Manual for Grade Separators and Elevated Structures

IRC SP 90 - Scope Summary

• Clause 2 (Scope, Page 2): Defines the extent of the document covering design, construction, and maintenance of bridge lighting and associated structures on roads.

• Clause 15.1.2 (Design Requirements & Specifications): Specifies lighting design inputs from manufacturers, including:

  • Spectral distribution (polar) curves
  • Iso-Candela diagrams
  • Iso-lux spacing curves
  • Iso-luminance diagrams
  • Coefficient of utilization

• Clause 8.1 (Materials): Details specifications for materials used in construction, ensuring compliance with relevant IRC standards.

Key Points:

This ensures a comprehensive approach from design to maintenance, emphasizing manufacturer data for lighting and standard materials for construction.

flowchart LR
    A[Scope: Bridge Lighting & Structures] --> B[Design Requirements]
    B --> C[Manufacturer Data]
    C --> D[Spectral Distribution Curves]
    C --> E[Iso-Candela Diagrams]
    C --> F[Iso-Lux Curves]
    C --> G[Iso-Luminance Diagrams]
    C --> H[Coefficient of Utilization]
    A --> I[Material Specifications (Clause 8.1)]

Key Specifications & Design Guidelines for Foot Over Bridges (IRC SP 90)

1. Design Loading

• Crowded footpath loading: 500 kg/m² as per IRC:6 (Section II - Loads and Stresses).
• Consider dynamic effects due to pedestrian movement and possible cycles/animals.

2. Clearances

• Follow IRC:5 for vertical and lateral clearances.
• Minimum vertical clearance over carriageway typically 5.5 m (refer IRC:5 or IRC:54 for underpasses).

3. Structural Forms

• Foot Over Bridges are pedestrian-exclusive structures.
• Common types: steel truss, RCC slab, prestressed girders, composite construction.
• Design as per IRC:21 (RCC), IRC:24 (Steel), and IRC:22 (Composite).

4. Geometric Design

• Minimum width depends on pedestrian volume; typically 3.0 m to 4.5 m.
• Ramps and stairs designed for easy access without obstructing footpaths.
• Access/exit should not encroach footpaths or obstruct pedestrian flow.

5. Relevant IRC Codes for Design & Construction

Example: Load Calculation for Foot Over Bridge Deck

[ \text{Design Load} = 500 , \text{kg/m}^2 = 5 , \text{kN/m}^2 ]

For a deck width ( b ) and span ( L ):

• Uniformly Distributed Load (UDL): ( w = 5 \times b , \text{kN/m} )
• Maximum bending moment (simply supported): ( M = \frac{w L^2}{8} )
• Maximum shear: ( V = \frac{w L}{2} )

Summary Diagram: Foot Over Bridge Components

graph TD
    A[Foot Over Bridge]
    A --> B[Deck Slab

Key Specifications for Deciding the Type of Facility (IRC SP 90 - Clause 5.7):

The decision on the type of grade separator depends on multiple factors:

• Location Attributes: Urban, semi-urban, or open/rural areas affect design complexity.
• Traffic Requirements: Analyze current & projected traffic volume and composition.
• Future Development Plans: Anticipate growth and expansion in the area.
• Roadway Classification & Capacity: Higher class roads typically remain at grade or flyover.
• Level of Service (LOS): Desired traffic flow and delay criteria.
• Local Constraints: Right-of-Way (ROW), utilities, environmental concerns.
• Design & Construction Requirements: Feasibility, cost, time, and structural considerations.

General Guideline:

• The road with lower traffic volume and lesser importance usually flies over the other.
• Exceptions apply based on site-specific constraints or environmental factors.

Summary Table for Facility Type Selection

Foundation Selection (Clause 7.4.3)

• Critical for cost and project duration.
• Compare alternatives (shallow vs deep foundations).
• Choose based on soil conditions, load, economy, and speed.

flowchart TD
    A[Start: Traffic & Site Analysis] --> B{Location?}
    B -->|Urban| C[Complex Grade Separator]
    B -->|Rural| D[Simple Grade Separator]
    C --> E{Traffic Volume}
    D --> E
    E -->|High| F[At-grade or Flyover for Lower Traffic Road]
    E -->|Low| G[Flyover or Underpass]
    F -->

Geometric Design & Clearances - IRC SP 90 Summary

IRC SP 90 refers to IRC codes and IRC:103 for detailed geometric design and pedestrian facility standards at grade separators.

