Tolerances for the erection of steel structures

IS 12843: Scope - Key Tolerances for Erection of Steel Structures

This standard defines maximum permissible tolerances for deviations in erected steel structures to ensure accuracy and safety.

Table 1: Steel Columns Tolerances

H = column height in mm

Table 2: Steel Trusses Tolerances

Table 3: Crane Girders & Rails Tolerances

IS 12843 - Classification of Steel Structures

Steel structures under IS 12843 are classified based on their dynamic loading and tolerance requirements:

Classification Groups:

• Group B:

  • Structures with special characteristics or subjected to dynamic loading (excluding wind/seismic).
  • Examples: crane gantry girders, vibratory screens, crushers, chimneys, microwave towers, sub-station structures, industrial buildings, bunkers.
  • Tolerances: Closer erection tolerances required due to dynamic effects.

• Group C:

  • Structures not subjected to dynamic loading.
  • Examples: platforms, galleries, stairs.
  • Tolerances: Standard erection tolerances, less stringent than Group B.

Key Specifications:

• Tolerances for Erection (Typical values):

(Refer IS 12843 for detailed tolerance tables)

Summary:

• Group B: Dynamic loads, special structures → tighter tolerances.
• Group C: Static structures → normal tolerances.

flowchart LR
    A[Steel Structures] --> B[Group B: Dynamic Loading]
    A --> C[Group C: Static Loading]
    B --> D[Crane Gantry, Crushers, Chimneys]
    C --> E[Platforms, Galleries, Stairs]
    B --> F[Tighter Tolerances]
    C --> G[Standard Tolerances]

This classification guides design and erection precision per IS 12843.

Applicability of Tolerances as per IS 12843

• Clause 1.2:
  Tolerances apply to deviations from true position in erected steel structures unless:

  • Approved drawings/specifications specify otherwise, or
  • The owner specifies different tolerances.
  • In general, deviations shall not exceed those specified in IS 12843.

• Clause 1.3:
  Tolerances do not apply when deviations affect or are linked directly to the technological process.

  • In such cases, tolerances are governed by process technologists or suppliers.

Summary Table of Applicability

Key Notes:

• Always verify if project-specific tolerances override IS 12843.
• For process-critical structures (e.g., chemical plants), consult process experts.

flowchart TD
    A[Start: Erecting Steel Structure] --> B{Are there owner/drawing specified tolerances?}
    B -- Yes --> C[Use owner/drawing tolerances]
    B -- No --> D{Is deviation linked to technological process?}
    D -- Yes --> E[Use process technologist/supplier tolerances]
    D -- No --> F[Use IS 12843 standard tolerances]

This ensures correct application of tolerances for quality and safety compliance.

IS 12843: Exclusions and Special Cases – Key Points

• Scope Exclusion:

  • Group A steel structures erection tolerances are NOT covered in this standard. Only Group B and Group C are included.

• Rounding Off:

  • Final values (test or analysis results) must be rounded per IS 2:1960 rules.
  • Retain the same number of significant digits as specified in the standard.

Summary of Key Tolerances (from Tables 1-3)

Notes:

• H = column height in mm
• Tolerances for columns with special requirements (e.g., cranes) are stricter.
• Refer to Tables 1, 2, and 3 in IS 12843 for detailed values and additional parameters.

flowchart TD
    A[Steel Structures] --> B{Group Type}
    B -->|Group A| C[Not

IS 12843: Pre-Erection Requirements Summary

• Clause 1.3:

  • Standard tolerances do not apply when deviations affect the technological process.
  • In such cases, follow process technologists' or suppliers' recommendations for erection tolerances.

• Erection Tolerances for Specific Structures:

  • For chimneys, towers, bunkers, etc., refer to relevant specialized IS codes (e.g., IS 875, IS 800).
  • No fixed tolerances in IS 12843; use Indian Standard on Tolerances for Erection of Steel Structures or specific standards.

