I am designing steel supports for piping using LRFD code. The loads on the supports are taken from Autopipe.
The question is what load cases to take from Autopipe and how accurately make the loading in Staad.
A pipe is supported by spring support+guide.
What is correct to do:
1) To take the worst case between GT & G from autopipe and place it as a dead load in Staad + to take the seismic loads from autopipe and place it under seismic case in Staad. To build combinations as per the LRFD code and analyze. Please note that i didn't add any seismic definitions in Staad, and didn't add any joint weights, just the seismic loads from autopipe.
2)To take the worst case between GT & G from autopipe and place it as a dead load in Staad. To define seismic data with joint weight=force of the spring supports, add the seismic cases and analyze as per LRFD combinations.
I am not sure regarding the joint weight. If i take the seismic loads from autopipe "as is", do i need to add joint weights - can i assume that spring supports loading is like a mass at a point?
There is one advantage with the second method.
For a seismic analysis, the period of the structure has to be calculated. This is influenced by the weights which are resting on the structure. Method 2 offers a way to specify the weights, and the program would use those for the period calculation, something which cannot be done with method 1.
Thank you SkLose.
I am still not sure about the both methods.
As I described in the example, I have spring support & a guide support at one point. The seismic loads from auto pipe based not only on the vertical load at spring support, but on all the piping weight + forces that in the system. I mean that if i define in staad joint weight only as the vertical load from the spring support, it won't take into account the other forces in the system during earth quake, and in addition there are also forces from the guide support during earthquake which I think I should add to the seismic case in staad.
In addition is it right to define the vertical load from the spring support as a mass at a point?