Code of practice for design and construction of steel chimneys, Part 2: Structural aspects

IS 6533 Part 2: Scope - Key Points & Formulas

• Scope: Covers design, dimensions, and stresses for steel shell structures under various loads.

Key Clauses & Tables:

• Clause 7.2: Basic Dimensions
  Defines fundamental geometric parameters for shell components.

• Clause 7.7.2: Maximum Permissible Stresses

  • Refer to Table 3 for allowable stresses.
  • Stresses derived using formulas in Annex C (typically stress = load/area with safety factors).

• Clause 7.8.1: Allowance for Large Openings

  • Table 7.11 (Temperature Coefficient, Kt):

• Intermediate values are linearly interpolated.

• Clause 5.8: Materials used with steel must conform to relevant Indian Standards.

• Clause 6: Specifies loading and load combinations for design.

Typical Stress Formula (from Annex C):

[ \sigma = \frac{M}{Z} \quad \text{or} \quad \sigma = \frac{P}{A} ]

• ( \sigma ) = stress
• ( M ) = bending moment
• ( Z ) = section modulus
• ( P ) = axial load
• ( A ) = cross-sectional area

If you need detailed tables or formulas from Annex C or Table 3, please specify!

IS 6533 Part 2: Definitions and Components — Key Points

1. Definitions (Clause 4.1 to 4.40)

• This section provides standardized terminology for pressure vessels, shells, components, and related structural elements.
• Essential for consistent interpretation of design and fabrication requirements.

2. Basic Dimensions (Clause 7.2)

• Specifies fundamental dimensions for components like shells, heads, and openings.
• Dimensions ensure compatibility and structural integrity.

3. Maximum Permissible Stresses (Clause 7.7.2 & Table 3)

• Stresses calculated using formulas in Annex C.
• These stresses guide design limits for materials under pressure and temperature.

4. Temperature Coefficient, Kt (Clause 7.8.1, Table 4)

• Kt adjusts allowable stresses for temperature effects.
• Intermediate values are linearly interpolated.

Summary Diagram of Component Relations

graph TD
  A[Pressure Vessel] --> B[Shell]
  A --> C[Heads]
  A --> D[Openings]
  B --> E[Basic Dimensions (7.2)]
  C --> F[Maximum Stresses (7.7.2)]
  D --> G[Temperature Coefficient Kt (7.8.1)]

Use these definitions, dimensions, and coefficients to ensure safe, code-compliant vessel design.

IS 6533 Part 2: Materials and Fabrication - Key Points

Materials (Clause 5.8)

• All materials associated with steel works must conform to relevant Indian Standards (IS) where applicable.
• Steel yield stress, fy = 250 MPa for IS 226 and IS 2062 steels.

Fabrication - Buckling and Stress Control (Clause 1.1, Table C-1 & Annex C)

• Compressive stresses to control buckling are calculated by:

[ \sigma_c = \frac{A \cdot fy}{B} ]

Where:

Table 2 (Effective Height (h_e)) - Example values (from amendment)

Fabrication Notes

• Thickness and diameter must be carefully controlled.
• Use IS-approved welding and fabrication practices.
• Load combinations per Clause 6 must be considered in design.

Summary Diagram: Buckling Stress Calculation Flow

flowchart TD
    A[Start: Known dimensions D, t, h_e] --> B[Calculate A]
    B --> C[Calculate B]
    C --> D[Calculate compressive stress σ_c = A * fy / B]
    D --> E[Check σ_c against permissible stress]

References:

• Clause 5.8 (Materials conformity)
• Clause 1.1 & Annex C (Buckling stress formula)
• Table 2 (Effective

IS 6533 Part 2: Load Combinations Summary

Key Load Combinations (Clause 6.5)

For chimney and foundation design, consider the following to find maximum stresses:

Foundation Design (Clause 7.14)

• Design for worst-case load combination.
• Ensure soil pressure ≤ safe bearing capacity.
• Account for temperature and seasonal effects.

Stress Increase for Earthquake (Clause 7.10)

• Permissible stresses may increase by 33% under earthquake loads.
• Steel thickness must not be less than minimum specified or thickness used without earthquake load.

Practical Notes:

• Always use the load combination that produces maximum design forces.
• Check foundation stability under combined vertical and horizontal loads.
• Refer to relevant IS codes for material specs and soil bearing capacity.

flowchart TD
    A[Start: Determine Loads] --> B{Select Load Combination}
    B --> C[Dead + Wind]
    B --> D[Dead + Earthquake]
    B --> E[Dead + Lining + Imposed + Wind]
    B --> F[Dead + Lining + Imposed + Earthquake]
    C --> G[Calculate Stresses]
    D --> G
    E --> G
    F --> G
    G --> H{Check Stress Limits}
    H -- Earthquake --> I[Allow 33% Stress Increase]
    H -- Else --> J[Use Normal Stress Limits]
    I --> K[Ensure Min Thickness]
    J --> K
    K --> L[Design Foundation for Max Load]
    L --> M[Check Soil Bearing Capacity]
    M --> N[Complete Design]

This concise summary aligns with IS 6533 Part 2 requirements for load combinations in chimney design.

