Impact Factor in Steel Bridges for Class AA Loading

Introduction:
In steel bridges, the impact factor is the ratio of the dynamic effects of moving loads to the static effects of the same loads. The dynamic effects of moving loads are caused by the acceleration and deceleration of the loads as they move across the bridge. The impact factor takes into account these dynamic effects, which can cause additional stresses in the bridge.

Span and Loading:
For spans less than 9 meters and class AA loading for wheeled vehicles, the impact factor is taken as 25%. This means that the dynamic effects of the moving loads are 25% greater than the static effects of the same loads.

Explanation:
The impact factor is used in the design of steel bridges to ensure that the bridge can withstand the additional stresses caused by the dynamic effects of moving loads. The impact factor is based on the span of the bridge and the loading conditions, which are specified by the classification of the vehicles that will use the bridge.

For class AA loading, which is the most common loading condition for wheeled vehicles, the impact factor is 25% for spans less than 9 meters. This means that the design of the bridge must take into account the additional stresses caused by the dynamic effects of the moving loads.

Conclusion:
The impact factor is an important consideration in the design of steel bridges. It takes into account the dynamic effects of moving loads and ensures that the bridge can withstand the additional stresses caused by these effects. For spans less than 9 meters and class AA loading for wheeled vehicles, the impact factor is taken as 25%.