Im needing to calculate the Zxx and Yxx for 2 shapes. The shapes are an H profile and a + profile however its not the basic profiles im needing but the moment of inertia for the weld profile surrounding them as the theory is they are welded to a vertical metal surface then a load is applied. It is the hatched area of the two attachments which shows it more clearly. I have formula for working out the basic shapes and I had hoped to be able to simply subtract the smaller profile from the larger profile but that doesent appear to work. I can get the answers from Autocad and Inventor but I need to be able to justify how I got my answers and im just not getting anywhere with it. Any help would be appreciated.