Prestressed Concrete Pipes (Including Fittings)

IS 784 - Scope Key Formulas, Tables, and Specifications

1. Scope Overview

IS 784 covers prestressed concrete pipes with specifications for dimensions, materials, design, and testing.

2. Key Formulas (Clause 4.5: Section Constant)

3. Indicative Dimensions of Socket and Spigot (Annex B)

*Note: Dimensions to be

IS 784 Key References, Formulas & Tables Summary

1. Annex G: Design Procedure for Prestressed Concrete Pipes

• Use Annex G for detailed design steps (Clause 3.3).
• Example data for 1200 mm dia pipe includes:
  • Core thickness, Te = 70 mm
  • Coat thickness, Tb = 22 mm
  • Ultimate tensile strength of wire = 1715 N/mm²
  • Modulus of elasticity of steel, E = 2 × 10⁵ N/mm²
  • Modular ratio, n = 5

2. Annex B: Socket & Spigot Dimensions (mm)

3. Annex F: Loss of Prestress Calculation

Where:

• f_si, f_g = initial prestress in wire (N/mm²)
• E_c = modulus of elasticity of concrete
• L = effective pipe length (mm)

4. Annex E: Thrust & Moment Coefficients for Bedding Angles

| Bedding Angle | Thrust Coefficients (Pipe, Water, Earth) | Moment Coefficients (Pipe, Water, Earth) |

IS 784 - Terminology: Key Specifications & Tables Summary

Terminology in IS 784 relates to prestressed concrete pipes, their dimensions, materials, and testing.

Key Tables & Specifications:

1. Indicative Dimensions of Socket and Spigot (Annex B)

Manufacturers to achieve these within 5 years.

2. Loss of Prestress (Annex F)

• fc, fsi_long = initial stresses; E = modulus of elasticity; L = pipe length.

3. Thrust and Moment Coefficients (Annex E)

IS 784: Key Materials Specifications & Tables

1. Materials Standards Referenced (Annex A)

• Steel for Reinforcement:
  • IS 432: Mild steel & medium tensile steel bars & hard-drawn wire for concrete reinforcement.
  • IS 1566: Hard-drawn steel wire fabric for reinforcement.
  • IS 1785 (Part 1 & 2): Plain hard-drawn steel wire for prestressed concrete.
  • IS 1786: High strength deformed steel bars & wires.
  • IS 2062: Steel for general structural purposes.
• Cement:
  • IS 455: Portland slag cement.
  • IS 8041: Rapid hardening Portland cement.
  • IS 8112: 43 grade ordinary Portland cement.
  • IS 12269: 53 grade ordinary Portland cement.
• Concrete Admixtures: IS 9103.

2. Indicative Dimensions of Socket & Spigot (Annex B)

• Applies to prestressed concrete pipes.
• Two joint types: Roll On & Confined Joint (dimensions similar).

3. Typical Design Parameters (Annex D & J)

• Pipe Diameter (D): e.g., 500 mm or 1000 mm.
• Core Thickness (te): e.g., 35 mm (500 mm pipe), 60 mm (1000 mm pipe).
• Coat Thickness (tb): e.g., 22 mm.
• Flexural Strength of spun concrete: ~6.87 N/mm².
• Wire Diameter (circumferential): 4 mm.
• Ultimate Tensile Strength of wire: 1715 N/mm².
• Area of circumferential wire: 0.240 mm²/mm.

4. Important Formula for Permissible Compressive Stress (Amendment)

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IS 784: Dimensions and Tolerances Summary

1. Internal Diameter Tolerances (Clause 5.3.2)

2. Minimum Core Thickness (Table 1, Clause 5.1)

Note: For diameters > 2500 mm or higher pressure, thickness increases with diameter reduction and multiple prestressing wire layers.

3. Core Thickness Tolerance (Clause 5.3.3)

• Core thickness shall not be less than design thickness - 5%.
• Manufacturer declares core thickness; tolerance applies to declared value.