IS 6533 Part 2: Design Stresses & Thickness Calculations

1. Maximum Permissible Stress (Clause 7.7 & Table 3)

• Controls buckling by limiting compressive stress (bending + direct load).
• Depends on:
  • Ratio ( h_e/D ) (effective height to diameter)
  • Ratio ( D/t ) (diameter to thickness)
  • Steel grade per IS 226 & IS 2062
• Stress values reduce for temperature and corrosion allowance.

Intermediate values can be linearly interpolated.

2. Key Parameters

• ( t ) = plate thickness (m)
• ( D ) = mean diameter at level (m)
• ( h_e ) = effective height for buckling (m)

3. Formulae (Annex C)

• Maximum compressive stress ( \sigma_{max} ) calculated considering bending and direct load.
• Use Table 3 values as limits for ( \sigma_{max} ).

Summary for Thickness Calculation:

• Choose ( t ) such that: [ \sigma_{actual} \leq \sigma_{permissible}(h_e/D, D/t) ]
• Adjust ( t ) for corrosion allowance.
• Check buckling via ( h_e/D ) ratio.

flowchart TD
    A[Input: D, h_e, Steel Grade] --> B[Calculate D/t ratio]
    B --> C[Refer Table 3 for max permissible stress]
    C --> D[Calculate actual shell stress]
    D --> E{Is actual stress ≤ permissible stress?}
    E -- Yes --> F[Thickness OK]
    E -- No --> G[Increase thickness t and repeat]

This ensures safe design against buckling and compressive failure per IS

Wind Load and Dynamic Effects (IS 6533 Part 2)

1. Static Wind Load (Clause 8.2)

• Calculate static transverse force (F_st,z), bending moment (M_st,z), and deflection (Y_st,z) at level z due to steady wind pressure.
• Use wind pressure coefficients and shape factors as per IS code.

2. Dynamic Wind Load (Clause 8.3)

• Dynamic effects consider oscillations; calculate dynamic transverse force (F_dyn,z), bending moment (M_dyn,z), and deflection (Y_dyn,z).
• Total design lateral force, bending moment, and deflection at level z are combined from static and dynamic components.

3. Resonance Effects (Clause 8.4.3)

• At resonance, design forces and moments are given by:

[ \begin{aligned} F_{\text{res},z} &= \sqrt{F_{\text{st},z}^2 + F_{\text{dyn},z}^2} \ M_{\text{res},z} &= \sqrt{M_{\text{st},z}^2 + M_{\text{dyn},z}^2} \ Y_{\text{res},z} &= \sqrt{Y_{\text{st},z}^2 + Y_{\text{dyn},z}^2} \end{aligned} ]

4. Total Design Wind Load for kth Zone (Clause 8.3.7)

[ \begin{aligned} P_k &= P_{\text{st},k} + \sqrt{\sum_{i=1}^s (P_{\text{dyn},k}^i)^2} \ M_k &= M_{\text{st},k} + \sqrt{\sum_{i=1}^s (M_{\text{dyn},k}^i)^2} \ Y_k &= Y_{\text{st},k} + \sqrt{\sum_{i=1}^s (Y_{\text{dyn},k}^i)^2} \end{aligned} ]

• s = number of oscillation modes considered.

Summary Table

IS 6533 Part 2: Stability & Foundation Design — Key Points

1. Foundation Design (Clause 7.14)

• Design for worst load combinations (dead, live, wind, seismic).
• Ensure soil pressure ≤ safe bearing capacity.
• Consider temperature and seasonal effects on soil and foundation.

2. Stability Checks (Clause 9.1.3)

• Ensure resultant soil pressure and shear forces do not cause foundation failure.
• Check overturning, sliding, and bearing capacity.

3. Design of Base Plate (Clause 8.6)

• Calculate max stresses in base plate, stiffeners, and foundation bearing pressure.
• Follow IS 800:1984 (steel structures) and IS 456:1978 (concrete design) for permissible stresses.

Essential Formulas:

• Soil Bearing Pressure:

[ q = \frac{P}{A} \leq q_{safe} ]

where:
(P) = total vertical load,
(A) = foundation area,
(q_{safe}) = safe bearing capacity of soil.

• Factor of Safety (FOS):

[ FOS = \frac{q_{ultimate}}{q_{allowable}} \geq 3 \text{ (typical)} ]

• Base Plate Bearing Pressure:

[ p = \frac{P}{A_{plate}} + \frac{M}{Z} ]

where:
(P) = axial load,
(M) = moment,
(Z) = section modulus of base plate.

Typical Checks for Stability:

• Overturning:

[ \sum M_{resisting} \geq \sum M_{overturning} ]

• Sliding:

[ F_{friction} \geq F_{horizontal} ]

where friction force (F_{friction} = \mu \times P).

flowchart TD
    A[Load Combinations] --> B[Calculate Resultant Forces]
    B --> C[Check Soil Pressure ≤ Safe Bearing Capacity]
    B --> D[Check Shear & Moment on Base Plate]
    C --> E[Design Foundation Dimensions]
    D --> F[Design Base Plate & Stiff

IS 6533 Part 2: Miscellaneous Components - Key Formulas & Tables

1. Temperature Coefficient, Kt (Clause 7.8.1, Table 4)

• Note: Intermediate values are linearly interpolated.
• Use: Adjust allowable stresses for large openings in shells based on temperature.

