Design and Construction of Floors and Roofs with Precast Reinforced Concrete Channel Units - Code of Practice

IS 14215 - Scope & Key Design Specifications (Clause 4.2)

• Scope: Design of precast concrete channel units (300 mm & 600 mm wide) for residential buildings under simply supported or continuous end conditions.
• Design Approach: Use provided design tables for reinforcement and moment/shear capacities or design as per actual conditions.
• Rounding Off: Final values must be rounded as per IS 2:1960.

Key Tables Summary (Clause 4.2)

Typical Design Parameters for 300 mm Wide Channel Units (Simply Supported)

Notes:

• Reinforcement Bars: Number and diameter specified directly from tables.
• Shear & Moment: Limit state values given for design.
• Continuity: Bottom bars of adjacent spans to be welded for continuous spans.
• Design Flexibility: Tables provide quick reference; detailed design can be done if conditions differ.

flowchart TD
    A[Start: Select Unit Width (300/600 mm)]
    B{Support Condition?

IS 14215 Key Design References & Tables Summary

• Design Approach (Clause 4.2):
  Units can be designed as simply supported or continuous, with reinforcement selected from Tables 1 to 8 for residential loads.

• Tables Overview:
  The tables provide effective span, depth, moment of resistance, shear capacity, and reinforcement details for 300 mm and 600 mm wide channel units under various support conditions:

• Reinforcement Notes:

  • Bottom bars of adjacent spans in continuous units are to be projected and welded for continuity.
  • Reinforcement diameters typically range from 8 mm to 16 mm depending on span and load.

• Rounding Off (IS 2:1960):
  Final calculated values must be rounded as per IS 2:1960 rules, retaining significant digits consistent with standard values.

Example: Simply Supported 300 mm Unit (From Table 1)

IS 14215: Materials/Elements of Roofs and Floors — Key Points

• Scope: Focuses on new materials and techniques for roofs/floors aiming at material savings, cost reduction, and speedy construction.

• Roof/Floor Finishing:

  • Can be applied directly over slabs made with these units.
  • Waterproofing standards to refer for treatment:
    • IS 1346:1976 (Bitumen Felts)
    • IS 4365:1967 (Waterproofing Compounds)
    • IS 3036:1992 (Bitumen-based Waterproofing)
    • IS 9918:1981 (Polymer Waterproofing)

• Precast Elements:

  • Precast reinforced concrete planks and joists are specified for flooring and roofing.
  • These elements ensure quality control, faster erection, and uniformity.

Typical Specification Highlights (from related IS codes):

General Formula for Load on Roof/Floor Slabs:

[ \text{Design Load} = \text{Dead Load} + \text{Live Load} + \text{Imposed Load} ]

• Dead Load includes self-weight of slab, finishes, waterproofing.
• Live Load depends on usage (refer IS 875 Part 2).

flowchart TD
    A[Materials/Elements of Roofs & Floors]
    A --> B[Precast Concrete Planks]
    A --> C[Precast Joists]
    A --> D[Waterproofing Treatments]
    D --> E[IS 1346, IS 4365, IS 3036, IS 9918]

For detailed design, refer to IS 14215 along with relevant IS codes mentioned.

IS 14215 Structural Design Summary

• Design Approach: Units are designed as simply supported or continuous based on end conditions (Clause 4.2).
• Reinforcement: Use steel as per IS 456:1978 (Clause 3.3).

Key Tables for 300 mm and 600 mm Wide Channel Units (Residential Loads)

Typical Design Parameters (from Tables)

Example: Simply Supported 300 mm Unit (Depth 150 mm, Span 3.0 m)

• Moment (Nm): 2,751
• Reinforcement: 2 bars of 8 mm dia
• Shear (N): 3,507

Notes

• Bottom bars of adjacent spans in continuous units must be projected and welded.
• Design moments and shear forces are provided directly in tables for quick reference.
• Follow IS 456 for detailed reinforcement detailing and concrete specifications.

flowchart LR
  A[Load] --> B[Determine Support Condition]
  B --> C{Simply Supported?}
  C -->|Yes| D[Use Table 1 or 4]
  C -->|No| E[Continuous - Use Tables 2,3 or 5,6]
  D --> F[Select span & depth]
  E --> F
  F --> G[Read Moment & Shear from table]
  G --> H[Select Reinforcement]
  H --> I[Design Complete]

For detailed reinforcement and moment

IS 14215: Storage, Transportation, and Erection of Precast Elements

Key Specifications from Clause 5:

• Handling & Sling Placement:

  • Slings must be placed at ~1/5th of the span from each end of the precast unit.
  • Avoid placing supports at the center of the span during handling.

