Input
Plastic limit; from manual or √(E/Fy) formula.
Inelastic-elastic limit.
BF = (Mp − 0.7·Fy·Sx)/(Lr−Lp).
1.0 = uniform moment.
Results
Plastic Mp = Z·Fy—
Cb—
Region—
Mn (LTB)—
ϕb Mn (LRFD, ϕb=0.9)—
Method
AISC 360 §F2.2 — Cb = 12.5·Mmax / (2.5·Mmax + 3·Ma + 4·Mb + 3·Mc) ≤ 3.0 (absolute values). If Lb ≤ Lp: Mn = Mp = Z·Fy. If Lp < Lb ≤ Lr: Mn = Cb·[Mp − BF·(Lb − Lp)] ≤ Mp. If Lb > Lr: elastic LTB, use full §F2.2 Eq. F2-4 (simplified here as Mn = Cb·Mp·(Lr/Lb)² conservative).