A steel pad supporting heavy machinery rests on four short, hollow, cast iron piers. The ultimate strength

Question:

A steel pad supporting heavy machinery rests on four short, hollow, cast iron piers. The ultimate strength of the cast iron in compression is 50 ksi. The outer diameter of the piers is d = 4.5 in., and the wall thickness is t = 0.40 in. Using a factor of safety of 3.5 with respect to the ultimate strength, determine the total load P that can be supported by the pad.