Cold Formed Light Gauge Structural Steel Sections –

IS 811 - Scope: Key Formulas, Tables & Specifications

Scope Summary:
IS 811 covers dimensions, properties, and design data of cold-formed steel sections such as angles, channels, and hat sections.

Key Specifications & Symbols (Clause 4.1)

Important Tables & Data

1. Reduction Factors (Clause 1.5 & 2.00)

• Ri = 1.5 × t (internal curve radius)
• Thickness reduction factors vary with section dimensions (e.g., 60×40×15×2.00, 80×50×25×4.00)

2. Typical Section Properties (Excerpt from Table 9 - Hat Sections)

IS 811 - Definitions & Key Symbols

Clause 4.1 defines key letter symbols used in IS 811 for cold-formed steel sections:

Important Notes:

• Ri (internal radius) is typically taken as 1.5 × t (Clause 1.5).
• Tables 1 to 11 provide detailed dimensions, moments of inertia, section moduli, and other properties for standard cold-formed sections (angles, channels, hat sections, etc.).
• Example from Table 1 (Equal Angles):

IS 811 - Designation of Cold-Formed Light Gauge Sections

Key Specification (Clause 3.1)

• Sections are designated by:
  Depth (mm) × Width (mm) × Thickness (mm)
  Example: 60 × 40 × 2.00

Important Tables for Section Properties

Example from Table 7 (Hat Sections - Square)

Summary of Designation & Properties

flowchart TD
    A[Designation] --> B[Depth (h) mm]
    A --> C

IS 811: Dimensions and Tolerances for Cold-Formed Light Gauge Steel Sections

Key Specifications:

• Dimensions of profiles are per Tables 1 to 10 (Clause 7.1).
• Internal radius of curvature, Ri = 1.5 × thickness (t) of virgin material (Clause 1.5).
• Thickness (t) is before cold forming.

Important Tables (Samples):

Key Formulas:

• Radius of Gyration:
  [ r = \sqrt{\frac{I}{A}} ]
• Section Modulus:
  [ Z = \frac{I}{y} ] where (I) = moment of inertia, (y) = distance to extreme fiber.

Notes:

• Use Tables 1 (Equal Angles) and 2 (Unequal Angles) for detailed properties.
• Mass/unit length and sectional properties aid in structural analysis and design.
• Dimensional tolerances align with cold-formed steel manufacturing standards.

flowchart LR
    A

IS 811: Mechanical Properties of Cold-Formed Light Gauge Steel Sections

Key Specifications & Assumptions

• Internal radius of curvature (Ri) = 1.5 × thickness (t) (Clause 7.2.3, 1.5)
• Thickness (t) is the virgin material thickness before forming.

Important Sectional Properties (from Tables 1 to 11)

Sample Data from Table 1 (Equal Angles)

Formula for Radius of Gyration:

[ R = \sqrt{\frac{I}{A}} ]

Where:

• (I) = Moment of inertia about the axis
• (A) = Cross-sectional area

Summary:

• Use **Ri = 1.

IS 811: Section Properties & Tables Summary

Key Points from IS 811 Clauses:

• Clause 7.2: Mass and sectional properties for cold-formed light gauge steel sections are tabulated in Tables 1 to 10.
• Clause 7.2.3: Sectional properties assume inside radius ( R_i = 1.5t ) (where ( t ) is thickness).
• Tables include:
  • Dimensions (h, d, t)
  • Mass per unit length (kg/m)
  • Cross-sectional area ( A ) (cm²)
  • Centroid location ( C_y ) (cm)
  • Moments of inertia ( I_{xx}, I_{yy} ) (cm⁴)
  • Radius of gyration ( r_x, r_y ) (cm)
  • Section modulus ( Z_{xx}, Z_{yy} ) (cm³)
  • Shear centre location ( X_0 ) (cm)
  • Torsion constant ( J ) (cm⁴)
  • Warping constant ( C_w ) (cm⁶)

Typical Section Properties Table Format (Example for Hat Sections):

IS 811 - Reduction Factors Summary (Clause 1.60 & Table A-2)

Key Points:

• Reduction factors account for thinning of steel strips during cold forming, affecting actual geometry vs theoretical.
• Provided for various channel sizes (e.g., 40×40, 50×50, 60×60 mm) and thicknesses (1.60 mm to 6.00 mm).
• Factors modify sectional properties like moment of inertia, section modulus, radius of gyration, etc.

