I'm looking for a transparent method of determining allowable loads on tank shell by brackets, for example, a platform support bracket. I'm familiar with a method distributed by a tank mother company (C#!) that's been passed down; it calculates the max allowable moment, as M=1390t^2(6+6BL+(B^2)(L^2)). I'd like to know what's in the coefficient 1390, B=1.285/sqrt(Rt) is also used in API 650 Appendix P. I'm also familiar with a method published by Blodgett (Lincoln Book) that also uses undefined coefficients. Can anyone help me get to the root of the above mentioned methods to determine max shell loads? Can anyone provide a more transparent method, or direction to determine max loads/stresses myself?