Bridge Loadings Around The World

Scope Summary from IRC SP 4 (Preliminary Designs & Specifications):

• Loading Types Covered:

  • Single truck loading with lateral displacement considerations.
  • Truck train and equivalent loadings referencing AASHO 1935 standards.
  • Impact effect: Increase load P by 40% to account for dynamic impact.

• Key Load Values (AASHO 1935):

  Load Type	Axle Load (kN)	Spacing (ft)	Notes
  Single Truck	6000 - 12000	14 - 30	Concentrated & uniform
  Truck Train	18000 (Moment)	14 - 30	Uniform load 640 lbs/ft

• Impact on Piers/Abutments:

  • Floating objects impact not explicitly detailed.
  • Ice pressure on piers: 400 lb/in² (site-specific).

• Clearance:

  • Interstate Highway bridges require 16 ft clear over entire roadway width.

• Footpath Loading:

  • Minimum width: 1.5 m (Canada).
  • Crowd load: up to 85 lb/ft² for spans up to 25 ft.
  • Accidental vehicle loading on footpath considered (e.g., 25-ton truck).

Important Formula for Crowd Load (Span > 100 ft):

[ P = 30 + 3 \sqrt{L \times W} \quad \text{(max 60 lb/ft}^2) ]

• (P) = live load per sq. ft.
• (L) = loaded length of sidewalk (ft)
• (W) = width of sidewalk (ft)

Impact Load Increase:

[ P_{design} = P \times 1.4 ]

flowchart LR
    A[Traffic Loading] --> B[Single Truck Loading]
    A --> C[Truck Train Loading]
    B --> D{Impact Effect}
    D -->|Increase by 40%| E[Design Load]
    C --> E
    E --> F[Apply to Bridge Components]

References:

• AASHO Standard Specifications (1961)
• B.S.

IRC SP 4: Vehicular Loadings — Key Formulas & Specifications

1. Impact Factor (Clause 1.1 & 50.0)

• Impact Load Increase:
  ( P_{impact} = P \times (1 + 0.40) = 1.4P )
  (40% increase for impact effect on vehicular loads)

• For steel bridges (Clause 50.0):

  • Span ≤ 10 m: 50% impact
  • Span ≥ 45 m: 15% impact
  • Intermediate spans: interpolate linearly

2. Load Types & Classifications (Clauses 201 & 207)

• Class AA: Tracked/wheeled heavy vehicles (worst case for 2-lane bridges)
• Class A: Standard train of vehicles for all roads
• Class B: Temporary bridges

3. Load Models

4. Load Distribution & Lane Loading (Clause 1.2)

• For heavy trucks, lane load distribution:
  • Two lanes fully loaded: 100% each
  • Remaining lanes: 50% each

5. Impact Factor Variation with Span (U.S. Bureau of Public Roads)

• For concrete bridges:
  [ I = \frac{50}{L + 125} \quad \text{(max 30%)} ] where (L) = span length in ft.

• For steel bridges: Impact factor ~30% (constant

Key Footbridge Loading & Dimension Specifications (IRC SP 4 & References)

1. Minimum Dimensions:

• Minimum width: Not explicitly specified in IRC SP 4; typical values:
  • Urban footbridges: ≥ 1.5 m (Italy standard)
  • Minimum footpath width: 0.75 m to 1.5 m (varies by country)
• Minimum headroom:
  • Overall roads: 16 ft 6 in (5.03 m)
  • Pedestrian subways: 7 ft (2.13 m)
  • Cycle/pedestrian subways: 7 ft 6 in (2.29 m)
  • Cattle creeps: 8 ft (2.44 m)

2. Loading on Deck:

• Vertical load on deck:
  • Urban areas: 400 to 500 kg/m² (Italy & Canada)
  • Rural areas: 240 to 350 kg/m²
• Lateral & vertical forces on footbridge:
  • 100 lb/ft (1.46 kN/m) applied simultaneously (IRC SP 4)
• Handrail loading:
  • Horizontal force of 250 kg/m run (India & Italy)
  • Horizontal & vertical load of 0.08 t/m (Austria)

