Guidelines for Steel Pedestrian Bridges (First Revision)

Scope of IRC SP 56 (Pedestrian Bridges)

Key Points:

• Applies to design, construction, and maintenance of pedestrian bridges.
• Covers layout, structural form, aesthetics, loads, deflection, minimum sections, width, headroom, clearance, handrails, parapets, drainage, lighting, vibration, and maintenance.
• Vibration serviceability is critical; fundamental natural frequency (f₀) must exceed:
  • 5 Hz (unloaded vertical)
  • 1.5 Hz (loaded horizontal)
• For vibration analysis, simplified formula for max vertical acceleration (a):

[ a = 4 \pi^2 f_0^2 y_s k v ]

where:

• (f_0) = fundamental natural frequency (Hz)
• (y_s) = static deflection under 0.7 kN load (m)
• (k) = configuration factor (Table B.2)
• (v) = dynamic response factor

Fundamental Natural Frequency (f_0):

[ f_0 = \frac{C}{2 \pi l^2} \sqrt{\frac{E I_g}{M}} ]

• (C) = configuration factor (Table B.1)
• (l) = span length (m)
• (E) = modulus of elasticity (kN/m²)
• (I_g) = second moment of area (m⁴)
• (M) = weight per unit length (kN/m)

Configuration Factors:

(Intermediate values by linear interpolation)

Minimum Plate Thickness (Appendix A):

IRC SP 56: General Considerations - Key Formulas & Tables

1. Vibration Serviceability (Clause B1 & B2)

• Frequency criteria:

  • Vertical unloaded bridge: ( f_0 > 5 , \text{Hz} )
  • Horizontal loaded bridge: ( f_0 > 1.5 , \text{Hz} )

• Max vertical acceleration: [ a = 4 \pi^2 f_0^2 y_s k v ] Where:

  • ( f_0 ) = fundamental natural frequency (Hz)
  • ( y_s ) = static deflection (m) under 0.7 kN load at mid-span
  • ( k ) = configuration factor (Table B.2)
  • ( v ) = dynamic response factor

• Fundamental natural frequency: [ f_0 = \frac{C}{2 \pi l^2} \sqrt{\frac{EI_g}{M}} ] Where:

  • ( C ) = configuration factor (Table B.1)
  • ( l ) = main span length (m)
  • ( E ) = modulus of elasticity (steel, per IRC:24)
  • ( I_g ) = second moment of area at mid-span (m(^4))
  • ( M ) = weight per unit length at mid-span (kN/m)

2. Configuration Factors

(Use linear interpolation for intermediate values)

3. Minimum Plate Thickness (Appendix A)

• 8 mm for members except parapets and packing plates

IRC SP 56: Layout and Structural Form – Key Points

Structural Form Selection (Clause 4.10 & Table 1)

Key Specifications:

• Span range guides the choice of structural form.
• For small spans (10-30 m), twin steel beams or plate girders are optimal.
• For medium spans (20-60 m), box girders, trusses, or composite girders are suitable.
• For long spans (40 m and above), cable-stayed or suspension bridges are recommended.
• Supports/foundations must consider underground utilities to minimize traffic disruption (Clause 3.6).

Summary Diagram of Span vs Structural Form

graph LR
    A[10m] --> B[Twin Steel beam/Plate girder]
    B --> C[Composite beams/Plate girder (up to 50m)]
    C --> D[Box girder/Truss (up to 60m)]
    D --> E[Arch bridge (25m+)]
    E --> F[Cable stayed bridge (40m+)]
    F --> G[Suspension bridge (70m+)]

Use this guideline to select the structural form based on span for pedestrian bridges.

Aesthetics in IRC SP 56 (Clause 5.1)

Key Guidelines:

• Harmony with Environment: Design bridge lines to blend with surrounding landscape or cityscape; use landscaping (trees) especially in flat areas.
• Proportions: Maintain good length/breadth/width ratios for visual harmony from all viewing angles and lighting conditions.
• Finish & Painting: Use external finishes and paint that enhance elegance and attractiveness.
• Lighting: Provide adequate, tasteful lighting that complements pedestrian safety and matches surrounding heritage/public structures.
• Clutter Avoidance: Minimize signs and signals near the bridge to avoid visual clutter.
• Detailing: Handrails and approach elements should be tastefully designed for close-up appreciation.

Additional References for Aesthetic Design:

• INSDAG Publication No. INS/PUB/109: Enhancing Urban Aesthetics: Design of Elegant Foot Over Bridges
• International fib Guidelines: Design of footbridges with aesthetic considerations.

