precast reinforced concrete planks and joists for roofing and flooring
1994 Edition

Overview of Scope and Key Requirements

• Scope: Defines specifications for precast reinforced concrete L-shaped panels utilized in roofing.

• Dimensional Tolerances (Clause 6.2.1.1):

• Rounding Guidelines (Clause 4.1.2 & IS 2:1960): Numerical results must be rounded in accordance with IS 2:1960, maintaining the specified number of significant figures.

Summary Highlights:

• Length tolerance: ±4 mm
• Width and depth tolerance: ±2 mm
• Follow IS 2:1960 for rounding off numerical values

flowchart LR
    A[Precast L-Shaped Panels] --> B[Check Dimensions]
    B --> C{Type of Dimension}
    C -->|Length| D[±4 mm]
    C -->|Width| E[±2 mm]
    C -->|Depth| F[±2 mm]
    B --> G[Apply Rounding]
    G --> H[As per IS 2:1960]

This ensures adherence to IS 13990 requirements for precast roofing components.

Key Reinforcement Requirements per IS 13990

• Primary Reinforcement (Clause 5.2.1):

  • Incorporate three bars spaced evenly along the plank's length.
  • Bar diameter as dictated by structural design.
  • Must comply with maximum spacing limits set forth in IS 456:1978.

• Distribution Reinforcement:

  • Should equal or exceed the minimum slab reinforcement specified in IS 456:1978.

• Steel Grade:

  • Use steel conforming to IS 456:1978 standards.
  • In absence of detailed design, use 6 mm diameter mild steel bars (Grade I, IS 432 Part 1:1982) as transverse reinforcement at 200 mm center-to-center spacing.

Summary of IS 456:1978 Reinforcement Limits:

Typical Reinforcement Arrangement (Mermaid.js):

graph LR
A[Main Bars: 3 bars] -->|Evenly spaced| B[Along plank length]
C[Distribution Bars] -->|≥ IS 456 minimum| D[Perpendicular to main bars]
E[Transverse Bars] -->|6 mm dia at 200 mm c/c| F[For joists under 1.5 m spacing]

Summary: Employ three evenly spaced main reinforcement bars along the length of planks, distribution reinforcement per IS 456 minimum, and 6 mm diameter mild steel transverse bars at 200 mm spacing for joists where detailed design is unavailable.

Summary of Shape, Dimensions, and Tolerances According to IS 13990

1. Mould Dimension Tolerances (Clause 6.2.1.1)

2. Casting Tolerances for Planks (Clause 4.3)

3. Reinforcement Covers

• Minimum clear cover of 15 mm for reinforcement in reinforced concrete planks as per IS 456:1978.

Notes:

• Maintaining these tolerances is critical for accuracy and structural reliability.
• Control of bow and twist is essential to ensure proper alignment and load transfer.

graph TD
A[Plank Dimensions] --> B[Length ±5 mm]
A --> C[Width ±3 mm]
A --> D[Thickness ±2 mm]
A --> E[Bow ±2 mm]
A --> F[Twist 1 mm]

These tolerances should be used as reference during quality inspections of precast RCC components.

Details of Reinforcement as per IS 13990 with Reference to IS 456

• Reinforcement Steel: Use steel conforming to IS 456:1978, typically Fe415 or Fe500.

• Main Reinforcement in Planks (Clause 5.2.1):

  • Three bars spaced evenly along plank length.
  • Distribution reinforcement equal to or more than minimum slab reinforcement per IS 456.
  • Bar spacing must not exceed maximum limits specified by IS 456 (≤ 3 times slab thickness or 300 mm).

• Reinforcement in RCC Joists (Clause 5.2.3):

  • Follow design guidelines of IS 13994:1994.
  • If detailed design is unavailable:
    • Use main reinforcement per IS 13990 Clause 1.5.
    • Use 6 mm dia mild steel transverse bars (IS 432 Part 1) at 200 mm c/c spacing.

Typical Maximum Bar Spacing (from IS 456):

Example Calculation for Main Reinforcement Area

[ A_s = \frac{M}{0.87 f_y d} ]

• (M): Design bending moment
• (f_y): Steel yield strength (e.g., 415 MPa)
• (d): Effective depth

flowchart LR
    A[Design Moment & Loads] --> B[Calculate Required \(A_s\)]
    B --> C[Select Bar Diameter & Quantity]
    C --> D[Verify Spacing per IS 456 & IS 13990]
    D --> E[Provide 3 Evenly Spaced Bars in Planks]
    D --> F[Provide Transverse Bars @ 200 mm c/c in Joists]

Summary: Utilize three main reinforcement bars spaced equally in planks, minimum distribution steel as per IS 456, and transverse mild steel bars of 6 mm diameter at 200 mm spacing in joists.