3. Impact Loads:

• Floating objects, vessels, ice: No specific formula in IRC SP 4; refer to site-specific investigations.
• Ice pressure on piers: up to 400 lb/in² (approx. 2.76 MPa) (USA)

4. Footbridge Load Formula (for spans > 30 m):

[ p = (0.3 + 0.9) \times L \times (5.5 \times W)^{1/3} \quad \text{t/m}^2 ]

• (L) = span length (m)
• (W) = footpath width (m)

5. Additional Notes:

• Accidental vehicle load on footpath: single axle load of 6–14 t considered in some standards.
• Surcharge effect on abutments due to live load on approach fill: 2 ft backfill equivalent (USA).

Summary Table:

Impact Factors & Load Effects — IRC SP 4 Key Points

1. Impact Factor (I) Formulas

• General formula:

[ p = 1.4 - 0.008 \times l_p \quad \text{with } p \geq 1.0 ]

• ( l_p ) = governing length in meters (length of loaded portion causing max effect)

• Timber bridges: Fixed impact factor ( I = 20% )

• HA Loading (Heaviest axle): Impact factor = 25% on the heaviest axle load only.

• HB Loading: No impact factor applied.

2. Impact Factor by Span Length (Steel & Concrete Bridges)

• ( L ) = span length in meters.

3. Impact Factor for Various Lanes (Great Britain Example)

4. Wind Load Considerations

• Lateral wind force: 100 lb/ft at 6 ft above deck (New South Wales clause).

• For bridges without load: 250 kg/m² assumed wind pressure on exposed area.

5. Summary Table for Impact Factor Calculation

Surcharge Effects on Abutments (IRC SP 4 Summary)

Key Specifications:

• Surcharge Load Consideration:

  • When an adequately designed RCC approach slab (minimum length 12 ft into the approach) covers the roadway width, no live load surcharge on abutments is required.
  • Otherwise, surcharge load equivalent to 2 ft to 4 ft of earth fill is considered depending on jurisdiction (e.g., 2 ft in USA/India, 4 ft in New South Wales).

• Surcharge Load Magnitude:

  • Typically, surcharge load = Equivalent height of earth fill (h_s) × unit weight of soil (γ)
  • Commonly, γ = 18 kN/m³ (or 120 lb/ft³)

• Load Dispersion:

  • Load disperses at 45° angle beneath the fill surface.
  • Surcharge acts as a uniformly distributed pressure on abutment backfill.

Important Tables & Formulas

Design Notes:

• If RCC approach slab is provided, surcharge from live load on approach fill may be ignored.
• For footpath loading, minimum width = 1.5 m; load = 400 kg/m² (varies by country).
• Impact loads (e.g., wheel load 4 tons over 12 in diameter) require stress increase by 25-50%.

flowchart LR
    LiveLoad -->|If no RCC slab| SurchargeLoad[2-4 ft earth surcharge]
    RCCSlab -->|Adequately designed| NoSurcharge[No surcharge considered]
    SurchargeLoad --> LoadDispersion[Load disperses at 45°]

Key Formulas and Specifications for Train and Axle Loadings (IRC SP 4)

1. Impact Factor (Clause 1.1 & 6.25)

• Impact Load Increase:
  ( P_{design} = P \times 1.4 )
  (40% increase for impact effect)

• For concrete, steel, and prestressed concrete bridges, impact factors vary with span length (L in meters):

  Span (m)	Impact Factor (Concrete)	Impact Factor (Steel)
  10	1.40	1.40
  30	1.20	1.10
  50+	1.00	1.00

2. Train and Axle Loadings (Clause 1.5 & 6.25)

• Maximum Axle Loads:

  • Single axle: 20 tons
  • Bogie (2 axles, ≤40 ft spacing): 40 tons

• Train Loading:

  • Class B Train: Nose-to-tail distance = 60 ft
  • No overlapping live loads on carriageway during train crossing

• Ground Contact Area for Axle Loads:

  Axle Load (lb)	Width (B) (in)	Length (W) (in)
  25,000	10	20
  15,000	8	15
  4,000	-	8

3. Load Distribution and Lane Loading

• Two lanes maximum loaded simultaneously with axle/train loads.
• For multiple lanes, loading on other lanes may be taken as 50% or 1/3 of main lane load depending on code.

4. Uniform Load Equivalent

• Uniform load equivalent for train loading:
  ( w = 640 \text{ lbs/ft} ) per lane (approximate from AASHO specs)

Summary Table: Axle Load and Impact

Key Wind Pressure Considerations from IRC SP 4

1. Wind Pressure on Moving Live Loads

• Wind pressure = 100 lb/linear ft acting at 6 ft above deck on moving live load (Clause 1.4.1).
• For group loading combinations only.

2. Lateral Wind Force on Moving Loads (Clause 212.4)

• Wind pressure on unloaded bridge: 250 kg/m² on exposed surface.
• Wind pressure on loaded bridge: 100 kg/m² on exposed surface + continuous strip 3 m high above roadway.

3. Impact Factor for Live Loads (Dynamic Effects)

• For Class A or B loading: [ I = \frac{15}{20 + T} ]

• For Class AA loading (tracked vehicles):

  • Span < 30 ft: 25% impact reducing linearly to 10% at 30 ft.
  • Span ≥ 30 ft: 10% up to 130 ft, then per Fig. 12 (Plate III).

• For wheeled vehicles: 25% impact up to 40 ft, then per Fig. 12.

• Dynamic coefficient for spans ≤ 100 m: [ \phi = 1 + \frac{(100 - L)^2}{100(250 - L)} ] Where (L) = span in meters.

• For spans > 100 m, (\phi = 1).

Summary Table: Wind Pressure & Impact Factors

IRC SP 4 - Accidental and Crowd Loads: Key Points

1. Impact (Accidental) Load Percentage (Clause 50.0 & 211.2)

• Impact factor reduces as span increases.
• Applies to Class A and Class B vehicle loadings.

2. Crowd Load (Clause 2.5)

• Standard crowd load: 400 kg/m² (approx. 8.3 kN/m²)
• Reduced load for special cases: 250 kg/m²
• Applies mainly to pedestrian bridges or areas with dense human occupancy.

3. Live Load Specifications (Clause 207.1)

• Class A: Wheeled vehicle trains, severe loading conditions.
• Class B: Lighter vehicle trains.
• For multi-lane bridges, consider one train of Class A vehicles per two traffic lanes.

4. Lateral Loads on Railings (Clause 2.5)

• Uniformly distributed lateral live load: 100 kg/m (vertical or horizontal).
• Horizontal live load on railing: 80-120 kg/m depending on urban/rural setting.

5. Summary Table: Impact Factor vs Span Length

Formula for Impact Load:

[ P_{total} = P \times (1 + \frac{I}{100}) ]

Where:

• (P) = Static load
• (I) = Impact percentage (from above table)

Notes:

• Accidental loads are considered by increasing static loads by impact factor.
• Crowd loads are uniformly distributed over the surface.
• For detailed vehicle configurations and axle loads, refer to Clause 207.1 and IRC load tables.

graph LR
    A[Static Load (P)] --> B[Apply Impact Factor (I%

International Loading Standards Comparison (IRC SP 4 Summary)

Key Loading Types & Impact Factors

Impact Factor Guidelines (IRC SP 4)

• 40% increase on static load for impact (Clause 1.1)
• For steel bridges (Clause 50.0):
  • Spans ≤ 10 m: 50% impact factor
  • Spans ≥ 150 ft (~45 m): 15% impact factor
• Impact factor decreases with increasing span length

Lateral Load Distribution

• Single truck lateral displacement considered as a fraction of roadway width.
• Multi-lane bridges: One vehicle train per two traffic lanes (Clause 207.1).

