Which concept explains the distribution of a moving load across multiple girders to avoid concentration on a single girder?

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

Answer: (D)

Distributing a moving load across multiple girders relies on the live load distribution factor. In a bridge with several girders, a vehicle’s load travels across the deck and is shared among the girders rather than being carried by one member alone. The live load distribution factor quantifies how much of the total live load each girder carries at a given position of the moving load, depending on girder stiffness, spacing, and boundary conditions. This factor is derived from methods like influence lines or stiffness-based analysis so that reactions, moments, and shears in every girder can be designed safely as the vehicle moves. The other concepts describe different ideas: wind load is an environmental effect, construction load relates to loads during erection, and the lever rule is a basic moment balance principle, not a mechanism for sharing a moving live load among girders.