Seismic Zones

Seismic Principles

In the past, seismic force levels were only considered in certain earthquake-prone locations. But major revisions to the International Building Code (IBC) have changed the requirements, which now mandate that every construction project must include and meet a seismic design category, even those locations that have not required seismic installations in the past.

The current IC-ES acceptance criterion (AC) used for the testing and evaluation of Seismic Clips is AC156, Acceptance Criteria for Seismic Qualification by Shake-Table Testing of Nonstructural Components and Systems. AC156 was not specifically designed to provide testing guidelines or pass/fail criteria for acoustical suspension systems in a seismic event. However, in the absence of a specific AC for this purpose, IC-ES allowed AC156 to act as the basis for all seismic testing and evaluation for the acoustical ceiling suspended ceilings industry.

Seismic construction standards have been established to control panic during an earthquake and provide life safety to building occupants during and after an earthquake. More than half of the United States is now considered to be at some level of risk for seismic activity, based on three factors:

Soil condition

A - Hard rock
B - Rock
C - Very dense soil and soft rock
D - Stiff soil (default)
E - Soft soil
F - Special soils

Building usage

Seismic Use Group III: essential facilities such as hospitals, fire departments and police departments that must function both during and after an earthquake

Seismic Use Group II: buildings that constitute a substantial public hazard, such as power plants and those that house over 300 people

Seismic Use Group I: everything else

Geographic location

California is not the only region considered at risk for seismic activity. More than 3,500 earthquakes have been recorded east of the Mississippi River since 1700.

By analyzing these three criteria for a construction project, you can determine the seismic design category (A-F). This is typically done by the project's structural engineer.

The design team performs the analysis required to assign the seismic design category for a construction project, and must include that information in the construction documents. This tells the construction team the required level of performance for the building.

Refer to local building codes to determine in which section of the specification the seismic design category must appear (usually in the general contractor section of the spec and on the first page of structural drawings). And make sure that your wall molding actually complies with the seismic code.