Code of Practice for Prestressed Concrete

IS 1343: Scope & Key Specifications

IS 1343 covers the design and construction of prestressed concrete structures using the Limit State Method.

Scope Highlights:

• Applies to prestressed concrete elements (beams, slabs, girders, etc.)
• Covers materials, design, analysis, construction, and testing
• Emphasizes safety, serviceability, and durability

Key Clauses:

• Clause 21.3 Design Values: Defines characteristic and design strengths for concrete and prestressing steel.
• Clause 15.1: Addresses work in extreme weather conditions.
• Section 3 (Clauses 19.1 - 19.6): General design requirements including effects of prestressing and erection stability.
• Section 4: Limit state design covering safety and serviceability (Clauses 20-24).

Important Design Values (from Clause 21.3):

Summary:

• Use Limit State Method for design.
• Adopt partial safety factors for materials.
• Ensure serviceability limits (deflection, cracking) and collapse safety.

flowchart LR
    A[Scope: Prestressed Concrete] --> B[Materials & Design]
    B --> C[Limit State Method]
    C --> D[Safety & Serviceability]
    D --> E[Design Values & Safety Factors]
    E --> F[Construction & Testing]

This provides a concise overview of the scope and key design parameters per IS 1343.

IS 1343: Materials, Workmanship, Inspection & Testing - Key Points

Materials (Section 2)

• Cement: Ordinary Portland Cement (IS 269), Portland Pozzolana Cement (IS 1489), Portland Slag Cement (IS 455).
• Aggregates: Coarse & fine aggregates per IS 383.
• Water: Clean, free from harmful impurities.
• Steel: Prestressing steel per IS 1785, IS 6006; Reinforcing steel per IS 432 (Part 1), IS 1786.
• Admixtures: Chemical & mineral admixtures as per relevant IS codes.

Workmanship

• Concrete production follows IS 456 and IS 4926 for batching, mixing, placing, compacting, and curing.
• Prestressing operations per clauses 12 & 13 (assembly, tensioning, grouting).
• Special care in extreme weather (Clause 15.1).

Inspection & Testing (Clauses 16, 17, 18)

• Sampling & Strength Tests: As per IS 1199 and IS 516.
• Acceptance Criteria: Concrete strength must meet design values with standard deviation assumed as 5 N/mm².
• Tests on Sheathing Ducts: Workability, transverse load, tension, water loss, bond, and compression tests (Annex B).

Key Formulas & Specifications

References (Annex A)

• IS 456: Plain & Reinforced Concrete
• IS 516: Test for Strength of Concrete
• IS 1199: Sampling & Analysis of Concrete
• IS 1785, IS 6006: Prestressing Steel
• IS 4926: Ready-mixed Concrete

flowchart TD
    A[Materials] --> B[C

IS 1343: General Design Requirements - Key Points

1. Design Values (Clause 21.3):

   • Use characteristic strengths of materials (concrete, steel) as per relevant IS codes.
   • Design values = Characteristic strength / Partial safety factor (γ).
   • Partial safety factors typically:
     • Concrete (γ_c) ≈ 1.5
     • Steel (γ_s) ≈ 1.15

2. Minimum Requirements (Clause 5.6.1.2.1):

   • Adopt minimum requirements from relevant IS codes (e.g., IS 456 for concrete, IS 800 for steel).
   • Ensure compliance with durability, safety, and serviceability criteria.

Typical Design Value Formula:

[ f_{design} = \frac{f_{characteristic}}{\gamma} ]

Summary:

• Use partial safety factors for design values.
• Refer to relevant IS codes for minimum requirements.
• Ensure durability and safety per IS 1343 and related standards.

flowchart TD
    A[Material Properties] --> B[Characteristic Strength]
    B --> C[Apply Partial Safety Factor (γ)]
    C --> D[Design Strength for Calculations]
    D --> E[Structural Design & Checks]

IS 1343: Structural Design - Limit State Method

Key Concepts (Clause 20.1)

• Limit State Design ensures safety and serviceability.
• Design for ultimate loads (strength limit state) and service loads (serviceability limit state).
• Structure must not reach a limit state (failure or unserviceability).

