FEMA E-74 Example Ceilings

FEMA E-74 Example Ceilings

FEMA E-74 Example 6.3.4.3 Suspended Heavy Ceilings

6.3.4.3 Suspended Heavy Ceilings

Download «6.3.4.3 Suspended Heavy Ceilings» (PDF 920KB)

This category covers several different types of overhead ceilings suspended from above including dropped furred gypsum board ceilings and suspended lath and plaster ceilings. Suspended ceilings with wood or metal panels would also fit into this category. These systems typically have finish material attached to a two-way furring grid which is suspended from above. In order to reduce damage and prevent falling hazards the finish material must be well secured to the furring grid. Damage can be reduced if the ceiling is attached to the walls along two adjacent sides but separated from the walls along the opposite two sides and the furring grid is laterally braced to the structure above.

Provisions

Building Code Provisions

Suspended heavy ceiling systems are subject to the force requirements of Minimum Design Loads for Buildings and Other Structures (ASCE/SEI 7-10). Chapter 13, Nonstructural Components. Ceiling assemblies of gypsum board and plaster are also subject to the requirements of the 2012 International Building Code (IBC 2012) .

  • Section 13.5.6 of ASCE /SEI 7-10 contains requirements for special seismic perimeter details and lateral bracing assemblies for suspended ceilings but includes several significant exemptions from these requirements as follows.
    • Seismic detailing is not required for suspended ceilings less than or equal to 144 square feet that are surrounded by walls or soffits that are laterally braced to the structure (this exemption applies to heavy or light suspended ceiling systems).
    • Seismic detailing is not required for suspended ceilings constructed of screw- or nail-attached gypsum board on one level (constructed in a single plane) that are surrounded by and connected to walls or soffits that are laterally braced to the structure above. Note that this exemption does not apply to plaster ceilings or to gypsum board ceilings on multiple levels (constructed in more than one ceiling plane elevation).
  • Chapter 25 of IBC 2012 contains general provisions for horizontal assemblies of gypsum board and plaster, including prescriptive requirements for installation. There are, however, no provisions for lateral design of suspended ceilings.
  • The Division of the State Architect sets forth ceiling standards for California schools in Drywall Ceiling Suspension, Conventional Construction—One Layer (IR 25-3). This document provides general guidance for design and detailing of heavy suspended ceilings.

Retrofit Standard Provisions

Seismic Rehabilitation of Existing Buildings (ASCE/SEI 41-06)  classifies ceilings into one of four types. Suspended ceiling systems are classified into one of two categories:

  • Category b, short-dropped gypsum board sections (less than 2 ft drop) attached to wood or metal furring supported by carrier members.
  • Category c, dropped gypsum board sections greater than 2 and suspended metal lath and plaster.

These ceiling systems are considered force and deformation sensitive. Compliance with the requirements of the standard is necessary when:

  • The performance level is Immediate Occupancy.
  • The performance level is Life Safety or Hazards Reduced in high or moderate seismicity areas.

If the performance level is Hazards Reduced and the ceiling is located in areas of public occupancy or egress, the ceiling must meet the Life Safety performance level.

Note that even if the ceiling system is exempt, light fixtures and air diffusers in the ceiling system may still be subject to support and bracing requirements.

 Typical Causes of Damage

  • Suspended heavy ceilings may be damaged both by direct acceleration and by deformation. Direct acceleration may cause connectors to become loose or deform, and differential movement of the ceiling relative to structural elements such as columns or walls or nonstructural elements such as partitions, lights, diffusers, or sprinklers may also damage the ceiling.
  • As these systems are heavier than acoustic tile ceilings, the consequences of failure may be more hazardous for occupants since both the finish material and the furring grid may fall. Ceiling failures are often costly because the space underneath may be unusable while the ceiling is repaired or replaced.
  • Ceiling finishes may crack unless adequately isolated from the motion of the surrounding structural and nonstructural elements. Crack repair in gypsum board and plaster ceilings is a common expense following earthquakes.

Damage Examples

Figure 6.3.4.3-1 Damage to ornate wire lath and plaster ceiling in the 2010 magnitude-8.8 Chile Earthquake (Photo courtesy of Eduardo Fierro, BFP Engineers). Wire lath is attached to arches or to wood furring suspended from the roof framing.

