This is how I start when I want to make something and need to figure how strong something will be. The internet is a great place now to do this. You have to do your homework first to be safe. Can't count how many times I have looked on sites for ways to build stuff better and proper. Save this search in your favorites there is a lifetime of knowledge here to learn from. https://www.google.com/search?q=calculating+lifting+loads+with+box+steel&tbm=isch&tbo=u&source=univ&sa=X&ved=2ahUKEwjk1fzi1InfAhUhL30KHSA2DgcQsAR6BAgDEAE&cshid=1544046384815000&biw=1339&bih=728 I just love looking thru all these sites learning how to do things they never teach you in High School!