Code of Practice for the use of Aluminium Alloys in Structures

IS 8147 - Scope Summary & Key Specifications

Scope (Clause 1):
IS 8147 covers design, materials, loads, and structural specifications for steel structures, including:

• Structural steel sections, materials, and manufacturing tolerances.
• Types of loads: erection, temperature effects, and load combinations.
• Design criteria including permissible stresses, combined stresses, thickness, deflections, and camber.

Key Symbols & Definitions (Clause 3.1)

Important Parameters

• Permissible Stresses:

  Stress Type	Symbol
  Permissible bearing stress	( P_b )
  Permissible bending compressive	( P_{bc} )
  Permissible bending tensile	( P_{ot} )
  Permissible axial compressive	( P_c )
  Permissible maximum shear stress	( P_a )
  Permissible axial tensile stress	( P_t )

• Geometric Properties:

  Property	Symbol
  Thickness	( t )
  Web thickness	( t_1 )
  Flange thickness	( t_2 )
  Cross-sectional area	( A )
  Radius of gyration	( r )
  Second moment of area (x

IS 8147: Nomenclature and Material Designations (Clause 4.2.1)

• Material designation follows IS:6051-1970 system.
• Appendix A: Guidelines on alloy nomenclature.
• Appendix B: Foreign equivalents of Indian Aluminium alloys (not exact, for reference only).

Key Table: Foreign Equivalents of Aluminium Alloys (Appendix B)

Permissible Stresses (Example from Clause C-2.1)

Summary

• Use IS:6051-1970 for alloy designation.
• Refer

IS 8147: General Design Considerations - Key Points

1. Design Requirements (Clause 7.3)

• Structural members must satisfy strength, serviceability, and durability.
• Consider combined stresses, temperature effects, and load combinations.
• Use permissible stresses as per alloy and fabrication method.

2. Permissible Stresses (Table 4, Clause 7.4)

• Defined for principal aluminium alloys.
• Adjusted for factors like temperature, fatigue, and fabrication.

3. Combined Stresses (Clause 7.5)

• Use interaction formulas for combined axial, bending, and shear stresses.

  [ \frac{\sigma_x}{f_x} + \frac{\sigma_y}{f_y} + \frac{\tau_{xy}}{f_{xy}} \leq 1 ]

4. Thickness and Deflection Limits (Clauses 7.7 & 7.8)

• Minimum thickness specified to avoid buckling.
• Deflections limited to ensure serviceability, typically span/250 or as per application.

5. Load Considerations (Section II)

• Include dead, live, wind, temperature, and erection loads.
• Load combinations per Clause 6.4.

6. Effective Length and Buckling (Tables 6, 7 & Appendices J, K)

• Effective length factors depend on end conditions.
• Buckling checks for compression members and beams.

7. Material Selection (Clause 4)

• Use alloys with specified mechanical properties.
• Refer to Table 1 for alloy properties and Table 2 for bolt/rivet materials.

Summary Table Extract: Permissible Stresses (Example)

flowchart TD
    A[Design Requirements] --> B[Material Selection]
    B --> C[Load Considerations]
    C --> D[Stress Calculations]
    D --> E[Check Permissible Stresses]
    E --> F{Pass?}
   

IS 8147: Material Properties & Permissible Stresses Summary

Key Points from IS 8147:

• Permissible stresses depend on alloy type, form, thickness, and condition (see Clause 4.4.1, 7.4.1, 8.3.1).
• Temperature range considered: 20 to 100°C.
• Modulus of rigidity ( G ) = 0.38 × Modulus of elasticity ( E ).
• For immersion in fresh/sea water, special conditions apply (Clause 4.4.1).

Permissible Stress Table (Excerpt for Principal Alloys, N/mm²):

Values in parentheses are kgf/mm² (1 N/mm² = 0.102 kgf/mm²).

Important Formulas:

• Modulus of Rigidity: [ G = 0.38 \times E ]

• Permissible Stress for Buckling (Beams & Thin Plates):
  Refer to Fig. 2 and Clause 8.4.1 for lateral/local buckling adjustments.

Notes:

IS 8147: Design of Structural Members — Key Formulas & Specifications

1. Design of Tension Members (Clause 8.1)

• Tensile Strength:
  [ P_u = A_s \times f_y ] Where:

  • (P_u) = Ultimate tensile load
  • (A_s) = Net cross-sectional area
  • (f_y) = Yield stress of material

• Net Area Calculation:
  (A_s = A_g - \text{Area of holes})

• Permissible Stress:
  [ \sigma_{perm} = \frac{f_y}{\text{Factor of Safety}} ]

2. Design of Compression Members (Clause 8.2)

• Buckling Load (Euler's formula for slender columns):
  [ P_{cr} = \frac{\pi^2 E I}{(K L)^2} ] Where:

  • (E) = Modulus of elasticity
  • (I) = Least moment of inertia
  • (K) = Effective length factor
  • (L) = Unsupported length

• Design Strength:
  [ P_u = A_g \times f_{cd} ] Where (f_{cd}) is the design compressive stress considering buckling.

