Guidelines for Steel Pedestrian Bridges (First Revision)
2011 Edition

Overview of IRC SP 56 Scope

• Covers design, construction, and maintenance of pedestrian steel bridges.

• Includes aspects such as structural layout, aesthetics, load considerations, deflection limits, minimum section requirements, width, headroom, clearances, handrails, parapets, drainage, lighting, vibration, and upkeep.

• Vibration serviceability is emphasized with fundamental natural frequency (f0) requirements:

  • Greater than 5 Hz for unloaded vertical vibration
  • Greater than 1.5 Hz for loaded horizontal vibration

• Simplified formula for maximum 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 (refer Table B.2)
  • (v): dynamic response factor

Fundamental Frequency Calculation

[ 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 of steel (kN/m²)
• (I_g): moment of inertia of cross-section (m⁴)
• (M): mass per unit length (kN/m)

Configuration Factors Summary

(Intermediate values to be interpolated linearly)

Minimum Plate Thickness

Refer to Appendix A for detailed plate thickness requirements.

Essential Formulas and Tables in IRC SP 56

Vibration Serviceability Criteria (Clauses B1 & B2)

• Frequencies to be met:

  • Unloaded vertical vibration: ( f_0 > 5 \text{ Hz} )
  • Loaded horizontal vibration: ( f_0 > 1.5 \text{ Hz} )

• Maximum vertical acceleration:

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

  where:

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

• Fundamental frequency formula:

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

  with parameters as defined in Section 1.

Configuration Factors Table

(Intermediate values are derived by linear interpolation)

Minimum Plate Thickness

• Structural members (except parapets, packing plates): 8 mm minimum thickness.

Key Points on Structural Arrangements (Clauses 4.10 & Table 1)

• Span ranges guide the selection of the appropriate structural form.
• For shorter spans (10–30 m), twin steel beams or plate girders are ideal.
• Medium spans (20–60 m) are suited for box girders, trusses, or composite girders.
• Longer spans (over 40 m) typically require cable-stayed or suspension types.
• Foundations should be designed considering underground utilities to reduce traffic disruption (Clause 3.6).

Visual Guide to Span vs Structural Form

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

Aesthetic Guidelines (Clause 5.1)

• Environmental Harmony: Bridge designs should integrate seamlessly with their natural or urban surroundings, incorporating landscaping such as planting trees, particularly in flat terrains.
• Proportional Balance: Maintain visually pleasing length, breadth, and width ratios for harmonious views from various angles and lighting conditions.
• Surface Finish and Coating: Utilize finishes and paints that add elegance and enhance visual appeal.
• Lighting Design: Provide appropriate and tasteful illumination that promotes pedestrian safety and complements nearby heritage or public structures.
• Minimize Visual Clutter: Limit signage and signals near the bridge to avoid distraction.
• Detailed Elements: Handrails and approach components should feature refined designs for close inspection.

Reference Materials for Aesthetic Design

• INSDAG Publication INS/PUB/109: "Enhancing Urban Aesthetics: Design of Elegant Foot Over Bridges"
• International fib recommendations on aesthetic footbridge design

Minimum Section Thickness (Appendix A, Clause 8)

Diagrammatic Summary of Aesthetic Considerations

graph TD
    A[Bridge Design] --> B[Environment Compatibility]
    A --> C[Proportionality]
    A --> D[Surface Finish]
    A --> E[Lighting]
    A --> F[Signage Minimization]
    A --> G[Detailed Handrail Design]

Load Specifications in IRC SP 56

1. Vertical Imposed Loads (Clause 6.1):

• Account for pedestrian crowd loads, vehicular maintenance loads, and any other applicable imposed loads.
• Vehicle load models as per IRC standards (e.g., Class A, Class AA) should be used where relevant.
• Total load on the deck includes pedestrian and vehicle loads plus maintenance equipment.
• Apply load factors as prescribed by relevant design codes.

2. Horizontal Imposed Loads (Clause 6.2):

• Consider forces generated by braking, acceleration, and centrifugal effects on curved sections.