Typical Load Representation (AASHTO Example)

Summary Diagram: Impact Factor vs Span Length

graph LR
A[Span ≤ 10 m] -->|Impact 50%| B[Span 50 m]
B -->|Impact decreases| C[Span 45 m]
C -->|Impact 15%| D[Span ≥ 150 ft]

Note: For detailed design, refer to respective national codes for vehicle configurations, axle loads, and load combinations. IRC SP 4

IRC SP 4: Load Distribution and Lateral Positioning - Key Points

1. Load Increase for Impact

• Impact factor: Increase concentrated load P by 40% to account for impact effects.
  [ P_{design} = 1.4 \times P ]

2. Load Distribution Angle

• Concentrated loads disperse through a 45° angle in load-distributing layers, reaching the centroidal axis of the structural element.

3. Lane Loadings

• Lane loads are considered uniformly distributed over lane widths of 3.0 to 3.75 m.
• Typical design includes two axles of 18 t each with lateral positions as per Fig. 1 and 3 (Plate I).

4. Lateral Positioning

• Without lateral distribution analysis, wheel loads are placed 18" (450 mm) from kerb line.
• Accidental wheel load of 4 t is considered at the parapet edge with a 25% increase in permissible stresses.

5. Equivalent Uniform Load (UDL)

• For design simplification, concentrated loads can be converted to an equivalent UDL or knife-edge load.

6. Typical Load Values (from AASHTO 1935 & IRC)

Summary Diagram: Load Distribution and Lateral Positioning

flowchart LR
    A[Concentrated Load P] --> B[Load Dispersed at 45° Angle]
    B --> C[Load Distributed over Lane Width (3.0 - 3.75 m)]
    C --> D[Structural Element Centroidal Axis]
    E[Lateral Positioning] --> F[Wheel Load 18" from Kerb]
    F --> G[Accidental Load at Parapet Edge]

References

• IRC SP 4 Clause 1.1, 1.

IRC SP 4: Load Combinations and Calculation Methods — Key Points

1. Loadings & Impact Factors

• Impact Increase: Load ( P ) shall be increased by 40% to account for impact effects (Clause 1.1).
• Wind Pressure:
  • 100 lb/ft acting at 6 ft above deck on moving live load (Clause 1.4.1).
  • Applied only for group loading combinations.
• Equivalent Uniformly Distributed Load (UDL):
  • For train loading: 640 lbs/ft of lane (AASHO 1961).
• Concentrated Loads:
  • May be dispersed at 45° angle through load distributing layer (Clause 1.3.2).

2. Load Combinations

• Single Truck Loading:
  • 3 axle loads per lane, spaced 1.5 m apart.
  • Increase by 15% for main roads if considered exceptional (Clause 1.5).
• Two-Lane Loading:
  • Maximum 2 lanes loaded simultaneously with axle or train loads.
• Group Loading:
  • Includes live load + wind load + impact factor.

3. Impact Factor Formula (Concrete Bridges)

[ I = \frac{50}{L + 125} ]

• ( I ) = Impact factor (max 0.30)
• ( L ) = Span length in feet under maximum stress (Clause 1.2.12).

4. Typical Impact Factors (Span Length in meters)

5. Summary Table: Load Types & Factors

Clearance and Dimensional Requirements (IRC SP 4 - Summary)

1. Minimum Clearances:

• Roadway Clearance over Interstate Highways:
  Minimum 16 ft (4.88 m) clear over entire roadway including shoulders.

