Guidelines for the Design of Integral Bridges
2018 Edition

Scope Overview of IRC SP 115

• Covers integral bridges characterized by the absence of expansion joints between the deck and abutments.
• Encompasses design, analysis, construction, inspection, and upkeep aspects.
• Structures deviating from standard criteria necessitate specialized analysis.
• Emphasizes instrumentation-based performance monitoring.

Performance Metrics and Sensors (Derived from Table 10.1)

Notes:

• Sensor deployment must account for variables such as location, span, abutment height, and geotechnical properties.
• Refer to specialized literature like BA 42 and FHWA reports for comprehensive design and monitoring guidance.

flowchart TD
    IB[Integral Bridge] --> DA[Design and Analysis]
    IB --> C[Construction]
    IB --> IM[Instrumentation and Monitoring]
    IM --> DS[Displacement Sensors]
    IM --> SG[Strain Gauges]
    IM --> PC[Pressure Cells]
    IM --> TS[Temperature Sensors]

For specific design formulations and load combinations, consult Clauses 6 and 8.

Worldwide Integral Bridge Applications (According to Clause 1.3)

• United States: Early adopters since the 1930s-1960s, with continuous span construction and integral abutments; states such as Ohio, Oregon, and Tennessee are pioneers.
• United Kingdom: Since the 1970s, integral bridges are applied for spans under 60 meters with skew angles up to 30°, limiting abutment thermal movement to ±20 mm.
• Japan: Usage since 1996, with span restrictions up to 30 meters.
• Australia: Queensland Main Roads have implemented integral bridges since 1975.
• China: Initiated integral bridge construction during the 1990s.

Classification of Integral Bridges

Design Constraints

• Maximum span length varies: UK (<60 m), Japan (<30 m).
• Skew angle limited to 30° in UK.
• Thermal movement allowance at abutments capped at ±20 mm (UK).

Thermal Expansion Formula

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

• (\Delta L): Change in length due to temperature (mm)
• (\alpha): Coefficient of thermal expansion (~10-12 × 10⁻⁶ /°C for concrete)
• (L): Length of the bridge (mm)
• (\Delta T): Temperature differential (°C)

graph LR
IB[Integral Bridge Types] --> MP[Monolithic Pier & Abutment]
IB --> MA[Monolithic Abutment & Pier Bearing]
IB --> SI[Semi-Integral]
IB --> FB[Framed Bridge]

Refer to IRC SP 115 for detailed design criteria.

Definitions and Terminology as per IRC SP 115 (Clause 3.1)

This segment standardizes the terminology and symbols used throughout the code to ensure consistent communication in design and analysis.

Highlights:

• Defines structural components, types of loads, and essential design parameters.
• Symbols denote physical quantities such as:
  • P: Load or force
  • L: Span length
  • f: Stress or force intensity
  • E: Modulus of elasticity
• Emphasizes consulting specialized documents for atypical structures (Clause 2.4).

Representative Definitions:

Usage Notes:

• These definitions form the basis for load calculations, structural analysis, and detailing.
• Refer Clause 6 for load combinations and Clause 7 for analysis methods.

Sample Symbol Table

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

For an exhaustive list, see Clause 3, page 8 of the standard.

Abutment Types in Integral Bridge Design (Clause 4.5 & Figure 1.2)

1. Bank Seat Abutments

   • Deck extends and rests directly on backfill.
   • Slides over foundation soil to accommodate thermal expansions and contractions.
   • Requires sufficient mass for stability.
   • Variants include those founded on soil or single-row piles with integral pile caps.

2. Framed Abutments

   • Serve as retaining walls while supporting the deck.
   • Can have fixed bases (supported on open foundations or multiple pile rows) or hinged bases (supported by single pile rows).
   • Foundation can be spread footings or pile systems.

3. Embedded Wall Abutments

   • Constructed using contiguous/secsant piles, sheet piles, or diaphragm walls extending beneath the fill.
   • Integral with the deck, commonly utilized in dense urban settings with short spans.

4. Flexible Support Abutments

   • Deck supported on flexible piles or columns, housed in sleeves or positioned ahead of reinforced soil walls.
   • Permits pile bending without soil displacement; only the end screen moves into the backfill.

Design and Specification Notes (Clause 8.1):

• Rigid connections vary by superstructure type; lateral movements and vibrations must be considered.
• Elastomeric or natural rubber pads on 150 mm concrete pedestals aid initial girder rotation.
• To mitigate lateral soil resistance and pile stresses, oversized pre-drilled holes filled with loose sand are recommended around bored piles in stiff soils.

