Guidelines for the Design of Integral Bridges

Scope of IRC SP 115: Key Points & Specifications

• Scope (Clause 2) covers integral bridges—bridges without expansion joints between deck and abutments.
• Applies to design, analysis, construction, inspection, and maintenance of integral bridges.
• Structures outside defined criteria require specialist analysis (Clause 2.4).
• Focus on performance monitoring via instrumentation is emphasized.

Key Performance Parameters & Sensors (Table 10.1)

Notes:

• Instrumentation schemes must consider location, span length, abutment height, and geotechnical parameters.
• Refer to specialist literature (e.g., BA 42, FHWA reports) for detailed design and monitoring guidelines.

flowchart TD
    A[Integral Bridge] --> B[Design & Analysis]
    A --> C[Construction]
    A --> D[Instrumentation & Monitoring]
    D --> E[Displacement Sensors]
    D --> F[Strain Gauges]
    D --> G[Pressure Cells]
    D --> H[Temperature Sensors]

For detailed design formulas and load combinations, refer to Clauses 6 and 8 of IRC SP 115.

Integral Bridge Practices Worldwide (IRC SP 115 - Clause 1.3)

• USA (since 1930s-60s): Early adopters with continuous construction and integral abutments; states like Ohio, Oregon, Tennessee lead.
• UK (since 1970s): Integral bridges for spans < 60 m, skew ≤ 30°. Thermal movement at abutments limited to ±20 mm.
• Japan (since 1996): Integral bridges limited to 30 m span length.
• Australia: Queensland Main Roads Dept. uses integral bridges since 1975.
• China: Started integral bridge construction in 1990s.

Types of Integral Bridges (IRC SP 115)

Key Specifications

• Span length limits:
  • UK: < 60 m
  • Japan: < 30 m
• Skew angle: ≤ 30° (UK)
• Thermal movement at abutments: ±20 mm (UK)

Typical Thermal Expansion Calculation

[ \Delta L = \alpha \times L \times \Delta T ]

• (\Delta L): Thermal expansion (mm)
• (\alpha): Coefficient of thermal expansion (typically 10-12 × 10⁻⁶ /°C for concrete)
• (L): Length of bridge (mm)
• (\Delta T): Temperature change (°C)

graph LR
A[Integral Bridge Types] --> B[Monolithic with Pier & Abutment]
A --> C[Monolithic at Abutment & Bearing at Pier]
A --> D[Semi-Integral Bridge]
A --> E[Framed Bridge]

For detailed design guidelines, refer to IRC SP 115 sections on integral bridge design.

IRC SP 115: Definitions and Terminology (Clause 3.1)

This clause establishes the fundamental terms and symbols used throughout the code to ensure clarity and uniformity in bridge design and analysis.

Key Points:

• Definitions cover structural elements, load types, and design parameters.
• Symbols represent physical quantities like:
  • P = Load or force
  • L = Span length
  • f = Stress or force per unit area
  • E = Modulus of elasticity
• The code emphasizes referring to specialist literature for structures outside standard criteria (Clause 2.4).

Typical Definitions Include:

Usage:

• Use these definitions as a baseline for load calculations, analysis, and detailing.
• Refer to Clause 6 for load combinations and Clause 7 for analysis methods.

Example Symbol Table (Excerpt):

flowchart TD
    A[Definitions & Symbols] --> B(Loads)
    A --> C(Structural Elements)
    A --> D(Design Parameters)
    B --> E(Dead Load)
    B --> F(Live Load)
    B --> G(Impact Factor)

For detailed terms and symbols, see Clause 3, Page 8 of IRC SP 115-2018.

Types of Abutments (IRC:SP:115-2018, Clause 4.5 & Fig.1.2):

1. Bank Seat Abutments

   • Extension of deck seated on backfill.
   • Slides on foundation soil for thermal expansion/contraction.
   • Must have adequate weight for stability.
   • Variants: On soil or on single row piles (pile cap integral with deck).

2. Framed Abutments

   • Act as retaining walls and support deck.
   • Fixed base (open foundation or multi-row piles) or hinged base (single row piles).
   • Supported on spread footings or pile foundations.

3. Embedded Wall Abutments

   • Contiguous/secsant piles, sheet piles, diaphragm walls extending below fill.
   • Integral with deck, used in congested urban areas for short spans.

4. Flexible Support Abutments

   • Deck supported on flexible piles/columns (in sleeves or in front of reinforced soil walls).
   • Allows pile flexure without soil displacement; only end screen moves into fill.

Key Specifications & Design Notes (Clause 8.1):

• Rigid connection details vary with superstructure type; consider lateral movements & vibrations.
• Use natural/elastomeric rubber pads on 150 mm concrete pedestal for precast/steel girders to allow initial rotation.
• To reduce lateral resistance and pile stresses, provide oversized pre-drilled holes filled with loose sand around bored piles in stiff soils.