4. Length Tolerance (Clause 5.3.1)

• ±1% of specified pipe length.

IS 784: Design Requirements for Prestressed Concrete Pipes

Key Design References:

• Clause 3.3 & Annex G: Adopt the procedure in Annex G for detailed design.
• Annex J: Design of prestressed concrete pipes for drainage, sewerage, and culverts.
• Annex D (Clause 7.4.2): Typical calculation for longitudinal design of pipes ≤ 600 mm diameter.

Important Parameters & Symbols (Annex J & K)

Indicative Dimensions of Socket & Spigot (Annex B)

Typical Design Formulae (From Annex D & General Practice)

• Flexural Stress in Concrete:

[ \sigma_c = \frac{M}{Z} ]

Where:

• ( M ) = bending moment

• ( Z ) = section modulus

• Prestressing Force Required:

[ P = \frac{M}{e} ]

Where:

• ( e ) = eccentricity of prestressing force

• Wire Stress:

[ \sigma_s = \frac{P}{A_s} ]

Where:

• ( A_s ) = area of prestressing wire

Summary of Design Steps:

1. Determine pipe diameter (D), core thickness (t_e

Key Specifications & Formulas for Prestressing Wire and Reinforcement (IS 784):

1. Prestressing Steel Requirements (Clause 4.5.1)

• Prestressing wires conform to:
  • IS 1785 (Part 1 & 2), or
  • IS 6003, or
  • IS 6006.
• For longitudinal prestressing, tensile strength up to 15% less than ultimate tensile strength is permissible to avoid wire damage during threading or anchoring.

2. Typical Properties for Prestressing Wire

3. Spacing & Cover (Clause 8.3)

• Longitudinal wire spacing ≤ 2 × core thickness or 150 mm (whichever is greater).
• Minimum concrete cover over all reinforcement: 12 mm.

4. Loss of Prestress (Annex F)

• Where:
  • ( f_c, f_s, f_g ) = initial stresses,
  • ( E_c, E_s ) = modulus of elasticity,
  • ( L ) = effective pipe length (mm).

5. **Mod

IS 784 - Manufacturing Process: Key Formulas & Specifications

1. Prestress Loss Calculation (Annex F)

Loss of prestress in wires includes:

• E = Modulus of elasticity of wire (2.00×10^5 N/mm² stress relieved)
• L = Effective pipe length (mm)
• fsi_long, fg = Initial stresses in wire (N/mm²)

Note: Factory test pressure losses ≈ 90% of total losses.

2. Pipe Geometry (Annex B)

Indicative socket and spigot dimensions for prestressed concrete pipes:

3. Design Parameters (Annex G)

Example for 1200 mm dia pipe:

• Core thickness, Tc = 70 mm
• Coat thickness, Tb = 22 mm
• Working pressure, Pw = 0.7 N/mm²
• Site test pressure, Ps = 1.05 N/mm²
• Factory test pressure, Pf = 1.15 N/mm²
• Wire diameter (circumferential & longitudinal) = 4 mm
• Ultimate tensile strength of wire = 1715 N/mm²
• Modulus

IS 784: Testing & Quality Control Key Points

1. Tests Required for Non-Pressure Pipes (Clause 14.2)

• Permeability test (IS 3597 method): Final permeability ≤ 0.3 cm³
• Dimensional checks (socket & spigot)
• Three edge bearing test (Table 2)

2. Three Edge Bearing Test Loads (Table 2)

• Load to produce max 0.25 mm crack varies by pipe diameter & class (Np2, Np3, Np4).
• Example for 1000 mm dia pipe:
  • Np2: 24.27 kN/m
  • Np3: 47.90 kN/m
  • Np4: 72.60 kN/m

3. Sampling & Acceptance Criteria (Table 3)

• Number of samples and allowable defectives depend on lot size.
• For lot size 101-300 pipes, e.g., 3 samples for three edge bearing test, 0 defectives allowed.

