I am trying to build a cart for risers that are heavy and unwieldy. The cart is going to be somewhere around 8.5'x3.5' flat bed style. I'm looking to figure out the best way to make the frame for it. I want to use angle steel so steel plate casters can be welded on. I was thinking about using 2"x2"x1/4" angle steel welded at the corners and possible steel square beams underneath welded across. My question is as to whether or not this cart, using .5" plywood as the bed, bolted to the angle steel frame, will hold up to 3,500 pounds. The max load would be 2,800 but I want to account for people screwing around with it or dropping things on it. Does anyone know if this is going to hold such a load? Or if it won't, how I can make it do so?