Minimum Sections (Appendix A, Clause 8):

Summary Diagram of Aesthetic Considerations

graph TD
    A[Bridge Design] --> B[Environment Harmony]
    A --> C[Proportions]
    A --> D[Finish & Painting]
    A --> E[Lighting]
    A --> F[Clutter Avoidance]
    A --> G[Detailing]

Note: For vibration and post-construction maintenance, refer to IRC:24 and Appendix-B of IRC SP 56.

IRC SP 56 - Loads: Key Formulas & Specifications

1. Imposed Vertical Loads (Clause 6.1)

• Consider vehicular loads, pedestrian loads, and maintenance loads.
• Loads vary by bridge type; use standard IRC vehicle load models (e.g., IRC Class A, Class AA).
• Load on bridge floor = Sum of vehicle loads + pedestrian loads + maintenance loads.
• Apply load factors as per design codes.

2. Imposed Horizontal Loads (Clause 6.2)

• Horizontal forces from braking, acceleration, centrifugal forces on curves.

• Formula for centrifugal force, ( F_c ):

  [ F_c = \frac{m v^2}{g r} ]

  where:

  • ( m ) = mass of vehicle,
  • ( v ) = velocity,
  • ( r ) = radius of curve,
  • ( g ) = acceleration due to gravity.

• These loads act on parapets, barriers, and supporting structures.

3. Vehicle Collision Load (Clause 6.5)

• Consider impact forces from vehicle collision on piers and barriers.
• Use impact factor ( I_f ) typically between 1.5 to 2.0 on static loads.
• Design barriers and piers to resist lateral collision forces as per IRC guidelines.

Summary Table: Load Types and Application

graph LR
A[Imposed Vertical Loads] --> B[Bridge Deck]
C[Imposed Horizontal Loads] --> D[Barriers & Parapets]
E[Vehicle Collision Loads] --> F[Piers & Barriers]

For detailed vehicle load models and impact factors, refer to IRC:6 and IRC SP 56 clauses.

Deflection of Girders (IRC SP 56)

Key Limits:

• Total vertical deflection due to live load ≤ Span/300 (Clause 7.1).
• Dead load deflection controlled by camber.
• Temperature effects considered as per IRC:6 (Clause 6.6).

Fundamental Natural Frequency (f₀)

[ f_0 = \frac{C^2}{2 \pi l^2} \sqrt{\frac{EI_g}{M}} ]

• (l) = span length (m)
• (E) = modulus of elasticity (kN/m²)
• (I_g) = second moment of area (m⁴)
• (M) = weight per unit length (kN/m)
• (C) = configuration factor (Table B.1)

Maximum Vertical Acceleration (a)

[ a = 4 \pi^2 f_0^2 y_s k v ]

• (y_s) = static deflection at mid-span under 0.7 kN load (m)
• (k) = configuration factor (Table B.2)
• (v) = dynamic response factor

Tables

Notes:

• Use mid-span values of (I_g) and (M) if uniform.

IRC SP 56: Minimum Sections for Pedestrian Bridges

Key Specifications (Appendix A, Clause 8)

• Plate Thickness:

  • Minimum 8 mm for all structural members (except parapets and packing plates) if both sides are accessible or adequately protected against corrosion.
  • For floor plates and parapets not designed to carry stresses:
    • 6 mm if both sides accessible.
    • 8 mm if only one side accessible.
  • Packing plates: minimum 1.5 mm thickness.

• Rolled Sections & Angles:

  • Main girder angles: no less than 75 mm x 50 mm.
  • Other angles: no less than 65 mm x 45 mm.
  • Flats: minimum width 50 mm (except hand railings and shear connectors).
  • End angles connecting stringers/cross girders: thickness ≥ ¾ of web plate thickness.

Vibration & Stiffness (Clause 7.2 & 20.2)

• Horizontal deflection and vibrations must comply with Clause 20 to ensure pedestrian comfort.
• For vibration serviceability, refer to Appendix B or use advanced software analysis.

Summary Table: Minimum Thicknesses

flowchart TD
    A[Minimum Section Requirements]
    A --> B[Plate Thickness]
    B --> B1[8 mm (both sides accessible)]
    B --> B2[6 mm (floor/parapets, both sides accessible)]
    B --> B3[8 mm (floor/parap

IRC SP 56: Width and Headroom for Pedestrian/Cycle Track Bridges

1. Minimum Widths (Clause 9.4, Table 2)

2. Minimum Headroom (Clause 9.2)

• Minimum clear headroom: 2.5 m
  Measured from finished floor level to underside of any overhead support/member.