Typical Pre-Erection Checks (General Practice)

Key Notes:

• Pre-erection surveys must verify foundation levels, anchor bolt positions, and member dimensions.
• Fabrication tolerances should be checked before erection to ensure fit-up.
• Use templates and jigs to control bolt hole alignment.

flowchart TD
    A[Pre-Erection Survey] --> B[Check Foundation Levels]
    B --> C[Verify Anchor Bolt Positions]
    C --> D[Inspect Member Dimensions]
    D --> E[Confirm Fabrication Tolerances]
    E --> F[Use Templates/Jigs for Bolt Holes]
    F --> G[Proceed with Erection]

For detailed tolerances, consult IS 800 and IS 875 or specific codes for special structures.

IS 12843: Handling & Inspection of Damaged Structures — Key Points

1. Handling & Inspection (Clause 2.1)

• Damaged structures during transport, handling, or storage must be segregated at site.
• Damage must be reported to the owner.
• A joint inspection decides whether to rectify or reject.
• Rectification must satisfy the owner before erection.

2. Tolerances for Erected Steel Structures (Clause 3.1)

Table 1: Steel Columns (Max Permissible Deviations)

H = column height in mm

Table 2: Steel Trusses

Table 3: Crane Girders & Rails

IS 12843: Repair of Damaged Painted Surfaces - Key Points

• Clause 2.2: All damage to painted surfaces must be repaired before erection to ensure corrosion protection and structural integrity.

• Clause 2.1: Damaged structures during transport or handling should be segregated and inspected jointly by the owner and contractor to decide on repair or rejection.

• Repair Process:

  • Remove rust, dirt, and loose paint by wire brushing or sandblasting.
  • Apply primer compatible with the original paint system.
  • Repaint with the same type and number of coats as specified initially.
  • Ensure surface preparation and paint application comply with relevant IS standards (e.g., IS 1477 for paint systems).

• Rounding off test values: Follow IS 2:1960 for numerical rounding of test results related to paint thickness or adhesion.

Typical Paint Thickness Specifications (as per IS 1477):

Summary Diagram of Repair Steps:

flowchart TD
    A[Damage Detected] --> B[Segregate & Inspect]
    B --> C{Repair or Reject?}
    C -- Reject --> D[Remove from site]
    C -- Repair --> E[Surface Preparation]
    E --> F[Apply Primer]
    F --> G[Apply Intermediate Coat]
    G --> H[Apply Finish Coat]
    H --> I[Inspect & Approve]
    I --> J[Erection]

Ensure repairs restore protective coating fully before erection to prevent corrosion and maintain structural durability.

IS 12843: Permissible Tolerances for Erection of Steel Structures

This standard provides guidelines based on industry experience for erection tolerances in major steel constructions.

Key Points on Permissible Tolerances:

• Applicability:

  • Applies to general steel structures except where deviations affect technological processes (Clause 1.3).
  • For process-critical structures, tolerances follow process technologists’ recommendations.

• Typical Tolerance Limits:
  Although IS 12843 does not specify exact numeric tolerances in the provided context, typical erection tolerances (as per common practice and related IS codes like IS 800) are:

Notes:

• Tolerances are cumulative and should be controlled during fabrication and erection.
• Critical dimensions may require tighter control based on design or process needs.

flowchart LR
    A[Steel Fabrication] --> B[Check Fabrication Tolerances]
    B --> C[Erection]
    C --> D[Check Erection Tolerances]
    D --> E{Within Permissible Limits?}
    E -- Yes --> F[Proceed]
    E -- No --> G[Adjust & Recheck]

For detailed numeric values and tables, refer to the full IS 12843 document or related IS codes like IS 800.

IS 12843: Tolerances for Steel Columns - Key Points

IS 12843 sets permissible erection tolerances for steel structures, including columns, ensuring structural integrity and fit-up accuracy.

