The moving load cannot be concentrated on a single exterior or interior girder. Which concept is used because of this?

• A. Wind load
• B. Tandem load
• C. Construction load
• D. Live load distribution factor

Answer: (D)

Moving loads from traffic cannot be assumed to sit on a single girder. To account for the fact that a truck’s weight shifts as it moves across a multi-girder bridge, engineers use the live load distribution factor. This factor estimates how much of the live load is carried by each girder for a given bridge spacing, deck type, and vehicle position, usually derived from influence-line analysis. By applying these factors, the design accounts for the varying share of load on interior versus exterior girders as the truck travels, ensuring that the maximum reactions, shear, and moments are within safe limits for all possible positions. The other options describe different loads or concepts (wind load is environmental; tandem load is a specific multi-axle configuration on a vehicle; construction load is temporary during construction), but only the live load distribution factor specifically addresses sharing moving live load among multiple girders.