Summary Table of Abutment Types:

IRC SP 115: Planning and Construction Considerations (Summary)

1. Planning Considerations (Clause 4)

Key factors for feasibility of Integral Bridges (IB):

• Length of Structure
• Climatic Conditions (thermal expansion/contraction)
• Seismic Zone
• Type of Superstructure
• Type of Abutments
• Foundations and Sub-soil Conditions
• Geometry of the Structure
• Complexity in Analysis and Design

2. Construction Considerations (Clause 5)

• Emphasis on soil-structure interaction, earth pressure coefficients, and thermal movements.
• Use of design earth pressure coefficients (K*) for integral abutments.
• Consider thermal movement (d) and deflection (ď') of abutments.
• Account for earth pressure coefficients: active (Ka), passive (Kp), at rest (K0), max, min values.
• Apply partial safety factors (Y*) and model factors (Ysd) at ULS and SLS.

Key Formulas & Symbols

Example: Thermal Movement Calculation

[ d = \alpha \times L \times \Delta T ]

• d = thermal movement at abutment
• α = coefficient of thermal expansion
• L = length of the bridge deck
• ΔT = temperature change

Earth Pressure Coefficients (Typical Values)

IRC SP 115 - Loads and Load Combinations: Key Points

• Design Approach: Integral bridges follow the Limit State Design method.
• Partial Load Factors: Use values as per Annex B of IRC:6 for load combinations.
• Backfill Placement:
  • Backfill behind abutments only after concrete deck reaches 75% strength.
  • Backfill must be placed simultaneously on both sides.
  • Height difference of backfill should not exceed 500 mm.
  • Sequence of backfill placement affects design and must be considered.

Typical Load Combinations (per IRC:6 Annex B)

Load Combination Examples:

• Ultimate Limit State (ULS):
  ( 1.35 \times DL + 1.5 \times LL + 1.5 \times IM )

• Serviceability Limit State (SLS):
  ( DL + LL )

Notes on Backfill Load:

• Backfill load is considered as earth pressure acting on abutments.
• Sequence and height difference influence lateral earth pressure.

flowchart LR
    A[Concrete Deck] -->|75% Strength| B[Backfill Placement]
    B --> C{Backfill Height Difference ≤ 500mm?}
    C -->|Yes| D[Simultaneous Placement Both Sides]
    C -->|No| E[Adjust Backfill Height]

For exact partial factors and load combinations, always refer to Annex B of IRC:6 alongside IRC SP 115.

IRC SP 115-2018: Design and Detailing Aspects (Clause 8)

Though the exact clause text isn't provided, key design and detailing aspects for bridges per IRC SP 115 typically include:

Key Design Considerations:

• Load Combinations: Follow IRC:6 and IRC:112 for vehicular, wind, seismic loads.
• Material Specifications: Use IS codes for concrete (IS 456), steel (IS 800).
• Structural Analysis: Ensure serviceability and ultimate limit states.
• Integral Bridges: Design for thermal expansion, soil-structure interaction, and restrained movements.

Detailing Specifications:

• Reinforcement: Minimum cover, spacing as per IS 456.
• Joints: Proper detailing of expansion and contraction joints.
• Anchorage & Lapping: As per IS 456 guidelines.
• Corrosion Protection: Use epoxy coatings or stainless steel in aggressive environments.

Typical Tables (from IS codes and IRC):

Formula Examples:

• Lap Length (L_lap):
  [ L_{lap} = 40 \times \phi ] where (\phi) = bar diameter

• Thermal Expansion:
  [ \Delta L = \alpha \times L \times \Delta T ] where (\alpha) = coefficient of thermal expansion, (L) = member length, (\Delta T) = temperature change

flowchart TD
    A[Loads & Load Combinations]
    B[Structural Analysis]
    C[Material Selection]
    D[Design Detailing]
    E[Inspection & Maintenance]

    A --> B
    B --> C
    C --> D
    D --> E

Summary: Follow IRC SP 115 Clause 8 for integral bridge detailing, emphasizing load effects, reinforcement detailing, joint design, and corrosion protection. Use IS codes for concrete and steel detailing.

Key Specifications & Design Guidelines for Approach Slab & Approach System (IRC SP 115):

1. Approach Slab Length & Connection

• Minimum length: 6 m (6000 mm).
• Connection: Positively attached to back-wall with 12Ø hooked dowels (reinforcement bars).
• Acts as a pin connection transferring tension steel into abutment back-wall.
• Allow tolerance for settlement to avoid damage.

2. Sleeper Slab

• Located at roadway end of approach slab.
• Provides solid foundation for expansion/contraction.
• Must accommodate superstructure expansion to prevent compression and pavement spalling.

3. Expansion Joint & Pavement Interface

• Use closed-cell, non-gassing backer rod.
• Seal with two-component elastomeric concrete joint seal system.
• Provide saw cuts and filler boards (50mm x 300mm) under reinforcement bars.
• Minimum cross camber: 300 mm.