2. Coefficient of Pulsation of Speed Thrusts, mk (Clause 8.3.4, Table 6)

• Type A: Open locations (steppe, desert, sea coast).
• Type B: Outskirts, forests, regular obstacles >10 m.

3. Maximum Permissible Stresses (Clause 7.7.2)

• Derived using formulas in Annex C (not provided here).
• Used for design stress limits in components.

4. Basic Dimensions (Clause 7.2)

• Defines standard dimensional parameters for components (refer to IS 6533 Part 2 for specifics).

Summary Diagram: Temperature Effect on Allowable Stress

graph LR
A[Temperature (℃)] --> B[Kt Value]
B --> C{Stress Adjustment}
C --> D

Key Specifications and Formulas for Construction (IS 6533 Part 2)

1. Foundation Design (Clause 7.14)

• Design for worst load combinations (Clause 6).
• Ensure soil pressure ≤ safe bearing capacity.
• Consider dead weight, movements, horizontal forces.
• Account for temperature & seasonal effects.

2. Loading and Load Combinations (Clause 6)

• Use maximum permissible stresses from Table 3.
• Stresses calculated using formulas in Annex C.

3. Buckling and Compressive Stress Control (Annex C, Clause 1.1)

• Compressive stress formula controlling buckling:

[ \sigma = A \cdot f_y / B ]

Where:

4. Material Specifications (Clause 5.8)

• Materials must conform to relevant Indian Standards.

Summary Table: Buckling Parameters

flowchart TD
    A[Start: Load Combinations] --> B[Calculate Soil Pressure]
    B --> C{Pressure ≤ Safe Bearing Capacity?}
    C

IS 6533 Part 2: Inspection and Maintenance Key Points

Inspection & Maintenance Records (Clause 12.6)

• After each inspection, submit a detailed record describing:
  • Condition observed
  • Recommended maintenance actions

Inspection Door (Clause 10.5)

• Provide an inspection door near the base for internal access and ash removal.
• Minimum size:
  • Width = 500 mm
  • Height = 800 mm
• Refer Fig. 3 for door and boiler duct details.

Guy Wire & Fittings (Clause 12.7)

• Examine for:
  • Security
  • Proper tension
• Clean and grease if necessary.

Surface Preparation & Metal Spraying (Clause 13.4.2)

• Follow IS 6586:1972 for surface preparation and metal spraying.
• Consider surface temperature of the shell during treatment.

Typical Base Details (Fig. 2)

• Stiffener: ISMB 250 section
• Stiffener plate thickness: 12 mm
• Anchor channel: 15MC 150
• Foundation bolt and cast steel base in sections

flowchart TD
    A[Inspection] --> B[Record Condition & Recommendations]
    A --> C[Check Guy Wire & Fittings]
    C --> D[Clean & Grease if needed]
    A --> E[Inspect Door (500x800 mm)]
    A --> F[Surface Prep & Metal Spraying per IS 6586]

Summary: Maintain detailed inspection logs, ensure access via specified door size, check and maintain guy wires, and follow IS 6586 for surface treatments.

IS 6533 Part 2: Surface Preparation & Protective Treatment Key Points

Surface Preparation (Clause 13.4.3 & 13.4.3.1)

• Follow IS 6586:1972 for surface prep and metal spraying.
• Surface temperature considerations per recognized practices.
• Blast-cleaned surface roughness (amplitude):
  [ 0.1 \pm 0.05 \text{ mm} ]
• Surface must be clean and sufficiently rough to ensure proper adhesion of sprayed aluminum coating.

Specifications (Clause 13.4.2)

• Surface prep and metal spraying must comply with IS 6586:1972.
• Ensure removal of contaminants before coating.

Application of Sealing Coats (Clause 13.4.4.5)

• Apply only on clean, dry surfaces.
• Remove oil/grease by washing with thinners until no contamination visible.
• Dry surface for at least 15 minutes before sealing.
• Apply sealing coats to produce a wet appearance.
• Follow manufacturer’s instructions strictly.
• Apply sealing coat immediately after spraying, preferably at contractor’s works.

Summary Table

flowchart TD
    A[Surface Preparation] --> B[Blast Cleaning]
    B --> C{Surface Roughness}
    C -->|0.1 ± 0.05 mm| D[Clean & Rough Surface]
    D --> E[Metal Spraying]
    E --> F[Sealing Coat Application]
    F --> G[Clean, Dry Surface]
    G --> H[Remove Contaminants with Thinners]
    H --> I[Dry for ≥15 mins]
    I --> J[Apply Sealing Coat (Wet Appearance)]

This ensures optimal adhesion and corrosion protection per IS 6533 Part 2.