Why are live load reductions permitted in design codes?

Live load reductions are permitted in design codes because these reductions recognize that in practical scenarios, the full magnitude of live loads is seldom present at the same time in a structure. For example, in a building designed to accommodate a variety of occupants, not every person will occupy every space at once; thus, the likelihood of all potential live loads being simultaneously present is low.

This principle allows engineers to design more efficiently by reducing the design loads for certain areas, meaning that structures can be built with lighter materials while still maintaining safety and performance standards. The concept is grounded in real-world use and occupancy patterns, which shows that the simultaneous application of maximum live loads is rare, thus justifying the reduction in calculations. The other options do not capture this reality of load occurrence, and therefore, they do not underpin the rationale for live load reductions in design codes.