3. Design of Beams (Clause 8.3)

• Bending Stress:
  [ \sigma_b = \frac{M}{Z} ] Where:

  • (M) = Bending moment
  • (Z) = Section modulus

• Shear Stress:
  [ \tau = \frac{V}{A_v} ] Where:

  • (V) = Shear force
  • (A_v) = Shear area (web area)

4. Tables & Specifications

• Section Modulus & Moment of Inertia: Refer IS 8147 Section 4.5 for standard rolled sections.
• Effective Length Factor (K): Depends on end conditions (fixed, pinned, free).
• Permissible Stresses: Clause 7.4 lists allowable stresses for

IS 8147 – Loads and Load Combinations (Clause 6.4)

Key Load Combinations (General Guidance)

Important Notes:

• Wind and seismic loads are mutually exclusive for design but must be checked separately.
• Erection loads must be considered during construction phases (Clause 6.2).
• Live load partial factors depend on the likelihood of simultaneous occurrence with wind/seismic loads.

Typical Load Symbols:

• D = Dead Load
• L = Live Load
• W = Wind Load
• E = Earthquake (Seismic) Load
• Er = Erection Load

Example Load Combination Formula:

[ 1.0D + 1.0L ]

[ 1.0D + 1.0W ]

[ 1.0D + \alpha L + 1.0W \quad (\alpha \leq 1.0) ]

[ 1.0D + \alpha L + 1.0E + Erection , Loads ]

flowchart TD
    D[Dead Load]
    L[Live Load]
    W[Wind Load]
    E[Seismic Load]
    Er[Erection Load]

    D --> C1[Load Combination (a)]
    D --> C2[Load Combination (b)]
    L --> C2
    D --> C3[Load Combination (c)]
    W --> C3
    D --> C4[Load Combination (d)]
    L --> C4
    W --> C4
    D --> C5[Load Combination (e)]
    L --> C5
    W --> C5
    Er --> C5

Reference: IS

IS 8147 - Design Criteria Key Points

1. Design Requirements (Clause 7.3)

• Structures must be safe, serviceable, and economical.
• Consider all relevant loads (dead, live, wind, temperature).
• Account for material properties and manufacturing tolerances.
• Design for durability and maintenance ease.

2. Permissible Stresses (Clause 7.4)

• Use allowable stresses based on material yield or ultimate strength.
• For steel, typical permissible stress ( \sigma_{perm} = \frac{f_y}{\text{Factor of Safety}} ).
• Factors of safety usually range from 1.5 to 2.0.

3. Combined Stresses (Clause 7.5)

• Combine axial, bending, shear stresses using interaction formulas.

• For example, combined bending and axial load:

  [ \frac{\sigma_x}{\sigma_{perm}} + \frac{\sigma_a}{\sigma_{perm}} \leq 1 ]

4. Load Combinations (Clause 6.4)

• Combine loads as per code, e.g.:

  [ 1.5 \times \text{Dead Load} + 1.5 \times \text{Live Load} ]

  or

  [ 1.2 \times \text{Dead Load} + 1.6 \times \text{Live Load} + 0.5 \times \text{Wind Load} ]

5. Thickness & Deflection Limits (Clauses 7.7 & 7.8)

• Minimum thickness to avoid buckling.
• Deflection limits typically span/250 to span/300 depending on use.

Summary Table: Permissible Stresses (Steel)

flowchart TD
    A[

IS 8147: Design of Beams and Compression Members - Key Points

1. Design of Compression Members (Clause 8.2)

• Axial compressive stress, ( f_c ), must not exceed permissible compressive stress ( p_c ).
• ( p_c ) is obtained from Table 4 and Fig. 1 (relates to slenderness ratio ( \lambda = \frac{l}{r} )).
• Euler critical stress for buckling:

[ b_e = \frac{\pi^2 E}{(l/r)^2} ]

where:

• ( E ) = Modulus of Elasticity,
• ( l/r ) = slenderness ratio (effective length to radius of gyration).

2. Design of Beams (Clause 8.3)

• Bending stresses must be within permissible bending compressive stress ( P_{be} ) from Table 4 and Fig. 2.
• For combined bending and axial compression (Clause 7.5.2):

[ f_c + f_{be} \leq p_c + P_{be} ]

where:

• ( f_{be} ) = compressive stresses due to bending about both axes,
• ( p_c ), ( P_{be} ) = permissible stresses from tables/figures.