• Stacking Orientation:

  • Main reinforcement should be at the bottom when stacking.
  • Units should be stacked with the trough facing downwards to avoid damage.

Additional Guidelines (Referenced Codes):

• For high seismic zones, strengthen floors and roofs per Clause 9 of IS 4326:1993.
• Refer to IS codes for:
  • Design of precast reinforced concrete L-panels for roofs.
  • Specifications for precast reinforced concrete planks and joists.

Sling Placement Diagram (Span = L):

graph LR
A[End] ---|1/5 L| B(Sling) ---|3/5 L| C(Sling) ---|1/5 L| D[End]

• Sling points at 0.2L and 0.8L from one end.

Summary Table:

Note: Always check unit weight and sling capacity before lifting. Use appropriate lifting gear and follow safety norms.

Curing of In-situ Concrete as per IS 14215

Key Specifications (Clause 6.1)

• Minimum curing duration:
  • 7 days by continuous sprinkling of water (wet curing).
  • Followed by 7 days of air curing.
• Post-curing treatment:
  Apply a coat of cement slurry on joints to fill hairline cracks.

Concrete Grade & Materials (Clause 3.2)

• Use M15 grade concrete as per IS 456:1978.
• Maximum aggregate size: 12 mm.
• Proper compaction by vibration or rodding is essential.

Design Reference

• For monolithic connections between precast units, design per IS 3935:1966.

Summary Table for Curing Duration

Important Notes:

• Proper curing prevents early drying, which can cause shrinkage cracks.
• Wet curing maintains moisture for hydration of cement.
• Cement slurry application improves joint durability.

flowchart TD
    A[Place In-situ Concrete] --> B[Compact Concrete (Vibration/Rodding)]
    B --> C[Wet Curing (Sprinkling Water) - 7 Days]
    C --> D[Air Curing - 7 Days]
    D --> E[Apply Cement Slurry on Joints]
    E --> F[Final Structure with Durable Joints]

IS 14215: Provisions for Fixtures and Openings in Precast Units

Key Provisions (Clauses 7.1 to 7.1.3.3)

• Fixtures (7.1): Designers must specify provisions for fan hooks, inserts, electric conduits, etc., to be embedded in precast units or in-situ joints.
• Openings & Holes (7.1.2):
  • Holes/openings must be fixed accurately during precasting with adequate embedment.
  • No drilling or cutting after precasting.
• Wooden Plugs (7.1.3.3):
  • Used for electrical wiring or fixtures.
  • Size: 30 mm × 30 mm wooden plugs embedded as per Fig. 4 (typical illustration).

Balcony Projection (Clause 4.2)

• Units designed as simply supported or continuous depending on end conditions.
• Main reinforcement guided by Tables 1 to 8 for residential loads (refer IS 14215 for detailed reinforcement values).

Summary Table: Wooden Plug Size

Diagram: Wooden Plug Fixing (Fig. 4)

graph TD
A[Precast Concrete Unit] --> B[Embed Wooden Plug]
B --> C[30 mm × 30 mm Plug]
C --> D[Provides fixture anchorage]

For detailed reinforcement and fixture embedment, refer to IS 14215 Tables 1-8 and Clause 7 illustrations.

IS 14215: Projection of Balcony (Clause 8)

• Projection Direction: Balcony projection aligned with unit length can be cantilevered by designing reinforcement per IS 456:1978 for cantilever moments.

• Support During Hardening: The projecting precast channel unit must be supported until the in-situ concrete in the joint hardens.

• Alternative Method: Cantilever portion can be cast in-situ with reinforcement projecting from the precast units or joints (see Fig. 5).

• Safety: No walking on floor/roof for 3 days after casting in-situ concrete in joints.

Key Design Notes:

• Use IS 456:1978 for cantilever moment and shear design.
• Reinforcement must be continuous or projecting out for composite action.
• Temporary supports are essential until concrete gains strength.

