Code of practice for high-strength bolts in steel structures

IS 4000: Scope - Key Points & Tables

1. Scope Summary:

• Applies to testing and calibration of high-strength steel bolts in structural joints.
• Minimum 3 specimens per test; 5 preferred.
• Loading by tensile force only.
• Slip load detection via deformation or audible slip.

2. Slip Factor (μ) - Annex C (Clause 5.4.1)

3. Maximum Permissible Forces in Bolts (Table 5.3.2)

IS 4000: Terminology & Symbols (Clauses 3.1, 3.2)

Recommended Slip Factors (Annex C, Clause 5.4.1)

Notes on Bolt Tension Inspection (Torque Wrench)

• Torque calibration depends on thread, bearing surface, lubrication, galling, and time lapse.
• Torque wrench method is practical for verifying bolt tension.

flowchart LR
    A[Bolt Diameter (d)] --> B[Edge Distance (e)]
    B --> C[Minimum edge distance includes half bolt dia]
    D[Force on Bolt] --> E[Tensile (Pt) & Shear (V)]
    E --> F[Max permissible forces (Pto, Vob)]
    G[Surface Treatment] --> H[Slip Factor (p)]
    H --> I[Effect on friction and bolt slip resistance]

This summary provides essential symbols, slip factors, and inspection notes from IS 4000 for steel bolted joints.

Key Specifications and Tables for Bolts, Nuts, and Washers (IS 4000)

1. Standards Referenced:

• Bolts: IS 3757:1985
• Nuts: IS 6623:1985
• Washers: IS 6649:1985

Important Symbols (Clause 3.2)

Table 1: Allowance for Bolt Length (Clause 4.1.1)

• Includes thickness of 1 nut + 1 standard washer.
• Ensures safe bolt end protrusion after tightening.
• Minimum 2 free threads beyond nut face required.

Table 2: Minimum Bolt Tension (kN) (Clause 7.2.1)

Notes:

• Bolt length allowance varies with joint type (friction or bearing).
• For bearing joints excluding threads

IS 4000: Design of Joints (Key Formulas & Tables)

1. Maximum Permissible Forces on Bolts (Table 5.3.2)

2. Shear Force Limits on Bolts (Clause 5.3.2)

• For bearing type joints < 500 mm long:
  [ V_{bolt} \leq V_{ob} \quad \text{(from Table 5.3.2)} ]

• For joints 500 mm to 1200 mm long:
  [ V_{bolt} \leq \frac{6}{7} V_{ob} ]

• For joints > 1200 mm long:
  [ V_{bolt} \leq \frac{4}{7} V_{ob} ]

3. Additional Specifications

• Slip-critical joints (no slip allowed) → Use friction-type joints (Clause 5.3.1).
• Bearing type joints must be designed considering bolt shear and bearing

IS 4000: Types of Joints and Limitations

1. Types of Joints

• Bearing Type Joints (Clauses 5.3, 5.5.2):

  • Transfer forces through bearing of bolts on connected plates.
  • Suitable where slip is acceptable.
  • Shear force resisted by bolt shear and bearing on plate.

• Friction Type Joints (Clause 6.4.2, 5.3.1):

  • Transfer forces through friction between plates.
  • Slip is not acceptable.
  • Bolts are pre-tensioned to develop frictional resistance.
  • Used in shear and moment connections where slip must be prevented.

2. Limitations (Clause 5.3.1)

• If slip is not acceptable, design as friction-type joints.
• Bearing joints are not suitable for connections requiring zero slip.
• Friction joints require proper bolt pretensioning.

3. Key Formulas

• Bearing Type Joint Shear Capacity:

  [ V_{Rd} = n \times \min (V_{b}, V_{pb}, V_{pl}) ]

  Where:

  • (V_b) = Bolt shear capacity
  • (V_{pb}) = Plate bearing capacity on bolt
  • (V_{pl}) = Plate tear capacity

• Friction Type Joint Slip Resistance:

  [ R = \mu \times N_b \times f_{ub} \times A_b ]

  Where:

  • (\mu) = Coefficient of friction (usually 0.3-0.5)
  • (N_b) = Number of bolts
  • (f_{ub}) = Ultimate tensile strength of bolt
  • (A_b) = Tensile stress area of bolt

4. Typical Bolt Pretension for Friction Joints

flowchart LR
    A[Load Applied] --> B{Slip Acceptable?}
    B --

IS 4000: Preparation of Surfaces in Contact (Clause 6.4 & Annex C)

Key Points:

• Contact surfaces must be clean 'as-rolled' or equivalent.
• Surfaces must be free from paint, lacquer, galvanizing, or other finishes unless approved.
• Slip factor (p) depends on surface treatment; if "as rolled" and clean, p = 0.35 (Clause 6.2).
• If surface finish differs, use slip factors from tests (Annex B) or recommended values from Annex C.