• Centrifugal force (F_c) calculated by:

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

  where:

  • (m): vehicle mass
  • (v): velocity
  • (r): curve radius
  • (g): acceleration due to gravity

• These forces influence parapets, barriers, and supporting elements.

3. Vehicle Impact Loads (Clause 6.5):

• Design barriers and piers to resist lateral collision impacts.
• Use an impact factor (I_f) typically ranging from 1.5 to 2.0 on static lateral loads.

Load Types and Application Summary

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

Girder Deflection Criteria

• Maximum vertical deflection under live load should not exceed ( \frac{span}{300} ) (Clause 7.1).
• Dead load deflection to be managed by cambering.
• Temperature effects must be included as per IRC:6 guidelines (Clause 6.6).

Natural Frequency Formula

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

• Variables as previously defined.

Maximum Vertical Acceleration

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

• Where (y_s), (k), and (v) represent static deflection, configuration factor, and dynamic response factor respectively.

Configuration Factors

Use mid-span values for (I_g), (M) when uniform along the span.

Minimum Section Specifications (Appendix A, Clause 8)

• Plate Thickness:

  • Structural members (excluding parapets and packing plates): minimum 8 mm when accessible on both sides or adequately protected.
  • Floor plates and parapets not designed for load-bearing:
    • 6 mm if both sides accessible.
    • 8 mm if only one side accessible.
  • Packing plates: minimum 1.5 mm thickness.

• Rolled Sections and Angles:

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

Vibration and Stiffness

• Horizontal deflections and vibrations must adhere to Clause 20 to ensure pedestrian comfort.
• For vibration serviceability, Appendix B or specialized software analyses may be used.

Minimum Thickness Summary

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/parapets, one side accessible)]

**Minimum Width and Vertical Clearance (Clause 9)

• Minimum headroom clearance: 2.5 meters from finished floor to underside of overhead members.
• Adequate stiffness to control horizontal deflection and vibrations is mandatory to ensure pedestrian comfort (Clauses 7.2 & 20).
• Refer to Appendix A for minimum section details.

flowchart TD
    A[Bridge Design] --> B[Width Requirements]
    B --> C{Segregation Type}
    C -->|Kerb ≥ 50 mm or White Line| D[3.6 m (1.8 + 1.8)]
    C -->|Railings ≥ 900 mm| E[4.0 m (2.0 + 2.0)]
    C -->|No Segregation| F[3.0 m]
    A --> G[Headroom]
    G --> H[Minimum 2.5 m clearance]

Minimum Clearance Distances Between Pedestrian Bridges and Power Lines (Clause 10.2)

• Vertical clearance is critical for preventing electrical hazards.
• Horizontal spacing ensures lateral safety from conductors.
• These are minimum clearances; local regulations may require more stringent values.

graph LR
    A[Pedestrian Bridge] -- Vertical Clearance --> B[Power Line]
    A -- Horizontal Clearance --> C[Power Line]
    B -. Voltage Dependent .-> D[Minimum Clearance Table]
    C -. Voltage Dependent .-> D

Approach Stairs

• Maximum height of any stair flight is limited to 3 meters (Clause 11.1.9).
• Stairs exceeding 3 meters in height must include intermediate landings.

Approach Ramps

• When used instead of stairs, ramps must comply with gradient requirements specified in Clauses 12.2 to 12.7.
• Typical ramp slopes range from 1:12 (steepest) to 1:20 (preferred) for safety and accessibility.

Clearance From Power Lines

• Minimum horizontal clearance is calculated as:

  [ 2.0 \text{ m} + 0.3 \text{ m per each additional } 33,000 \text{ volts or fraction thereof} ]

  (As per Indian Electricity Rules, 1956, Clause 2.0)

Summary Table

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

Approach Ramp Requirements

• Maximum flight height for ramps is 3 meters (Clause 11.1.9).
• Preferred maximum gradient is 1:20 (5%).
• For special circumstances, maximum gradient can be 1:15 (6.67%).
• Absolute maximum gradient permitted is 1:12 (8.33%).