FEMA E-74 Example 6.3.4.3 Suspended Heavy Ceilings

6.3.4.3 Suspended Heavy Ceilings

Download «6.3.4.3 Suspended Heavy Ceilings» (PDF 920KB)

This category covers several different types of overhead ceilings suspended from above including dropped furred gypsum board ceilings and suspended lath and plaster ceilings. Suspended ceilings with wood or metal panels would also fit into this category. These systems typically have finish material attached to a two-way furring grid which is suspended from above. In order to reduce damage and prevent falling hazards the finish material must be well secured to the furring grid. Damage can be reduced if the ceiling is attached to the walls along two adjacent sides but separated from the walls along the opposite two sides and the furring grid is laterally braced to the structure above.

Provisions

Building Code Provisions

Suspended heavy ceiling systems are subject to the force requirements of Minimum Design Loads for Buildings and Other Structures (ASCE/SEI 7-10). Chapter 13, Nonstructural Components. Ceiling assemblies of gypsum board and plaster are also subject to the requirements of the 2012 International Building Code (IBC 2012) .

  • Section 13.5.6 of ASCE /SEI 7-10 contains requirements for special seismic perimeter details and lateral bracing assemblies for suspended ceilings but includes several significant exemptions from these requirements as follows.
    • Seismic detailing is not required for suspended ceilings less than or equal to 144 square feet that are surrounded by walls or soffits that are laterally braced to the structure (this exemption applies to heavy or light suspended ceiling systems).
    • Seismic detailing is not required for suspended ceilings constructed of screw- or nail-attached gypsum board on one level (constructed in a single plane) that are surrounded by and connected to walls or soffits that are laterally braced to the structure above. Note that this exemption does not apply to plaster ceilings or to gypsum board ceilings on multiple levels (constructed in more than one ceiling plane elevation).
  • Chapter 25 of IBC 2012 contains general provisions for horizontal assemblies of gypsum board and plaster, including prescriptive requirements for installation. There are, however, no provisions for lateral design of suspended ceilings.
  • The Division of the State Architect sets forth ceiling standards for California schools in Drywall Ceiling Suspension, Conventional Construction—One Layer (IR 25-3). This document provides general guidance for design and detailing of heavy suspended ceilings.

Retrofit Standard Provisions

Seismic Rehabilitation of Existing Buildings (ASCE/SEI 41-06)  classifies ceilings into one of four types. Suspended ceiling systems are classified into one of two categories:

  • Category b, short-dropped gypsum board sections (less than 2 ft drop) attached to wood or metal furring supported by carrier members.
  • Category c, dropped gypsum board sections greater than 2 and suspended metal lath and plaster.

These ceiling systems are considered force and deformation sensitive. Compliance with the requirements of the standard is necessary when:

  • The performance level is Immediate Occupancy.
  • The performance level is Life Safety or Hazards Reduced in high or moderate seismicity areas.

If the performance level is Hazards Reduced and the ceiling is located in areas of public occupancy or egress, the ceiling must meet the Life Safety performance level.

Note that even if the ceiling system is exempt, light fixtures and air diffusers in the ceiling system may still be subject to support and bracing requirements.

 Typical Causes of Damage

  • Suspended heavy ceilings may be damaged both by direct acceleration and by deformation. Direct acceleration may cause connectors to become loose or deform, and differential movement of the ceiling relative to structural elements such as columns or walls or nonstructural elements such as partitions, lights, diffusers, or sprinklers may also damage the ceiling.
  • As these systems are heavier than acoustic tile ceilings, the consequences of failure may be more hazardous for occupants since both the finish material and the furring grid may fall. Ceiling failures are often costly because the space underneath may be unusable while the ceiling is repaired or replaced.
  • Ceiling finishes may crack unless adequately isolated from the motion of the surrounding structural and nonstructural elements. Crack repair in gypsum board and plaster ceilings is a common expense following earthquakes.

Damage Examples

Figure 6.3.4.3-1 Damage to ornate wire lath and plaster ceiling in the 2010 magnitude-8.8 Chile Earthquake (Photo courtesy of Eduardo Fierro, BFP Engineers). Wire lath is attached to arches or to wood furring suspended from the roof framing.


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