# D1.A.5.3 Flexural Design Strength

The Design Flexural Strength (LRFD), φ_{b}·M_{n}
, and the Allowable Flexural Strength (ASD), M_{n}/Ω_{b}
, are being calculated by the program.

The Nominal Flexural Strength, M_{n}, is determined according to Sections F2 through F12 of unified code specifications, for different types of rolled sections.

Doubly symmetric, I-shaped sections with slender flanges are also checked, as per Section F3 of AISC 360-10.

The Nominal Flexural Strength of a member is determined by the limit states of Yielding (Y), Lateral-Torsional Buckling (LTB), Flange Local Buckling (FLB), Web Local Buckling (WLB), Tension Flange Yielding (TFY), Leg Local Buckling (LLB), and Local Buckling (LB).

The program internally calculates the Lateral-Torsional Buckling Modification Factor (C_{b}) for non-uniform moment diagrams when both ends of the unsupported segment are braced. The purpose of this factor is to account for the influence of the moment gradient on lateral-torsional buckling.

To specify laterally unsupported length, the parameter `UNF` can be used, by default which takes the value of the member length.