IS 8147 : 1976Code of Practice for the use of Aluminium Alloys in Structures

IS 8147:1976 is the code of practice for use of aluminium alloys in structures — the design code for structural aluminium: roofing/space frames, walkways, gratings, ladders, façade structural members, and weight-critical or corrosion-critical structures where steel is unsuitable. It is the aluminium counterpart to IS 800.

It is read with the aluminium stack:

• IS 733 — wrought aluminium alloy bars, rods & sections (the material it designs)
• IS 737 — aluminium sheet & strip · IS 1285 — extruded round tube & sections
• IS 1868 — anodic coatings (durability/finish)
• IS 875 — loads · IS 800 — steel (for comparison/backup)

Aluminium is not light steel — IS 8147 design is driven by properties that differ fundamentally from steel:

• Modulus of elasticity ≈ 70 GPa (~⅓ of steel) → deflection and buckling govern far more often than yield; slender members and serviceability dominate
• Strength depends on alloy + temper (e.g. 63400/64430 in T5/T6) — permissible stresses are alloy/temper-specific, set per IS 733
• No distinct yield point — a 0.2% proof stress is used
• Heat-affected-zone (HAZ) softening at welds — welded aluminium loses strength locally; design must use reduced HAZ properties or favour bolted/riveted connections
• Thermal expansion ≈ 2× steel → movement provision is mandatory
• Galvanic corrosion with steel/concrete → electrical isolation required

IS 8147 gives permissible stresses, slenderness limits, and connection rules reflecting these. The member that 'works' on a steel-style check is often grossly over-stressed once aluminium's low E and HAZ effects are applied.

Member: a simply-supported aluminium walkway beam, alloy 63400-T6, pedestrian live load.

Step 1 — loads: dead + pedestrian live UDL to IS 875; compute span moment & shear.

Step 2 — permissible stress: from IS 8147 for 63400-T6 → allowable bending stress; required Z = M / σ_allow.

Step 3 — deflection governs: check mid-span δ ≤ limit (e.g. span/325 for walkways). Because E ≈ 70 GPa, the section that passes stress almost always fails deflection first — size on stiffness.

Step 4 — connections: prefer bolted/riveted; if welded, apply HAZ-reduced strength at and near welds.

Step 5 — detailing: provide thermal-movement joints (≈2× steel), and isolate the aluminium from steel supports/concrete with gaskets/coatings to stop galvanic attack. Select the lightest IS 733 section passing the deflection limit.

1. Designing aluminium like light steel. Using steel E or steel allowable stresses massively over-states capacity — aluminium is stiffness- and buckling-governed.

2. Ignoring HAZ softening at welds. Welded aluminium loses substantial strength in the heat-affected zone; designing on parent-metal strength at welds is unsafe.

3. Strength-only design. Deflection (and local buckling of thin extrusions) usually governs — a stress-only member is too flexible.

4. No thermal-movement / galvanic isolation. ~2× steel expansion and aluminium-vs-steel/concrete contact cause buckling and corrosion failures that look structural but are detailing errors.

5. Unspecified alloy/temper. Permissible stress varies several-fold by temper — 'aluminium section' without alloy + temper is meaningless.

• IS 733 — wrought aluminium alloy bars/rods/sections (extrusions)
• IS 737 — aluminium sheet & strip · IS 1285 — extruded sections/tube · IS 740 — castings
• IS 1868 — anodic coatings on aluminium (durability)
• IS 800 — steel construction (comparison / hybrid structures)
• IS 875 — loads · IS 816 / welding codes — aluminium welding (HAZ)

IS 8147 is old (1976) and permissible-stress based; international aluminium-structures practice (Eurocode 9, the Aluminum Design Manual) is far more developed on local buckling, HAZ and limit-state design. On Indian projects IS 8147 is the locally-referenced code, and for anything beyond simple members designers commonly supplement with EC9/ADM and document the basis — acceptable and usually necessary.

The enduring engineering message does not change with the code edition: aluminium structures are governed by stiffness, buckling, HAZ and movement — not yield strength. Specify alloy + temper, size members on deflection/buckling, treat welded zones with reduced HAZ properties (or avoid structural welds), and detail thermal movement and galvanic isolation. The right use of structural aluminium is weight-critical or corrosion-critical work (offshore-adjacent, chemical, architectural, portable) — using it as 'cheaper light steel' is the recurring, expensive mistake IS 8147 exists to prevent.