Summary of Abutment Types

Planning and Construction Aspects (Summary from IRC SP 115)

Planning Considerations (Clause 4)

• Evaluate feasibility based on structure length, climatic conditions, seismic zones, superstructure type, abutment style, foundation and subsoil characteristics, geometry, and design complexity.

Construction Aspects (Clause 5)

• Pay attention to soil-structure interaction, earth pressure coefficients, and thermal movement effects.
• Employ design earth pressure coefficients (K*) tailored for integral abutments.
• Account for thermal movement (d) and abutment deflection (δ').
• Use earth pressure coefficients like active (Ka), passive (Kp), at rest (K0), and their maximum and minimum values.
• Apply appropriate partial safety factors (Y*) and model factors (Ysd) for ultimate and serviceability limit states.

Key Symbols and Formulas

Thermal Movement Calculation

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

• d: Thermal expansion/contraction at abutment
• α: Coefficient of thermal expansion
• L: Bridge deck length
• ΔT: Temperature difference

Typical Earth Pressure Coefficients

Loads and Load Combinations for Integral Bridges (IRC SP 115)

• Design Philosophy: Employ Limit State Design principles.
• Partial Load Factors: Adopt values from Annex B of IRC:6.
• Backfill Placement Guidelines:
  • Backfill behind abutments should commence only after the concrete deck attains at least 75% of its design strength.
  • Backfill must be placed simultaneously on both sides of the abutment.
  • Differential backfill height should not exceed 500 mm.
  • Sequence of backfill placement affects earth pressure calculations and must be considered.

Load Combinations (Excerpt from IRC:6 Annex B)

Example Combinations:

• Ultimate Limit State (ULS): 1.35 × DL + 1.5 × LL + 1.5 × IM
• Serviceability Limit State (SLS): DL + LL

Backfill Load Notes

• Backfill exerts earth pressure on abutments.
• Placement sequence and height differences influence lateral earth pressures.

flowchart LR
    DeckConcrete -->|75% Strength Achieved| BackfillPlacement
    BackfillPlacement --> HeightCheck{Height Diff. ≤ 500mm?}
    HeightCheck -->|Yes| BothSidesPlacement
    HeightCheck -->|No| AdjustBackfillHeight

Refer to Annex B of IRC:6 and IRC SP 115 for comprehensive load combination details.

Design and Detailing Guidelines (Clause 8 of IRC SP 115)

Although the exact text is not provided, typical design and detailing criteria include:

Design Essentials:

• Follow IRC:6 and IRC:112 for vehicular, wind, and seismic loading.
• Use IS codes such as IS 456 for concrete and IS 800 for steel materials.
• Ensure checks for both serviceability and ultimate limit states.
• Consider thermal effects, soil-structure interaction, and restraint forces specific to integral bridges.

Detailing Aspects:

• Reinforcement cover and spacing per IS 456.
• Proper detailing of joints to accommodate expansion and contraction.
• Anchorage and lap splices adhere to IS 456 prescriptions.
• Corrosion protection measures including epoxy coatings or stainless steel where environmental aggressiveness is high.

Typical Parameters (Based on IS and IRC Codes):

Formulae:

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

• Thermal Expansion: [ \Delta L = \alpha \times L \times \Delta T ]

flowchart TD
    Loads --> StructuralAnalysis
    StructuralAnalysis --> MaterialSelection
    MaterialSelection --> Detailing
    Detailing --> InspectionMaintenance

Follow Clause 8 for integral bridge detailing, focusing on loads, reinforcement, joint design, and durability.

Design Criteria for Approach Slabs and Approach Systems as per IRC SP 115

Approach Slab Length and Attachment

• Minimum length: 6 meters.
• Securely connected to the abutment back-wall with 12 mm diameter hooked dowels in reinforcement.
• Acts as a pin connection to transfer tension forces to the abutment back-wall.
• Allowance for settlement movement to prevent damage.

Sleeper Slab

• Positioned at the end of the approach slab adjacent to the roadway.
• Provides a stable foundation to accommodate expansion and contraction movements.
• Prevents compression forces and pavement damage.

Expansion Joint and Pavement Interface

• Utilize closed-cell, non-gassing backer rods.
• Seal joints with a two-component elastomeric concrete sealant.
• Include saw cuts and filler boards (50 mm × 300 mm) beneath reinforcement bars.
• Maintain a minimum cross camber of 300 mm.

