Code of Practice for Use of Cold-Formed Light Gauge Steel Structural Members In General Building Construction
1975 Edition

The basic allowable design stress (F) for cold-formed steel members is determined based on the specified minimum yield strength (Fy) of the unformed steel. When cold working increases steel strength, F may be adjusted using the average yield point of the full section as per Clause 6.1.1. For tension members, stresses on the net section should not exceed F, while for flexural members, tension and compression on the extreme fibers must remain within F. Complex configurations not covered by standard calculations require testing and evaluation according to Clause 9. This applies to carbon and low-alloy cold-formed steels used structurally.

Connections must be designed to safely transfer the maximum member stresses, accounting for eccentricities. For members experiencing stress reversal (excluding wind or earthquake loads), connections should be designed for the cumulative stresses. Bolted connections have specific shear stress limits based on bolt type (e.g., precision bolts max 970 kgf/cm² shear). The spacing of connections in compression elements must not exceed the minimum of shear transmission requirements, a function of plate thickness and design stress, or three times the narrowest unstiffened width with minimum spacing limits. Intermittent fillet welds parallel to stress require spacing equal to clear distance plus 13 mm; otherwise, center-to-center spacing is used.

Bracing is required when neither flange is attached to decking or sheathing to prevent lateral deflection, and when loads act in the web plane. Braces should be fixed to both the top and bottom flanges at ends and at intervals no greater than one-quarter of the span length (L/4). If a concentrated load exceeding one-third of the total load is applied over a length less than or equal to L/12, an additional brace near the center of the loaded region is required. End braces should be designed for half the bracing forces calculated, ensuring no local crippling occurs at attachment points. Maximum compression stresses are calculated using the bracing interval length instead of the full span.

For elements without intermediate stiffeners, flanges are considered fully effective (effective width b equals actual width w) if the width-to-thickness ratio (w/t) is below a limiting value, defined as 1435 divided by the square root of a stress parameter V. Closed square or rectangular tubes have a similar limit of 1540 divided by the square root of V. If w/t exceeds these limits, the effective width is reduced according to formulas specified in the code. When multiple or edge stiffeners are present and w/t is above 60, the effective width is further reduced by an amount proportional to (w - 60t). For short spans less than 30 times the flange projection, effective width ratios are limited as per a table in the standard, with ratios decreasing as the span-to-flange projection ratio decreases.

Tensile yield point is determined as per Clause 9.1.6. Compression yield point tests require short specimens of the full cross-section; the yield point is the lesser of maximum compressive strength divided by cross-sectional area or stress determined via autographic diagrams or strain methods, depending on whether the steel exhibits sharp or gradual yielding characteristics. Bending yield is assessed by testing specimens from flanges plus part of the web with appropriate width ratios. Acceptance testing involves two full-section tests per lot of 30-50 tonnes, or one test if less. Manufacturers may select tension or compression tests if proven consistent. These procedures ensure reliable mechanical property evaluation for safe structural design and quality control.