Reinforced Concrete Poles for Overhead Power and Telecommunication Lines

IS 785: Scope & Key Specifications

• Scope: Defines standard requirements for poles (material, dimensions, strength).
• Rounding Off: Final test/analysis values must be rounded per IS 2:1960, maintaining the same significant figures as specified.

Sampling & Testing (Clause 9.2.1)

• If any pole fails transverse strength, double the sample size is retested.
• No failures in retest means lot acceptance.

Notes:

• Number of poles tested is negotiable between purchaser & supplier.
• Refer to Annex A for related Indian Standards (subject to revision).

This ensures quality control via statistically valid sampling and testing.

IS 785: Key Definitions & Specifications

1. Definitions (Clause 3.0)

• Terms used in the standard are defined for clarity and uniform interpretation.
• Final test or analysis results must be rounded off per IS 2:1960 rules.
• Rounded values retain the same significant figures as specified values.

2. Formwork Requirements (Clause 7.4.1)

• Forms must maintain shape during concrete placing and compaction.
• Must be tight enough to prevent loss of concrete liquid.

3. Sampling & Testing (Clause 9.2.1)

Table: Number of Tests and Acceptance Criteria

• If failure occurs, double the sample size is retested.
• No failures in retest → lot accepted.

Summary:

• Use IS 2:1960 for rounding results.
• Ensure formwork integrity during casting.
• Follow sampling sizes and acceptance numbers from Table 9.2 for quality control.

flowchart TD
    A[Lot of Poles] --> B[Select Sample Size]
    B --> C{Test Poles}
    C -->|Pass| D[Lot Accepted]
    C -->|Fail| E[Double Sample Size]
    E --> F{Retest}
    F -->|Pass| D
    F -->|Fail| G[Lot Rejected]

IS 785 - Materials: Key Specifications & References

Materials covered in IS 785 relate mainly to cement, aggregates, and reinforcement steel, referencing several IS standards:

Important Notes:

• Material Quality must comply with the respective IS specifications for strength, grading, and durability.
• Forms and Molds (Clause 7.4.1): Must maintain shape during concrete placement and prevent loss of liquid.
• Rounding Off: Test results are rounded per IS 2:1960 rules.

Typical Material Properties (from referenced IS codes):

For detailed mix design or reinforcement detailing, refer to IS 456:1978 (Plain and Reinforced Concrete Code).

flowchart LR
    Cement --> Concrete
    Aggregates --> Concrete
    Water --> Concrete
    Admixtures --> Concrete
    Steel --> Reinforced_Concrete
    Concrete --> Structure
    Reinforced_Concrete --> Structure

Summary: IS 785 refers to established IS standards for materials — cement, aggregates, steel — ensuring quality and compliance for concrete products.

Overall Length of Poles (IS 785 Key Points):

• Clause 6.3 - Depth of Planting (Table 1):

• Clause 3.5 - Working Load:
  The maximum transverse load is assumed acting 600 mm below the top with the pole planted to the required depth.

• Clause 9.1.3 & 9.2.1 - Sampling & Testing:
  Poles are selected per Table 2 (lot size based), tested for:

  • Overall length
  • Cross-section
  • Uprightness

  Poles failing any are defective; acceptance based on sample defect limits.

Summary Formula for Overall Length:

[ L_{overall} = L_{above\ ground} + D_{planting} ]

Where:

• (L_{overall}) = Total pole length
• (D_{planting}) = Minimum depth of planting (from Table 1)

Typical Pole Detail Notes:

• Holes (for earthing, kicking blocks) generally 20 mm diameter.
• Pole length and planting depth ensure stability against transverse wind load at 600 mm below top.

flowchart TD
    A[Working Load at 600 mm below top] --> B[Pole length above ground]
    B --> C[Minimum Depth of Planting (Table 1)]
    C --> D[Overall Length of Pole]

This ensures structural stability and compliance with IS 785.