Foundation Requirements

• Spread footings or single/double row piles supporting the abutment.
• Piles embedded at least 600 mm into the abutment wall.
• In stiff soils, piles are placed in pre-augered holes filled with loose sand.
• Ground improvement measures if settlement is anticipated.

Reinforcement and Dimensions Summary

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

Ensure the approach slab is appropriately sized and connected to maintain durability and function.

Inspection and Maintenance Guidelines for Integral Bridges (Clause 9 & 10)

Key Maintenance Tasks

• Repair cracks in abutment walls, wing walls, deck slabs, crash barriers, approach slabs, and junctions.
• Overlay, grout, or replace approach slabs if excessive settlement is detected.
• Repair or replace expansion joints located at sleeper slabs.
• Maintain kerbs and crash barriers, repairing or replacing damaged elements.
• Regularly clean drains and spouts to ensure proper drainage.

Performance Monitoring

• Visual inspections identify local visible defects but cannot fully assess global structural integrity.
• Sensor-based Structural Health Monitoring (SHM) provides timely, objective, and quantitative data.
• SHM aids in prioritizing maintenance, strengthening, or retrofitting measures.
• Geotechnical and thermal considerations are essential for assessing performance and span limitations.

Reference Documents

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

Maintenance Focus Areas

flowchart TD
    VisualInspection --> DefectDetection{Defects Present?}
    DefectDetection -- Yes --> LocalRepairs
    DefectDetection -- No --> SHM
    SHM --> DataAnalysis
    DataAnalysis --> MaintenanceDecision{Adequate Performance?}
    MaintenanceDecision -- Yes --> RoutineUpkeep
    MaintenanceDecision -- No --> StrengtheningActions

This approach promotes reduced maintenance through proactive inspection and monitoring.

Monitoring the Performance of Integral Bridges (From Clause 10.1 & Table 10.1)

• Objective: To capture the real-time behavior of bridge elements under load using embedded sensors.
• Instrumentation Planning: Based on structural modeling, span length, abutment height, geotechnical conditions, and site specifics.

Additional Insights:

• Visual inspections are subjective and limited to local defect detection.
• Sensor-based SHM offers accurate, quantitative, and timely assessments.
• Continuous monitoring validates design assumptions and guides maintenance prioritization.
• Geotechnical and thermal parameters are critical to performance and span restrictions.

Reference Standards

• Refer to IRC:SP:35, IRC:SP:40 for maintenance and repair.
• Consult specialized literature cited in IRC SP 115 for detailed SHM techniques.

flowchart LR
    BridgeComponents --> PerformanceMetrics
    PerformanceMetrics --> SensorDevices
    subgraph Components
      Abutment
      Piles
      Backfill
      GirdersDeck
      ApproachSlab
      EndScreen
    end
    Abutment --> PerformanceMetrics
    Piles --> PerformanceMetrics
    Backfill --> PerformanceMetrics
    GirdersDeck --> PerformanceMetrics
    ApproachSlab --> PerformanceMetrics
    EndScreen --> PerformanceMetrics
    PerformanceMetrics --> SensorDevices

Effective monitoring is integral to long-term bridge health.

Summary of References & Additional Guidelines in IRC SP 115

Essential Documents (Clause 11, Page 29)

• Lists authoritative references for integral bridge design, construction, and performance monitoring.
• Table 10.1 details performance parameters and suitable sensor types vital for monitoring and maintenance.

Additional Recommendations

• For bridges not covered by standard provisions, consult specialized literature.
• Important references include:
  • BA 42 Design Manual (Highways Agency)
  • FHWA Special Reports on Integral Bridges
  • Eurocode 2 (EN 1992-1-1:2004)
  • Various academic and technical research on integral bridge behavior and instrumentation.

Instrumentation Planning

• Use Table 10.1 to strategize sensor deployment according to expected parameters and bridge components.
• Site-specific factors such as soil conditions, span length, and abutment height should guide design and monitoring strategies.

flowchart TD
    BridgeComponents --> PerformanceParameters
    PerformanceParameters --> Sensors
    BridgeComponents --> IntegralAbutment
    BridgeComponents --> PileFoundation
    BridgeComponents --> GirdersDeck
    BridgeComponents --> ApproachSlab
    BridgeComponents --> EndScreen
    IntegralAbutment --> PerformanceParameters
    PileFoundation --> PerformanceParameters
    GirdersDeck --> PerformanceParameters
    ApproachSlab --> PerformanceParameters
    EndScreen --> PerformanceParameters
    PerformanceParameters --> Sensors

Consult these references for comprehensive design and evaluation.