CFS MEMBER CHECKER
The CFS Member Checker calculates the properties and strength of cold-formed steel studs and tracks. It also gives the coil width for any arbitrary C or U section and the unit weight. This tool also enables any arbitrary member analysis and comprehensive member checks in accordance with AISI S100-16, BS EN 1993-1-3, CSA 136, and AS/NZS 4600.
SCOTTSDALE CONSTRUCTION SYSTEMS
ScotCalc
ENGINEERING TOOLS
CFS Member Calculator v2.20
Profile
Units
Lipped C-channel cross-section. All dimensions are outside-to-outside.
Required coil width
—in
Weight per linear foot
—lb/ft
Approximate starting blank width — see notes below before cutting production stock.
Calculation Breakdown
Web straight portion—
Both flanges (straight portions)—
Both lips (straight portions)—
Bend allowances (4 corners)—
Total developed length—
Notes & assumptions (read before production)
This result is a starting estimate, not a guaranteed blank size. It uses a centerline approximation: the bent corners are treated as if the steel follows an arc along the middle of its own thickness. This is the simplest, most common assumption and is accurate to within roughly ±2–3% for typical cold-formed light-gauge sections.
Why it's not exact.
When steel bends, the inside of the corner compresses and the outside stretches. The layer
that doesn't change length (the neutral axis) actually sits slightly toward the
inside of the bend, not at the centerline. The shift depends on material temper, bend radius
vs. thickness ratio, tooling, and springback — all of which vary shop to shop.
Engineers handle this with a "K-factor"; this calculator hardcodes K = 0.5
(centerline) for simplicity.
Recommended workflow. Use this number to estimate coil stock. Before running production, fabricate one sample part and measure the actual coil width consumed. If the predicted width is off, scale your stock width by the same delta on subsequent runs — it'll be consistent for that material/tooling combination.
Formulas used. Bend allowance per 90° corner: BA = (π/2)(R + t/2). Stud (4 bends): D + 2F + 2L − 8(R+t) + 4·BA. Track (2 bends): D + 2F − 4(R+t) + 2·BA. All linear inputs must use the same units.
More codes coming soon
Gross & effective section properties
Please select a design code from the dropdown above to view section properties and moment strengths.
Typical: 33 ksi (230 MPa) for lighter gauges, 50 ksi (345 MPa) for heavier.
Gross properties
| A | area | — |
| x̄ | centroid from back of web | — |
| Ix | moment of inertia, strong | — |
| Sx | section modulus, strong | — |
| rx | radius of gyration, strong | — |
| Iy | moment of inertia, weak | — |
| Sy | section modulus to lip face | — |
| ry | radius of gyration, weak | — |
Element slenderness (b/t)
| Web | — | — |
| Flange | — | — |
| Lip | — | — |
Effective area (uniform compression at f = Fy)
| Ae | effective area | — |
| Ae/A | section utilization | — |
Effective section moduli & moment strength (simplified, first-yield)
Strong axis (about x)
| Sx,eff | effective section modulus | — |
| Mnx | nominal moment, Sx,eff·Fy | — |
| φMnx | LRFD design (φ = 0.95) | — |
| Mnx/Ω | ASD allowable (Ω = 1.67) | — |
Weak axis (about y, lip in compression)
| Sy,eff | effective section modulus | — |
| Mny | nominal moment, Sy,eff·Fy | — |
| φMny | LRFD design (φ = 0.95) | — |
| Mny/Ω | ASD allowable (Ω = 1.67) | — |
Shear capacity (web shear, governs C / U sections)
| h | web flat depth = D − 2(R + t) | — |
| h/t | web slenderness | — |
| — | shear regime (kv = 5.34, unreinforced web) | — |
| Vn | nominal shear strength, Aw·Fv | — |
| φVn | LRFD design (φv = 0.95) | — |
| Vn/Ω | ASD allowable (Ωv = 1.60) | — |
Compression capacity (length-independent, local-buckling only)
| Ae | effective area (uniform compression at f = Fy) | — |
| Pn | nominal axial strength, Ae·Fy | — |
| φcPn | LRFD design (φc = 0.85) | — |
| Pn/Ωc | ASD allowable (Ωc = 1.80) | — |
The row above is the cross-section yielding / local-buckling limit only. For length-dependent global buckling (flexural & flexural-torsional), see the Member Checks section below.