IS 785: Reinforcement Key Points

1. Types of Reinforcement (Clause 5.3)

• Mild steel & medium tensile steel bars/wires:
  Conform to IS 432 (Part 1 & 2)
• High strength deformed bars/wires:
  Conform to IS 1786

2. Placement & Cover (Clauses 7.1 & 7.2)

• Reinforcement must be accurately placed and fixed during manufacture.
• Use corrosion-resistant chairs/buttons to maintain cover.
• Minimum concrete cover:
  [ \text{Cover} \geq \max(\text{aggregate size} + 2 \text{ mm}, 20 \text{ mm}) ]

3. Surface Condition (Clause 5.3.1)

• Reinforcement surface must be clean and free from:
  • Loose scale or rust
  • Oil, grease, clay
  • Any material affecting bond with concrete

Summary Table: Reinforcement Specifications

flowchart TD
    A[Reinforcement Bars/Wires] --> B{Type}
    B --> C[Mild/Medium Tensile (IS 432)]
    B --> D[High Strength Deformed (IS 1786)]
    A --> E[Surface Cleanliness]
    E --> F[Free from scale, rust, oil, grease]
    A --> G[Placement]
    G --> H[Accurate positioning]
    G --> I[Corrosion-resistant chairs/buttons]
    G --> J[Cover ≥ max(aggregate+2mm, 20mm)]

This ensures durability, bond strength, and structural integrity of reinforced concrete poles per IS 785.

IS 785: Design Requirements - Key Formulas, Tables, and Specifications

1. Sampling and Testing (Clause 9.2.1)

• If any pole fails transverse strength test, double the sample size is retested.
• No failure in retest = lot accepted.

2. Load Factor (Clause 3.2)

[ \text{Load Factor} = \frac{\text{Ultimate Transverse Load}}{\text{Transverse Load at First Crack}} ]

• Design transverse load at first crack ≥ working load.

3. Formwork (Clause 7.4.1)

• Forms must maintain shape during concrete placement.
• Must be tight to prevent leakage of concrete liquid.

4. Rounding Off (General)

• Follow IS 2:1960 for rounding final values.
• Retain the same significant figures as specified.

flowchart TD
    A[Lot of Poles] --> B{Sample Size per Table}
    B --> C[Dimensional Test]
    B --> D[Transverse Strength Test]
    D --> E{Pass?}
    E -- Yes --> F[Lot Accepted]
    E -- No --> G[Double Sample Retest]
    G --> H{Pass Retest?}
    H -- Yes --> F
    H -- No --> I[Lot Rejected]

This concise summary covers key design and quality control requirements per IS 785. For detailed design, refer to the full code.

IS 785: Manufacture - Placing, Compaction and Curing of Concrete

Key Specifications (Clause 7.5)

• Placing:

  • Use concrete immediately after mixing.
  • Do not use concrete that has started initial set.
  • After placing and compacting, do not disturb concrete during setting.
  • For hot weather concreting, refer to IS 7861 (Part 1).

• Compaction (Clause 7.5.2):

  • Use mechanical methods: spinning, vibrating, shocking.
  • Hand compaction is prohibited.
  • Ensure full compaction to avoid honeycombing and voids.

• Formwork (Clause 7.4.1):

  • Forms must maintain shape during placing and compaction.
  • Forms must be tight to prevent loss of concrete liquid.

Typical Compaction Methods

Curing (General Practice)

• Maintain moisture for minimum 7 days (28 days for high-strength concrete).
• Use water curing, wet coverings, or curing compounds.
• Prevent rapid drying to avoid shrinkage cracks.

flowchart TD
    A[Mix Concrete] --> B[Place in Formwork]
    B --> C[Compact Mechanically]
    C --> D[Do Not Disturb Concrete]
    D --> E[Curing (≥7 days)]

Summary: Use fresh concrete, compact mechanically, ensure formwork integrity, and cure properly for durable, defect-free concrete as per IS 785 Clause 7.5.

IS 785: Transverse Strength Test of Reinforced Concrete Poles

Key Points from IS 785 and IS 2905

• Test Standard: Transverse strength test per IS 2905.
• Acceptance Criteria: Ultimate transverse load ≥ Design ultimate transverse load.
• Design Requirements (Clause 6.4):
  • Poles must resist transverse wind load × load factor.
  • Include snow load if applicable.
  • At working load, stresses must avoid harmful cracking.

Load Factor (Clause 3.2)

[ \text{Load Factor} = \frac{\text{Ultimate Transverse Load}}{\text{Transverse Load at First Crack}} \geq 1 ]

• Transverse load at first crack ≥ working load.

Sampling (Clause 9.2.2)

• Number of poles for testing as per Table 2, Column 4 (IS 785).
• Poles may be selected from those already tested.

