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 2026-07-31 (calculation changelog) · fixture-verified on every build — most recently 2026-09-14.

Built and fixture-verified by Matthew Norris, P.E. — active P.E. licensure in Arizona, California, Kansas, Missouri, North Carolina, Texas.

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 inputs — typed from your governing edition, or autofilled on paid tiers from the embedded datasets enumerated there, always cited by standard, edition, table and line. Where a page does reproduce specific ASME data (the B16.5 ratings, the quick-reference tables), it 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 data firewall by design, and it also happens to match how the check gets used. A_g, r, Z, F_y and E are entered by you from the section you actually have, and the calculator applies the AISC 360 equations to whatever properties you give it, embedding no shapes table of its own. That posture costs you a lookup when the member is a standard rolled shape — and buys you a check that works on the members no table covers: built-up sections, vendor pipe-support products with published properties but no Manual entry, and existing steel identified in the field from measured dimensions. When you want the full shapes database driving the same arithmetic, PiperSTR carries 1,506 AISC shapes transcribed from the freely published Shapes Database v16.0 and runs this member check as one stage of the whole support load path. Either way, record where the section properties came from on the calculation sheet — the check is only as auditable as its inputs.

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 — in AISC 360 the 200 figure is a User Note recommendation rather than a strength provision, which is exactly why the tool warns instead of refusing. Treat a nominal pass up there with suspicion for physical reasons: elastic buckling stress falls with the square of slenderness, so at KL/r = 220 the member is hanging onto a few ksi of capacity and everything the calculation ignores — incidental moment from connection eccentricity, a bump during erection, vibration from the line it supports — is proportionally enormous against that margin. The fixes are geometric, in the usual order of cheapness: add a brace point to cut KL, orient the section so the weak-axis r works harder, or step up to a section with more radius of gyration rather than more area. The warning stays on the report either way, so the disposition is visible to the reviewer.

Related calculators & tools

• 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
• PiperSTR — pipe support structural design (Ultimate) — The same member check run as one stage of the whole support load path