Important Formulas & Specifications

Typical Partial Safety Factors (IS 1343 & IS 456 reference)

Serviceability Checks

• Deflection: Use span/limit ratios (e.g., span/250 for beams).
• Crack Width: Limit crack width to prevent corrosion and durability issues.
• Stress: Ensure stresses under service loads do not exceed elastic limits.

flowchart LR
    A[Start: Define Loads] --> B[Apply Load Factors]
    B --> C[Calculate Design

IS 1343: Properties of Materials - Key Points

1. Characteristic Strength (Clause 21.1)

• Characteristic strength is the value below which not more than 5% of the test results are expected to fall.
• Used as a basis for design to ensure safety.

2. Mechanical Properties (Clause 5.6.1.2)

• Defines modulus of elasticity (E), yield strength (fy), ultimate strength (fu) for prestressing steel.
• Typical values:
  • E = 2 × 10^5 MPa
  • fy = 1860 MPa (for high tensile wires)
  • Stress-strain behavior follows a linear elastic up to yield, then plastic.

3. Design Values (Clause 21.3)

• Design strength = characteristic strength / partial safety factor (γ)
• Partial safety factors:
  • For steel, γ = 1.15
  • For concrete, γ = 1.5
• Design stress, ( f_d = \frac{f_k}{\gamma} )

Summary Table: Material Properties

flowchart LR
    A[Characteristic Strength \(f_k\)] --> B[Partial Safety Factor \(γ\)]
    B --> C[Design Strength \(f_d = \frac{f_k}{γ}\)]
    C --> D[Used for Structural Design]

Use these values for safe design of prestressed concrete structures per IS 1343.

IS 1343: Concrete Properties & Mix Design Key Points

1. Concrete Properties (Clause 6.2)

• Characteristic compressive strength (f_ck) at 28 days is the basis.
• Concrete should have adequate workability, durability, and strength.
• Properties depend on water-cement ratio, quality of materials, and curing.

2. Concrete Mix Proportions (Clause 8.2.4)

• Mix proportions decided based on:
  • Target mean strength ( f_{tm} = f_{ck} + k \times s )
    where ( k = 1.65 ) (for 95% confidence), ( s ) = standard deviation.
  • Water-cement ratio as per strength and durability requirements.
  • Aggregates grading and quality.

3. Design Mix Concrete (Clause 9.2)

• Steps:
  1. Select target mean strength.
  2. Choose water-cement ratio from IS 456 or IS 10262.
  3. Determine water content for required workability.
  4. Calculate cement content = Water content / (Water-cement ratio).
  5. Select aggregate proportions based on grading.
  6. Trial mixes to confirm strength.

Key Formula: Target Mean Strength

[ f_{tm} = f_{ck} + 1.65 \times s ]

Typical Mix Design Table (Example)

flowchart TD
    A[Start: Select f_ck] --> B[Calculate target mean strength f_tm]
    B --> C[Select water-cement ratio]
    C --> D[Determine water content for workability]
    D --> E[Calculate cement content]
    E --> F[Select aggregate proportions]
    F --> G[Prepare trial mix]
    G --> H[Test strength & adjust]
    H -->

IS 1343: Prestressing Steel and Tendons

Key Specifications (Clause 12.1 & 5.6)

• Types of Prestressing Steel: High tensile wires, strands, and bars.
• Tensile Strength: Minimum characteristic tensile strength, ( f_{pu} ), typically 1860 MPa for wires and strands.
• Modulus of Elasticity, ( E_p ): Usually 2.0 × 10^5 MPa.
• Relaxation: Limits on relaxation losses per IS 1343.

Important Formulas

• Initial Prestressing Force, ( P_i ):
  [ P_i = A_p \times f_{pi} ]
  where ( A_p ) = area of prestressing steel, ( f_{pi} ) = initial stress in steel (usually 0.7 to 0.8 of ( f_{pu} )).

