Richard -
Sorry ... I now realize how confusing my original post was. Let me see if I can do better this time.
The 3 different ratios can be called performance ratios. The idea is that the closest you can get to 1 without exceeding 1 is the most economical design. The thing is that all 3 ratios must satisfy this requirement for it to work. For the example I posted if I look at thickness of t.g = 0.375 in and using Grade 55 ksi steel (row 3, column 2 in the performance ratios) I can see the requirement is satisfied for Mu/Mr = 0.002 and CSR = 0.944 however for Pu/Pr = 1.077. So this would not work. My goal is to write a routine that can find the first one that satisfies this requirement for all three as this would be the most economical. And then the ultimate goal would be for the routine to return the thickness and grade to me. For my example that would be t.g= 0.438in using 50 ksi steel (row 4, column 1. All of the performance ratios are less than 1.0).
PS ... The example that I posted is poor because I forgot to input a value for Mu.that has any significance. In most instances this will be approx. 500 kip-ft or more.
Thanks for taking the time to respond to me. I really appreciate it.
