Code of Practice for the use of Aluminium Alloys in Structures
1976 Edition

The standard categorizes aluminium alloys into primary ones such as 64430 H30, 65032 H20, 63400 H9, and 54300 N8, and secondary categories. Allowable stresses are determined based on the 0.2% proof stress as a benchmark. For main alloys, permissible values for axial, bending, shear, and bearing stresses are provided in tabulated form (Clause 7.4.1). Non-standard alloys or tempers require derivation of permissible stresses through specific guidelines in Appendix F. Design must also account for buckling effects and manufacturers' data for alloys with assured enhanced properties.

Welding procedures must be thoroughly documented according to the information outlined in Table 16 and require formal approval from an authorized engineer prior to fabrication. These procedures must be validated by mechanical testing consistent with IS 7273-1974 standards, ensuring butt welds meet criteria in Table 17. Fillet welds are subject to fracture tests verifying complete root penetration. Welder qualifications must be regularly assessed and approved to maintain consistent quality. Permissible stresses for welds depend on type: fillet weld allowable stress is based on minimum expected shear strength divided by 3, while butt weld allowable stress is the minimum 0.2% proof stress divided by 1.5.

Fabrication tolerances include length variation between holes set at ±0.5 mm for components up to 10 meters and ±3 mm for longer members. Hole spacing within fastener groups should not deviate by more than 1 mm from specified dimensions. Aluminium’s lower stiffness and higher thermal expansion compared to steel necessitate accommodating these tolerances to ensure precise assembly and structural integrity. Machining capabilities allow for high workmanship quality, while temporary bracing during erection helps maintain stability under construction loads.

The standard requires that fatigue permissible stresses for non-standard alloys be established through supervised testing. Fatigue cracks typically initiate at stress concentration zones such as fastener holes, welds, and abrupt geometric changes. Design practices must minimize these concentrations using smooth transitions, proper hole sizing, and careful welding details as outlined in Appendix N. Fatigue acceptance testing is mandatory for critical members, with detailed fatigue stress versus cycle data provided in Tables 39-47. Emphasis is placed on design and fabrication methods that enhance fatigue life and reduce crack initiation risk.

Aluminium alloys are non-combustible and do not contribute to fire spread; however, significant strength loss begins at temperatures above approximately 250°C, with melting occurring near 650°C. Due to aluminium’s high thermal expansion, fire protection measures should mitigate damage from heat-induced stresses. Roof venting systems are recommended to exhaust smoke and limit fire propagation; in their absence, roof decks may intentionally soften or melt to provide venting. Structural designs must consider thermal effects on stability and deflections, ensuring adequate safety under fire exposure as per the standard’s clauses.