Elements and components that provide the capacity of the structure to resist collapse under seismic forces induced by ground motion in any direction shall be classified as primary. Other elements and components shall be classified as secondary.

In a typical building, nearly all elements, including many nonstructural components, will contribute to the building;s overall stiffness, mass and damping, and consequently its response to the earthquake ground motion. However, not all these elements are critical to the ability of the structure to resist collapse when subjected to strong ground shaking. The secondary designation will be used when a component or element does not contribute significantly or reliably in resisting earthquake effects because of low lateral stiffness, strength or deformation capacity.