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AISC 341-22 Special Concentrically Braced Frame — Brace Capacity Design

§F2.3 expected brace strengths: tension R_yF_yA_g; compression the lesser of R_yF_yA_g and 1.14F_creA_g (F_cre from AISC 360 §E3 with R_yF_y); post-buckling 0.3 × the compression strength. The two capacity cases and, for V / inverted-V pairs, the unbalanced force on the beam. Slenderness L_c/r ≤ 200 (§F2.5b).

Brace

A_g in²

r (buckling axis) in

Brace length, end to end in

Material

F_y ksi

R_y

HSS presets from AISC 341-22 Table A3.2 (v459): A500 Gr B R_y = 1.4, Gr C = 1.3, A1085 = 1.25 — the apparent “1.3 vs 1.4” disagreement between sources was Gr C vs Gr B.

Brace angle from horizontal °

P_u (code-level, optional) kip

Results

L_c/r §F2.5b ≤ 200—

F_e · F_cre ksi—

Expected tension P_t = R_yF_yA_g—

Expected compression P_c—

Post-buckling 0.3P_c—

Design check φP_n (F_y, φ = 0.9)—

§F2.3Case (i): braces in tension at P_t, braces in compression at P_c. Case (ii): tension at P_t, compression at 0.3P_c (post-buckling). Columns, beams and connections are designed for the larger effects.

V / inverted VUnbalanced vertical force on the beam at the brace intersection = (T − C)·sinθ; it is largest in case (ii).

VerifyPublished example (civilbay, HSS 6.875×0.500, F_y 46 ksi, R_y 1.3, L 144 in): F_cre 42.09 ksi, P_c 449.1, P_t 559.7, post-buckling 134.7 kip — all reproduced. Rules unchanged from AISC 341-16 (Dlubal; LADBS correction sheet 2024).

NoteSome references state the post-buckling strength as “1.1R_y × buckling strength” or the slenderness limit as 100 — both incorrect for SCBF (0.3 × and 200).

ScopeBrace forces only. Brace connections, gusset plates, protected zones and width-to-thickness limits for braces (Table D1.1a) are separate checks.

Preliminary calculation tool. Final design requires the full text of the referenced standard (see the sources on this page) and review by a licensed PE.