Standard Plan for Highway Bridges — Prestressed Concrete Beams and RCC Slab Type Superstructure Volume-II

Scope Summary from MORTH 256 Part 2

1. Public Utility Services

• Carried through 150 mm dia ducts in footpaths.
• Max load: 1.0 kN/m per footpath.

2. Bituminous Wearing Coat

• Mastic Asphalt Layer: 6 mm thick (12 mm in high rainfall areas).
• Asphaltic Concrete: 50 mm total in two layers of 25 mm each.
• Alternative for high traffic: 40 mm bituminous concrete + 25 mm bitumen mastic layer.
• Work as per Section 500 of MOST Specification.

3. Design Loads

4. Exposure Conditions

• Designs for moderate and severe exposure.
• For severe, provide anti-corrosion treatment as approved.

5. Materials Specifications

Key Formula for Load Combination (Typical)

[ \text{Total Load} = \text{Vehicle Load} + \text{Footpath Load} + \text{Wearing Coat Load} ]

Diagram: Load Distribution on Bridge Cross-Section

graph LR
A[Carriageway: IRC 70R or IRC A] --> B[Superstructure]
C[Footpath Load: 5 kN/m²] --> B
D[Wearing Coat: 2 kN/m²] --> B
E

MORTH 256 Part 2: General Notes and Definitions - Key Points

This section applies to Standard Drawings for Prestressed Concrete Girders and RC Slab Type Composite Superstructure (with/without footpaths).

Key References

• General Notes: SD/501 (Sheets 1 & 2)
• Bill of Quantities: Included in Part 2
• Dimensions and Anchorage Details: SD/511, SD/512, SD/521, SD/531, SD/541, etc.
• Prestressing Cables: SD/512, SD/522, SD/532, SD/542
• Reinforcement Details: SD/535, SD/545

Typical Definitions & Specifications:

• Prestressing Cable Systems: Multi-wire strands detailed per drawing.
• Span Lengths Covered: 30m, 35m, 40m spans with or without footpaths.
• Anchorage Details: Critical for transfer of prestress, shown in respective drawings.
• Dimensions: Govern girder width, depth, cable profile, and anchorage zones.

Common Formulas (from prestressed concrete design principles):

• Loss of Prestress (ΔP):
  [ \Delta P = \Delta P_{\text{elastic}} + \Delta P_{\text{creep}} + \Delta P_{\text{shrinkage}} + \Delta P_{\text{relaxation}} ]
• Ultimate Moment Capacity (M_u):
  [ M_u = f_{pu} \times A_p \times (d - a/2) ] where (f_{pu}) = ultimate stress in prestressing steel, (A_p) = area of prestressing steel, (d) = effective depth, (a) = depth of equivalent stress block.

Summary Table: Span vs Drawing Nos.

flowchart LR
    A[General Notes SD/501] --> B[Prestressing Cable Details]

MORTH 256 Part 2: Key Materials Specifications

Concrete

• Design Mix Concrete: Minimum 28-day characteristic strength = 40 MPa (150 mm cubes).
• Cement: OPC as per IS: 269 or High Strength OPC as per IS: 8112.
• Cement Content: 400 to 540 kg/m³.
• Water-Cement Ratio: Max 0.40 for deck slabs and precast girders.
• Admixtures: Permitted as per IS: 6925 & IS: 9103; avoid admixtures generating hydrogen, nitrogen, chlorides.

Reinforcement

• HYSD bars, Grade S:415 per IS: 1786.

Prestressing Steel

• Strand: Single 12.7 mm dia, 7-ply Class 2 strands per IS: 6006-1983.
• Max tensioning force per strand: 128.6 kN.
• Use mono strand jacks; strands protected by polyethylene sheathing and grouted.

Wearing Coat Specifications

• Mastic Asphalt Layer: 6 mm thick (12 mm in high rainfall).
• Asphaltic Concrete Wearing Coat: 50 mm thick in two layers (25 mm each).
• Alternative for high traffic: 40 mm bituminous concrete + 25 mm bitumen mastic.
• Wearing coat load: 2 kN/m².

Load Considerations

• IRC Class 70R (1 lane) or IRC Class A (2 lanes).
• Footpath load: 5 kN/m².
• Public utility ducts: 150 mm dia, max load 1.0 kN/m per footpath.

