Cold Formed Light Gauge Structural Steel Sections –
1987 Edition

According to IS 811 (1987), cold-formed light gauge steel sections have a minimum thickness of 1.25 mm. The standard specifies dimensional data, mass, and sectional properties for open steel profiles such as C, Z, and U sections designed for light gauge structural applications. Thickness commonly ranges from 1.25 mm up to about 3.15 mm depending on the specific use case. Width, depth, flange, and lip dimensions vary according to section type and design requirements. Detailed tables within the standard provide exact sectional properties and mass per unit length for each size.

IS 811 provides tabulated values for sectional properties including moment of inertia about principal axes (Ixx, Iyy), torsional constant (J), and warping constant (Cw) across various standard cold-formed sections. These properties are calculated assuming an internal radius of curvature Ri equal to 1.5 times the thickness (t) of the virgin material, as per Clause 7.2.3. The tables include cross-sectional area, moments of inertia, section moduli, radius of gyration, shear centre coordinates, torsion and warping constants to enable comprehensive structural analysis.

IS 811 addresses cold-formed light gauge steel sections typically used for structural framing in residential, commercial, and industrial buildings. Covered profiles include standard cold-formed shapes such as C-sections, Z-sections, U-sections, and hat sections. While the standard mainly lists these common profiles, it also allows for special or custom shapes upon consultation with manufacturers. These sections are intended for light to moderate load applications including purlins, girts, joists, and roof trusses.

IS 811 recognizes that cold forming processes cause slight thinning of steel at curved areas due to pressure exerted during bending, which affects actual geometry compared to theoretical dimensions. Clause 2.1 provides a method to calculate reduced thickness (t_red) at curves using formulas based on the inside radius of curvature (Ri) and original thickness (t). Designers should use this reduced thickness to compute section properties, ensuring accurate assessment of strength and stability. This consideration is particularly important for sections typically 10 mm thick or less.

IS 811 employs a designation approach that identifies cold-formed steel sections by their profile shape and nominal dimensions. Typical designation formats include the profile type (e.g., C, Z, L, U) followed by numeric values indicating depth (d), flange width (b), and thickness (t) in millimeters. For instance, a C-section labeled 'C 100 x 50 x 2.5' refers to a profile with 100 mm depth, 50 mm flange width, and 2.5 mm thickness. This system facilitates easy identification and specification for design and fabrication purposes.