4. Socket & Spigot Dimensions (Annex B)

• External spigot diameter (B) and internal socket diameter (C) are standardized.
• Example for 500 mm pipe:
  • Spigot (B) = 594 mm
  • Socket (C) = 612 mm

5. Permeability Test Notes (Clause 13.3)

• Initial absorption ≤ 2.0 cm³
• Difference between two initial absorption readings ≤ 0.8 cm³

Summary Table: Key Tests & Limits

Fabrication of Specials as per IS 784

• Material: Steel plates must conform to IS 2062 (Clause 4.6).
• Definition: Specials include bends, air valves, scour valve tees, etc. (Clause 3.3).
• Fabrication Process (Clause 10.1):
  • Steel plates are cut, shaped, and butt-welded to achieve required shape and internal dimensions.
  • Adjacent segments joined by butt welding.
  • After welding, test using hot oil or dye penetrant test as per IS 3658.
  • Weld defects must be repaired and retested.
• Dye Penetration Test:
  • Apply whitewash on one side of weld.
  • Apply colored paraffin on opposite side.
  • No colored spot should appear on whitewash within 4 hours.
  • If spots appear earlier, weld must be repaired.
• Plate Thickness: As per IS 1916 (refer IS 1916 for thickness tables).

Summary Table for Fabrication Checks

flowchart TD
    A[Steel Plates (IS 2062)] --> B[Cut & Shape]
    B --> C[Butt Welding]
    C --> D[Weld Testing (Hot Oil / Dye Penetrant IS 3658)]
    D -->|Pass| E[Coating & Lining]
    D -->|Fail| F[Repair Weld & Retest]
    F --> D

This ensures specials meet dimensional and quality standards before lining/coating.

Inspection Procedures as per IS 784

1. Sampling & Acceptance (Clause 14.2, Table 3):

• For non-pressure pipes (drainage, sewerage, culverts), test:
  • Permeability (from Table 3)
  • Dimensions
  • Three Edge Bearing Test (Table 2)
• Sample sizes and acceptable defective limits depend on lot size (see Table 3).

2. Three Edge Bearing Test Loads (Table 2):

• Loads (kN/m) to produce max 0.25 mm crack vary by pipe diameter and class (Np2, Np3, Np4).
• Example: For 300 mm dia pipe, loads are:
  • Np2: 13.48 kN/m
  • Np3: 15.5 kN/m
  • Np4: 26.4 kN/m

3. Dimensional Checks (Clause 15.1.1):

• Measure internal diameter at both ends (~50 mm from ends) and center (if >700 mm dia).
• Take two measurements at 90° to each other.
• Use Go/No Go gauges:

• Example for 1200 mm dia pipe with ±9 mm (ends) and ±12 mm (centre) tolerance:

4. Marking (Clause 14.3):

• After acceptance, pipes are marked with colour bands indicating pressure class.

flowchart TD
    A[Sampling] --> B{Tests Required}
    B -->|Non-pressure pipes| C[Permeability]
    B -->|All pipes|

IS 784: Marking and Identification of Prestressed Concrete Pipes

Key Marking Requirements (Clause 16.1)

Each pipe shall be clearly marked with:

• Manufacturer's identification
• Size and hydrostatic factory test pressure
• Date of manufacture

Use of Standard Mark (Clause 16.2)

• Pipes may be marked with the Standard Mark as per the Bureau of Indian Standards Act, 1986.
• License conditions for the Standard Mark are governed by BIS rules.

Indicative Dimensions of Socket and Spigot (Annex B)

Note: Dimensions apply to both Roll On and Confined joints.

Summary Diagram of Marking Elements

flowchart TD
    A[Pipe] --> B[Mark Manufacturer ID]
    A --> C[Mark Size & Factory Test Pressure]
    A --> D[Mark Date of Manufacture]
    A --> E[Optional: BIS Standard Mark]

Use these markings for traceability and quality assurance as per IS 784.