About these numbers
Gross properties use the centerline (line-element) method (±~1% vs finite-thickness
calcs for typical light-gauge sections); global-buckling constants (xo, ro,
J, Cw) come from sectorial integration along the midline. Effective properties follow
the effective-width method of the selected design code.
Length-dependent buckling and combined actions are checked in the
Member Checks and Interaction Checks sections below.
Member Checks (length-dependent compression & flexure)
Please select a design code from the dropdown above to view length-dependent member checks.
Column buckling (axial compression)
For a singly-symmetric C-channel, only two independent global modes exist: flexural buckling about the strong x-axis (Fex) and coupled flexural-torsional buckling (Fe,ft). Pure weak-axis flexure (Fey) and pure torsion (Fet) cannot occur alone — they are mathematically combined into Fe,ft, so they are shown below as inputs to the coupling formula rather than as separate candidates. The lower of (Fex, Fe,ft) governs.
Effective lengths for flexural buckling about x (strong) and y (weak) axes, and for torsional buckling. Reduce KyLy and KtLt if the member is laterally / torsionally braced (e.g., by sheathing or strap bracing). Enter 0 to suppress buckling about that axis (fully braced).
| xo | centroid→shear-center offset (along x) | — |
| ro | polar radius of gyration about shear center | — |
| J | St. Venant torsion constant | — |
| Cw | warping constant | — |
| Fex | elastic flexural buckling, strong axis | — |
| Fey | elastic weak-axis flexural component (input to Fe,ft) | — |
| Fet | elastic torsional component (input to Fe,ft) | — |
| Fe,ft | coupled flexural-torsional buckling | — |
| Fe | governing elastic buckling stress | — |
| — | governing mode | — |
| λc | column slenderness, √(Fy/Fe) | — |
| Fn | nominal column stress | — |
| Ae(Fn) | effective area at f = Fn | — |
| Pn,g | global nominal, Ae(Fn)·Fn | — |
| φcPn,g | LRFD design (φc = 0.85) | — |
| Pn,g/Ωc | ASD allowable (Ωc = 1.80) | — |
Governing Pn = min(local, global) = — · φcPn = —
Code references & assumptions
Lateral-torsional buckling (beam in flexure)
A beam bent about its strong axis can fail by lateral-torsional buckling (LTB): the compression flange swings sideways while the section twists — one coupled mode, distinct from the column-buckling modes above. Governing flexural strength Mn = min(cross-section Mnx from Step 7, LTB-controlled Mne).
Unbraced length Lb for lateral-torsional buckling of the beam (lateral support of the compression flange). Cb is the moment-gradient modifier — 1.0 for uniform moment (conservative); typical values: 1.14 (simply-supported, uniform load), 1.30 (mid-span point load). Enter 0 for Lb to suppress LTB (fully braced).
| σey | elastic flexural buckling about weak axis (at Lb) | — |
| σt | elastic torsional buckling (at Lb) | — |
| Fcre | elastic LTB stress, (CbroA/Sf)√(σeyσt) | — |
| Mcre | elastic critical LTB moment, Sx·Fcre | — |
| My | first-yield moment, Sx·Fy | — |
| — | LTB regime | — |
| Mne | nominal LTB-controlled moment | — |
| φMne | LRFD design (φ = 0.95) | — |
| Mne/Ω | ASD allowable (Ω = 1.67) | — |
Governing Mnx = min(braced, LTB) = — · φMnx = —
Code references & assumptions
Interaction Checks (factored load effects vs design capacities)
Please select a design code from the dropdown above to view interaction checks.
Enter factored (LRFD / LSD / Eurocode design) load effects to check the member against code-prescribed interaction equations. Each ratio = demand ÷ design capacity; the member passes if every ratio ≤ 1.0. Capacities below come live from the Member Checks section above.
Design method
LRFD: enter factored loads; they are checked against design strengths φRn.
Single-action utilizations
| Action | Demand | Design capacity | Ratio | Status |
|---|---|---|---|---|
| Axial compression | — | — | — | — |
| Flexure, strong axis (governing) | — | — | — | — |
| Flexure, weak axis | — | — | — | — |
| Shear | — | — | — | — |
Combined-action interaction
| Equation | Expression | Ratio | Status |
|---|
Enter factored loads above to check the member.
Code references & assumptions
Download the complete step-by-step calculation report (HTML — opens in any browser; use File > Print > Save as PDF for a PDF copy).