Recommended Slip Factors (Annex C):

Additional Notes:

• Surfaces shall be blasted before treatment.
• Slip factors are crucial for friction-type joints design.
• Use torque wrench calibration carefully considering thread condition, lubrication, and timing.

flowchart LR
    A[Surface Preparation] --> B{Surface Condition}
    B -->|Clean as rolled| C[Slip factor = 0.35]
    B -->|Blasted + Rust removed| D[Slip factor = 0.50]
    B -->|Blasted + Painted Zinc Silicate| E[Slip factor = 0.30]
    B -->|Blasted + Hot Dip Galvanized| F[Slip factor = 0.10]
    B -->|Other Treatments| G[Refer Annex C Table]

For detailed design, always verify slip factor by testing per Annex B if surface differs from standard conditions.

Assembly and Tensioning of Bolts (IS 4000 Key Points)

Part-turn Method (Clause 7.2.2)

• Step 1: Tighten all bolts/nuts to snug-tight to ensure contact.
• Step 2: Mark bolt and nut positions for rotation control.
• Step 3: Final tension by turning the nut as per Table 4 below, without rotating the component.

Tolerance: ±60° (1/6 turn), no under-tolerance.

Bolt Tension Calculation (if no load cell available) - Clause 1.2

[ R = E \times 4 \times 10^{-3} \times (a + b + \frac{c}{2}) ]

• R = Bolt tension (kN)
• E = Young's modulus = 200,000 MPa
• a = Length of unthreaded bolt in grip (mm)
• b = Length of threaded bolt in grip (mm)
• c = Nut thickness (mm)

Inspection (Clause 8.2)

• Check snug-tight condition.
• Confirm final tension by:
  • Measuring nut rotation (part-turn method).
  • Using direct-tension indication devices.
• Torque wrench inspection only detects gross under-tensioning.

Summary Diagram of Part-Turn Tensioning

flowchart TD
    A[Snug-tighten all bolts] --> B[Mark bolt & nut positions]
    B --> C[Turn nut per Table 4 rotation]
    C --> D[Check no rotation of component]
    D --> E[Inspect tension & marks]

References: Use IS 1367 (Part 3) for bolt properties and IS 6623

IS 4000: Inspection and Testing of High Strength Structural Bolts

Key Points from Clause 2.2 & Annex D (Calibration & Inspection)

• Calibration Samples: Minimum 3 bolts of same size and condition are tensioned in a calibrating device.
• Calibration Tension: Tension bolts to minimum tension from Table 3 (IS 4000).
• Inspection Torque: Measure torque to turn nut/bolt head by 5° (approx. 25 mm at 300 mm radius). Average torque of 3 bolts = Job Inspection Torque.
• Inspection Sample: Suggested 10% of bolts, minimum 2 per connection.
• Acceptance Criteria: If no nut/head turns at job inspection torque, tension is adequate.
• Retensioning: Bolts turning under inspection torque must be retensioned and re-inspected.

Slip Factor (Clause 5.4.1, Annex C)

Inspection Torque Calculation (Summary)

• Torque to turn nut/head 5° on tensioned bolt = Job Inspection Torque.
• Use hardened washer under bolt head/nut during calibration.
• Torque wrench inspection detects gross under-tensioning only.

Tensioning Procedure (Clause 8.2)

• Part-turn Tensioning: Check correct part-turn from snug-tight.
• Direct-Tension Indication: Follow manufacturer's procedure and verify tension indicator.
• Permanent marks on bolts/nuts after tensioning.

flowchart TD
    A[Select 3 bolts for calibration] --> B[Tension bolts to Table 3 tension]
    B --> C[Apply torque wrench to turn nut 5°]
    C --> D[Record torque for each bolt

IS 4000: Storage and Handling — Key Formulas, Tables, and Specifications

1. Allowance for Bolt Length (Clause 4.1.1, Table 1)

• Includes thickness of 1 nut + 1 washer.
• Ensures safe bolt end protrusion beyond nut after tightening.
• For additional washers, add their thickness to grip length.
• Minimum 2 free threads beyond nut face required.