Typical Parameters in Table A-2:

Important Notes:

• Reduction Factor (k) is multiplied with theoretical properties to get actual values.
• Values depend on cross-section size and thickness.
• Use these factors to calculate effective section properties for design.

Formula for Effective Property:

[ \text{Effective Property} = k \times \text{Theoretical Property} ]

Application:

• Use Table A-2 reduction factors for cold-formed steel channel sections.
• Adjust design calculations for bending, shear, and axial load accordingly.

flowchart LR
    A[Cold Forming] --> B[Thinning of Steel Strip]
    B --> C[Reduction in Section Properties]
    C --> D[Apply Reduction Factors (k)]
    D --> E[Calculate Effective Properties]
    E --> F[Design Calculations]

For detailed values, refer to IS 811 Table A-2 Clause 1.60 for your specific section size and thickness.

IS 811 Design Considerations: Key Formulas, Tables & Specs

1. Section Properties (from Tables for Cold-Formed Steel Sections)

2. Internal Radius of Curvature (Clause 1.5)

[ R_i = 1.5 \times t ]

• ( R_i ) = Internal radius of curvature (mm)
• ( t ) = Thickness before cold forming (mm)

3. Typical Section Dimensions & Properties Examples

IS 811: Marking and Identification Key Points

Marking Requirements (Clause 10.1)

Each bundle/section must be legibly marked with:

• Designation (profile type)
• Trade-mark or manufacturer's name
• Specification and grade of material
• Lot number or production identification

Standard Mark (Clause 10.1.1)

• Use of the Standard Mark is regulated by BIS.
• It guarantees compliance with IS 811 under BIS supervision.
• Licensing conditions for using the Standard Mark are available from BIS.

Important Symbols (Clause 4.1)

Tolerances on Length (Clause 8.6)

Summary Diagram: Marking Flow

flowchart TD
    A[Bundle/Section] --> B[Mark with Designation]
    A --> C[Mark with Manufacturer's Name]
    A --> D[Mark with Spec & Grade]
    A --> E[Mark with Lot Number]
    F[Standard Mark] -->|BIS Licensed| A

This ensures traceability, quality assurance, and compliance with IS 811.

IS 811 Annex: Property Tables for Cold-Formed Steel Sections

Key Points from IS 811 Clause 7.2 & 7.2.3

• Sectional properties for cold-formed light gauge steel sections are tabulated in Tables 1 to 11.
• Calculations assume inside radius (Ri) = 1.5 × thickness (t).

Typical Sectional Properties Provided (per unit length)

Example Table Extract (Unequal Angles)

IS 811: Amendments and Revisions Summary

• Amendment No. 1 (Nov 2011) updates IS 811:1987 (Second Revision) for cold-formed light gauge structural steel sections.
• The standard includes reduction factors for thicknesses (e.g., 2.55 mm, 3.15 mm) used in design.
• Key table (Table 11) provides properties of 90° corner sections:

• Reduced thickness (Éred) accounts for corner radius effects.
• Amendments are issued by BIS to update specifications and improve accuracy.

Usage Tips:

• Use reduced thickness for calculating section properties.
• Refer to Table 11 for design parameters of standard corner sections.
• Always check for latest amendments from BIS for compliance.

flowchart LR
    A[IS 811:1987] --> B[Second Revision]
    B --> C[Amendment No. 1 (2011)]
    C --> D[Updated Reduction Factors]
    C --> E[Updated Section Properties Table]
    E --> F[Design Calculations]

For detailed design, always consult the latest IS 811 document and BIS amendments.