Typical Design Formula for Transverse Strength

[ P_u \geq \text{Load Factor} \times P_w ]

Where:

• (P_u) = Ultimate transverse load capacity (kN)
• (P_w) = Working transverse load (wind + snow) (kN)

Summary Table (Example)

flowchart TD
    A[Design Working Load (Pw)] --> B[Apply Load Factor]
    B --> C[Design Ultimate Load (Pu)]
    C --> D[Test Pole for Ultimate Load]
    D -->|Pu Test ≥ Pu Design| E[Pass]
    D -->|Pu Test < Pu Design| F[Fail]

This ensures poles meet transverse strength requirements as per IS 785 and IS 2905.

IS 785 - Sampling and Inspection: Key Points

1. Sampling Scale & Sample Size (Clause 9.1 & Table 9.2.1)

• Sample size: Number of poles tested from the lot.
• Acceptance number: Maximum allowable defective poles for dimensional and transverse strength tests.

2. Inspection Procedure (Clause 9.2.1)

• If any pole fails the transverse strength test, double the original sample size is tested.
• If no failure in the second test, the lot is accepted.
• If failures persist, the lot is rejected.

3. Rounding Off (Clause None)

• Test results are rounded per IS 2:1960.
• Retain the same decimal places as specified values.

Summary Diagram:

flowchart TD
    A[Select Lot] --> B[Determine Sample Size]
    B --> C[Test Poles for Dimensional & Strength]
    C --> D{Failures?}
    D -- No --> E[Accept Lot]
    D -- Yes --> F[Double Sample Size Test]
    F --> G{Failures?}
    G -- No --> E
    G -- Yes --> H[Reject Lot]

This ensures quality control with statistically valid sampling and acceptance criteria.

IS 785 - Marking and Identification of Concrete Poles

Key Specifications (Clause 10.1 & 10.2)

Poles must be clearly and indelibly marked either during or after manufacture but before testing, at a visible position after erection, with:

• Source of manufacture
• Month and year of manufacture
• Serial number of the pole
• Position of centre of gravity (marked as 'C.G')

BIS Certification Marking (Clause 10.2)

• Poles may carry the BIS Standard Mark as per the Bureau of Indian Standards Act, 1986.
• Use of the Standard Mark is subject to BIS licensing conditions.

Important Notes

• Markings should be durable and legible after erection.
• Follow IS 2:1960 for rounding off numerical values in test results.

flowchart LR
    A[Manufacture] --> B[Marking]
    B --> C[Source of Manufacture]
    B --> D[Month & Year]
    B --> E[Serial Number]
    B --> F[Centre of Gravity (C.G)]
    B --> G[Optional: BIS Standard Mark]
    G --> H[License Conditions]
    F --> I[Visible after erection]

This ensures traceability, quality control, and compliance with BIS standards for concrete poles.

IS 785 - List of Referenced Indian Standards

The key referenced IS standards in IS 785 cover materials, testing, design, and construction practices for concrete and reinforcement:

Important Notes:

• These referenced standards provide material specifications, testing methods, and design guidelines essential for compliance with IS 785.
• Always check for the latest edition of these standards for current requirements.
• BIS Certification Mark usage is governed by the Bureau of Indian Standards Act, 1986 (Clause 10.2.1).

Example: Concrete Strength Test (IS 516:1959)

• Compressive strength, f_c = P / A
  where P = load at failure (N), A = cross-sectional area (mm²)

flowchart LR
    A[IS 785] --> B[Material Specs]
    A --> C[Testing Methods]
    A --> D[Design Codes]
    B --> IS269["IS 269: Cement"]
    B --> IS383["IS 383: Aggregates"]
    C --> IS516["IS 516: Concrete Strength"]
    D --> IS456["IS 456: Concrete Practice"]
    D --> IS875["IS 875: Wind Loads"]

This concise list and structure help ensure compliance with IS 785 by referencing appropriate Indian Standards.

IS 785: Committee Composition - Key Details

Committee: Cement Matrix Products Sectional Committee, CED 53
Location: Annex B of IS 785 standard (Foreword)

Composition Highlights

Notes:

• Each member often has an alternate.
• The committee includes experts from government, industry, research, and standards bodies.
• This diverse composition ensures comprehensive technical input for the standard.

No specific formulas or tables are provided for committee composition in IS 785.

Refer to Annex B for full member details.

flowchart TD
    A[Chairman: Shri S. A. Reddi] --> B[Municipal Corporations]
    A --> C[Rural Electrification Corporation]
    A --> D[Construction Technology Pvt Ltd]
    A --> E[Research & Standards Organizations]
    A --> F[Pipe Manufacturers Associations]
    A --> G[National Test House]
    A --> H[Public Works Department]
    A --> I[BIS Director General (Ex-officio)]

For certification and marking details, see Clause 10.2.1.