Summary Table: Concrete & Steel

Design Loads and Criteria (MORTH 256 Part 2)

• Public Utility Services Load: Max 1.0 kN/m on each footpath through 150 mm ducts.

• Wearing Coat:

  • Mastic asphalt: 6 mm thick (12 mm in high rainfall areas).
  • Asphaltic concrete: 50 mm in two layers (25 mm each).
  • Alternative for high traffic: 40 mm bituminous concrete + 25 mm bitumen mastic.
  • Wearing coat load: 2 kN/m².

• Design Loads:

  • IRC Class 70R (one lane) or two lanes of IRC Class A, whichever governs.
  • Footpath load: 5 kN/m².
  • Wearing coat load: 2 kN/m².

• Exposure Conditions: Designs for moderate and severe; anti-corrosion treatment required for severe.

Materials Specifications

Expansion Joints

• Movement capacity: ±40 mm.
• Waterproof membrane and elastomer cushion mandatory.
• Initial gap ≥ 38 mm.
• Must cover full deck width including footpaths and kerbs.
• Only approved manufactured joints allowed.

Summary Table: Loads for Design

flowchart LR
    A[Bridge Deck] --> B[Wearing Coat Load (2 kN/m²)]
   

MORTH 256 Part 2: Prestressing Cables and Systems

Though the code clauses are unspecified, typical key points for prestressing cables in road/bridge works include:

Key Specifications:

• Cable Types: High tensile steel strands (7-wire), conforming to IS 14268.
• Ultimate Tensile Strength (fpu): Usually 1860 MPa for strands.
• Relaxation: Should not exceed 5% at 1000 hours under specified stress.

Essential Formulas:

1. Initial Prestress Force (P_i):
   [ P_i = A_p \times f_{pi} ]
   Where:

   • (A_p) = Area of prestressing steel
   • (f_{pi}) = Initial prestress stress (typically 0.7 to 0.8 of (f_{pu}))

2. Losses in Prestress:
   Total losses = Elastic shortening + Creep + Shrinkage + Relaxation + Anchorage slip

3. Effective Prestress Force (P_e):
   [ P_e = P_i - \text{Total losses} ]

Typical Table: Prestressing Strand Area (IS 14268)

System Specifications:

• Anchorage devices must ensure no slip beyond 0.1 mm.
• Grouting of ducts to protect cables from corrosion.
• Minimum cover as per MORTH for durability.

flowchart LR
    A[Prestressing Cable] --> B[Initial Stress (f_pi)]
    B --> C[Apply Prestress Force (P_i)]
    C --> D[Losses (Relaxation, Creep, etc.)]
    D --> E[Effective Prestress Force (P_e)]
    E --> F[Structural Element Strength]

Summary: Use high tensile strands, apply initial prestress ~70-80% of ultimate strength, account for losses, and ensure proper anchorage and protection per MORTH and IS guidelines.

MORTH 256 Part 2: Reinforcement Details (Dimensions & Anchorage)

While specific clauses are not provided, typical MORTH and IS code practices for reinforcement details include:

Key Specifications:

• Minimum Anchorage Length (Development Length):
  As per IS 456:2000, development length (L_d) depends on bar diameter (d_b), concrete grade, and bar stress.
  [ L_d = \frac{\sigma_{s} \times d_b}{4 \times \tau_{bd}} ] where (\sigma_s) = stress in steel, (\tau_{bd}) = design bond stress.

• Hook and Bend Dimensions:

  • 90° hook length = 12 × bar diameter (d_b)
  • 135° hook length = 8 × d_b

• Clear Cover:

  • For mild exposure: 25 mm
  • For moderate exposure: 40 mm
  • For severe exposure: 50 mm or more

Prestressing Cables Anchorage:

• Anchorage zones must have adequate concrete strength (usually M40 or above).
• Use of anchorage devices as per manufacturer and IS 1343 guidelines.
• Ensure minimum embedment length as per design.

Typical Table: Development Length (IS 456:2000)

flowchart TD
    A[Reinforcement Bar] --> B[Development Length]
    B --> C[Anchorage Length]
    B --> D[Hooks & Bends]
    A --> E[Clear Cover]
    A --> F[Prestressing Cables]
    F --> G[Anchorage Devices]
    F --> H[Concrete Strength]

Summary: Ensure proper anchorage length, hooks, and cover as per IS 456 and MORTH. For prestressing, follow IS 1343 and manufacturer specs for anchorage.