3. Summary Table:

4. Design Steps:

1. Calculate slenderness ratio ( \lambda

IS 8147: Joints and Connections Key Points

1. Types of Joints Covered

• Bolted joints
• Riveted joints
• Welded joints

2. Permissible Stresses (Clause 9)

• Bolts and rivets: Tensile, shear, bearing stresses as per material and grade.
• Welds: Tensile and shear permissible stresses based on weld type and loading.

3. Key Formulas

• Bolt Shear Stress: [ \tau = \frac{F}{A_s} = \frac{F}{\pi d^2 / 4} ] where (F) = shear force, (d) = bolt diameter

• Bolt Bearing Stress: [ \sigma_b = \frac{F}{d \times t} ] where (t) = thickness of plate

• Rivet Shear Stress: Same as bolt shear stress formula.

• Weld Stress: [ \sigma_w = \frac{F}{A_w} ] where (A_w) = weld throat area

4. Typical Tables (Refer Clause 9.2)

5. Additional Notes

• Use double shear conditions where applicable.
• Allowable stresses depend on material grade and factor of safety.
• Ensure edge distances and pitch meet minimum IS requirements to avoid tearing.

flowchart LR
    A[Load Applied] --> B{Joint Type}
    B -->|Bolted| C[Calculate Shear & Bearing Stress]
    B -->|Riveted| D[Calculate Shear Stress]
    B -->|Welded| E[Calculate Weld Throat Stress]
    C --> F[Compare with Permissible Stress]
    D --> F
    E --> F
    F --> G{Safe?}
    G -->

Fatigue and Stress Concentrations per IS 8147

1. Fatigue Considerations (Clause 10.1):

• Fatigue failure occurs under fluctuating loads at stresses lower than static permissible stresses.
• Fatigue cracks initiate near stress concentrations (holes, welds, geometric discontinuities).
• Design must minimize stress concentrations to preserve fatigue strength.
• Welded joints require special attention; see Appendix N for design guidance.

2. Fatigue Stress Curves (Figures 17 to 24):

• Curves relate maximum stress, stress ratio (R), and number of cycles (N) for different member classes (Class 2 to 9).
• Stress ratio ( R = \frac{\sigma_{\min}}{\sigma_{\max}} ) varies from -1 to +1.
• These curves help determine permissible fatigue stresses for cyclic loading.

3. Fatigue Acceptance Test (Clause 11.3):

• For non-standard alloys, fatigue permissible stresses must be established via tests under supervision.

Key Formula for Stress Ratio:

[ R = \frac{\sigma_{\min}}{\sigma_{\max}} ]

Stress Concentration Avoidance:

• Avoid sharp corners, sudden section changes.
• Use smooth transitions and proper hole sizing.
• Proper welding details per Appendix N.

Summary Table of Fatigue Curves (Representative)

For detailed permissible stresses and fatigue curves, refer to Tables 39-47 and Figures 17-24 in IS 8147.

graph LR
A[Load Fluctuation] --> B[Stress Concentration]
B --> C[Fatigue Crack Initiation]
C --> D[Crack Propagation]
D --> E[Fatigue Failure]

Tip: Always validate fatigue design with testing or conservative design curves

IS 8147 - Testing and Inspection: Key Points

1. Visual & Non-Destructive Testing (Clause 9.3.1)

• Welds must be visually inspected for:
  • Correct size
  • Good appearance
  • Crack-free surface
• Tools: weld gauges, magnifying glasses, dye penetrants (used cautiously)
• Radiographic or other NDT methods mandated if specified.

2. Welding Procedure (Table 16, Clause 14.5)

For TIG & MIG welding, specify:

• Parent metal details
• Edge preparation & setup
• Cleaning method
• Electrode type & size
• Welding current, wire feed speed
• Filler rod/wire type & size
• Gas nozzle size & flow rate
• Weld runs & sequencing
• Welding position and sequence
• Preheat/inter-run temperature
• Arc travel speed (for mechanized welding)
• Shop/site conditions

3. Fatigue Acceptance Test (Clause 11.3)

• Refer to Appendix Q for fatigue stress tables.
• Testing based on stress ratio and cycles (Tables 39-47).

4. Permissible Stresses & Inspection Tables

Summary Diagram: Inspection Flow for Welded Joints

flowchart TD
    A[Start: Weld Fabrication] --> B[Visual Inspection]
    B -->|Pass| C[Dimensional Checks]
    B -->|Fail| F[Reject/Repair]
    C --> D[Non-Destructive Testing (if required)]
    D -->|Pass| E[Final Approval]
    D -->|Fail| F

Use IS 8147 Tables & Clauses for detailed values and procedures.