4. Foundation Design

• Use spread footings or single/double row piles.
• Piles embedded 600 mm into abutment wall.
• Piles in stiff soil placed in pre-augured holes filled with loose sand.
• Ground improvement if settlement likely.

Typical Reinforcement & Dimensions

flowchart LR
    BridgeDeck --> AbutmentBackWall
    AbutmentBackWall -->|12Ø Hooked Dowels| ApproachSlab
    ApproachSlab --> SleeperSlab
    SleeperSlab --> RoadwayPavement
    ApproachSlab -->|Expansion Joint| Pavement
    AbutmentBackWall -->|Pile Embedment 600mm| FoundationSoil

Summary:
Ensure approach slab is 6m long, positively connected to abutment with hooked dowels,

IRC SP 115 — Inspection and Maintenance of Integral Bridges

Key Maintenance Measures (Clause 9.3)

• Crack repair: Abutment walls, wing walls, deck slabs, crash barriers, approach slabs, and abutment-superstructure junctions.
• Approach slab: Overlaying, grouting, or replacement if excessive settlement occurs.
• Expansion joints: Repair/replacement at sleeper slab locations.
• Kerbs and crash barriers: Repair or replacement if damaged.
• Drainage: Periodic cleaning of clogged drains and spouts.

Performance Monitoring (Clause 10)

• Visual inspection detects local, visible defects but cannot assess global strength or deformation capacity.
• Sensor-based Structural Health Monitoring (SHM):
  • Provides objective, quantitative, and timely data.
  • Helps prioritize strengthening or retrofitting.
• Geotechnical and thermal effects crucial for performance and span limits.

Recommended References

• IRC:SP:35 and IRC:SP:40 for detailed repair and maintenance strategies.

Summary Table: Maintenance Focus Areas

flowchart TD
    A[Inspection] --> B{Visible Defects?}
    B -- Yes --> C[Local Repairs]
    B -- No --> D[Sensor-based SHM]
    D --> E[Quantitative Data]
    E --> F{Performance Adequate?}
    F -- Yes --> G[Routine Maintenance]
    F -- No --> H[Strengthening/Retrofitting]

This approach ensures reduced maintenance with regular inspection focusing on strategic, vulnerable elements.

Performance Monitoring of Integral Bridges (IRC SP 115)

Key Points from Clause 10.1 & Table 10.1:

• Purpose: Capture behavior of bridge components under load via sensors embedded during construction.
• Instrumentation scheme: Decided based on mathematical modeling, span length, abutment height, geotechnical parameters, and location.

Additional Notes:

• Visual inspection is subjective and detects local defects only.
• Sensor-based SHM offers objective, quantitative, and timely evaluation.
• Monitoring helps verify design assumptions and prioritize maintenance.
• Geotechnical and thermal effects are critical for performance and span limits.

Recommended Reference Standards:

• IRC:SP:35, IRC:SP:40 for maintenance and repair.
• Specialist literature listed in IRC SP 115 for detailed SHM strategies.

flowchart LR
    A[Bridge Components] --> B[Performance Parameters]
    B --> C[Sensors]
    subgraph Components
      A1(Integral Abutment)
      A2(Pile Foundation)
      A3(Backfill)
      A4(Girders & Deck Slab)
      A5(Approach Slab)
      A6(End Screen)
    end
    A1 --> B1(Longitudinal, Transverse, Rotational Displacement, Tilt)
    A2 --> B2(Strain, Deformation, Temperature

IRC SP 115 - References & Additional Guidelines Summary

Key Specifications:

• Clause 11 (Page 29): Lists essential references for integral bridge design, performance monitoring, and construction.
• Clause 10.1 (Table 10.1): Details performance parameters and sensor types for various bridge components, crucial for monitoring and maintenance.

Performance Parameters & Sensors (Excerpt from Table 10.1):

Additional Guidelines:

• For structures outside standard criteria, refer to specialist literature.
• Referenced documents include:
  • BA 42 (Highways Agency) Design Manual
  • FHWA Special Reports on Integral Bridges
  • Eurocode 2 (EN 1992-1-1:2004)
  • Various research papers and technical reports on integral bridge behavior, seismic performance, and instrumentation.

Recommended Approach:

• Use Table 10.1 to plan instrumentation based on bridge component and expected performance parameters.
• Consult listed references for detailed design, analysis, and monitoring methodologies.
• Consider site-specific factors (soil, span, abutment height) for instrumentation and design optimization.

flowchart TD
    A[Bridge Components] --> B[Performance Parameters]
    B --> C[Sensors]
    A --> D[Integral Abutment]
    A --> E[Pile Foundation]
    A --> F[Girders & Deck]
    A --> G[Approach Slab]
    A --> H[End Screen]
    D --> B
    E --> B
    F --> B
    G --> B
    H --> B
    B --> C

Note: For detailed design and performance evaluation