Design and Construction of Floor and Roof with Precast Reinforced Concrete Planks and Joists - Code of Practice

IS 13994: Scope & Key Specifications for Precast RC Flooring/Roofing

Scope Summary:

• Covers precast reinforced concrete planks and joists for flooring and roofing.
• Includes partially precast joists with specific dimensions and reinforcement detailing.
• Compliance with IS 2:1960 for rounding off numerical values.

Key Specifications & Tables

1. Partially Precast Joist Dimensions

• Width = 150 mm
• Depth of precast portion = 150 mm
• Overall depth with in-situ concrete = 210 mm

2. Moment of Resistance & Reinforcement Area

• Mild steel bars conform to IS 432 (Part 1): 1982.
• Cold twisted deformed bars conform to IS 1786:1985.

Typical Construction Layers (Roof/Floor)

• 12 mm Bitumen Board
• Lime concrete slope 1:50 (for roof/floor finish)
• Bitumen painting (roof only)
• Precast RC joist + plank
• M15 in-situ concrete topping
• 120 mm cement-sand plaster (floor)

Rounding Off Rule (IS 2:1960)

• Final test/analysis values must be rounded off to the same significant figures as specified in the standard.

flowchart TD
    A[Precast RC Joist] --> B[150 mm Width]
    A --> C[150 mm Precast Depth]
    A --> D[210 mm Overall Depth]
    A --> E[Reinforcement]
    E --> F[Mild Steel Bars (IS 432)]
    E --> G[Deformed Bars

IS 13994 references several key Indian Standards essential for implementation. While Annex A lists these standards, typical referenced IS codes include:

• IS 456: Code of Practice for Plain and Reinforced Concrete
• IS 800: General Construction in Steel — Code of Practice
• IS 875: Code of Practice for Design Loads (Dead, Live, Wind, Seismic)
• IS 1893: Criteria for Earthquake Resistant Design
• IS 383: Specification for Coarse and Fine Aggregates for Concrete

Important Notes on Compliance:

• Rounding off: Follow IS 2:1960 for rounding numerical values.
• Retain the same number of significant digits as specified in the standard.

Summary Table Example for Referenced IS Codes

This ensures consistency and accuracy in structural design and testing per IS 13994.

IS 13994: Materials & Elements of Roof/Floor - Key Points

1. Materials

• Reinforcement: Mild steel bars per IS 432 (Part 1):1982 or cold twisted bars per IS 1786:1985.
• Concrete: M-15 grade for in-situ concrete topping.
• Other materials: Lime concrete, bitumen board (12 mm), bitumen painting (roof only), cement-sand plaster (120 mm thick).

2. Structural Elements

• Partially Precast Joist: Width 150 mm, precast depth 150 mm, overall depth 210 mm with in-situ topping.
• Precast RC Joist and Planks with anchorage details using 6 mm MS anchor bars.

3. Moment of Resistance & Reinforcement Area (for partially precast joist)

(Refer Table 5, Clause 4.2.2.2 for detailed combinations)

4. Typical Construction Layers (Roof/Floor)

• 12 mm bitumen board
• Lime concrete (100 mm thick) laid to slope 1:50 (roof/floor finish)
• Bitumen painting (roof only)
• Precast RC joist and plank
• M-15 in-situ concrete topping
• 120 mm cement-sand plaster

Summary Diagram of Partially Precast Joist Section:

graph TD
  A[12 mm Bitumen Board] --> B[Lime Concrete 100 mm (Slope 1:50)]
  B -->

IS 13994: Structural Design of Roof/Floor - Key Points

1. Partially Precast Joist Dimensions

• Width = 150 mm
• Depth of precast portion = 150 mm
• Overall depth with in-situ concrete = 210 mm

2. Moment of Resistance & Reinforcement Area (Clause 4.2.2.2, Table 5)

• Use Mild steel conforming to IS 432 (Part 1):1982 or cold twisted bars IS 1786:1985.
• Reinforcement combinations include multiple bar sizes for required moment resistance.

3. Material Layers for Roof/Floor

• 12 mm bitumen board
• Lime concrete 100 laid to slope 1:50 (roof/floor finish)
• Bitumen painting (roof only)
• Precast RC joist and plank with in-situ M15 concrete topping
• Anchor bars: 6 mm MS bars

4. Typical Details

• Simply supported joist reinforcement welding at bottom
• Plank bearing details to avoid leakage
• Continuity of joist at supports for intermediate floors

Basic Moment of Resistance Formula for Reinforced Concrete Section:

[ M_u = 0.87 f_y A_s (d - \frac{a}{2}) ] Where:

• (f_y) = yield strength of steel (N/mm²)
• (A_s) = area of tension reinforcement (mm²)
• (d) = effective depth (mm)
• (a = \frac{A_s f_y}{0.36 f_{ck} b}) (depth of equivalent stress block)

flowchart TD
    A[Roof

IS 13994: Key Specifications & Formulas for Erection of Floor/Roof

1. Structural Design (Clause 4.2 & 4.2.2.2)

• Partially Precast Joist Dimensions:

  • Width = 150 mm
  • Depth of precast portion = 150 mm
  • Overall depth with in-situ concrete = 210 mm

• Moment of Resistance & Reinforcement:

• Reinforcement Standards:
  • Mild steel: IS 432 (Part 1) : 1982
  • Cold twisted bars: IS 1786 : 1985

2. Materials & Layers (Typical Section)

• Roof/Floor Build-up:
  • 12 mm Bitumen board (roof)
  • Lime concrete 100 mm laid to slope 1:50 (roof/floor finish)
  • Precast RC joist & plank
  • M-15 in-situ concrete topping
  • 120 mm smooth cement sand plaster

3. Important Notes

• Welding of bottom reinforcement is essential for continuity.
• Use ¢6 mm MS anchor bars at supports.
• For high seismic zones, strengthen roofs/floors per IS 4326:1993.

4. Design Formula (Moment of Resistance)

[ M_r = f_y \times A_s \times (d - \frac{a}{2}) ]

Where:

• (M_r) = Moment of resistance
• (f_y) = Yield strength of steel
• (A_s) = Area of steel reinforcement
• (d) = Effective depth
• (a) = Depth of equivalent stress block

5. Typical Joist Support Detail (

IS 13994 - Floor/Roof Finishing Key Points

1. Minimum Clear Cover (Clause 5.12)

• Clear cover to reinforcement bars = max(15 mm, bar diameter)

2. Structural Design (Clause 4.2.2.2)

Partially Precast Joist Dimensions:

• Width = 150 mm
• Depth of precast portion = 150 mm
• Overall depth with in-situ concrete = 210 mm

3. Moment of Resistance & Reinforcement Area (Table from Clause 4.2.2.2)

Note: Mild steel to conform IS 432 (Part 1):1982; Cold twisted bars to IS 1786:1985.

4. Typical Floor/Roof Finishing Layers (Fig.1 Summary)

• Roof:

  • 12 mm bitumen board
  • Lime concrete (100 mm thick) laid to 1:50 slope
  • Bitumen painting (roof only)
  • Precast RC joist + plank + M15 in-situ concrete topping
  • 6 mm MS anchor bars for anchorage
  • 120 mm smooth cement-sand plaster finish

• Floor:

  • Similar layering without bitumen painting

5. Important Notes

• Use M15 grade concrete for in-situ topping.
• Ensure welding of bottom reinforcement in joists.
• Provide proper detailing at supports to avoid leakage and ensure continuity.

flowchart TD
    A[Precast RC Joist & Plank] --> B[M15 In-situ Concrete Topping (60 mm)]
    B --> C[12 mm Bitumen Board (Roof only)]
    C --> D[Lime Concrete (100 mm) laid

Care During and After Erection (IS 13994: Clause 7)

Key Points:

• Protection of Waterproofing: For waterproofing with bitumen felts, mastic, glass fibre tissue, and lime concrete, refer to IS 1346:1978, IS 4365:1967, IS 9918:1991, IS 3036:1992.
• Propping: Use 30 mm thick wooden planks and fan hooks (212 mm diameter) for temporary support of partially precast joists during erection.
• Reinforcement Continuity: Provide 2 no. negative reinforcement bars for continuity up to L/4 span on either side of supports.
• Plaster and Coating: Apply 12 mm thick smooth cement plaster and bitumen painting on roofs to avoid leakage.
• Post-Erection Care: Ensure proper curing of in-situ concrete (M-15 grade) and maintain the slope (1:50) for lime concrete terracing on roofs/floors.
• Seismic Zones: Strengthen roofs/floors as per IS 4326:1993 when precast units are used in high seismic zones.

Moment of Resistance & Reinforcement (Table from Clause 4.2.2.2)

Note: Use mild steel conforming to IS 432 (Part 1):1982 or cold twisted bars per IS 1786:1985.

Typical Details for Erection

• Propping of Joists: Use wooden planks and fan hooks as shown in Fig. 2.
• Fixing Fan Hooks: Use 8 mm MS bar + 6 mm MS bar (Fig. 3).
• Bearing Details: Refer to Fig. 4 for end wall, intermediate wall, and beam support bearing details.

flowchart

IS 13994: Service Area Provisions - Key Points

1. Partition Walls (Clause 7.3)

• Partition walls must not be constructed over planks, only over joists or walls.
• Weight of partition walls must be included in joist design.