2. Recommended Slip Factors (Annex C, Clause 5.4.1)

Note: Surfaces must be blasted; no sanding.

3. Bolt Tension Calculation (Clause 1.2)

When load cell unavailable, bolt tension R (kN) is calculated as:

[ R = E \times 4 \times 10^{-3} \times (a \times \epsilon_b + \frac{c}{2}) ]

Where:

• ( E = 200,000 ) MPa (Young’s modulus)
• ( a ) = length of unthreaded bolt in grip (mm)
• ( \epsilon_b ) = bolt strain (measured extension / gauge length)
• ( c ) = nut thickness (mm)

4.

IS 4000: Use of Oversize and Slotted Holes — Key Points

1. Oversize Holes (Clause 6.3.1 & 6.3.2a)

• Maximum size:
  [ \text{Oversize hole diameter} \leq \min(1.25d, d + 8 \text{ mm}) ] where d = nominal bolt diameter.
• Use: Allowed in bearing and friction-type connections.
• Condition: Hardened washers must be installed over oversize holes.

2. Short Slotted Holes (Clause 6.3.2b)

• Use: Allowed in shear-type connections for friction and bearing joints.
• Condition: Hardened washers required.
• Direction:
  • Friction joints: Slots can be any direction.
  • Bearing joints: Slots only normal (perpendicular) to load and no eccentric loading.

3. Long Slotted Holes (Clause 2.5c & 6.3.2c)

• Dimensions:
  [ \text{Width} \leq d + 2 \text{ mm}, \quad \text{Length} \leq 2.5d ]
• Use: Only in shear-type connections, alternate plies of friction or bearing joints.
• Condition: Special coverplate or washer ≥ 8 mm thick to cover exposed holes.

4. Standard Hole Sizes (Clause 1.5)

• Bearing-type joints: Hole diameter = (d + 1.5) mm
• Friction-type joints: Hole diameter = (d + 2.0) mm

Summary Table

Key Formulas & Specifications for Alignment and Assembly (IS 4000)

1. Alignment of Parts (Clause 7.1.5)

• Holes must align to avoid damage to bolt threads.
• Drifting to align holes must not distort or enlarge holes.

2. Bolt Tension Calculation (Clause 1.2)

When no load cell is available, bolt tension R (kN) is calculated by:

[ R = E \times 4 \times 10^{-3} \times (a \times b + \frac{c}{2}) ]

Where:

• (E = 200,000 \text{ MPa}) (Young's Modulus)
• (a) = length of unthreaded bolt shank in grip (mm)
• (b) = length of threaded portion in grip (mm)
• (c) = nut thickness (mm)

3. Bolt Tensioning Procedures

• Snug-tight: finger tight (initial condition).
• Final tensioning: Use displacement transducer (resolution ≤ 0.003 mm) to measure bolt extension.
• Bolt tension from calibration curve or formula.

4. Part-turn Method (Clause 7.2.2 & Table 4)

• Length refers to grip length (mm).
• Tolerance: ±60° (1/6 turn).
• Final tension ≥ minimum bolt tension (Table 3).

5. Hole Size for Bolts

Summary

IS 4000 Key Points on Retensioning and Reuse of Bolts

Retensioning (Clause 7.1.7)

• Avoid retensioning fully tensioned bolts.
• Allowed only once if:
  • Bolt remains in the same hole.
  • Same grip length is maintained.
• Do not reuse fully tensioned bolts in different holes.

Tensioning Procedures (Clause 8.2)

• Inspect at snug-tight and final tension stages.
• Methods to verify full tension:
  • Part-turn tensioning: Check correct part-turn rotation from snug-tight.
  • Direct-tension indication: Follow manufacturer’s procedure and verify tension via tension indication device.
• Torque wrenches only detect gross under-tensioning (Annex D).

Part-turn Method (Clause 7.2.2)

1. Tighten all bolts to snug-tight.
2. Mark bolt and nut positions.
3. Final tension by rotating nut as per Table 4 (not provided here).
4. Prevent rotation of non-turned component.