Typical Reinforcement Detailing for Balcony Projection

flowchart LR
    A[Precast Channel Unit] --> B[Reinforcement projecting out]
    B --> C[Cast in-situ cantilever portion]
    C --> D[Support till concrete hardens (3 days)]
    D --> E[Safe load application]

References:

• IS 14215: Clause 8.1
• IS 456:1978 (Cantilever design)

IS 14215 provides general guidance on floor/roof finishing using precast units but refers to other IS codes for detailed finishing and waterproofing.

Key Points on Floor/Roof Finishing (Clause 9.1):

• Finishing may be applied directly over the precast slab.
• Use relevant IS codes for specific materials and methods.
• For waterproofing, refer to:
  • IS 1346:1976 – Bitumen felts for damp proofing
  • IS 4365:1967 – Bitumen and bituminous materials
  • IS 3036:1992 – Bitumen primers
  • IS 9918:1981 – Polymer modified bitumen membranes

Typical Finishing Layers:

• Cement-sand screed (1:3 or 1:4 mix) with thickness 20-40 mm
• Waterproofing membrane (bituminous or polymer-based)
• Protective screed or tiles as top surface

General Specification for Finishing:

flowchart LR
  Slab --> Screed[20-40mm Cement-Sand Screed]
  Screed --> Waterproof[Waterproofing Layer (Bitumen/Polymer)]
  Waterproof --> Surface[Surface Finish (Tiles/Terrazzo)]

For detailed design and finishing, always consult the relevant IS codes mentioned above.

Precautions During and After Construction (IS 14215: Clause 10)

• Avoid heavy loading on precast units until the in-situ concrete in joints attains full strength (Clause 10.1).
• Proper compaction and watertightness of in-situ concrete in joints between adjacent units is essential to prevent moisture ingress (Clause 10.4).
• Joints may be finished with 'V' or ruled joints to conceal cracks from differential shrinkage (Clause 9.2, Fig. 6).

Key Specifications:

References for Further Detailing:

• IS 456:1978 — Plain and Reinforced Concrete Code
• IS 875 (Part 2):1987 — Imposed Loads on Structures
• IS 1346:1991 — Waterproofing of Roofs with Bitumen Felts

flowchart TD
    A[Precast Units Placed] --> B[In-situ Concrete Filled in Joints]
    B --> C{Concrete Cured Fully?}
    C -- No --> D[No Heavy Loading Allowed]
    C -- Yes --> E[Allow Loading]
    B --> F[Ensure Proper Compaction & Watertightness]
    F --> G[Finish Joints with 'V' or Ruled Lines]

Summary: Ensure full curing of joint concrete before loading, proper compaction and waterproofing of joints, and use appropriate joint finishing to prevent cracks and moisture ingress.

IS 14215: List of Referred Indian Standards (Key References)

Important Notes:

• These standards complement IS 14215 for design, construction, waterproofing, and reinforcement.
• Clause 10.4 emphasizes proper compaction and watertightness during in-situ concreting at joints.
• Refer to IS 456 for concrete design formulas and IS 875 for load calculations.

Example: Basic Load Calculation (from IS 875 Part 2)

[ \text{Imposed Load} = \text{Characteristic Load} \times \text{Load Factor} ]

Where:

• Characteristic Load = Typical imposed load as per usage
• Load Factor = Safety factor (usually 1.5)

flowchart TD
    A[IS 14215] --> B[Reinforcement: IS 432]
    A --> C[Concrete Design: IS 456]
    A --> D[Waterproofing: IS 1346 & IS 991

IS 14215: Committee Composition - Key Points

• Committee responsible for the standard formulation: Housing Sectional Committee, CED 51.
• Chairman: Dr. P. S. A. Sundaram.
• Members: Representatives from Ministry of Urban Development, Municipal Corporations, Housing Boards, CPWD, DDA, National Housing Bank, CSIR labs, BIS, and private sector firms.
• Member Secretary: Shri J. K. Prasad, Joint Director (Civil Engg), BIS.
• Annex B of IS 14215 lists the full committee composition including alternates and their organizations.

Summary Table of Committee Composition (Excerpt)

Notes:

• The committee includes experts from government, research institutions, and industry.
• This ensures comprehensive coverage of technical, practical, and policy aspects.
• For detailed names and affiliations, refer to Annex B of IS 14215.

If you need design formulas or tables, please specify the section or topic (e.g., design of channel units, reinforcement details).