2. Balcony/Chhajja Projections (Clause 9.1)

• Balconies are supported by partially precast joists with overhangs.
• Joist design must consider:
  • Self-weight
  • Superimposed balcony loads (per IS 875 Part 2: 1987)
  • Railing loads
• Main reinforcement provided at the top in in-situ concrete; precast portion handles compression.
• Free end of joist must be propped until in-situ concrete attains strength.

3. Moment of Resistance for Partially Precast Joist (Table from Clause 4.2.2.2)

• Joist dimensions: Width = 150 mm, Precast Depth = 150 mm, Overall Depth = 210 mm.
• Use IS 432 (Part 1): 1982 for mild steel and IS 1786: 1985 for high strength deformed bars.

Design Load Reference:

• Use IS 875 (Part 2): 1987 for imposed loads on balconies.

Summary Diagram of Balcony Joist Load Transfer:

flowchart LR
    BalconyLoad[Balcony Load + Railing Load]
    JoistOverhang[Joist Overhang (Precast + In-situ Concrete)]
    JoistSupport[Joist Support (Wall/Beam)]
    Prop[Temporary Prop at Free End]

    BalconyLoad --> JoistOverhang
    JoistOverhang --> JoistSupport
    Prop -.-> JoistOverhang

Note: Always ensure proper curing and strength gain of in-situ concrete before removing props.

For detailed

IS 13994 Key Points on Balcony/Chhajja Projections

Balcony/Chhajja Projections (Clause 9.1)

• Balcony projections are provided on partially precast joists with an overhang.
• Joists carry:
  • Self-weight
  • Superimposed balcony loads (per IS 875 Part 2)
  • Railing loads
• Main reinforcement is at the top in in-situ concrete; precast portion handles compression.
• Free end of joist must be adequately propped until in-situ concrete gains strength.

Projection Limits (Clause 5.10)

• For roofs without parapet:
  • Planks project max 100 mm on either side to avoid leakage.
  • Alternatively, max 500 mm projection across joists with shuttering, reinforcement, and concreting flush with roof.
  • Up to 1000 mm (1 m) projection along joists by providing negative reinforcement projecting in the joist top.

Reinforcement & Moment Resistance (Clause 4.2.2.2, Table)

Typical Details (Fig. 5 & 6)

• Fig. 5: Roof without parapet with max 100 mm plank projection or 500 mm with shuttering.
• Fig. 6: Cantilever joist with negative reinforcement for balcony projection.

Summary Formula for Moment of Resistance (M):

[ M = f_y \times A_s \times (d - \frac{a}{2}) ]

Where:

• (f_y) = yield strength of steel (N/mm²)
• (A_s) = area of tension reinforcement (mm²)
• (d) = effective depth (mm)
• (a) = depth of equivalent stress block (mm)

Design Loads Reference:

• IS 875 (Part 2): Imposed loads on balconies

IS 13994 references several Indian Standards essential for design and construction of lightweight steel structures. Although Annex A lists these, key commonly referred IS codes include:

• IS 800: General Construction in Steel — Code of Practice
• IS 875 (Part 1 to 5): Design Loads (Dead, Live, Wind, Snow, Earthquake)
• IS 1893: Criteria for Earthquake Resistant Design of Structures
• IS 456: Plain and Reinforced Concrete Design
• IS 2062: Steel for General Structural Use
• IS 808: Dimensions for Hot Rolled Steel Sections

Typical use:

These standards complement IS 13994 for safe, efficient design of steel framed lightweight buildings.

graph LR
A[IS 13994] --> B[IS 800]
A --> C[IS 875]
A --> D[IS 1893]
A --> E[IS 2062]
A --> F[IS 456]

For detailed tables or formulas, refer to respective IS codes.

Committee Composition - IS 13994

Reference: Annex B (Foreword) of IS 13994 specifies the composition of the Housing Sectional Committee, CED 51, responsible for the standard.

Key Points:

• Chairman: Dr. P.S.A. Sundaram (Ministry of Urban Development, New Delhi)
• Members: Representatives from various government bodies, municipal corporations, housing authorities, research institutions, and industry experts, including:
  • Municipal Corporation of Delhi
  • School of Planning and Architecture, New Delhi
  • Housing and Urban Development Corporation
  • Central Public Works Department
  • Maharashtra Housing and Area Development Authority
  • Delhi Development Authority
  • National Housing Bank
  • National Council for Cement and Building Materials
  • Structural Engineering Research Centre (CSIR), Madras
  • Public Works Departments of various states
  • Industry representatives (e.g., M/s B. G. Shirke and Co)

Purpose:

• The committee ensures comprehensive expertise covering urban development, architecture, structural engineering, materials technology, and construction practices.

Summary Table of Committee Composition (Excerpt)

If you need details on technical specifications or design tables, please specify the clause or topic.