Building codes classify inhabited buildings based on the risk to human life, health, and welfare in association with an acceptable level of structural damage. Following the proper classification of the building, engineers and architects can develop their design parameters, such as design loads, story drift criteria, and lateral force resisting system. Building codes in the U.S. generally reference the ASCE 7 provisions for appropriate building classification criteria.
Earlier versions of ASCE 7 utilized the term “Occupancy Category” to define a building classification. However, the term “occupancy” is primarily used with life safety issues and not necessarily related to the building performance. Recently, the ASCE 7-10, introduced the term “Risk Category” in lieu of “Occupancy Category.” The ASCE 7 lists four risk categories. However, a fifth risk category, designated as Risk Category V, is added to address facilities that are considered National Strategic Military Assets. These structures are mission critical facilities that are anticipated to survive an extreme event without business interruption. Among other considerations, these assets are designed to remain in the elastic range and make use of many design provision of ASCE 4-98. However, maintaining business continuity requires that some non-structural components, such as mechanical/electrical/plumbing elements, be designed to continue functioning following a seismic event.
This article will discuss the design provisions for Risk Category V structures, and the certification process for the mission critical non-structural components. Also, the construction and design challenges will be highlighted.