In case the piping and structural design jobs are split between different companies there is always the same classical problem that you are having now.
From my experience one option to solve this problem is to use iteration in load reporting and letting the structural design company about what you are doing.
I guess you know the locations of the support beams and columns, and you can determine vertical support locations of piping. This will give you the opportunuty of reporting possible vertical loads and their locations if you have pipe sizes, thicknesses, contents, insulation/lining type and thickneses etc...
After that report the structural design company will have the opportunuty to priliminary size the beams and columns. They will add wind and seismic loading to the structure at this stage by using the the mass of pipng and the wind area on the structure.
Second, start running preliminary analyses of piping groups to determine locations of the lateral and axial pipe supports. After reporting this the structural company will do second order analysis to finalise the sizes of the beams, columns and braces necessary. Braces need a clash check with piping route at this stage.
Third, your final piping analysis will validate the piping loads that you have forwarded earlier. You need to report the final loads as well. If there is no change the structural analysis is final. Otherwise there will be some minor modifications on the structure to suit the loading.
Of course there will be some communication mishaps during this process. You need to very close to the structural design company or vica versa to eliminate problems.
If you can provide the final piping analysis in early stage, the communication problems can disappear and you can expect the structural and civil design can finish the job earlier. Shorter design process time is the benefit for the companies.
Hope it helps.
Ibrahim Demir