Important Guidelines for Casting and Curing Precast Concrete Elements (IS 13990)

1. Mould Preparation

• Apply a suitable bond release agent on the internal surfaces of moulds.
• Position moulds on a smooth concrete base treated with bond release or covered with wrinkle-free old newspaper.

2. Reinforcement Cover

• Maintain a minimum clear cover of 15 mm for planks.
• Maintain a minimum clear cover of 25 mm for joists at the bottom.

3. Concrete Mix and Placement

• Use well-graded aggregates:
  • Maximum size 10 mm for planks.
  • Maximum size 20 mm for joists.
• Place concrete in layers, compacting each with a plate vibrator.
• Finish plank top surfaces with rough trowel marks for better bonding.

4. Casting Sequence for Planks

• Pour an initial 30 mm thick concrete layer and compact.
• Position longitudinal and tapering components.
• Complete pouring of remaining concrete and compact.
• Remove tapering members after approximately 0.5 hours.
• Strip moulds after about 2 hours, depending on weather.
• After 24-30 hours, slide and tilt units for vertical curing.

5. Casting Sequence for Joists

• Place reinforcement cage with stirrups extending outwards.
• Install top spacers.
• Pour concrete and compact using plate or needle vibrators.
• Demould after 3-4 hours.
• After 48-72 hours, slide and transport units for curing.

Summary Table:

flowchart TD
    A[Prepare Mould & Apply Bond Release] --> B[Arrange Reinforcement]
    B --> C[Pour Initial Concrete Layer]
    C --> D[Compact Using Plate Vibrator]
    D --> E[Place Additional Components]
    E --> F[Complete Concrete Pouring & Compact]
    F --> G[Demould After Specified Time]
    G --> H[Transport & Cure Units]

These steps are crucial for ensuring the durability and dimensional accuracy of precast components.

Guidelines on Sampling and Marking as per IS 13990

Sampling (Clause 7.2)

• For batches up to 300 units: randomly select 5 units.
• For batches exceeding 300 units: add 5 units for each additional 300 units or fraction thereof.
• Follow random selection methodology outlined in IS 4905:1968.

Marking (Clause 7.3)

• Each sampled unit must be clearly marked for traceability back to its batch.

Testing (Annex A)

• Precast planks should be tested 28 days after the casting of in-situ concrete in haunch areas.
• Precast joists are tested between 28 to 33 days after casting.

Rounding Off

• Apply IS 2:1960 rules for rounding numerical test results, maintaining the prescribed number of significant digits.

Sampling Summary Table

Marking Requirements

• Mark samples legibly with batch identification.
• Ensure consistent traceability throughout testing and documentation.

flowchart TD
    A[Batch of Units] --> B{Is batch size ≤ 300?}
    B -- Yes --> C[Select 5 Samples]
    B -- No --> D[Select 5 + 5 per extra 300 units]
    C & D --> E[Mark Samples with Batch ID]
    E --> F[Conduct Required Tests]

This process guarantees representative sampling and effective traceability as required by IS 13990.

Testing Procedures for Precast Reinforced Concrete Planks and Joists (IS 13990)

Testing Age (Annex A-1)

• Planks: Tested 28 days after casting of in-situ concrete haunch.
• Joists: Tested between 28 and 33 days after casting.

Dimensional and Deflection Recovery Tests (Clause 8.1)

• Routine testing includes verifying dimensions and deflection behavior under load.
• Failure load testing is designated as a type test, applicable to new designs or size modifications.

Load Application for Deflection Test (Annex A-3.2)

• Apply a uniformly distributed load equal to 1.25 times the imposed design load.
• Load application can be through concrete or steel blocks, or hydraulic jacks with a self-reacting frame.
• Load maintained for 24 hours while deflection is recorded.
• After load removal, residual deflection is measured following an additional 24-hour period.

Rounding Off

• Adhere to IS 2:1960 for rounding off test results, maintaining the number of significant figures.

Deflection Test Summary Table

flowchart LR
    A[Start Testing] --> B{Component Type}
    B -->|Plank| C[Wait 28 days after haunch concrete]
    B -->|Joist| D[Wait 28-33 days after casting]
    C & D --> E[Apply 1.25 × design load uniformly for 24 hrs]
    E --> F[Record Deflection]
    F --> G[Remove Load]
    G --> H[Record Residual Deflection after 24 hrs]
    H --> I[Compare with Acceptance Criteria]

This ensures compliance with IS 13990 for mechanical performance and durability of precast elements.