MORTH 256 Part 2: Superstructure Layout and Dimensions (Prestressed Concrete Beams & RCC Slab Type)

While the code lacks explicit clause numbering, key points on superstructure layout and dimensions typically include:

1. Standard Span Lengths for PSC Beams

• Common span lengths: 6m, 9m, 12m, 15m, 18m
• Beam spacing depends on slab thickness and wheel load distribution, usually 1.2m to 2.5m

2. Typical Cross-Section Dimensions

3. Anchorage Length (Prestressing Steel)

• Calculated as per IS:1343, typically:

  [ L_a = \frac{\sigma_{pu} \times A_{ps}}{f_{bd} \times \pi \times d} ]

  where:

  • (L_a) = Anchorage length
  • (\sigma_{pu}) = Ultimate stress in prestressing steel
  • (A_{ps}) = Area of prestressing steel
  • (f_{bd}) = Bond stress
  • (d) = Diameter of prestressing strand

4. Clear Cover

• Minimum 40 mm for PSC beams, 25 mm for RCC slabs

5. Superstructure Layout

• Beam spacing aligned with wheel load paths
• Expansion joints placed at intervals (typically every 30m to 40m)

graph TD
A[Superstructure Layout] --> B[PSC Beams]
A --> C[RCC Slab]
B --> D[Span Lengths 6-18m]
B --> E[Beam Depth 500-1200mm]
C --> F[Slab Thickness 150-250mm]
C --> G[Beam Spacing 1.2-2.5m]

Summary: Use standard spans (6-18m), beam depths (500-1200mm), slab thickness (150-250mm), and

Key Specifications & Formulas for Cable Anchorage and Stressing (MORTH 256 Part 2)

Cable Properties:

• Area per cable (A) = 1616.3 mm²
• Wobble coefficient (k) = 0.0091 rad/m
• Friction coefficient (μ) = 0.25
• Modulus of Elasticity of steel (Es) = 2.1 × 10⁵ MPa
• Slip = 0 to 6 mm

Concrete Strength:

• Minimum concrete strength at tensioning = 35 MPa or as per manufacturer.

Cable Types:

• Main prestressing: 12 strands, 12.7 mm dia, 7-ply Class 2 Strand (IS:6006-1983)
• Future prestressing: Single 12.7 mm dia strand (IS:6006-1983)

Anchorage:

• Use live-end type anchorages at both ends (no buried dead-end anchorages).
• Pre-block strands at dead end to avoid slip; add slip to stressing extension if slip occurs.

Stressing Procedure:

1. Friction Loss Calculation:

[ T_x = T_0 e^{-(\mu \alpha + k x)} ]

Where:

• (T_x) = tension at distance (x)
• (T_0) = initial tension
• (\mu) = friction coefficient
• (\alpha) = total angle of cable curvature (radians)
• (k) = wobble coefficient
• (x) = length of cable (m)

2. Elongation and Gauge Pressure Control:

• Continue tensioning until calculated gauge pressure is reached or elongation is 1.05× calculated elongation.
• If elongation < 0.95× calculated elongation at 1.05× gauge pressure, check gauge calibration, jack, and cable duct for blockage.
• Do not finish operations without engineer approval if elongation is insufficient.

Sheathing:

• "Drossbach" type, 75 mm ID, 0.4 mm thick bright metal strip (IRC:18-1985 Appendix 1)

Summary Table for Cable Length & Extension (Example for 30m span):

| Cable No. | Length (mm) | Extension

Key Specifications & Formulas from MORTH 256 Part 2: Construction Joints & Future Prestressing

1. Construction Joints

• Locations: As per drawings.
• Reinforcement:
  • Minimum cover: 50 mm (unless specified).
  • Lap length: 63 × d (d = bar diameter).
  • No welding allowed; bending per IS: 2502-1963.
  • Use polymer cover blocks for cover.
• Concrete Detailing:
  • Chamfer sharp edges: 10 mm × 10 mm.
  • Use stiffened shuttering plates and full-width screed vibrator for compaction.

