The measure used to indicate how long structural assemblies will maintain their load-bearing ability under fire conditions is:

The measure used to indicate how long structural assemblies will maintain their load-bearing ability under fire conditions is known as the fire resistance rating. This rating is crucial as it defines the performance of a building element during a fire, specifying the duration—often measured in hours—that the component can withstand exposure to heat and flames while retaining its structural integrity.

Fire resistance ratings are determined through standardized testing under controlled conditions, and they inform architects, engineers, and fire protection professionals about the fire safety characteristics of materials used in construction. This information is essential for ensuring that buildings can survive a fire long enough for occupants to evacuate and for firefighters to control the blaze.

The other options, while related to building regulations and fire safety, do not specifically define the duration for which structural assemblies can support loads under fire exposure. Fire codes and the National Building Code set standards for safety and design but do not quantify fire resistance in the same way a fire resistance rating does. Similarly, the NFPA ratings pertain to various fire protection measures and equipment but do not focus solely on the fire resistance duration of structural assemblies.