Will the exported AutoPIPE information to STAAD include weight and stiffness, as to analyze both mode shapes at the same time?
Please see the the Item #3 answer above for exactly what is exported by AutoPIPE to STAAD.
AutoPIPE's Geometry and loads can be seen in STAAD. However, the piping geometry does not have pipe properties, it is just a graphical representation showing the piping layout. The STAAD structural model is only able to import the support reactions as loads from AutoPIPE. Subsequently one can do a frequency analysis in STAAD in which these imported loads can be considered as masses along with the structural masses. The stiffness of the pipe cannot be considered.
A better option would to be exporting the STAAD structure back to AutoPIPE for a complete dynamic analysis the considers both piping and structure. See following file for workflow scenarios:
C:\ Bentley\ AutoPIPE V8i SELECTseries\ Documents\ PIPELINK_tutorial.pdf
Export Model to STAAD Using PipeLink (*.pipelink)