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Before greater attention was placed on what happens to the interior of buildings during earthquakes, the majority of repair costs came from non-structural components that in many cases failed during a seismic event. Seismic codes continue to address ceiling systems to further protect buildings and occupants from the dangers of earthquakes. The main driver in US code changes was the advent of the International Building Code in 2000, which was an important thing that spilled into the Canadian market. The code placed a greater focus towards seismic and then later, non-structural components.

Acoustical ceilings have seen a few changes to their installation with respect to seismic conditions, says Terry Kastner, technical consultant to the Northwest Wall and Ceiling Bureau.
“At this time, they primarily deal with the restrictive use of Power Actuated Fastener (PAFs) for suspension wires under a seismic load, such as lateral bracing wires. Drilled-in anchors are generally required for seismic load conditions and PAFs are generally allowed for vertical suspension wires that are not under seismic loads, but rather dead loads.”

It was fairly recently that the IBC addressed fasteners and cracked concrete and their capabilities to hold in a seismic event, he adds. PAFs are now required for anything under a seismic load and acoustical ceilings utilize drilled in anchors, and framing members are engineered so their attachment to the structure is secure.

Lee Tedesco, manager of seismic systems for USG, says major earthquakes in California gave the industry a lot of data about how non-structural components and suspended ceiling systems acted in a seismic event.
“There are certain buildings that need to operate immediately after an earthquake. Some fallen non-structural items won’t cause serious harm, but they may stop critical functions,” says Tedesco. “That’s a kind of disconnect that can appear with suspended ceilings and that is why they are connected to earthquake study.”

Determining the level of risk a building is at during an earthquake depends on several factors: where it is located, what it is used for, and the soil condition underneath, in which there are six categories: A) hard rock, B) rock, C) very dense soil and soft rock, D) stiff soil, E) soft soil, and F) special soils.

Ceilings of buildings in categories A and B carry no seismic design requirements, nor do ceilings with an area of less than 144 square feet, or ceilings made of plaster and lath.

A revised document from NWCB, Suspension Systems for Acoustical Lay-in Ceilings Seismic Design Categories D, E & F, makes recommendations as outlined by the IBC-2009 and CISCA (Ceilings and Interior Systems Construction Association) zones 1-2 and 3-4.

Partitions greater than six feet in height, and those tied to the ceiling should be laterally braced to the structure, and bracing should be independent of the ceiling splay bracing system. Ceilings must be attached on two adjacent walls.

Cross tees should be capable of carrying the design load without exceeding deflection equal to 1/360 of its span, and all main beams are to be heavy duty. System connections need to withstand a minimum  strength of 180 pounds.

For ceiling areas exceeding 2,500 square feet, a seismic separation joint or full height wall partition that breaks the ceiling shall be provided unless analyses are performed of the ceilings bracing system, closure angles, and penetrations to avoid sufficient clearance. Ceiling areas larger than 1,000 square feet require horizontal restraint every 144 square feet consisting of four diagonal splay wires or rigid braces in combination with a compression post.
Ceilings for buildings in design category C must be free-floating systems with main and cross tees needing a minimum of three-eights of an inch clearance from the walls. All perimeter grid components must be tied together to prevent spreading using spacer bars or other means.

“The seismic performance main driver for ceilings is that they have to be installed properly. There are some prescriptive requirements laid out and if they are followed one can be fairly certain they will perform well,” says Paul Hough, manager of product fire and seismic performance at Armstrong Industries.

Manufacturers like Armstrong and USG have spent a lot of time and effort trying to find ways to improve ceiling performance durring earthquakes. In many cases, they have ended up with something different than what a code mandates, but still accomplishes the same result.

In the case of these alternative products or methods of installation, ESR Reports play an important role. Issued by the International Code Council – Evaluations Services (ICC-ES), ESR Reports are used by code officials to determine the compliance of new products and materials or their acceptability as an alternative material, design or method of construction.

The reports provide the evidence that the alternative products or systems were tested to withstand seismic forces in all IBC categories and meet or exceed code requirements. 

For manufacturers, this evaluation and confirmation by ICC-ES provides the necessary data supporting the new system or installation method as a code-compliant alternative to IBC requirements.

“The main driver is making sure people are safe and that they can use the building immediately following an earthquake,” says Hough. “That’s why we’re always striving towards more performance-based products, including alternative materials and construction methods.”

The ultimate goal is to level the playing field to make life easier for those working with the requirements. Current requirements are geared towards ensuring the grid stays in place, and now there is a possibility to work towards ensuring the panels stay in place too, which is the next step.

Ceiling manufacturers may be paying more attention to designing and testing seismically sound ceilings products, but knowing where to find further recommendations for constructing safer ceilings is essential before beginning work on any new project.