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Generally, the impact factors are applied as a fraction of dead load. For the case of India, the value and

## Calculations of Impact Factor are Described Below as per IRC: 6-2000

I=A/(B+L)

Where,

• I = Impact factor fraction
• A= A constant having the value of 4.5 for reinforced concrete bridges and 9.0 for steel bridges
• B = A Constant having a value of 6.0 for reinforced concrete bridges and 9.0 for steel bridges
• L = Span in Meters

### Impact Factor for the IRC Class AA or 70 R Loading

#### For spans less than 9 m

For tracked vehicle – 25% of the span up to 5 m linearly reduced to 10% for span of 9 m

For wheeled vehicle – 25%

#### Impact Factor for spans of 9 m and above

For tracked vehicles on RC Bridges, the value of impact factor is 10% up to a span of 40 m and for bridge built up of steel truss 25% for spans up to 23 meters.

### Values of Impact Factor allowance for the British standard loading could be calculated as follows.

Types of Road Bridges as Per Different Criteria

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