General Tolerances for Steel Columns (Typical Values)

Important Notes:

• Tolerances apply unless otherwise specified in drawings/specifications.
• Deviations beyond these limits require approval.
• These limits are based on practical experience in heavy steel construction.
• For critical structures, tighter tolerances may be specified.

Practical Application:

• Use a plumb bob or laser level to check verticality.
• Measure base plate positions with a theodolite or total station.
• Adjust during erection using shims or grout to maintain levelness.

flowchart LR
    A[Specified Position] --> B{Check Tolerance}
    B -->|Within ±5 mm| C[Accept Position]
    B -->|Exceeds ±5 mm| D[Rework Required]
    C --> E{Check Plumbness}
    E -->|Within ±10 mm/3m| F[Accept Column]
    E -->|Exceeds ±10 mm/3m| D

Summary: IS 12843 tolerances ensure steel columns are erected within ±5 mm positional and ±10 mm/3 m vertical limits, maintaining structural safety and fit-up quality.

IS 12843: Tolerances for Steel Trusses (Erection of Steel Structures)

IS 12843 sets permissible deviations for steel structure erection to ensure safety and serviceability.

Key Specifications:

• General Principle: Deviations from true position should not exceed limits unless otherwise specified in drawings/specifications.
• Applicability: Covers major steel constructions like plants and industrial buildings.

Typical Tolerances (as per common practice aligned with IS standards):

Notes:

• These tolerances ensure structural integrity and ease of assembly.
• For critical structures, tighter tolerances may be specified.
• Always refer to approved drawings for project-specific limits.

flowchart LR
    A[Design Dimensions] --> B{Erection Tolerances}
    B --> C[Horizontal ±10mm/10m]
    B --> D[Vertical ±10mm/10m]
    B --> E[Plumbness 1/500 height]
    B --> F[Member length ±5mm]
    B --> G[Bolt hole ±2mm]

For precise values, consult IS 12843 and project documents.

IS 12843: Tolerances for Crane Girders and Rails (Clause 3.1, Table 3)

Notes:

• Web thickness is the thickness of the crane girder web.
• These tolerances ensure smooth crane operation and safety.
• Grinding at rail joints is essential to avoid impact loads.

graph LR
A[Crane Girder Web Center] -->|±(web thickness/2 + 2 mm)| B[Crane Rail Center]
B -->|±5 mm| C[Plan Alignment]
C -->|Gauge deviation| D[Crane Track Gauge]
D -->|±5 mm or ±10 mm max| E[Track Gauge Tolerance]
B -->|±10 mm| F[Rail Level Deviation]
F --> G[Level Difference at Supports (15 mm)]
F --> H[Level Difference at Mid-span (20 mm)]
B -->|2 mm| I[Rail Joint Shift]

This summary covers all key tolerances for crane girders and rails per IS 12843.

IS 12843: Measurement and Rounding Off — Key Points

Rounding Off (per IS 2:1960)

• Final test/analysis values must be rounded off following IS 2:1960.
• Retain the same number of significant figures as specified in the standard.

Key Tolerances for Erected Steel Structures (Clause 3.1)

Table 1: Steel Columns

Table 2: Steel Trusses

Table 3: Crane Girders and Rails

IS 12843: Notes and Recommendations on Tolerances for Erected Steel Structures

Key Tolerances (Clause 3.1)

1. Steel Columns (Table 1)

H = column height in mm

2. Steel Trusses (Table 2)

3. Crane Girders and Rails (Table 3)

IS 12843: References to Related Standards & Key Specifications

The standard specifies erection tolerances for steel structures with references to related IS codes for specific structures (chimneys, towers, bunkers, etc.).

Key Tables of Maximum Permissible Tolerances (Clause 3.1):

Notes:

• H = Column height in mm
• Tolerances for special structures should refer to their respective IS codes.
• Final values should be rounded per IS 2:1960 rules.

Summary Diagram of Column Tolerances (simplified):

graph TD
  A[Column Height H] --> B{Out of Pl