2. Expansion Joints

• Must be robust, durable, watertight, and replaceable.
• Full width of deck, including kerb, footpath, fascia.
• Approved manufactured joints only; no site fabrication.
• Movement capacity: ± 40 mm total.
• Waterproof membrane to prevent leakage.
• Elastomer cushion to absorb vehicular shock.
• Initial gap ≥ 38 mm at concreting.
• Position steel parts accurately before concreting slab beyond girder ends.
• Manufacturer's representative presence mandatory during installation.

3. Future Prestressing Provisions

• Use single 12.7 mm dia., 7-ply Class 2 strands (IS: 6006-1983).
• Max tensioning force per strand: 128.6 kN.
• Use mono strand jack and approved prestressing system.
• External strands protected by polyethylene sheathing and grouted.

4. Construction Sequence (Typical)

5. Jacking Force

• Each cable jacking force: 1543 kN (single-end stressing) or **1776.

Wearing Coat & Drainage Details (MoRTH 256 Part 2)

Wearing Coat Specifications:

• Prime coat: Applied over deck before wearing coat.
• Mastic Asphalt Layer:
  • 6 mm thick normally
  • 12 mm thick for high rainfall areas
• Asphaltic Concrete Wearing Coat:
  • Total 50 mm thick in two layers of 25 mm each
• Alternative for high traffic:
  • 40 mm bituminous concrete + 25 mm bitumen mastic layer

Load Considerations:

• Wearing coat load = 2 kN/m²
• Footpath load = 5 kN/m²
• Traffic load: IRC Class 70R (one lane) or IRC Class A (two lanes)

Drainage Details:

• Public utilities (except water/sewer) through 150 mm dia ducts in footpaths
• Max load of utilities = 1.0 kN/m on each footpath

Material Specs for Wearing Coat:

• Follow Section 500 of MOST Specification for detailed procedures.

Summary Table: Wearing Coat Thickness

flowchart TD
    Deck -->|Prime Coat| Mastic_Asphalt
    Mastic_Asphalt -->|Layer 1 (25 mm)| Asphaltic_Concrete_Layer1
    Asphaltic_Concrete_Layer1 -->|Layer 2 (25 mm)| Asphaltic_Concrete_Layer2
    Asphaltic_Concrete_Layer2 --> Wearing_Coat_Complete

Note: Ensure proper drainage slope and anti-corrosion treatment for severe exposure conditions.

Expansion Joints (MORTH 256 Part 2)

• Movement Capacity: ± 40 mm total movement.
• Waterproofing: Must include a waterproof membrane to prevent leakage beneath the joint.
• Shock Absorption: Cushion of elastomer to absorb vehicle shock.
• Width & Profile: Full width of deck including kerb, footpath, fascia; must follow deck profile.
• Initial Gap: Minimum 38 mm at concreting, finalized with manufacturer.
• Fabrication: Only approved, proven manufactured joints allowed; site fabrication prohibited.
• Installation: Steel parts positioned accurately before concreting beyond main girders; manufacturer’s representative presence mandatory.

Bearings (Refer SD/306 Drawings)

• Detailed bearing specifications and types are provided in SD/306 (Sheets 1, 2 & 3).
• Bearings must accommodate movements and rotations as per design loads.
• Material and installation details follow standard bridge design practices.

Construction Timeline (Key for Deck & Expansion Joint Installation)

Summary Table for Expansion Joint Features

flowchart LR
    A[Deck Slab] --> B[Expansion Joint]
    B --> C{Features}
    C --> D[±40 mm Movement]
    C --> E[Waterproof Membrane]
    C --> F[Elastomer Cushion]
    C --> G[Robust & Replaceable]
    B --> H[Initial Gap ≥ 38 mm]
    B --> I[Full Width Coverage]

For detailed bearing design and installation, refer to **SD

Key Specifications & Reference Details from MoRTH 256 Part 2: Standard Drawings

1. Standard Drawings for Prestressed Concrete Girders & Composite Superstructures

• General Notes:
  • SD/401 (Part 1 Strand System) & SD/501 (Part 2 Multi Wire System) cover general notes and bill of quantities.
• Span Types & Corresponding Drawings:

2. Prestressing Strand Specifications (Clause 12.7)

• Use 12.7 mm dia 7-ply Class 2 strand as per IS:6006-1983 for future prestressing.
• Max tensioning force per strand = 128.6 kN.
• Use mono strand jack for tensioning.
• External strands must be polyethylene sheathed and grouted for protection.

