A few points here.
It looks like you are taking the static equivalent approach. Static seismic loads are usually entered as g loads. That implies using U1, U2 & U3 for the X, Y, & Z shock components. D1, D2 & D3 would be used for the relative displacements of the boundary condtions (e.g. for a system bridging between two structures that are wagging around during the earthquake).
Your comprehensive list of combinations would be unnecessary for linear systems (i.e. no nonlinear restraints). You could isolate the seismic load from the sutained and operating loads. In fact, because of the stress combination offered by most piping codes, you should not evaluate the sustained loads with the seismic loads - instead, add the (unsigned) stresses together (scalar summation).
I cannot offer guidance with what we have here for static seismic analysis of nonlinear support configurations.
I suggest you start small with your load cases to get a good feel of the system response. Once the numbers look "right" then you can run through the wide variety of combinations.
_________________________
Dave Diehl
Previous Topic
Index