• Great Britain (B.S. 153):

  • Overall roads: 16 ft 6 in (5.03 m)
  • Pedestrian subways: 7 ft (2.13 m)
  • Cycle subways: 7 ft 6 in (2.29 m)
  • Cattle creeps: 8 ft (2.44 m)

• Federal Republic of Germany:
  Clearance between wheel outer edge and kerb varies with carriageway width (18 ft to 24 ft and above), ranging from 1 ft 4 in to 4 ft.

2. Load Contact Area & Impact:

3. Ice Pressure on Piers (Ontario):

• Ice pressure = 400 lb/in²
• Thickness and height based on site investigation.

4. Impact Loads from Floating Objects:

• No fixed formula; depends on site conditions (river size, velocity).
• Floating timber and vessels: No detailed specs, consider site-specific.

5. Additional Notes:

• For multi-lane bridges, minimum clearance between passing vehicles and kerb is specified and increases with carriageway width.
• Load dispersal under wheel loads is typically taken at 45°.
• For span lengths >150 m, equivalent uniformly distributed loads may be applied.

Example: Minimum Clearance Table (Germany)

Key Formulas & Specifications from IRC SP 4 on Special Load Cases and Exceptions

1. Impact Factor for Live Loads (Clause 1.1 & 1.5)

• Increase load ( P ) by 40% for impact effect: [ P_{\text{impact}} = 1.4 \times P ]
• For single truck loading on main roads, increase by 15% (exceptional loading): [ P_{\text{single truck}} = 1.15 \times P ]

2. Load Dispersion (Clause 1.3.2)

• Concentrated loads disperse under a 45° angle through load distributing layers.
• For slabs on soil, load dispersion is circular.
• For other structures, follow AASHTO specifications for load dispersion.

3. Equivalent Uniformly Distributed Load (UDL)

• For train loads, equivalent UDL can be adopted for design simplification.

4. Special Loadings (From Various Standards)

5. Load Application Rules

• Maximum two lanes loaded simultaneously with axle or train loads.
• Each side of divided highway treated as a separate bridge.
• For long bridges, deductions in loading may be applied.

Summary Table: Impact Factors for Concrete Bridges (Example)

Visual: Load Dispersion

IRC SP 4 - References to Other Standards: Key Highlights

1. Footpath & Footbridge Loading:

   • Minimum footpath width (India): No fixed minimum; Toronto suggests normal use load = 100 lb/sq.ft.
   • Footbridge minimum width (Japan): 1.5 m.
   • Footbridge loading (India): Vertical & lateral forces each 100 lb/linear ft simultaneously.
   • Handrails: Horizontal force of 250 kg/m run.

2. Impact on Piers & Abutments (Floating Objects):

   • No detailed formulas given for floating timber, vessels, or ice.
   • Ice pressure on piers (Ontario): 400 lb/sq.in; thickness & height by site investigation.

3. Surcharge on Abutments due to Live Load on Approach Fill:

   • Typically considered as 2 ft of backfill surcharge.
   • No surcharge if RCC approach slab is provided.

4. Clearance Requirements:

   • Interstate Highway System: Minimum 16 ft clear over full roadway width including shoulders.

5. Loading Standards from Other Countries (Summary):

Example: Footpath Crowd Load for Span > 100 ft (USA)

[ P = 30 + \frac{3L}{W} \quad (lb/sq.ft), \quad \text{max } 60 , lb/sq.ft ]

• (L) = loaded length of sidewalk (ft)
• (W) = width of sidewalk (ft)

Impact Load on Piers (Ontario Ice Pressure)

|

IRC SP 4: Annexures and Illustrative Figures - Key Specifications & Tables

1. Loadings on Bridges and Footpaths

2. Surcharge Effect on Abutments

• Surcharge load considered as 2 ft depth of backfill live load on approach fill.
• No surcharge if adequately designed RCC approach slab is provided.

3. Footpath Crowd Load Formula (U.S. Standard)

For spans > 100 ft:

[ P = 30 + 3 \times L \times W ]

Where:

• ( P ) = Live load per sq.ft (max 60 lb/sq.ft)