Tolerances for fabrication of steel structures

IS 7215: Scope & Key Specifications Summary

IS 7215 covers tolerances for fabrication of steel structures, classifying structures into three groups based on accuracy and dynamic loading:

• Group A: Steel railway/road bridges and dynamic load structures (highest accuracy)
• Group B: Structures with special characteristics or dynamic loading excluding wind/seismic (e.g., crane gantries, chimneys)
• Group C: Structures without dynamic loading (e.g., platform galleries, stairs)

Key Tables & Formulas

1. Deviations on Hole Dimensions for Riveting & Bolting (Clause 10.2.1, Table 7)

Ovality = difference between max and min hole diameter.

2. Edge Distance Deviation (Clause 10.5)

• Group B: ±1 mm
• Group C: ±1.5 mm

3. Maximum Permissible Gap in Built-up Members (Clause 2.3, Table 1)

IS 7215: Built-up Section Key Specifications

1. Maximum Permissible Gap in Built-up Members (Clause 2.3, Table 1)

Note: Smaller thickness to be considered if thicknesses differ.

2. Maximum Permissible Deviation in Depth/Width at Joints (Clause 2.4, Table 2)

3. Maximum Permissible Out-of-Square of Flanges (Clause 2.9.1, Table 3)

Additional Notes:

• The gap and deviation limits ensure proper fit and structural integrity.
• Out-of-square limits control flange alignment critical for load distribution.
• All dimensions in millimeters.
• Applies to riveted or welded built-up members,

IS 7215: Tolerances on Dimensions of Steel Members

Key Tolerances:

1. Depth of Girders (Clause 3.1):

   • Solid & open web girders depth deviation: +3 mm / -2 mm
   • Refer Fig. 10 for tolerance illustration.

2. Alignment of Lattice Beams (Clause 5.1):

   • Lateral deviation of nodal points perpendicular to axial plane:
     [ \pm 0.001 \times \text{span} \quad \text{(max ±10 mm)} ]
   • See Fig. 17 for deviation details.

3. Maximum Permissible Gap in Built-up Members (Clause 2.3):

• Smaller thickness is considered when thicknesses differ.
• See Figs. 1, 2, 3 for gap locations.

Summary Diagram (Tolerance on Depth of Girders)

graph LR
A[Nominal Depth] --> B[+3 mm]
A --> C[-2 mm]

Note: All dimensions in millimeters; refer to IS 7215 for detailed figures and fabrication guidelines.

IS 7215: Column Height and Straightness Tolerances

1. Permissible Deviation in Column Heights (Clause 4.1, Table 5)

2. Straightness Deviation (Clause 4.2)

• Maximum deviation from straightness in both longitudinal and transverse planes:

  [ \text{Max deviation} = 0.001 \times l \quad \text{subject to a max of } 10 \text{ mm} ]

3. Buckling of Webs in Plate Girders (Clause 3.5)

Summary Diagram of Tolerances:

graph LR
A[Column Height l] --> B{Length ≤ 10 m?}
B -- Yes --> C[± 5 mm]
B -- No --> D[± 0.0005 × l, max 8 mm]

E[Straightness Deviation] --> F[≤ 0.001 × l, max 10 mm]

G[Web Buckling] --> H{Length}
H -- ≤ 500 mm --> I[0.5 mm max]
H -- 501 to 1000 mm --> J[1.0 mm max]
H -- > 1000 mm --> K[2.0 mm max]

Use these limits to ensure column fabrication and erection meet IS 7215 standards for structural safety and performance.

IS 7215: Deviations in the Alignment of Beams

1. Lateral Deviation of Nodal Points (Clause 5.1 & 5.2)

• Lateral deviation (δ) perpendicular to the beam's axial plane must satisfy:

  [ \delta \leq \pm 0.001 \times l \quad \text{(where } l = \text{span of beam in mm)} ]

• Maximum deviation capped at ±10 mm.

• Between consecutive nodal points (panel length (a)):

2. Deviation in Depth and Width at Joints (Clause 2.4, Table 2)

Summary Diagram (Beam Alignment)

graph LR
A(Theoretical Axis of Beam) --- B(Actual Axis of Beam)
B --- C(Nodal Points)
C --- D(Panel Length \(a\))

Note: Always check lateral deviations after fabrication or trial assembly to ensure alignment within prescribed limits.

