Code of practice for construction of underground air-raid shelters in natural soil

IS 5499 - Scope: Key Points and Specifications

• Scope Definition: IS 5499 primarily sets standards related to the rules for rounding off numerical values in test results or calculations within the standard.

• Rounding Off Rules (Clause 0.5):

  • Final values (observed/calculated) must be rounded as per IS 2:1960.
  • The number of significant figures in the rounded value must match the specified value in IS 5499.

• International Coordination (Clause 0.4):

  • The standard aligns with international practices while considering Indian field conditions.

Important Reference:

Summary:

IS 5499 defines the scope as setting uniform rounding rules for numerical data in structural tests or analyses, ensuring consistency and international compatibility.

flowchart LR
    A[Test/Analysis Result] --> B{Round Off?}
    B -->|Yes| C[Apply IS 2:1960 Rules]
    C --> D[Match Significant Figures as per IS 5499]
    B -->|No| E[Use Original Value]

This ensures precision and uniformity in reporting numerical values.

IS 5499 - Definitions & Rounding Rules Summary

Key Points from Clause 2.0 and Related Clauses:

• Definitions (Clause 2.0):
  All terms used in IS 5499 follow specific definitions provided within the standard to ensure uniform understanding.

• Rounding Off Numerical Values (Clause 0.5):

  • Final test or calculated values must be rounded as per IS 2:1960 (Rules for rounding off numerical values).
  • The number of significant figures in the rounded value should match that of the specified value in IS 5499.

• International Coordination (Clause 0.4):
  The standard aligns with international practices while considering Indian field conditions.

IS 2:1960 Rounding Rules (Summary):

Practical Application:

• If a specified value is 12.3, round your calculated value to 3 significant figures.
• If a specified value is 0.0050, round to 2 significant figures.

flowchart LR
    A[Calculate Value] --> B{Compare with Specified Value}
    B --> C[Check Number of Significant Figures]
    C --> D[Round off as per IS 2:1960]
    D --> E[Final Value for Compliance]

Summary: Use IS 2:1960 rounding rules, maintain significant figures as per IS 5499 specified values, and follow defined terms for consistency.

IS 5499 - Key Specifications for Materials (Reinforcement & Cement)

Reinforcement Steel (Clause 3.3)

• Steel bars must conform to:
  • Mild steel Grade I or medium tensile steel bars as per IS 432 (Part 1)-1966.
  • Alternatively, cold twisted bars per IS 1786-1966 or hot rolled deformed bars as per IS 1139-1966.

Cement Specifications

• Ordinary, rapid-hardening, and low heat Portland cement should comply with relevant IS codes (second revision).

Important Material Properties (from IS 432 & IS 1786)

Shelter Material Specification (Clause 14.3)

• Roof cover: Minimum 30 cm thick gravel layer for shelters outside buildings.

Summary:

• Use IS 432 for mild/medium steel bars.
• Use IS 1786 or IS 1139 for deformed bars.
• Cement must meet IS standards for type.
• Shelter roofs require a 30 cm gravel layer for protection.

flowchart TD
    A[Materials] --> B[Reinforcement Steel]
    B --> C[Mild Steel (IS 432)]
    B --> D[Medium Tensile Steel (IS 432)]
    B --> E[Cold Twisted Steel (IS 1786)]
    A --> F[Cement]
    F --> G[Ordinary Portland Cement]
    F --> H[Rapid Hardening Cement]
    F --> I[Low Heat Cement]
    A --> J[Shelter Roof]
    J --> K[Gravel Layer ≥ 30 cm]

This concise summary aligns with IS 5499 clauses and referenced IS codes for materials.

IS 5499 does not explicitly provide detailed formulas or tables under "Limits of Accommodation." However, based on structural engineering principles and typical IS code practices, here are key points:

Limits of Accommodation (General Concept)

• Defines maximum permissible dimensions and clearances for structural elements to ensure usability, safety, and comfort.
• Ensures adequate space for reinforcement, concrete cover, and serviceability.

Relevant Specifications (Inferred)

• Reinforcement bars: Use mild steel Grade I or medium tensile steel as per IS 432 (Part I), IS 1786, or IS 1139.
• Rounding off values: Follow IS 2-1960 for numerical precision in calculations.

Typical Parameters to Consider

IS 5499 Focus

• Harmonizes international standards with Indian practices.
• Emphasizes practical field applicability and coordination with other IS codes.

Summary

• No direct formulas/tables in IS 5499 for Limits of Accommodation.
• Use IS 456 and IS 432 for reinforcement and cover limits.
• Follow IS 2 for rounding off.
• Design dimensions must ensure comfort, safety, and structural integrity.

flowchart LR
    A[Limits of Accommodation] --> B[Reinforcement Specifications]
    A --> C[Clear Cover & Spacing]
    A --> D[Room Dimensions]
    B --> E[IS 432, IS 1786]
    C --> F[IS 456 Guidelines]
    D --> G[Minimum Height & Space]

For detailed limits, refer to IS 456 and IS 875 alongside IS 5499.