Bolt Tension Calculation (When load cell unavailable)

[ R = E \times 4 \times 10^{-3} \times (a \times b + \frac{c}{2}) ]

Where:

• (R) = bolt tension (kN)
• (E = 200,000) MPa (Young’s modulus)
• (a) = length of unthreaded shank in grip (mm)
• (b) = length of threaded portion in grip (mm)
• (c) = nut thickness (mm)

Important Dimensions (from Fig. 1)

• Hole diameter: (22 \text{ mm}) or ((d+2) \text{ mm})
• Grip length and bolt dimensions depend on bolt size (d).

flowchart TD
    A[Snug-tight tightening] --> B[Mark bolt & nut positions]
    B --> C[Final tensioning by part-turn]
    C --> D[Inspection at full tension]
    D -->|If retension needed| E{Same hole & grip?}
    E -->|Yes| F[Retension once only]
    E -->|No| G[Do

IS 4000: Slip Factor & Joint Performance Key Points

Slip Factor (μ)

• Definition: Ratio of slip load to bolt tension, reflecting friction at joint interfaces.
• Design Slip Factor (μ) depends on surface treatment (Annex C, Clause 5.4.1):

Note: Surfaces must be blasted before treatment.

Slip Load (Pₛ)

• Determined by tensile testing of specimens (3 minimum, 5 preferred).
• Slip load corresponds to sudden deformation increase or slip displacement of 0.13 mm.
• Loading increments: ≤ 25 kN or 25% of slip load, rate ≤ 50 kN/min.

Joint Design Formula (Clause 5.4.2)

For shear-only friction joints:

[ \text{Bolt Force} \leq \frac{\mu \times N \times T_{min}}{\text{Factor of Safety}} ]

Where:

• ( \mu ) = slip factor
• ( N ) = number of effective interfaces
• ( T_{min} ) = minimum bolt tension

Bolt Tension Inspection

• Use torque wrench calibration considering thread condition, lubrication, and timing.
• Calibration specimen torque correlates to actual bolt tension with some variability.

flowchart LR
    A[Surface Treatment] --> B[Determine Slip Factor μ]
    B --> C[Calculate Slip Load Pₛ]
    C --> D[Perform Tensile Test on Specimens]
    D --> E[Measure Deformation & Slip]
    E --> F[Use μ in Joint Design Formula]
    F --> G[Check Bolt Force ≤ μ × N × T_min / FS]

**

IS 4000 Tightening Patterns & Sequences Summary

1. Tightening Pattern (Clause 7.1.6)

• Tighten bolts from the stiffest part of the joint toward free edges.
• High strength bolts used temporarily must be finally tensioned only after all bolts are snug-tight in sequence.

2. Part-turn Method (Clause 7.2.2)

• Step 1: Snug-tighten all bolts.
• Step 2: Mark bolt & nut positions for rotation control.
• Step 3: Final tension by turning nuts as per Table 4.
• The component not turned by wrench must not rotate during final tensioning.

3. Nut Rotation Table (Table 4)

• Tolerance: ±1/6 turn (60°) over, no under tolerance.
• Rotation ensures minimum bolt tension per Table 4.

4. Direct-Tension Indication (Clause 7.2.3)

• Snug-tighten first.
• Use tension-indicator device to reach minimum tension (Table 3).

5. Inspection (Clause 8.2)

• Verify snug-tight and final tension stages.
• Part-turn: Check correct nut rotation.
• Direct-tension: Follow manufacturer's procedure and device indication.
• Torque wrench only detects gross under-tensioning (Annex D).

Visual: Tightening Sequence Concept

graph TD
    A[Start at St

Relationship between IS 4000:1992 and IS 800:1984

• IS 4000 is complementary to IS 800:1984 (Code of Practice for General Construction in Steel).
• Clause 1.3 of IS 4000 states:

  Provisions not covered in IS 4000 shall conform to IS 800:1984.

• IS 4000 specifically deals with high strength bolts in steel structures, while IS 800 covers the general steel construction practices.
• For any design, fabrication, or erection aspects not explicitly detailed in IS 4000, IS 800 provisions apply.

Key Specification Summary:

Bolt Tensioning (from IS 4000 Clause 2.2):

• Minimum tension for bolts is given in Table 3 (IS 4000).
• Job inspection torque is determined by tensioning sample bolts and measuring torque to turn nut/head 5°.
• Sample size: minimum 10% bolts or at least 2 per connection.
• If any bolt turns under inspection torque, retension all bolts.

Summary Diagram (Mermaid.js):

graph TD
    A[IS 4000: High Strength Bolts] --> B[Specific Bolt Provisions]
    A --> C[Refer IS 800 for Other Provisions]
    C --> D[General Steel Construction]
    B --> E[Bolt Tensioning & Inspection]
    D --> F[Design, Fabrication, Welding]

In brief: Use IS 4000 for bolt-specific rules; defer to IS 800 for all other steel construction aspects.