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IS 801:1975 is the Indian Standard (BIS) for use of cold-formed light gauge steel structural members in general building construction. This code covers the design criteria and construction guidelines for cold-formed light gauge steel structural members used in building construction. It is primarily based on the Working Stress Method (WSM) and is frequently used for designing roof purlins, side girts, and light-frame structures.
Specifies design and construction practices for cold-formed light gauge steel structural members in buildings.
Overview
Status
Current
Usage level
Specialized
Domain
Structural Engineering — Structural Design and Loading
BIM-relevant code. See the BIM Hub for ISO 19650, IFC, and LOD/LOIN frameworks used alongside it.
Practical Notes
! IS 801:1975 is based on the outdated Working Stress Method (WSM). Many modern structural engineers and PEB designers prefer using AISI S100 or Eurocode 3 Part 1-3 for Limit State Design of cold-formed steel.
! Local buckling is the most critical design consideration. Ensure effective width calculations are performed accurately for thin compression elements.
! For open unsymmetrical sections like C and Z purlins, torsional-flexural buckling must be carefully evaluated as they tend to twist under load.
AISI S100-16 (R2020)American Iron and Steel Institute (AISI), USA/Canada/Mexico
HighCurrent
North American Specification for the Design of Cold-Formed Steel Structural Members
Covers design of cold-formed steel members; IS 801 was historically based on an early version of the AISI specification.
AS/NZS 4600:2018Standards Australia / Standards New Zealand, Australia/New Zealand
HighCurrent
Cold-formed steel structures
Specifies design rules for cold-formed steel members, sharing a similar design methodology to modern AISI standards.
EN 1993-1-3:2006European Committee for Standardization (CEN), Europe
MediumCurrent
Eurocode 3: Design of steel structures – Part 1-3: General rules – Supplementary rules for cold-formed members and sheeting
Provides comprehensive design rules for cold-formed steel, but with a distinct European limit state design philosophy.
Key Differences
≠IS 801:1975 is based on the Allowable Stress Design (ASD) method, using a global factor of safety, whereas modern standards like AISI S100 and Eurocode 3 primarily use Limit State Design (LSD/LRFD) with partial safety factors for loads and resistances.
≠IS 801 does not explicitly address the failure mode of distortional buckling, which is a critical consideration for lipped C and Z sections. Modern codes like AISI S100 and AS/NZS 4600 have mandatory, detailed provisions for calculating distortional buckling capacity.
≠The effective width calculation formulas in IS 801 are simpler and based on older research. Modern standards use more refined, unified effective width formulas that better predict the post-buckling behavior of slender elements under various stress conditions.
≠IS 801 lacks specific provisions for seismic design of cold-formed steel structures, while standards like AISI S100 have companion documents (e.g., AISI S400) dedicated entirely to seismic design requirements and system capacity.
Key Similarities
≈All standards are fundamentally based on the 'effective width' concept, which accounts for the reduction in strength and stiffness of thin plate elements due to local buckling when subjected to compression.
≈The basic modes of failure considered are similar, including local buckling, overall flexural buckling (bending), torsional-flexural buckling (for asymmetric sections), and web crippling.
≈The general scope of all standards covers the design of common open sections (C, Z, Hat, Angle) and built-up sections used as beams, columns, studs, and purlins in building construction.
≈All codes provide methods for analyzing the interaction between combined axial load and bending, ensuring members are checked for combined stresses or actions.
Parameter Comparison
Parameter
IS Value
International
Source
Primary Design Philosophy
Allowable Stress Design (ASD)
Limit State Design (LSD/LRFD) and Allowable Strength Design (ASD)
AISI S100-16
Factor of Safety on Bending (Yielding)
1.65
1.67 (for ASD method, Ωb)
AISI S100-16
Resistance Factor for Bending (LRFD)
Not Applicable
0.90 to 0.95 (φb)
AISI S100-16
Distortional Buckling Check
Not explicitly required.
Mandatory check with specific strength calculation methods.
AS/NZS 4600:2018
Web Crippling Provisions
Provides coefficients for four specific loading conditions based on experimental formulas of the era.
Provides more extensive and refined coefficients for a wider range of conditions, including different flange types (fastened/unfastened).
AISI S100-16
Maximum Flat-Width/Thickness (w/t) Limit for Elements
Capped at 500. Stiffened element limit depends on stress level (e.g., 1810/√f for full effectiveness).
No absolute cap, but strength is reduced based on slenderness. The unified approach does not use a simple stress-based limit for full effectiveness.
AISI S100-16
Consideration of Inelastic Reserve Capacity
Not permitted; design is based on elastic behavior.
Permitted for certain compact sections, allowing for moment redistribution and capacities beyond first yield.
EN 1993-1-3:2006
⚠ Verify details from original standards before use
Key Values5
Quick Reference Values
Basic permissible stress in tension and bending0.60 fy
Maximum flat-width ratio (unstiffened element)60
Maximum flat-width ratio (stiffened element)500
Maximum flat-width ratio (sub-stiffened element)60
Basic permissible shear stress0.40 fy
Key Formulas
b = (253 * t / sqrt(f)) * (1 - 50.3 / ((w/t) * sqrt(f))) — Effective width for stiffened compression elements
Fb = 0.60 * fy — Basic allowable design stress
Tables & Referenced Sections
Key Tables
Table 1 - Minimum Thickness of Steel Sheets
Table 2 - Basic Allowable Design Stresses
Key Clauses
Clause 5 - Properties of Sections
Clause 6.1.1 - Basic Design Stress
Clause 6.2 - Effective Width of Stiffened Compression Elements