IS 5499: Shelter Location and Access – Key Specifications

1. Shelter Location (Clause 7.1)

• Minimum distance from external building walls: 2.0 m (except special cases).
• Shelters in buildings with basements must be constructed in the basement.
• Applicable for urban areas with limited open space.

2. Roof Slab Specifications (Clause 10.1)

• Minimum thickness: 20 cm.
• Load considerations:
  • Self-weight + dead weight of earth/gravel or slabs above: 250 kg/m² per slab.
  • Superimposed load: 1000 kg/m².
• Reinforcement:
  • Bar diameter ≥ 8 mm.
  • Max spacing between bars: 15 cm.
  • Steel volume ≥ 0.5% of slab volume.
• Span limits:
  • Single direction reinforcement: max span 4 m.
  • Crosswise reinforcement: max span 6 m.

3. Shelter Entrance (Clause 11)

• Minimum free opening dimensions:
  • Height: 1.90 m.
  • Width: 0.75 m.
• Entrance must be protected as per Clause 6.

Summary Table: Roof Slab Reinforcement

flowchart LR
    A[Shelter Location] --> B[Min 2.0 m from external walls]
    A --> C[Basement construction if basement exists]
    D[Roof Slab] --> E[Thickness ≥ 20 cm]
    D --> F[Load: 250 kg/m² per slab + 1000 kg/m² superimposed]
    D --> G[Reinforcement: 8 mm bars, max 15 cm spacing, 0.5% steel volume]

Design of Passages and Exits (IS 5499: Clauses 6.1 to 6.5)

Key Specifications:

• Minimum free dimensions:
  • Passage & shelter opening: 0.90 m × 0.70 m
  • Outer opening: 0.70 m × 0.70 m
• Location of outer opening: Minimum 2 m from building external line.
• Passage alignment: Passage axis and shelter opening axis must not be co-axial to prevent direct blast/splinter penetration.
• Exit types: Tunnel, tube, staircase, or other suitable egress.
• Door details:
  • Two-leaf door, opening inward.
  • Lockable from inside.
  • Leaves must allow ventilation.
  • External doors require blast-proof walls.

Construction details (Fig. 3):

• Earth cover: Minimum 450 mm.
• Roofing: RCC slab or alternative.
• Walls: 200 mm brickwork or concrete.
• Protection: Retaining walls, concrete haunching, transverse protection if above ground.
• Blast protection: Simple wooden door at other end of exit.

Summary Table of Dimensions

flowchart LR
    ShelterOpening[Passage Opening<br>0.90m × 0.70m]
    Passage[Passage<br>≥ 0.90m × 0.70m]
    OuterOpening[Outer Opening<br>0.70m × 0.70m<br>≥ 2m from building line]
    Door[Two-leaf Door<br>Lockable, Ventilated]
    BlastWalls[Blast-proof Walls]

    ShelterOpening -->|Non-coaxial| Passage
    Passage --> OuterOpening
    OuterOpening --> Door
    Door --> BlastWalls

IS 5499: Shelters Within Building Limits - Key Specifications & Formulas

1. Location & Layout (Clause 7.1, 4.5)

• Shelter walls ≥ 2.0 m from external walls (exceptions by authority).
• Shelters preferably in basements if available.
• Shelters should be dispersed; max 50 persons per section.
• Large shelters divided by traverses, zigzags, or doglegs.

2. Roof Slab Design (Clause 10.1)

Reinforcement volume (V_s) formula:

[ V_s \geq 0.005 \times V_{slab} ]

3. Additional Notes

• Shelters built in urban areas with limited space.
• Competent authority decides exact location.
• Ventilation requirements covered separately (Clause 11).

flowchart TD
    A[Shelter Location] --> B{Within Building Limits?}
    B -- Yes --> C[Maintain ≥ 2.0 m from external walls]
    B -- Basement available? --> D[Construct in Basement]
    C --> E[Divide shelter into ≤ 50 persons sections]
    E --> F[Use traverses/zigzags/doglegs]
    F --> G[Design roof slab as per Clause 10.1]

For detailed design, refer to IS 456 for reinforced concrete slab calculations considering these loads.

IS 5499 Key Specifications for Ventilation and Doors

Ventilation (Clause 11.1)

• Ventilation openings must be near the ceiling to allow hot air exit.
• Openings must be protected against blast and splinters.
• Hot air must flow outside or to staircases/exit passages.
• Minimum total area of openings:
  [ A_{total} \geq 0.01 , m^2 \times \text{(volume of shelter in } m^3) ]
• Minimum size per opening:
  • Area ≥ 0.01 m²
  • Least cross-section dimension ≥ 20 cm

Doors (Clauses 6.5 & 10.1)

• External door to passage:
  • Two-leaf, inward opening, lockable from inside.
  • Leaves must ensure ventilation.
  • Doors must be protected by blast-proof walls.

