AISC 360 Steel Member Check Calculator (ASD) for Pipe-Support Steel

Returns the slenderness KL/r, elastic buckling stress F_e, critical stress F_cr per AISC 360 Chapter E, nominal/allowable axial and flexural capacities P_n/P_c and M_n/M_c, and the governing H1 interaction ratio for a compact, non-slender member under combined axial load and bending — ASD, Ω = 1.67.

Method last updated 2026-07-30 (calculation changelog) · fixture-verified on every build — most recently 2026-07-30.

Checks a single compact, non-slender steel member — a pipe-support leg, dummy leg, trunnion bracket post, or pipe-rack column stub — for combined axial load and bending under ASD, following AISC 360 Chapters E (compression), D (tension), F (flexure) and H (combined forces). Section properties (A_g, r, Z) and material properties (F_y, E) are entered by you from the actual shape and material spec — no AISC shapes database is embedded, so the calculator never guesses which section you have in the field.

Method

Flexural buckling only, compact non-slender section, ASD (Ω = 1.67):

F_e = π²E / (KL/r)² (E3-4)

F_cr = 0.658^(F_y/F_e)·F_y when KL/r ≤ 4.71√(E/F_y) (E3-2)

F_cr = 0.877·F_e otherwise (E3-3)

P_n = F_cr·A_g (compression, E3-1) or F_y·A_g (tension, D2-1)

M_n = F_y·Z (F2-1, plastic yielding only)

P_c = P_n/1.67, M_c = M_n/1.67

H1-1a: P_r/P_c + (8/9)(M_r/M_c) ≤ 1.0 when P_r/P_c ≥ 0.2

H1-1b: P_r/(2P_c) + M_r/M_c ≤ 1.0 when P_r/P_c < 0.2

The axialTension flag switches the axial capacity path from E3 compression buckling to D2 tension yielding — bending capacity and the H1 interaction logic are unchanged either way.

Limitations — what this calculator is not

• Compact, non-slender member with flexural buckling only: slender elements, lateral-torsional buckling (unbraced length beyond Lp), shear, and local buckling are not checked — confirm with a full AISC 360 member check where those govern.
• KL/r > 200 raises a warning but does not block the result — AISC discourages compression members beyond that slenderness; a pass near the limit still needs a second look at bracing.
• No AISC shapes database is embedded — Ag, r, Z, Fy and E are entered by you from the actual section and material spec; verifying you pulled the right properties for the real steel in the field is on you.
• Single member, single load case: this is not a frame or braced-bay stability check (no second-order P-Δ/P-δ amplification) — pair with a proper structural analysis for governing pipe-rack or support-frame load combinations.
• ASD only (Ω = 1.67); no LRFD path.

Worked example — fixture-verified

Pipe-support leg, Ag=5 in², r=1.5 in, Z=6 in³, unbraced length 150 in, K=1.0, Fy=36 ksi, E=29000 ksi, applied Pr=25 kip axial compression and Mr=40 kip·in bending.

Step by step

1. Slenderness: KL/r = 1.0·150/1.5 = 100.
2. Elastic buckling: Fe = π²·29000/100² = 28.62185 ksi.
3. Inelastic-buckling limit: 4.71√(29000/36) = 133.68 > 100, so the inelastic branch governs.
4. Critical stress: Fcr = 0.658^(36/28.62185)·36 = 21.26526 ksi.
5. Capacities: Pn = Fcr·Ag = 21.26526·5 = 106.326 kip; Mn = Fy·Z = 36·6 = 216 kip·in.
6. ASD allowables (Ω=1.67): Pc = 106.326/1.67 = 63.668 kip; Mc = 216/1.67 = 129.341 kip·in.
7. Demand ratio: Pr/Pc = 25/63.668 = 0.393 ≥ 0.2 → H1-1a governs.
8. Interaction: 25/63.668 + (8/9)·(40/129.341) = 0.393 + 0.275 = 0.66756.
9. 0.668 ≤ 1.0 → PASS.

H1-1a governs here because axial demand already exceeds 20% of the allowable axial capacity — checking bending alone against Mc would have understated the demand. Note that Ag, r and Z came from a section table you supplied; the calculator carries no embedded AISC shapes database, so confirming those properties match the actual back-up steel in the field is the modeler's job, not the tool's.

Additional verified cases in this fixture

input:  {"Ag":5,"r":1.5,"Z":6,"L":150,"K":1,"Fy":36,"E":29000,"pApplied":60,"mApplied":20,"axialTension":true}
expect: {"Pn":180,"Pc":107.784,"interaction":0.69412,"equation":"H1-1a"}
tol:    0.001

Sources & citations

• AISC 360 — Specification for Structural Steel Buildings, Chapter E (Compression Members).
• AISC 360 — Specification for Structural Steel Buildings, Chapter D (Tension Members) and Chapter F (Members Subject to Flexure).
• AISC 360 — Specification for Structural Steel Buildings, Chapter H (Members Under Combined Forces).

Per the source & citation policy, allowable-stress and factor table values are user-supplied. Where a page does reproduce specific ASME data (the B16.5 ratings, the quick-reference tables), it does so under ASME authorization and states the source table and conditions inline.

FAQ

Does this replace checking against an actual AISC shape from the Steel Construction Manual?

No — it's a licensing firewall by design. Ag, r, Z, Fy and E are entered by you from the section you actually have (rolled shape, built-up member, or vendor pipe-support product); the calculator applies the AISC 360 equations to whatever properties you give it, but embeds no shapes table of its own.

What happens if KL/r comes out above 200?

The check still runs and reports pass/fail off the H1 interaction, but a warning flags that KL/r exceeds the AISC-recommended slenderness limit for compression members. Treat a nominal 'pass' at that slenderness as a prompt to shorten the unbraced length or add bracing, not as a clean result.

Related calculators

• Variable Spring Hanger Load Variability Calculator — The hanger the checked support steel usually carries
• Pipe Support Spacing Calculator — Maximum Deflection-Limited Span — Sets the load the support member must take
• Pipe Thermal Growth Calculator (in / 100 ft) — Thermal growth drives the moments on support steel