Looking at AISC 360-10, Appendix 6, 6.3 Beam Bracing (Relative Bracing).
We have equations A-6-5: Prb = 0.008*Mr*Cd/h0
And equation A-6-6: βbr = (1/Φ)*(4*Mr*Cd/Lb*h0).
h0 is defined as the distance between the flange centroids. But what if the beam you are bracing is not a W, S, or HP...