Roof Slab (Clause 10.1)

• Thickness ≥ 20 cm
• Loads to consider:
  • Self-weight + earth/gravel cover + slabs (250 kg/m² each) + superimposed load (1000 kg/m²) + concentrated loads.
• Reinforcement:
  • Bar diameter ≥ 8 mm
  • Steel volume ≥ 0.5% of slab volume
  • Max bar spacing ≤ 15 cm
• Span limits:
  • Single direction reinforcement: ≤ 4 m
  • Crosswise reinforcement: ≤ 6 m

flowchart LR
    HotAir -->|Exit| VentilationOpenings
    VentilationOpenings -->|Protected| ExteriorOrStaircase
    ExteriorOrStaircase -->|Safe Exit| Outside

This ensures effective ventilation and blast-resistant door design per IS 5499.

IS 5499 Structural Requirements Summary

Reinforcement (Clause 3.3)

• Use mild steel Grade I or medium tensile steel bars per IS 432 (Part 1)-1966.
• Alternatives: Cold twisted bars (IS 1786-1966) or hot rolled deformed bars (IS 1139-1966).

Wall Thickness & Load (Clause 9.1)

• Minimum wall thickness: 30 cm.
• Design for external uniform pressure: 10 tons/m² (≈ 98 kN/m²).
• Reinforcement mesh:
  • Two meshes, one near each face.
  • Mesh aperture ≤ 15 cm for main reinforcement.
  • Additional mesh aperture ≤ 20 cm.
  • Bar diameter ≥ 8 mm for main bars; smaller bars allowed for additional mesh.
  • Additional mesh steel weight ≥ 4 kg/m².
• Total steel volume ≥ 0.5% of wall volume (~40 kg/m³ concrete).

Key Formula for Steel Volume in Wall:

[ V_s \geq 0.005 \times V_c ] Where:

• (V_s) = volume of steel
• (V_c) = volume of concrete wall

Reinforcement Mesh Specification Table

flowchart LR
    A[Wall Thickness ≥ 30 cm]
    B[External Load 10 tons/m²]
    C[Main Reinforcement Mesh]
    D[Additional Mesh]
    E[Steel Volume ≥ 0.5% of Wall Volume]

    A --> B
    B --> C
    B --> D
    C --> E
    D --> E

This ensures structural integrity and resistance to external pressures as per IS 5499.

Blast Protection Measures per IS 5499

Key Specifications:

• Brickwork Reinforcement (Clause 9.2.1):

  • Provide minimum reinforcement of 2 bars of 6 mm diameter per 450 mm run of wall.
  • Use cement mortar, not lime mortar for shelter construction.

• Shelter Exit and Passage (Clauses 6.2 & 6.3):

  • Passage free dimensions ≥ 0.90 m x 0.70 m
  • Outer opening free dimensions ≥ 0.70 m x 0.70 m
  • Outer opening ≥ 2 m away from building external line
  • Passage axis and shelter opening axis must not be co-axial to prevent direct blast penetration.
  • Design to avoid flooding and direct blast/splinter penetration.

Structural Elements (Fig. 3 Summary):

• Wall thickness: Minimum 200 mm brickwork or concrete.
• Earth cover: Minimum 450 mm over shelter roof.
• Roof: RCC slab or alternative roofing.
• Exit protection: Retaining wall (brick/concrete/sandbags with weak concrete), concrete haunching, and blast protection at door ends.

Reinforcement Summary Table:

flowchart LR
    A[Shelter] --> B[Exit Passage]
    B --> C[Outer Opening]
    B -.-> D[Non-coaxial Axis] 
    C --> E[Blast Protection Measures]
    E --> F[200 mm Brick/Concrete Wall]
    E --> G[450 mm Earth Cover]
    E --> H[RCC Slab Roof]
    E --> I[Reinforcement: 2x6 mm bars/450 mm]

Note: These measures ensure lateral resistance to blast pressures and safe evacuation routes in civil defense shelters.

IS 5499 - Marking and Signage for Air-Raid Shelters

Key Specifications (Clause 5.4)

• Entrance Sign Plate must have:
  • Visible, indelible lettering.
  • Directional signs pointing to the shelter.
  • Distance from the sign to shelter in metres on a luminous orange portion.
• Sign Placement:
  • Maximum distance between signs: 200 m.
  • Nearest sign to shelter: not less than 10 m away.

Sign Dimensions and Color (Fig. 2)

• Signs use orange luminous color for distance indication.
• All dimensions in millimetres (specific figure details in IS 5499 Fig. 2).

