Specifying seismic ceiling safety

by Mark Taylor
The International Building Code (IBC) sets minimum requirements for life safety and preservation of property. All 50 states and the U.S. Virgin Islands use the code at local or statewide levels. Following its requirements helps increase safety and may decrease possible long-term liability costs. Properly specified and installed in commercial buildings, ceiling suspension systems with acoustic panels can meet current codes and seismic performance requirements across the United States.

According to the 2012 IBC, a Seismic Design Category (SDC) must be established for each construction project based on anticipated ground motion, the type of soil in a specific geographic area, and the occupancy category. These SDCs determine specific product performance and installation methods required by code to withstand certain seismic activity levels.

A professional engineer or a registered architect must specify the SDC on the project drawings. Structural engineers ultimately have responsibility for building elements and systems that carry the structure’s loads. However, these components only represent 25 percent of a typical commercial building’s inventory. The remaining 75 percent are non-structural components—such as is the case for suspended ceiling systems—where responsibilities are assigned to multiple team members.

Industry standard construction
Ceilings are important non-structural components vulnerable to earthquake damage, even in well-designed buildings. Suspended, acoustic panel ceilings have been the preferred design choice in commercial buildings since the 1950s. The interconnected ceiling systems typically consist of a metal grid comprising cross-tees and main runners.

The main runners are suspended by hanger wires from the structure above, and wall channels or angles provide a clean look around the perimeter. Lay-in and snap-up ceiling panels, such as stone wool acoustic ceiling tiles, are used to conceal the visible structure, pipes, wires, HVAC equipment, and suspension system.

For frequently accessed plenum areas, ceiling suspension systems with snap-up torsion spring panels allow maintenance staff access without completely removing the panel. The connection’s strength to the suspension system enables torsion spring panels to be effective in areas concerned with seismic activity.

During a seismic event, damage can occur at the perimeter when the vibration period of ceiling systems significantly differs from the surrounding building structure and other nonstructural components, such as non-load-bearing partition walls. This can compromise structural integrity at the perimeter, increasing ceiling motion and also potentially leading to total failure of the ceiling system. Ceilings with heavy lighting fixtures may be susceptible to damage around the fixtures, causing light fixtures to fall into the occupied spaces. The consequences may include damaged property, blocked egress, and life-safety hazards.

Intended to minimize risk and damage, installation standards for ceiling suspension systems in SDCs are specified to ensure:

• ceiling suspension systems are strong enough to resist lateral force imposed upon them without failing; and
• border panels are prevented from falling from the ceiling plane.

ASTM E580/E580M, Standard Practice for Installation of Ceiling Suspension Systems for Acoustical Tile and Lay-in Panels in Areas Subject to Earthquake Ground Motions, covers acoustical ceiling suspension systems and their additional requirements for SDC C, D, E, and F as outlined in IBC 2012 (Figure 1). Local authorities having jurisdiction (AHJs) determine the application of these practices often using project specifications and detailed information from ceiling manufacturers and industry associations.

The 2014 Ceilings & Interior Systems Construction Association (CISCA) Seismic Construction Handbook summarizes industry standard construction per the 2012 IBC for acoustical ceiling suspension systems. The chart in “IBC 2012 Industry Standard Construction” references the CISCA handbook and shows the substantial differences for SDC C and SDCs D, E, and F with respect to the significance of a particular project’s seismic vulnerability.