• Losses in Prestress:
  Total losses ( = ) elastic shortening + creep + shrinkage + relaxation + friction.

• Effective Prestress, ( P_e ):
  [ P_e = P_i - \text{Total losses} ]

Tables (Typical values from IS 1343)

flowchart LR
    A[Prestressing Steel] --> B[High Tensile Wires]
    A --> C[Strands]
    A --> D[Bars]
    B & C & D --> E[Initial Stress \( f_{pi} \)]
    E --> F[Losses: Relaxation, Creep, Shrinkage, Friction]
    F --> G[Effective Prestress \( P_e \)]

Summary: Use prestressing steel with ( f_{pu} \approx 1860 ) MPa, initial stress ~70-80% of ( f_{pu} ),

IS 1343: Concrete Durability & Mix Proportioning Key Points

1. Concrete Durability (Clause 8.2)

• Compaction: Ensure full compaction without segregation using proper workability and equipment, especially near joints and reinforcement.
• Finishing: Avoid overworking and adding water/cement on surface to prevent laitance, which reduces strength and durability.
• Curing: Essential to reduce permeability and enhance hydration, especially at the surface. Use adequate curing methods (water curing, membrane curing, etc.).

2. Mix Proportioning (Clauses 8.2.4 & 8.2.5.1)

• Select materials carefully to limit deleterious constituents.
• Control water-cement ratio (w/c) to ensure durability.
• Use minimum cement content and maximum w/c ratio as per exposure conditions (refer IS 456 for w/c values).
• Adjust mix for workability, strength, and durability.

Typical Limits for Durability (from IS 456 & IS 1343 guidance):

Summary Diagram: Durability Process Flow

flowchart LR
    A[Select Materials] --> B[Control w/c Ratio]
    B --> C[Mix Proportioning]
    C --> D[Proper Compaction]
    D --> E[Good Finishing]
    E --> F[Adequate Curing]
    F --> G[Durable Concrete]

Note: Refer to IS 1343 Clause 14 for detailed curing methods and IS 456 for mix design and durability criteria.

IS 1343: Testing and Quality Control - Key Points

Quality Assurance Plan (Clause 10.1.3)

• Each party must implement a Quality Assurance Plan (QAP) integrated into the general project QAP.
• QAP must define:
  • Tasks & responsibilities
  • Control & checking procedures
  • Documentation of processes and results

Documentation Includes:

• Test reports & manufacturer certificates (materials, concrete mix design)
• Pour cards for concrete placement clearance
• Site inspection records & field tests
• Non-conformance reports & change orders
• Quality control charts (recommended for continuous concrete production)
• Statistical analysis of quality data

Sampling and Strength Test of Concrete (Section 16)

• Concrete samples must be taken and tested as per IS guidelines.
• Acceptance criteria (Section 17) define when concrete is accepted or rejected based on strength tests.

Sheathing Ducts Testing (Annex B)

• Tests on corrugated HDPE sheathing ducts include:
  • Workability test (Fig. 9)
  • Transverse load rating test
  • Tension load test
  • Water loss test (water loss ≤ 1.5%)
  • Bond test
  • Compression test for wall thickness loss

Volume Calculation for Water Loss Test

[ \text{Relative profile volume} = V_p - (V_b) ] where,

• (V_p) = premeasured water volume,
• (V_b) = water left after filling sample,
• (l) = specimen length,
• (\phi) = internal diameter of sheathing.

Summary Table: Key Documents in QAP

This structured approach ensures traceability, accountability, and consistency in prestressed concrete quality control as per IS 1343.

IS 1343 - Quality Assurance Measures (Clause 10.1)

Key Specifications:

• Quality Assurance Plan (QAP):
  • Must cover all parties: contractors, suppliers, subcontractors.
  • Define tasks, responsibilities, control & checking procedures.
  • Ensure documentation of the entire process.

