Nominal flexural strength accounts for the moment gradient via C_b. Equation depends on whether the unbraced length L_b falls below L_p (plastic), between L_p and L_r (inelastic LTB), or above L_r (elastic LTB).
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Open Steel Section DesignEditorial paraphrase for fast lookup — the official AISC 360 text is authoritative. For exact wording, refer to the published code.