3. Additional Notes

• Ensure adequate stiffness to limit horizontal deflection/vibrations per Clause 7.2 and Clause 20 for pedestrian comfort.
• Refer to Appendix A for minimum section details of pedestrian bridges.

flowchart TD
    A[Bridge Design] --> B[Width Specification]
    B --> C{Segregation Type}
    C -->|Kerb ≥ 50 mm or White Line| D[Width = 3.6 m (1.8 + 1.8)]
    C -->|Railings ≥ 900 mm| E[Width = 4.0 m (2.0 + 2.0)]
    C -->|Unsegregated| F[Width = 3.0 m]
    A --> G[Headroom]
    G --> H[Minimum 2.5 m clearance]

This ensures safe, comfortable pedestrian and cycle traffic flow with adequate overhead clearance.

IRC SP 56: Clearance Specifications for Pedestrian Bridges near Power Lines

Key Table: Minimum Clearance Between Pedestrian Bridge and Power Line (Clause 10.2)

Additional Notes:

• Clause 10.1: Clearance over roadways/railways must comply with IRC or relevant authority standards.
• Vertical clearance is critical for safety against electrical hazards.
• Horizontal clearance ensures safe lateral distance from power lines.

Summary:

• For low voltage (≤11kV) lines, maintain 3.7 m vertical and 1.2 m horizontal clearance.
• For medium voltage (11kV-33kV) lines, horizontal clearance increases to 2.0 m.
• For extra-high voltage (>33kV), add 0.3 m clearance vertically and horizontally per additional 33kV increment.

This ensures safe design and compliance with electrical safety norms near pedestrian bridges.

IRC SP 56: Approach Stairs and Other Elements - Key Points

1. Approach Stairs

• Height of flight: Limited to 3 m (Clause 11.1.9).
• Flights exceeding 3 m should have intermediate landings.

2. Approach Ramps

• When ramps are used instead of stairs, their gradient must comply with Clauses 12.2 to 12.7 (not detailed here).
• Generally, ramps have gentle slopes for safety and accessibility, often between 1:12 to 1:20.

3. Clearance from Electrical Lines

• Minimum horizontal clearance =
  [ 2.0 \text{ m} + 0.3 \text{ m for every additional } 33,000 \text{ volts or part thereof} ]
  (Source: Indian Electricity Rules, 1956, Clause 2.0)

Summary Table: Flight Height & Clearance

flowchart TD
    A[Approach Stairs] --> B{Flight Height ≤ 3m?}
    B -- Yes --> C[Single flight]
    B -- No --> D[Intermediate landing]
    A --> E[Approach Ramps]
    E --> F[Gradient as per Clauses 12.2-12.7]

For detailed ramp gradients and other elements, refer directly to Clauses 12.2 to 12.7 in IRC SP 56.

Approach Ramps - IRC SP 56 Key Points

• Height of Flight (Clause 11.1.9):
  Maximum height of a ramp flight = 3 m

• Ramp Gradient (Clause 12.2):

  • Preferred max gradient = 1:20 (5%)
  • For special cases, max gradient = 1:15 (6.67%)
  • Absolute max gradient = 1:12 (8.33%)

• Geometry & Accessibility (Clause 4.3):

  • Simple, practical geometry
  • Provide landings at intervals for rest, especially for wheelchair users
  • Avoid straight ramps with 180° turns
  • Spiral ramps with large radii are acceptable

Summary Table: Ramp Gradient Limits

Recommended Landing Spacing (General Guidance)

• Landings every 9-10 m of ramp length or at every 1.5 m rise
• Landing size: minimum 1.2 m x 1.2 m

flowchart TD
    A[Start of Ramp] --> B{Gradient}
    B -->|≤ 1:20| C[Preferred Ramp]
    B -->|1:20 < Gradient ≤ 1:15| D[Special Case Ramp]
    B -->|1:15 < Gradient ≤ 1:12| E[Max Steep Ramp]
    B -->|> 1:12| F[Not Allowed]
    C --> G[Simple Geometry + Landings]
    D --> G
    E --> G
    G --> H{Turns?}
    H -->|180° Turns| I[Avoid]
    H -->|Spiral with Large Radius| J[Acceptable]

Note: Always ensure compliance with local accessibility norms alongside IRC SP 56.

Key Specifications for Hand Rails and Parapets (IRC SP 56)

• Design Loads (Clause 1.1):

  • Horizontal lateral force = 150 kg/m (≈ 1.47 kN/m)
  • Vertical force = 150 kg/m (≈ 1.47 kN/m)
  • Both applied simultaneously at 1.1 m above finished floor level (datum).

• Structural Requirements:

  • Railings and parapets + supporting members must resist combined lateral and vertical loads.
  • Provide additional structural members at 1.1 m height if necessary.

• Measurement Datum:

  • Datum level = finished bridge floor level.

• Curved Ramps (Clause 12.7):

  • Effective gradient as per straight ramps.
  • Measure at 900 mm from walkway edge inside curve.
  • Minimum inside radius = 5.5 m.