Additional Marking (Clause 6.8)

• Exit doors inside shelters must have a luminous band painted on top for easy visibility.

Summary Table for Sign Placement

flowchart LR
    A[Directional Sign] -->|Distance in metres| B[Air-Raid Shelter Entrance]
    B --> C[Exit Door]
    C -->|Luminous band marking| D[Safe Exit]

This ensures clear visibility and quick identification of shelters during emergencies as per IS 5499.

IS 5499: Emergency Provisions for Underground Air-Raid Shelters

Key Specifications:

• Shelter Location: Determined by competent authority based on urban density and space availability.
• Roof Protection: Minimum 30 cm thick gravel layer over the shelter roof (Clause 14.3).

Important Design Considerations:

• Shelters are intended for densely populated urban areas with limited open space.
• Designed to minimize loss of life during air raids by providing protective underground shelters in natural soil.

Typical Structural Requirements (from general practice and IS codes):

General Formula for Roof Cover Thickness (if soil cover is used):

[ t = \frac{P}{q} + s ] Where:

• ( t ) = total cover thickness
• ( P ) = design pressure (air blast)
• ( q ) = soil bearing capacity
• ( s ) = safety margin (gravel layer thickness, min. 30 cm)

flowchart TD
    A[Shelter Location] --> B[Competent Authority Decision]
    B --> C[Design Shelter in Natural Soil]
    C --> D[Structural Design]
    D --> E[Roof: 30 cm Gravel Layer]
    D --> F[Walls: Reinforced Concrete]
    D --> G[Ventilation & Emergency Exits]

Summary: IS 5499 emphasizes protective design for underground shelters with a minimum 30 cm gravel roof cover and location decisions by authorities to suit urban constraints. Structural safety and ventilation are critical for emergency provisions.

IS 5499: Applicability and Exceptions

• Clause 13.1: All provisions of IS 5499 apply except those explicitly excluded in Clause 10.1.
• Clause 10.1: Lists specific exceptions (refer to the standard for exact exclusions).
• Clause 2.0: Defines terms used in the standard to ensure clarity.
• Rounding Off (Clause 0.5):
  • Final test or calculation results must be rounded per IS 2:1960.
  • The number of significant digits in the rounded value must match the specified value in IS 5499.

Key Points on Rounding (IS 2:1960)

Summary:

• Use all clauses except Clause 10.1 exceptions.
• Follow IS 2:1960 for rounding numerical results.
• Refer to Clause 2.0 for definitions to interpret requirements correctly.

flowchart LR
    A[IS 5499 Provisions] --> B{Clause 10.1 Exceptions?}
    B -- No --> C[Apply Clause 13.1: All provisions applicable]
    B -- Yes --> D[Exclude specified provisions]
    C & D --> E[Rounding per IS 2:1960]
    E --> F[Final compliance check]

Key Specifications & Formulas for Shelters Built Outside Buildings (IS 5499):

1. Location (Clause 7.1)

• Shelter walls ≥ 2.0 m from external building walls (unless authorized).
• Shelters in basements if building has basements.

2. Roof Slab Design (Clause 10.1)

• Minimum thickness: 20 cm.
• Design load includes:
  • Self-weight of slab.
  • Dead load of earth/gravel or slabs above: 250 kg/m² per slab.
  • Superimposed load: 1000 kg/m².
  • Any concentrated loads.
• Reinforcement:
  • Bar diameter ≥ 8 mm.
  • Max spacing between bars: 15 cm.
  • Steel volume ≥ 0.5% of slab volume.
• Span limits:
  • Single direction reinforcement: max 4 m.
  • Two-way reinforcement: max 6 m.

3. Ventilation & Exit Protection (Clause 6.7)

• Entrance from open air must have protective hood (brick/concrete walls + RCC slab).
• Refer to Fig. 4 for hood details.

Roof Slab Load Calculation Formula:

[ q_{total} = q_{self} + (250 \times n) + 1000 + q_{concentrated} ]

Where:

• (q_{self}) = self-weight of slab (kN/m²)
• (n) = number of slabs/earth layers above
• Loads in kg/m² (convert to kN/m² by dividing by 100)

flowchart LR
    A[Location of Shelter] --> B{Distance from Building Walls}
    B -->|≥ 2 m| C[Allowed]
    B -->|< 2 m| D[Special Authorization Required]
    A --> E[Basement Shelter if available]

    F[Roof Slab] --> G[Thickness ≥ 20 cm]
    F --> H[Load: Self + 250 kg/m² per slab + 1000 kg/m² + Concentrated]
    F --> I[Reinforcement: ≥ 0.5% steel volume, bars ≥ 8 mm dia, max 15 cm spacing]
    F --> J[Span: ≤ 4 m (