

I think that you should try to split the sistem, using anchors, in such way that you can analyze piping that belong to only two buildings. I presume that what I suggested previously is the worst case scenario, so no need to consider other situation. Do some tests, see what scenario is the worst, then limit the analysis to this. Otherwise you will have to build other files.

Regards,

In addition you can have
U1+U2+U3
U1-U2+U3
-U1+U2+U3
-U1-U2+U3
U1+U2-U3
U1-U2-U3
-U1+U2-U3
-U1-U2-U3

and I think that should be enough