Essential Documentation Includes:

• Material Certificates & Test Reports (e.g., concrete mix design).
• Pour Cards: Site organization and concrete placement clearance.
• Inspection Records: Workmanship, field tests during each concreting step.
• Non-Conformance Reports & Change Orders: Track deviations and corrections.
• Quality Control Charts: Monitor continuous concrete production quality.
• Statistical Analysis: Evaluate trends and quality consistency.

Quality Control Focus:

• Inputs: materials, batching, mixing, transport, placing, compaction, curing.
• Outputs: concrete in place, inspected before next step.

Summary Table of QA Elements

flowchart TD
    A[Start: Material Procurement] --> B[Material Testing & Certification]
    B --> C[Batching & Mixing]
    C --> D[Transport & Placement]
    D --> E[Compaction & Curing]
    E --> F[Inspection & Testing]
    F --> G{Quality OK?}
    G -- Yes --> H[Proceed to Next Step]
    G -- No --> I[Non-Conformance Report & Corrective Action]
    I --> F

Note: Inspect each step before proceeding to ensure quality and fitness for service.

IS 1343: Moulds and Fabrication - Key Points

1. Moulds for Pre-tension Work (Clause 11.1.1)

• Must be strong and rigid to resist:
  • Concrete placing and compaction stresses without distortion.
  • Prestressing forces when tendon is supported by the mould before transfer.
• Typically made of steel or other rigid materials.

2. Fabrication Specifications

• Tendons and reinforcement must be assembled and fixed securely before concrete casting.
• Ensure accurate positioning to maintain prestressing profile and cover.
• Follow IS 1343 and related IS codes for steel specifications (e.g., IS 1786 for reinforcement bars).

3. Related IS Codes for Materials & Fabrication

4. Concrete Properties & Testing (Clause 6.2, Section 16)

• Concrete mix must meet strength and workability requirements.
• Sampling and strength tests per IS 516 and IS 1199.
• Acceptance criteria and inspection per IS 1343 clauses 16-18.

Summary Table: Mould Requirements

flowchart LR
    A[Mould Design] --> B[Strong & Rigid Material]
    B --> C[Resist Concrete Pressure]
    B --> D[Resist Prestressing Forces]
    C & D --> E[No Distortion]
    E --> F[Secure Tendon Support]
    F --> G[Accurate Fabrication & Assembly]

Note: For detailed fabrication steps, prestressing tendon handling, and mould design dimensions, refer to IS 1343 Sections 11 & 12, and related IS codes for steel and concrete.

IS 1343: Assembly of Prestressing & Reinforcing Steel

Key Points from Clause 10.3 (Assembly):

• Proper positioning of prestressing tendons and reinforcement is essential to maintain design cover and spacing.
• Use chairs, spacers, and supports to avoid displacement during concrete placement.
• Ensure no damage or corrosion on prestressing steel during assembly.
• Maintain minimum clear cover as per design (usually 25-40 mm depending on exposure).

Prestressing Steel (Clauses 5.6.1 & 12.1):

• Use high tensile steel wires, strands, or bars conforming to specified grades.
• Tensile strength (fpu) and yield strength (fpy) values are critical for design (typical fpu ≈ 1860 MPa for strands).
• Allowable stresses during transfer and service are specified.

Important Formulas:

• Area of prestressing steel, Ap: [ A_p = \frac{P}{f_{pu} \times 0.8} ] where (P) = prestressing force, (f_{pu}) = ultimate tensile strength.

• Losses in prestress must be accounted (elastic shortening, creep, shrinkage, relaxation).

Typical Table: Minimum Cover (mm)

flowchart LR
    A[Cut & Prepare Steel] --> B[Position & Fix Steel]
    B --> C[Use Chairs & Spacers]
    C --> D[Check Cover & Spacing]
    D --> E[Inspect for Damage]
    E --> F[Concrete Placement]

Summary: Use specified grades, maintain cover and spacing, fix steel firmly with supports, and check for damage before concreting.