Geometry and Accessibility

• Ramps should have straightforward geometry.
• Landings must be provided at regular intervals, typically every 9-10 meters or after a 1.5 m rise, to allow rest and accommodate wheelchair users.
• Avoid straight ramps with 180° turns; large-radius spiral ramps are acceptable.

Ramp Gradient Table

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

Load and Structural Criteria (Clause 1.1)

• Handrails and parapets must withstand combined horizontal and vertical forces of 150 kg/m (approximately 1.47 kN/m), applied concurrently at 1.1 meters above the finished floor level.
• Structural supports must be designed to safely carry these loads, with provisions for additional members at the 1.1 m height if necessary.

Measurement Reference

• All load applications reference the finished floor level as datum.

Curved Ramp Considerations (Clause 12.7)

• Effective gradients should align with those for straight ramps.
• Measurement for gradient is taken 900 mm from the inside edge of the walkway curve.
• Minimum inside radius for curved ramps is 5.5 meters.

Load Table Summary

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

Structural Forms and Span Ranges (Clause 4.10, Table 1)

Width and Headroom (Clause 9)

• Minimum clear width depends on pedestrian traffic; a minimum of 1.5 m is usually acceptable for low volumes.
• Headroom clearance should be at least 2.5 m.

Deflection and Vibration Controls (Clauses 7.2 & 20)

• Horizontal deflections to be limited to between L/500 and L/1000 (where L = span length).
• Vibration criteria must ensure pedestrian comfort.

Minimum Section Dimensions

• Refer to Appendix A for minimum beam and slab cross-section sizes.

Deflection Limit Formula

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

Where:

• ( \delta_{max} ) is maximum deflection allowed
• ( L ) is span length

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

Structural Framing and Cladding (Clause 14.3)

• Choice of framing and cladding should be based on site-specific conditions and in consultation with relevant authorities.
• Cladding materials may include corrosion-resistant steel mesh or transparent solid panels.
• High parapets with inward-angled tops or fully enclosed structures are recommended for safety.
• Fully enclosed hoardings must provide ventilation openings and access for cleaning.

Restrictions and Conditions

• Generally, hoardings are not permitted on pedestrian bridges.
• If allowed, particularly in urban settings, hoardings must be integrated into the original design with planned location, size, and extent.
• Maintain a minimum clearance of 2 meters between the deck and the bottom of the hoarding.
• Hoardings should not obstruct ventilation or pedestrian visibility.
• Advertising hoardings outside handrails must not distract drivers.
• Provision for maintenance and renewal must be incorporated.

Wind Load Considerations (Clause 6.3)

• Wind loads on hoardings must be accounted for as per IRC:6.
• Consider hoarding size, location, and obstruction effect in wind load calculations.

Hoarding Specifications Table

Wind Load Formula

[ 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 based on hoarding shape
• (A) = Projected area of the hoarding (m²)

flowchart TD
    A[Site Conditions & Authority Consultation] --> B[Determine 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 for Fully Enclosed Structures]

Deck Material Recommendations (Clause 16.1)

• Materials should be corrosion resistant and suitable for exposure to the elements.
• Preferred options include concrete slabs or ribbed steel plates with anti-slip surfaces.

Walkway Surface Requirements (Clause 16.2.2)

• Surfaces must be slip-resistant, corrosion-resistant, and durable.
• Waterproofing and sealing are essential to prevent water penetration into the deck structure.

Cladding and Framing (Clause 14.3)

• Use corrosion-resistant steel mesh or transparent solid panels.
• Enclosures should incorporate ventilation openings.
• High parapets with inward-angled tops or fully enclosed decks are preferred for safety.

Hoarding Conditions

• Hoardings are permitted only if planned in the initial design.
• Minimum clearance of 2 meters from the deck to the hoarding bottom is required.
• Hoardings must not impair ventilation, pedestrian sightlines, or distract nearby drivers.

Material Properties Summary

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