IS 8147: Fabrication and Handling - Key Points

1. Fabrication Specifications

• Tolerances: Refer to Clause 4.6 (Manufacturing Tolerances) and Section V (Fabrication and Erection) for dimensional accuracy.
• Welding:
  • Use filler rods/wires as per Table 3.
  • Welding procedures and mechanical test requirements detailed in Tables 16 & 17.
  • Permissible stresses for welded joints and heat-affected zones are in Table 15.
• Bolting and Riveting:
  • Bolt/rivet materials and permissible stresses in Tables 2 & 13.
  • Hole clearances for bolts/rivets in Table 14.

2. Handling Guidelines

• Follow erection loads and temperature effect considerations (Clauses 6.2 & 6.3).
• Use proper lifting points and avoid overstressing members during handling.
• Ensure protection against environmental damage (Section VI).

3. Important Tables Summary

Example: Permissible Stress for Alloy 24345 (H15) (N/mm²)

Fabrication Handling Flow (Mermaid Diagram)

flowchart TD
    A[Material Selection] --> B[Cutting & Shaping]
    B

IS 8147: Welding Procedures and Approval (Clause 14.5)

Key Points:

• Welding Procedure must be documented, containing info per Table 16.
• Procedure requires engineer approval after mechanical testing.
• Tests follow IS 7273-1974; butt welds must meet Table 17 criteria.
• Fillet welds require fracture tests for root penetration.
• Visual and NDT inspections as per Clause 9.3.1 & 10.4.1.

Table 16: Welding Procedure Information (examples)

Table 17: Mechanical Test Requirements for Butt Welds

• Tensile strength transverse to weld, irrespective of temper.
• Bend tests thickness t usually 9.5 mm.

Summary Workflow for Welding Procedure Approval

flowchart TD
    A[Document Welding Procedure (Table 16 info)] --> B[Conduct Mechanical Tests (IS 7273)]
    B -->

IS 8147: Erection and Temporary Bracing - Key Points

1. Erection Loads (Clause 6.2)

• Loads from construction materials, equipment, and their operation during erection.
• Structure + temporary bracing must safely carry these loads without exceeding permissible stresses (see Section III).
• Temporary bracing is essential to resist these stresses during erection.

2. Effective Length for Trussed Structures (Clause 8.2.1.2, Table 7)

• k = effective length factor depending on end conditions.
• For compression members, use reduced effective lengths (e.g., 0.5L to 0.45L) based on bracing.

3. Permissible Stresses (Section III)

• Use permissible stresses for erection loads as per Section III.
• Combined stresses and slenderness ratios must be checked.

Summary Formula for Effective Length (Le):

[ L_e = k \times L ]

Where:

• (L) = actual length,
• (k) = factor from Table 7 depending on bracing and member type.

Temporary Bracing Design Checklist:

• Must resist all erection loads.
• Provide lateral support to compression members to reduce slenderness.
• Ensure no excessive deflections or instability during erection.
• Check combined stresses under erection load cases.

flowchart TD
    A[Erection Loads] --> B[Temporary Bracing]
    B --> C[Reduce Effective Length]
    C --> D[Check Permissible Stresses]
    D --> E[Safe Erection]

References:

• IS 8147 Clause 6.2, 8.2.1.2
• Section III (Permissible Stresses)

Fire Safety & Behaviour of Aluminium Structures (IS 8147 Key Points)

1. Fire Protection (Clause 25.1.1)

• Aluminium requires fire protection to minimize strength loss due to overheating.
• Also to reduce damage from thermal expansion.
• Consider fire risks both inside and outside the structure.

2. Fire Behaviour (Clause 25.4)

• In single-storey buildings, roof venting systems help exhaust smoke/fumes and limit fire spread.
• If venting is inadequate, roof deck failure at high temperature can help check fire spread.
• Aluminium softens/melts at relatively low temperatures (~660°C melting point), enabling useful venting if roof lining falls away.

3. Permissible Stress (Clause 4.4)

• Based on 0.2% proof stress of aluminium alloys.
• Common alloys: 64430 (H30), 65032 (H20), 63400 (H9), 54300 (N8).
• Design must consider alloy properties and temper.

4. Design Considerations

• Account for thermal expansion effects.
• Use protection tables for service environments (refer to IS 8147 tables).
• Welding by inert gas process is covered for fabrication safety.

Typical Fire-Related Design Formula

[ \sigma_{perm} = k_f \times f_{0.2} ]

Where:

• (\sigma_{perm}) = permissible stress under fire conditions
• (f_{0.2}) = 0.2% proof stress of alloy
• (k_f) = reduction factor due to elevated temperature (consult specific tables)

Summary Table: Aluminium Melting & Softening

flowchart TD
    A[Fire Occurs] --> B{Roof Venting Present?}
    B -- Yes --> C[Smoke & Fumes Exhausted]
    B -- No --> D[Roof Deck Heats Up]
    D --> E[Aluminium Softens/Melts]