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IS 3909:1986 is the Indian Standard (BIS) for aluminium unequal leg angles. This standard specifies the nominal dimensions, mass, and sectional properties of extruded aluminium unequal leg angles used for structural purposes.
Aluminium Unequal Leg Angles
Overview
Status
Current
Usage level
Specialized
Domain
Structural Engineering — Structural Engineering and Structural Sections
BIM-relevant code. See the BIM Hub for ISO 19650, IFC, and LOD/LOIN frameworks used alongside it.
Practical Notes
! This code provides geometric properties only. Always specify the required aluminium alloy grade (e.g., from IS 733) to ensure adequate mechanical strength.
! Pay special attention to the orientation of the unequal legs during detailing to maximize the moment of inertia against the primary bending axis.
! Tolerances for these sections are typically governed by IS 3965 rather than this geometric standard.
Standard Specification for Aluminum and Aluminum-Alloy Extruded Bars, Rods, Wire, Profiles, and Tubes
Covers the manufacturing, chemistry, and mechanical properties of extruded aluminium profiles, including angles.
EN 755-9:2016CEN, European Committee for Standardization
HighCurrent
Aluminium and aluminium alloys - Extruded rod/bar, tube and profiles - Part 9: Profiles, tolerances on dimensions and form
Specifies the tolerances on dimensions and form for extruded aluminium profiles, including angles.
ANSI H35.2-2017The Aluminum Association, USA
HighCurrent
American National Standard Dimensional Tolerances for Aluminum Mill Products
Provides standardized dimensional tolerances for all aluminium mill products, serving as a primary reference for ASTM B221.
AS/NZS 1866:1997Standards Australia / Standards New Zealand
MediumCurrent
Aluminium and aluminium alloys - Extruded rod, bar, solid and hollow shapes
Specifies requirements for extruded aluminium shapes, including material, properties, and dimensional tolerances.
Key Differences
≠IS 3909 uses an outdated 5-digit numerical system for alloy designation (e.g., 64430 for H30), whereas modern international standards universally use the 4-digit Aluminum Association (AA) system (e.g., 6082).
≠The Indian Standard was published in 1986 and only reaffirmed, while standards like ASTM B221 and the EN 755 series are frequently updated to include new alloys, tempers, and manufacturing process improvements.
≠IS 3909 provides a fixed and limited table of standard angle sizes. International standards generally define tolerances applicable to a broad range of dimensions, allowing for greater flexibility in standard and custom profiles.
≠Tolerance structures in modern standards like EN 755-9 are often more complex, with different tolerance classes based on alloy group, shape complexity, and dimension, whereas IS 3909 applies a single set of tolerances.
Key Similarities
≈All standards are based on the hot extrusion manufacturing process and its inherent capabilities and limitations.
≈The fundamental parameters for quality control are identical across standards: leg length, thickness, squareness, straightness, and freedom from injurious defects.
≈All standards utilize a temper designation system (e.g., IS 'WP' is equivalent to international 'T6') to define the final mechanical properties achieved through heat treatment.
≈The primary scope is the same: to specify the material, dimensional accuracy, and general quality for extruded aluminium unequal leg angles intended for structural and general use.
Parameter Comparison
Parameter
IS Value
International
Source
Common Structural Alloy
Grade 64430 (H30)
Alloy 6082 or 6061
EN 755-2 / ASTM B221
Min. Ultimate Tensile Strength (UTS) for H30-WP / 6082-T6
310 MPa (referenced from IS 733)
310 MPa (for thickness ≤ 25mm)
EN 755-2:2016
Leg Length Tolerance (for a 100mm leg)
±0.80 mm
±0.029 in (±0.74 mm)
ANSI H35.2-2017
Thickness Tolerance (for a 6mm wall)
±0.30 mm
±0.012 in (±0.305 mm)
ANSI H35.2-2017
Squareness/Angularity Tolerance (90° Angle)
1.2 mm max deviation on a 75 mm leg (approx. ±0.92°)
±1.5 degrees
EN 755-9:2016
Straightness Tolerance (per meter)
1.25 mm / meter
0.0125 in / foot (approx. 1.04 mm / meter)
ANSI H35.2-2017
⚠ Verify details from original standards before use
Key Values2
Quick Reference Values
assumed density2700 kg/m³
standard mass basisMass is calculated based on the standard density of aluminium
Tables & Referenced Sections
Key Tables
Table 1 - Dimensions, Mass and Sectional Properties of Aluminium Unequal Leg Angles