IS 784: Coating and Lining Specifications

Key Points from Clauses:

• Lining (Clause 10.2):

  • Steel plate specials are lined/coated with concrete, cement mortar, or approved materials.
  • Cement to aggregate ratio: minimum 1:3 by mass.

• Cover Coating (Clause 8.5):

  • Protective cover coatings are applied as specified (details in Clause 8.5).

• Bitumen/Other Protective Coating (Clause 4.8):

  • External/internal bituminous, epoxy, or approved coatings may be applied.
  • For potable water pipes, internal coatings must be non-soluble and odorless/tasteless.

• Welding & Testing (Clause 10.1):

  • Butt welding of segments, tested by hot oil or dye penetrant test per IS 3658.
  • Dye penetration test: No colored spot on whitewash within 4 hours; else weld repair needed.

Summary Table: Cement Mortar Lining Mix

Dye Penetrant Test Procedure (IS 3658):

1. Apply whitewash on weld side A.
2. Apply colored penetrant on weld side B.
3. Wait 4 hours.
4. No colored spots on whitewash → weld OK.
5. Colored spots → weld repair & retest.

flowchart TD
    A[Steel Plate Special Fabrication]
    B[Butt Welding of Segments]
    C[Dye Penetrant Test (IS 3658)]
    D{Colored Spots on Whitewash?}
    E[Weld OK]
    F[Repair Weld & Retest]

    A --> B --> C --> D
    D -- No --> E
    D -- Yes --> F --> C

Note: Refer to IS 1916 for steel plate thickness and IS 3658 for detailed dye penetrant testing.

Handling and Storage: Key Formulas & Specifications from IS 784

1. Stress Due to Transport and Handling (Clause 3.8)

• Bending Moment (M):
  ( M = 8.44 \times 10^7 , \text{Nmm} )
• Modulus of Section (Z):
  ( Z = 12,731,728 , \text{mm}^3 )
• Stress due to Transport and Handling (σ):
  [ \sigma = \frac{M}{Z} = \frac{8.44 \times 10^7}{12,731,728} = \pm 6.6291 , \text{N/mm}^2 ]

2. Load Combinations for Longitudinal Stresses (Clauses 6.9 & 3.10)

• Longitudinal stresses must be checked against permissible tensile and compressive stresses under different conditions like prestress after losses, during winding, handling, transport, and unloading.
• Example permissible compressive stress: +20 N/mm² (after losses + beam action)
• Example permissible tensile stress: -2.8 N/mm² (during winding)

3. Important Notes:

• For pipes diameter > 600 mm, checking load combination of transport and unloading is not necessary (Clause 7.50).
• Initial prestress in circumferential wire during winding (die process) is about 1114.75 N/mm².

Summary Diagram: Stress Check Flow for Handling & Storage

flowchart TD
    A[Start: Handling/Storage] --> B{Calculate Bending Moment}
    B --> C

IS 784 Annexes: Key Formulas, Tables & Specifications

Annex D (Design of Longitudinals for Pipes ≤ 600 mm)

• Permissible Compressive Stresses (Clause D-3.10 amendments):

Annex F (Wire Relaxation)

• Relaxation of wire:
  0.08 × Su or 0.08 × f'

Annex G

• Follow the detailed design procedure for further design steps.

Annex J (Prestressed Concrete Pipes for Drainage, Sewerage, Culverts)

Typical Design Steps (Annex J)

1. Calculate stresses using pipe geometry and loads.
2. Use ultimate tensile strength and wire area for prestress force.
3. Check flexural strength and load capacity.

flowchart TD
    A[Start: Pipe Geometry & Load] --> B[Calculate Stresses]
    B --> C[Compute Prestress Force]
    C --> D[Check Flexural Strength]
    D --> E{