Cold-Formed Steel Calculator

Cold-formed steel member design per AISI S100. Local buckling, distortional buckling, and global buckling capacity checks for Cee and Zee sections. Educational use only.

This page documents the scope, inputs, outputs, and computational approach of the Cold-Formed Steel Calculator on steelcalculator.app. The interactive calculator runs in your browser; this documentation ensures the page is useful even without JavaScript.

What this tool is for

Preliminary capacity screening of cold-formed steel (CFS) members under axial, flexural, or combined loading.
Understanding the interaction between local, distortional, and global buckling modes per AISI S100.
Comparing Cee and Zee section sizes for light-gauge framing and purlins.

What this tool is not for

It does not replace detailed CFS design software that handles bracing, bridging, web crippling, and combined bending-and-shear interaction.
It does not cover all section types (hats, tracks, built-up sections, custom profiles).
It does not guarantee compliance with AISI S100 or any other standard.

Key concepts this page covers

effective width method vs. direct strength method (DSM)
local buckling of compressed elements
distortional buckling of flanges and lips
global (flexural, torsional, flexural-torsional) buckling

Inputs and outputs

Typical inputs: section dimensions (web depth, flange width, lip length, thickness), steel yield strength Fy, unbraced length, end conditions, and applied loads.

Typical outputs: nominal and design capacities for flexure and compression, controlling buckling mode, effective section properties, and demand-to-capacity ratios.

Computation approach

The calculator evaluates three buckling limit states (local, distortional, global) using the Direct Strength Method (DSM) from AISI S100. Elastic buckling loads are computed from closed-form or approximate expressions for standard Cee/Zee profiles. The nominal strength is then determined from the DSM strength curves that relate elastic buckling stress to inelastic/post-buckling capacity.

Frequently Asked Questions

What is the difference between hot-rolled and cold-formed steel design? Hot-rolled shapes are thick enough that local buckling of individual plate elements rarely governs. Cold-formed sections have high width-to-thickness ratios, so local and distortional buckling interact with global buckling and often control the capacity. CFS design uses either the effective width method or the direct strength method to account for these thin-plate effects.

What is the Direct Strength Method (DSM)? DSM is an alternative to the effective width method introduced in AISI S100. Instead of computing effective widths for each element, DSM uses the elastic buckling load of the full cross-section (local, distortional, global) and applies strength curves calibrated to test data. It is generally simpler for complex cross-sections and is the preferred method in current editions of AISI S100.

Why does cold-formed steel have three buckling modes instead of one? Thin-walled open sections can buckle locally (plate elements buckle between fold lines), distortionally (the flange-lip assembly rotates about the flange-web junction), or globally (the entire member buckles as a column or beam). Each mode has a different half-wavelength and interacts differently with material yielding, so all three must be checked.

Disclaimer (educational use only)

This page is provided for general technical information and educational use only. It does not constitute professional engineering advice, a design service, or a substitute for an independent review by a qualified structural engineer. Any calculations, outputs, examples, and workflows discussed here are simplified descriptions intended to support understanding and preliminary estimation.

All real-world structural design depends on project-specific factors (loads, combinations, stability, detailing, fabrication, erection, tolerances, site conditions, and the governing standard and project specification). You are responsible for verifying inputs, validating results with an independent method, checking constructability and code compliance, and obtaining professional sign-off where required.

The site operator provides the content "as is" and "as available" without warranties of any kind. To the maximum extent permitted by law, the operator disclaims liability for any loss or damage arising from the use of, or reliance on, this page or any linked tools.