Key Points:

• Pedestrian Facilities (Clause 5.20):

  • Provide safe pedestrian crossings at all grade separator arms.
  • Facility types: signal crossings, subways, foot over bridges based on traffic volumes and feasibility.
  • Refer IRC:103 for detailed pedestrian facility design.

• Geometric Design Objectives (Clause 6):

  • Maximize traffic efficiency and safety at reasonable cost.
  • Follow IRC codes (e.g., IRC:73 for horizontal curves, IRC:112 for vertical curves).

Typical Geometric Design Parameters (from IRC standards):

Pedestrian Facility Design Reference (IRC:103):

• Foot Over Bridge width: Minimum 1.8 m
• Pedestrian subway width: Minimum 2.5 m
• Ramps slope: 1:12 max for accessibility

flowchart LR
    A[Traffic Volume & Pedestrian Volume] --> B{Select Facility Type}
    B -->|Low Pedestrian| C[Signal Crossing]
    B -->|Medium Pedestrian| D[Pedestrian Subway]
    B -->|High Pedestrian| E[Foot Over Bridge]
    C --> F[Design per IRC:103]
    D --> F
    E --> F

Summary: Use IRC codes for detailed geometric parameters. Provide adequate pedestrian facilities at grade separators based on traffic and pedestrian volumes to ensure safety and smooth flow.

IRC SP 90: Type of Construction and Structural Forms (Clause 7.2)

Structural Forms for Superstructure:

Choose based on site conditions, economy, and convenience:

• Solid slabs: RCC or Pre-stressed
• RCC Beam-slab arrangement: Suitable where underside aesthetics are not critical
• Box type superstructure
• Closely touching beams
• Voided slab
• Composite construction:
  • Pre-cast pre-stressed concrete beams or steel girders with RCC cast-in-situ deck slab
  • Pre-cast pre-stressed girders made continuous by cast-in-situ cross diaphragms
• Integral structures: Rigid frame units
• Extradosed structures
• Cable stayed structures

Key Specifications:

• Material quality as per Clause 8.1 (refer to IRC SP 90 for concrete grades, reinforcement, and prestressing steel specs)
• Construction methods per Clause 7.3 (includes casting, pre-casting, prestressing techniques)

Typical Structural Form Selection Factors:

flowchart LR
    A[Site Conditions] --> B{Structural Form Choice}
    B --> C[Solid Slab]
    B --> D[RCC Beam-Slab]
    B --> E[Box Girder]
    B --> F[Pre-cast Prestressed]
    B --> G[Integral / Rigid Frame]
    B --> H[Extradosed]
    B --> I[Cable Stayed]

For detailed design formulas and material specs, refer to IRC SP 90 Clauses 8 and 9.

IRC SP 90 - Materials of Construction & Specifications (Clause 8.1)

• Clause 8.1.8: All materials used must conform to relevant IS Codes (Indian Standards). This ensures quality, durability, and compatibility.

Key Materials & Relevant IS Codes (Typical Examples):

General Guidelines:

• Use tested and certified materials only.
• Ensure material properties meet design requirements.
• Follow storage and handling instructions to maintain material integrity.

flowchart TD
    A[Material Selection] --> B{Conforms to IS Codes?}
    B -->|Yes| C[Use Material]
    B -->|No| D[Reject Material]
    C --> E[Quality Control]
    E --> F[Construction]

This flow ensures compliance and quality in bridge construction materials.

IRC SP 90 Key Points: Embankments, Retaining Walls & Drainage

1. Embankments & Drainage (Clause 9.8.9)

• Drainage Layer: Must be designed to remain functional and prevent clogging by silt.
• Purpose: Avoid embankment failure due to water pressure buildup.
• Specification: Use well-graded granular material or geotextiles as per design.
• Maintenance: Ensure periodic inspection for silt accumulation.

2. Retaining Walls and Return Walls (Clause 9.7)

• Designed to resist lateral earth pressure.
• Consider active and passive earth pressures (Rankine or Coulomb theories).
• Key formula for active earth pressure (Rankine):

[ P_a = \frac{1}{2} \gamma H^2 K_a ]

Where:

• (P_a) = Active earth pressure
• (\gamma) = Unit weight of soil
• (H) = Height of wall
• (K_a = \tan^2(45^\circ - \frac{\phi}{2})) (Active earth pressure coefficient)
• (\phi) = Angle of internal friction of soil

3. Drainage Specifications

• Provide drainage behind retaining walls to relieve hydrostatic pressure.
• Use perforated pipes and filter media.
• Ensure outlet points are free from blockage.