IS 1343: Prestressing and Grouting Operations - Key Points

1. Prestressing Requirements (Clause 19.5)

• Losses in Prestress: Consider immediate (elastic shortening, friction, anchorage slip) and time-dependent losses (creep, shrinkage, relaxation).
• Effective Prestress (f_pe):
  [ f_{pe} = f_{pi} - \sum \text{losses} ] where ( f_{pi} ) = initial prestress.

2. Prestressing Equipment (Clause 13.1)

• Equipment must ensure accurate tensioning and safe anchorage.
• Use calibrated jacks and tension measuring devices.
• Maintain alignment to avoid eccentric loading.

3. Grouting Operations

• Grout should be non-shrink, flowable, and fill all voids.
• Pressure grouting recommended to ensure full bond.
• Grouting delays: Usually done after prestress transfer and initial curing.

Summary Table: Prestress Losses (Typical Values)

flowchart LR
    A[Prestressing] --> B[Tensioning of Strands]
    B --> C[Transfer of Stress]
    C --> D[Grouting]
    D --> E[Bonding & Protection]

Note: Refer to IS 1343 for detailed procedures and safety checks during prestressing and grouting.

IS 1343: Joints and Anchorage Details Key Points

1. Sheathing Duct Joints (Clause B-5)

• Joints must be cement slurry tight.
• Use sleeve couplers with length ≥ 150 mm, preferably 200 mm.
• Seal ends of coupler and duct with adhesive sealing tape to prevent slurry ingress.
• Stagger couplers in adjacent ducts; avoid curved zones.
• Heat-shrink couplers (bandage rolls with heat-sensitive adhesive) provide leak-proof joints after heating.

2. Anchorage Testing (Annex C)

• Static Load Test on tendon-anchorage assembly to verify performance and breaking load.
• Test specimen: reinforced beam with tendon embedded 40× duct diameter.
• Grout strength ≥ 27 N/mm².
• Failure capacity of bond ≥ anchorage efficiency or 0.95 × tendon failure load.
• Minimum 3 tests for adequacy.

3. Typical Sleeve Coupler Detail (Fig. 15)

• Length: 150–200 mm
• Coupler must ensure full load transfer and prevent grout leakage.

Summary Table: Anchorage Test Requirements

flowchart LR
    A[Sheathing Duct Joint] --> B[Sleeve Coupler (150-200mm)]
    B --> C[Adhesive Sealing Tape]
    A --> D[Heat Shrink Coupler]
    E[Tendon Anchorage] --> F[Embed 40× duct diameter]
    F --> G[Grout Strength ≥ 27 N/mm²]
    G --> H[Static Load Test]
    H --> I[Failure Load ≥ 0.95 × tendon capacity]

This ensures leak-proof joints and reliable anchorage per IS 1343.

IS 1343: Limit State Design Principles

Key Concepts (Clause 20.1)

• Limit State Design (LSD) ensures safety and serviceability throughout the structure's life.
• Design must prevent failure (ultimate limit state) and satisfy serviceability (deflection, cracking, compression limits).
• Limit State: The boundary beyond which the structure no longer fulfills intended function.

Characteristic & Design Values (Clause 20.3)

• Characteristic Load (Qk): Statistically defined load with a certain probability of exceedance.
• Design Load (Qd): ( Q_d = \gamma_f \times Q_k ), where (\gamma_f) is the partial safety factor for loads.
• Design Strength (Rd): ( R_d = \frac{R_k}{\gamma_m} ), where (R_k) is characteristic strength and (\gamma_m) is material safety factor.

Partial Safety Factors (Typical values)

Basic Design Equation

[ \sum \text{Design Load Effects} \leq \sum \text{Design Strength} ]

Summary Diagram

flowchart TD
    A[Characteristic Loads & Strengths] --> B[Apply Partial Safety Factors]
    B --> C[Design Loads & Strengths]
    C --> D{Check Limit States}
    D -->|Ultimate Limit State| E[Safety Against Collapse]
    D -->|Serviceability Limit State| F[Control Deflection, Cracking]
    E & F --> G[Safe & Serviceable Structure]

This framework ensures reliability and durability by balancing safety and usability in design.