Earthquakes in Colorado and along the Eastern seaboard are reminders that seismic risk isn't simply an issue for California. What's more, good seismic design means strengthening both structural and non-structural components, such as fire sprinklers, emergency power and emergency communications. Structural components have received the lion's share of the attention in the past, but in recent years, non-structural components have been the subject of increasing focus.
Seismic compliance of nonstructural components is a complicated matter. Buildings in areas of high seismic activity as set by U.S. Geological Survey data for ground accelerations — the West Coast; the eastern edge of the Rocky Mountains; the New Madrid, Mo., area; and the Charleston, S.C. area — have stringent requirements for mechanical and electrical non-structural components. Most areas of the United States, however, would be exempt from seismic compliance, according to Brian Gerber, principal structural engineer for the International Code Council's Evaluation Service (ICC-ES).
The code trigger for many seismic requirements in both structural and non-structural components is the building's "seismic design category." The seismic design category is based on a structure's occupancy category and the severity of expected ground motion at the site.
Other factors also come into play, according to Mike Giachetti, ICC senior staff engineer. "Seismic design categories depend on the location, soil classification and type of building," he says. "You can have two buildings right next to each other and one may have a much higher design category."
For example, a high-rise office building may require nonstructural emergency voice alarms that will stay operational during an actual earthquake. Similarly, a large assembly building or large shopping mall will have more emergency communications requirements and standby emergency power supplies that are seismic compliant than many data centers.
Data centers — unless they are considered as part of essential facilities and are located in one of the four major seismic activity zones — are generally not subject to the most stringent seismic compliance requirements. Those are saved for hospitals, fire and police stations, emergency preparedness locations, utilities, large public assembly buildings, facilities considered critical for national defense and the like.
International Building Code (IBC) models codes set seismic requirements based largely on NEHRP (National Earthquake Hazards Reduction Program) Recommended Provisions for Seismic Regulations for New Buildings and other Structures. For specific requirements, the code refers to the American Society of Civil Engineers Standard 7 (ASCE 7). Non-structural components, including fire sprinkler systems and pumps, emergency communications and standby emergency power, as well as others, are covered in Section 13 of this standard.
ASCE 7 says that, for structural performance and seismic issues, any reasonable reference document can be used by the jurisdictional authority. That wrinkle led to the development of a generalized test protocol, "Acceptance Criteria for Seismic Certification by Shake Table Testing of Nonstructural Components," referred to as AC-156. AC-156 was adopted through the ICC-ES hearing process in 2000 and gives manufacturers of non-structural components a way to establish that their fire/life safety systems, emergency communication systems or emergency power systems will survive and remain functional under earthquake conditions.
Seismic Readiness an Important Issue for Data Centers