Summary Table of Loads on Hand Rails and Parapets

flowchart LR
    A[Finished Floor Level] -->|1.1 m| B[Hand Rail / Parapet]
    B -->|150 kg/m Horizontal Load| C[Structural Support Members]
    B -->|150 kg/m Vertical Load| C

Note: For detailed cross-sectional dimensions and material specifications, refer to the full IRC SP 56 standard or relevant bridge design codes.

IRC SP 56: Enclosed Pedestrian Bridges - Key Specifications

1. Structural Forms & Span Ranges (Clause 4.10, Table 1)

2. Width and Headroom (Clause 9)

• Minimum clear width depends on pedestrian volume; typically 1.5 m minimum for low volume.
• Headroom clearance should be at least 2.5 m to ensure comfort.

3. Deflection & Vibration (Clause 7.2 & 20)

• Horizontal deflection limits to avoid discomfort; typically L/500 to L/1000 (L = span).
• Vibration criteria per Clause 20 to ensure pedestrian comfort.

4. Minimum Sections

• Refer to Appendix A for minimum cross-sectional dimensions of beams and slabs.

Quick Formula for Deflection Limit:

[ \delta_{max} = \frac{L}{500} \quad \text{to} \quad \frac{L}{1000} ]

Where:

• ( \delta_{max} ) = maximum permissible deflection
• ( L ) = span length

graph LR
A[Span Range] --> B[Twin Steel beam: 10-30m]
A --> C[Composite Girder: 10-50m]
A --> D[Box Girder: 20-60m]
A --> E[Truss: 15-60m]
A --> F[Vierendeel: 15-45m]
A --> G[Arch: 25+ m]
A --> H[Cable Stayed: 40+ m]
A --> I[Suspension: 70+ m]

Summary: Choose structural form based on span; maintain minimum width/headroom; control

IRC SP 56: Hoardings on Pedestrian Bridges - Key Points

• Structural Framing & Cladding (Clause 14.3):

  • Decide framing & cladding based on site conditions & authority consultation.
  • Cladding: corrosion-resistant steel mesh or transparent solid panels.
  • High parapets with inward canted tops or full enclosures recommended.
  • Full enclosures must have ventilation openings and cleaning provisions.

• Hoarding Restrictions:

  • Normally no hoardings on pedestrian bridges.
  • If allowed (urban areas), plan location, size, and extent in original design.
  • Maintain minimum 2 m clearance from bridge deck to hoarding bottom.
  • Hoardings must not obstruct ventilation or pedestrian vision.
  • Advertisements outside handrails must not distract drivers.
  • Provide maintenance/renewal facilities integrated with bridge structure.

• Wind Load (Clause 6.3):

  • Wind load on hoardings must be considered per IRC:6.
  • Include size, position, and obstruction effects in wind load calculations.

Summary Table for Hoarding Specifications

Wind Load Formula (per IRC:6)

[ P = 0.6 \times V^2 \times C_d \times A ]

Where:

• (P) = Wind pressure (kN/m²)
• (V) = Design wind speed (m/s)
• (C_d) = Drag coefficient (depends on hoarding shape)
• (A) = Projected area of hoarding (m²)

flowchart TD
    A[Site Conditions & Authority Consultation] --> B[Decide Structural Framing & Cladding]
    B --> C{Cladding Type}
    C -->|Steel Mesh| D[Use Corrosion-Resistant Steel Mesh]
    C -->|Solid Panels| E[Use Transparent Solid Panels]
    D & E --> F[Ensure Ventilation Openings if Fully En

IRC SP 56: Deck Material and Walkway Surfaces Key Points

• Deck Material (Clause 16.1):

  • Use materials resistant to corrosion and suitable for exposed conditions.
  • Preferred: Concrete slabs or ribbed steel plates with non-skid surfaces.

• Walkway Surface (Clause 16.2.2):

  • Must resist slip, corrosion, and ensure durability.
  • Surfacing should be waterproof and sealed to prevent water ingress into the deck.

• Cladding & Framing (Clause 14.3):

  • Use corrosion-resistant steel mesh or transparent solid panels.
  • Provide ventilation openings if fully enclosed.
  • High parapets with inward canted tops or full enclosures recommended for safety.

• Hoardings:

  • Allowed only if planned in design; minimum 2 m clearance from deck to hoarding bottom.
  • Should not obstruct ventilation, vision, or distract drivers.

Summary Table: Deck & Walkway Material Properties

flowchart LR
    A[Deck Material] --> B[Concrete Slab]
    A --> C[Ribbed Steel Plate]
    B --> D[Non-Skid Finish]
    C --> D
    D --> E[Waterproof & Sealed Surface]
    E --> F[Slip Resistance]
    E --> G[Corrosion Resistance]

Note: Always consult local site conditions and authorities for final selection and detailing.