Key Specifications & Formulas for Crane Gantry Girders (IS 7215)

1. Permissible Distortion in Plate Lattice & Box Girders

• Max distortion (transverse direction) = 0.001 × ( l )
  where ( l ) = length of diagonal of the profile (Clause 5.4)

2. Curvature of Crane Gantry Girders (Horizontal Plane)

• Max curvature = 3 mm per 12 m length (Clause 6.1)

3. Tolerances on Crane Girder Dimensions (from Table 5, Clause 4.1)

4. Maximum Permissible Out-of-Square of Flanges in Built-up Girders (Table 3, Clause 2.9.1)

Summary Diagram: Crane Girder Tolerances

graph LR
A[Crane Gantry Girder] --> B[Curvature ≤ 3 mm/12 m]
A --> C[Permissible Distortion ≤ 0.001 × diagonal length]
A --> D[Tolerances on Height & Distances]
D --> D1[Overall height ±5 mm (≤10

IS 7215 - Key Specifications on Deviation in Internal Dimensions of Openings

1. Tolerance on Internal Dimensions of Openings (Clause 7.1)

• Unless otherwise specified, tolerance = +0 mm / -3 mm on internal dimensions of openings (e.g., floor openings, crane bridge openings).

2. Tolerance on Depth of Girders (Clause 3.1)

• Depth deviation for solid/open web girders:
  +3 mm (max) / -2 mm (min)
  (Refer Fig. 10 in IS 7215 for details)

3. Hole Dimension Deviations (Clause 10.2.1, Table 7)

*Ovality = Difference between max and min diameter measured.

4. Crane Rail Eccentricity (Clause 6.4)

• Rail eccentricity on crane girders ≤ 0.5 × web thickness.

Summary Diagram: Tolerance on Opening Dimensions

graph LR
A[Opening Internal Dimension] --> B{Tolerance}
B -->|Standard| C[+0 / -3 mm]
A --> D[Depth of Girders]
D --> E{Tolerance}
E -->|Solid/Open web| F[+3 / -2 mm]

**Use these values for fabrication and erection to ensure compliance with IS 721

IS 7215: Limit Deviations - Profile of Structures

1. Permissible Deviation in Profile Depth (Clause 8.1 & Table 6)

• For depth Y ≤ 50 mm: ± 2 mm
• For depth Y > 50 mm: ± 0.04 × Y (max 4 mm)

Note: Curvature continuity must be maintained (Fig. 20).

2. Tolerance on Depth of Girders (Clause 3.1)

• Solid and open-web girders depth deviation: +3 mm / -2 mm (Fig. 10)

3. Permissible Deviation in Column Heights (Clause 4.1, Table 5)

4. Tolerance on Openings for Equipment (Clause 7.1)

• Internal dimension tolerance: 0 mm to +3 mm

Summary Diagram: Profile Deviation Limits

graph LR
A[Depth Y ≤ 50 mm] -->|± 2 mm| B[Permissible Deviation]
C[Depth Y > 50 mm] -->|± 0.04 × Y (max 4 mm)| B
D[Solid/Open-web Girders] -->|+3 / -2 mm| E[Depth Tolerance]
F[Column Height ≤ 10 m] -->|± 5 mm| G[Height Tolerance]
H[Column Height >

IS 7215: Permissible Deviations in Bearing

Key Permissible Deviations (Clause 9.1 & 9.2 & 9.3)

Profile Deviation (Clause 8.1 & Table 6)

• Note: Curvature continuity must be maintained after fabrication or assembly.

Summary

• Thickness & diameter deviations are tightly controlled for bearing components.
• Base/seating plates and overall height have specific limits to ensure proper fit and function.
• Profile deviations depend on the section depth, emphasizing precision in fabrication.

graph TD
    A[Bearing Components] --> B[Thickness ±0.5 mm]
    A --> C[Roller Diameter ±0.4 mm]
    C --> D[≥3 Rollers Diameter Diff ±0.025 mm]
    A --> E[Base Plate Length/Width ±1 mm]
    A --> F[Overall Height ±2 mm]
    G[Profile Deviation] --> H[Depth ≤ 50 mm: ±2 mm]
    G --> I[Depth > 50 mm: ±0.04Y (max 4 mm)]

This ensures structural integrity and smooth bearing operation as per IS 7215.

IS 7215: Deviations on Dimensions of Holes for Riveting and Bolting

1. Permissible Deviations on Hole Diameter (Table 7 Summary)

• Ovality = difference between max and min hole diameter.
• Perpendicularity: max 3% of plate thickness, up to 3 mm.
• Overlapping: max overlap between holes at connection, varies by group (B or C).

2. Pitch Distance Tolerance (Clause 10.1)

• Group B: ±1 mm
• Group C: ±2 mm

3. Scratch/Groove Limits on Hole Surface (Table 8)

Summary Diagram (Hole Deviation Parameters)

graph LR