can someone have a look at the spreadsheet attached and tell me if i have calculated Ix and Iy properties correctly. Also how do you calculate plastic modulus?
If your plates are centered than Ad^2 should be 0. You have them calculating out to a number (albeit small).
Also your plate b you've labeled in the diagram as h. And you haven't labeled other variables.
It's good practice (at least when I do spreadsheets) to highlight the cells that will need to be changed... That way you can quickly change the numbers and not accidentally skip a variable that should be changed (thus giving you inaccurate results).
I've found a good plastic modulus section in the past (although it IS hard to find). If i can rediscover that I'll see if I can put something together for you to use.