Summary Table

flowchart LR
    Soil_Backfill -->|Water flow| Drainage_Layer
    Drainage_Layer -->|Prevent silt clogging| Outlet
    Retaining_Wall -->|Resist lateral pressure| Soil_Backfill
    Drainage_Layer -.->|Relieves pressure| Retaining_Wall

For detailed design, refer to IRC SP 90 Clauses

IRC SP 90: Construction Methodology, Work Program & Quality Control

Key Points from Clause 10:

• Construction Methodology (10.1):

  • Prepare a detailed methodology statement for each major activity before construction.
  • Ensure conformity to design, traffic regulations, safety, and space availability.
  • Include specifications, equipment, materials, and duration for each activity.

• Quality Assurance and Control Plan (10.10):

  • Develop a Quality Assurance and Control Plan tailored to project/site requirements.
  • Strict adherence during construction is mandatory.

Recommended Approach:

Quality Control Checklist:

• Material testing (cement, aggregates, soil)
• Equipment calibration
• Workmanship monitoring
• Documentation & record keeping

gantt
    title Project Work Program Example
    dateFormat  YYYY-MM-DD
    section Construction Activities
    Site Preparation        :done,    des1, 2024-07-01, 10d
    Foundation Works        :active,  des2, after des1, 15d
    Superstructure          :         des3, after des2, 20d
    Finishing & QA          :         des4, after des3, 10d

Summary:
Advance planning of methodology and work program ensures smooth execution. A robust Quality Control Plan aligned with site conditions is essential for compliance and durability.

IRC SP 90 – Signage and Identification: Key Points

• Reference Standard: Signages should follow IRC:67 guidelines for design, placement, and materials (Clause 13.2).

• Design & Aesthetics (Clause 13.8):

  • Signages must be elegant, useful, and visually appealing.
  • Shape and size should balance visibility and aesthetic integration with surroundings.

• Visibility (Clause 13.5):

  • Ensure night-time visibility by providing adequate lighting.
  • Signages must be clearly distinguishable from a reasonable distance.

Typical Specifications from IRC:67 (Summary)

flowchart LR
    A[Signage Design] --> B[IRC:67 Guidelines]
    B --> C{Key Aspects}
    C --> D[Size & Shape]
    C --> E[Visibility & Lighting]
    C --> F[Aesthetics]
    E --> G[Night-time Illumination]

Summary: Use IRC:67 for detailed signage dimensions and materials. Ensure visibility day & night with proper lighting and reflective surfaces, while maintaining aesthetic appeal as per IRC SP 90 Clause 13.8.

Drainage of Roadway (IRC SP 90 - Clause 14)

Key points for effective roadway drainage:

• Transverse Drainage:

  • Achieved by providing a suitable camber (cross slope) on the road surface to direct water to the edges.
  • Typical camber: 2% to 3% slope for bituminous roads.

• Longitudinal Drainage:

  • Provided by scuppers, inlets, or drainage channels placed at regular intervals.
  • Size and number must be adequate to handle peak runoff from heavy rainfall.

• Drainage System Design:

  • Must prevent water stagnation on road or near grade separators.
  • Drainage spouts connected to horizontal and vertical pipes should discharge water safely into the overall project drainage system.

Typical Camber and Drainage Specifications

Formula for Runoff Estimation (for sizing drainage):

[ Q = CiA ]

Where:

• Q = peak runoff (m³/s)
• C = runoff coefficient (0.7-0.95 for paved roads)
• i = rainfall intensity (m/s)
• A = catchment area (m²)

flowchart LR
    RoadSurface -->|Camber| EdgeDrainage
    EdgeDrainage --> Scuppers/Inlets
    Scuppers/Inlets --> DrainagePipes
    DrainagePipes --> ProjectDrainageSystem

Summary: Provide a 2-3% camber for transverse drainage, use adequately sized scuppers/inlets for longitudinal drainage, and ensure all runoff is safely discharged to prevent water stagnation and road damage.