Deflection Recovery Test as per IS 13990 (Clause 9.2 & Annex A)

• Test Setup (Clause A-3.1 & A-3.2):

  • The precast unit is simply supported over a 50 mm bearing on smooth brick walls finished with 1:4 cement mortar.
  • Haunches are filled with M15 concrete and cured for 14 days.
  • A uniform load equal to 1.25 times the imposed design load is applied using loading blocks or hydraulic jacks.
  • Deflection is measured at mid-span using a dial gauge with a least count of ≤ 0.02 mm, zeroed under self-weight plus applied load.

• Loading and Measurement Procedure:

  • Load is applied and sustained for 24 hours.
  • Deflection under load is recorded at 24 hours (( \delta_{24h} )).
  • Load is then removed, and residual deflection is noted after another 24 hours (( \delta_{res} )).

• Acceptance Criteria (Clause 9.2):

  • The unit passes if residual deflection is at least 75% of deflection under load (( \delta_{res} \geq 0.75 \times \delta_{24h} )).
  • The unit fails if ( \delta_{res} < 0.75 \times \delta_{24h} ).
  • If maximum deflection under load is less than 40 times the ratio of effective span to overall depth (( < 40 \times \frac{l}{D} )), the deflection recovery test is not mandatory.

Core Formula:

[ ext{Deflection Recovery} = \frac{\delta_{res}}{\delta_{24h}} \times 100% \geq 75% ]

[ ext{Deflection recovery test may be omitted if } \delta_{max} < 40 \times \frac{l}{D} ]

Test Setup Illustration:

  graph LR
    A[Brick Wall] -->|50 mm bearing| B[Precast Unit]
    B -->|Uniform Load Application| C[Loading Blocks/Hydraulic Jacks]
    B -->|Deflection Measurement at Mid-span| D[Dial Gauge]

Summary: This test verifies that the precast unit recovers at least 75% of its deflection after load removal, indicating elastic behavior and structural soundness. If the residual deflection is insufficient, the unit is rejected.

Certification and Marking Requirements as per IS 13990

Certification Mark (Clause 10.2 & 10.2.1)

• Precast components may bear the BIS Standard Mark.
• The use of this mark is governed by the Bureau of Indian Standards Act, 1986.
• Licenses for the Standard Mark are issued by BIS under specified conditions.

Marking Criteria (Clause 10.1)

• Each precast unit must be clearly and permanently marked with:
  • Manufacturer’s identification.
  • Month and year of production.

Testing Specifications (Annex A)

• Testing ages:
  • Planks: 28 days after the placement of in-situ concrete in haunch.
  • Joists: 28 to 33 days after casting.
• Follow IS 2:1960 for rounding off test numerical results.

Summary Table: Marking and Testing

flowchart LR
    A[Manufacturing] --> B[Mark with ID, Month & Year]
    B --> C{Apply BIS Mark?}
    C -- Yes --> D[Affix BIS Standard Mark]
    C -- No --> E[No BIS Mark Applied]
    B --> F[Test at Designated Age]
    F --> G[Planks: 28 Days Post In-situ Concrete]
    F --> H[Joists: 28-33 Days Post Casting]

This ensures traceability, quality assurance, and conformance to IS 13990.

Testing Methodologies for Precast Planks and Joists (IS 13990)

Scope and Testing Ages

• Applies to precast reinforced concrete planks and joists up to 1.5 meters in length for roofing and flooring.
• Test age:
  • Planks: 28 days after in-situ concrete placement in haunch.
  • Joists: Between 28 and 33 days after casting.

Dimensional Compliance

• Ensures planks and joists conform to specified dimensions (Clause A-2).

Referenced Standards

• IS 432 (Part 1): Mild and medium tensile steel bars for reinforcement.
• IS 456: Code of practice for plain and reinforced concrete.
• IS 1199: Methods of concrete sampling.
• IS 15916: Guidelines for design and construction of floors and roofs using precast planks and joists.

Principal Test Methods

• Load testing to confirm strength and deflection under service and ultimate loads.
• Dimensional verification: length, width, thickness, reinforcement placement.
• Visual inspection for defects such as cracks and honeycombing.

Testing Schedule Summary

flowchart TD
    A[Cast Precast Joists/Planks] --> B{Type of Element}
    B -->|Planks| C[Place In-situ Haunch Concrete]
    C --> D[Wait 28 Days]
    B -->|Joists| E[Wait 28 to 33 Days]
    D & E --> F[Perform Load and Dimensional Testing]

For detailed procedures, consult Annex A of IS 13990 along with related IS codes.