3. Reference Drawings for Superstructure Details

Note: For non-standard railing types, prior approval is mandatory.

Summary Diagram: Standard Drawing Reference Flow

graph TD
    A[General Notes] --> B[Span Types]
    B --> C[30m without footpath]
    B --> D[30m with footpath]

Bill of Quantities (BoQ) - Key Specifications from MORTH 256 Part 2

1. Bill of Quantities Statement

• For each system type, BoQ of various items is appended to aid superstructure cost estimation.

2. Load Specifications for BoQ

• Public utilities (except water/sewer) through 150 mm dia ducts in footpaths.
• Max load on each footpath due to utilities: 1.0 kN/m.
• Wearing coat loads:
  • Bituminous wearing coat: 2 kN/m²
  • Footpath load: 5 kN/m²
• Traffic load considered:
  • One lane IRC Class 70R or two lanes IRC Class A.

3. Wearing Coat Thickness

4. Concrete & Reinforcement

• Concrete strength: 40 MPa (28 days)
• Cement content: 400 - 540 kg/m³
• Max water-cement ratio: 0.40 (Deck slab & Precast girder)
• Reinforcement: HYSD bars, Grade S415 (IS:1786)

Summary Table for BoQ Loadings and Materials

flowchart TD
    A[Bill of Quantities] --> B[Load Specifications]
    B --> B1[Utility Load: 1.0 kN/m]
    B --> B2[Wearing Coat Load: 2 kN/m²]
    B --> B3[Footpath Load: 5 kN/m²]
    A -->

Quality Control & Safety: Key Points from MORTH 256 Part 2

1. Water Quality for Concreting (Clause 5.1)

• Water must comply with IRC: SP: 33-1989, Clause 5.1(ii).
• Ensure no impurities that affect concrete strength/durability.

2. Expansion Joints (Clauses 12-18)

• Must be robust, durable, watertight, replaceable, covering full deck width.
• Total movement accommodated: ±40 mm.
• Waterproof membrane to prevent leakage.
• Elastomer cushion for shock absorption.
• Initial gap ≥ 38 mm during concreting.
• Use only approved manufactured joints; site fabrication prohibited.
• Manufacturer’s representative must supervise installation.

3. Construction Sequence

4. Workmanship & Detailing

• Minimum concrete cover: 50 mm (use polymer cover blocks).
• No welding of reinforcement.
• Lap length: 63 × bar diameter (d).
• Supporting chairs: 12 mm dia at intervals.
• Chamfer sharp edges: 10 mm × 10 mm.
• Use full-width screed vibrator for concrete compaction.
• Jacking force per cable: approx. 1543 - 1776 kN (multi-strand jack).

5. Materials Specifications

• Concrete: Design mix, fck = 40 MPa (28 days).
• Cement: IS: 269 or IS: 8112 OPC.
• Cement content: 400–540 kg/m³.
• Max water-cement ratio: 0.40.
• Reinforcement: HYSD bars, Grade S415 (IS: 1786).
• Admixtures per IS: 6925 & IS: 9103 (no hydrogen

Special Notes on Prestressing Operations (MORTH 256 Part 2, Clause 12.7 & 1.95)

Key Specifications:

• Strands: Single 12.7 mm dia., 7-ply Class 2 strands as per IS: 6006-1983.
• Tensioning Force per Strand: Maximum 128.6 kN.
• Tensioning Equipment: Mono strand jacks only, using approved prestressing systems.
• Protection: Externally placed strands must be sheathed with polyethylene and grouted.

Modulus of Elasticity:

• ( E_s = 1.95 \times 10^5 , \text{MPa} ) (for steel strands)

Prestressing Sequence:

• Superimposed dead loads applied immediately after Stage 2.

Additional Notes:

• Cables must have smooth profiles without kinks.
• Support cables firmly at every 1.0 m interval.
• Refer to drawings SD/401, SD/331, SD/333-337 for detailed reinforcement and anchorage.

flowchart TD
    A[Cast Girder] -->|14 days| B[Stage 1 Stressing: Cables 5,1,2,3,4,8]
    B -->|After 56 days or 35 days deck slab| C[Stage 2 Stressing: Cables 6,7]
    C --> D[Apply Superimposed Dead Loads]

This ensures safe, controlled prestressing and future strand tensioning for bridge durability.