Key Formulas & Specifications for Illumination and Electrical Installations (IRC SP 90)

1. Photometric Calculations (Clause 15.1.2.6 & 15.1.2.7)

• Inputs Required:

  • Geometric characteristics: mounting height, spacing between lanterns, arrangement type.
  • Road surface photometric class (CIE Classes R1 to R4).
  • Lantern photometric data: spectral distribution, iso-candela, iso-lux, iso-luminance curves.
  • Observer position and luminance/illuminance field.
  • Maintenance factor (MF).

• Maintenance Factor (MF):
  Accounts for lamp lumen depreciation, dirt accumulation, etc.
  Typical MF = 0.75 (from Table 15.5 for R3 pavement).

• Voltage Drop:
  Maximum allowed voltage drop at last pole = 3% of supply voltage.

2. Class of Pavement (CIE Classification) and Typical Values (Table 15.5)

3. Illumination Calculation Formula

[ E = \frac{I \times MF}{d^2} ]

• (E) = Illuminance on road surface (lux)
• (I) = Luminous intensity in the direction of the point (candela)
• (d) = Distance from the light source to the point (meters)
• (MF) = Maintenance factor

4. Design Recommendations

• Follow CIE recommendations for luminance distribution and uniformity.
• Use manufacturer's photometric data (iso-candela, iso-lux curves) for spacing and mounting height.
• Ensure uniformity ratios (longitudinal and transverse) meet CIE standards for safety.
• Electrical supply: 3-phase, 380

IRC SP 90: Environmental Measures Key Points

1. Climatic Data (Clause 5.15)

• Collect annual temperature range, probable wind velocity, rainfall pattern, relative humidity, salinity, presence of harmful chemicals, subsoil water table, and storm/cyclone susceptibility.
• Use this data for:
  • Design parameters
  • Durability considerations
  • Drainage requirements

2. Environmental Issues (Clause 5.19)

• Study all environmental impacts before project execution.
• Obtain necessary environmental clearances early.
• Prepare an Environment Management and Mitigation Plan.
• Consider:
  • Location and type of plants
  • Material selection
  • Construction methods to prevent pollution (air, soil, water)
  • Energy conservation

3. Space Standards (Clause 6.11)

• Ensure adequate space for environmental buffers, drainage, and green zones.

Typical Environmental Design Considerations Table

flowchart TD
    A[Climatic Data Collection] --> B[Design Parameters]
    B --> C[Durability & Drainage]
    A --> D[Environmental Impact Study]
    D --> E[Clearances & Mitigation Plan]
    E --> F[Material & Method Selection]
    F --> G[Pollution Control & Energy Saving]

Summary: Use detailed climatic and environmental data to guide design, ensure durability, prevent pollution, and meet regulatory clearances as per IRC SP 90 clauses 5.15, 5.19, and 16.3.

IRC SP 90: Inspection, Maintenance, and Safety - Key Points

1. Inspection & Maintenance (Clause 17)

• A Maintenance Manual must be prepared for all grade separators with special design or site-specific needs.
• The manual should detail:
  • Routine inspection schedules.
  • Maintenance procedures.
  • Safety checks.
• Ensures long-term structural integrity and safety.

2. Safety Requirements (Clause 12)

• Safety provisions must comply with IRC guidelines on:
  • Structural safety.
  • Construction safety.
  • Traffic safety during maintenance.

3. Maintenance Manual Content (Typical)

• Inspection frequency (daily, monthly, annual).
• Structural elements to inspect (joints, bearings, deck, substructure).
• Maintenance actions (cleaning drainage, repairing cracks, repainting).
• Emergency procedures.

Sample Inspection Frequency Table (Typical Practice)

Safety Checklist Highlights

• Barricades and signage during maintenance.
• Personal Protective Equipment (PPE) for workers.
• Load restrictions during repair.
• Emergency contact protocols.

flowchart TD
    A[Inspection Schedule] --> B[Identify Defects]
    B --> C{Defect Severity}
    C -->|Minor| D[Routine Maintenance]
    C -->|Major| E[Immediate Repair]
    E --> F[Safety Measures Implemented]
    D --> F
    F --> G[Re-inspection]

For detailed specifications, refer to IRC SP 90 Clause 17 and Clause 12 for safety. Always consult the latest amendments in Indian Highways journal.