Why are live load reductions permitted in design codes?

Live load reductions are permitted in design codes primarily due to the recognition that full live loads do not typically occur simultaneously across all parts of a structure. In practice, designs account for various scenarios where only a portion of the live loads—such as people, furniture, or movable equipment—are present at the same time. This phenomenon is known as the "probabilistic nature" of live loads.

When engineers design buildings and structures, they consider statistical data and behavior patterns associated with the anticipated use of the space. By allowing live load reductions, codes provide an opportunity to optimize material usage and construction costs while still ensuring safety and performance. This way, structures can be designed confidently, knowing that the probability of all live loads being at their maximum at the same time is low, thus justifying a reduction in the loads considered for structural design.