FEMA E-74 Example Protection Piping

FEMA E-74 Example Protection Piping

FEMA E-74 Example 6.4.4.1 Suspended Fire Protection Piping

6.4.4.1 Suspended Fire Protection Piping

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This category covers fire protection sprinkler systems and piping. These systems and piping are subject to the requirements in Standard Installation of Sprinkler Systems (NFPA 13). Fire sprinkler systems may include a number of components besides piping, including pumps, tanks, and control panels. Recommendations for these components are found in the appropriate sections in Chapter 6 .

Bracing provisions for fire protection piping were introduced in 1947, making it one of the earliest nonstructural standards to consider lateral bracing. NFPA 13 bracing provisions have developed continuously over time, in response to changes in construction practice and lessons learned from earthquakes. As a result, some fire protection piping systems may appear to be braced, even if installed 50 years ago. Unfortunately, older bracing installations may include features that have been shown to be vulnerable in strong ground shaking.

Provisions

Building Code Provisions

Minimum Design Loads for Buildings and Other Structures (ASCE/SEI 7-10) Section 13.1.3.1 specifies that systems required for life-safety purposes after an earthquake, such as fire protection systems, be classified as designated seismic systems and designed using a component importance factor, Ip. of 1.5. Designated seismic systems may require engineering calculations, equipment certification, special inspection, etc. ASCE/SEI 7-10 specifies that fire protection piping conform to NFPA 13. as follows:

  • NFPA 13 provides specific requirements for fire suppression systems and piping. Fire protection piping installations conforming to the 2007 or later editions of NFPA 13 may be considered to comply with the requirements of ASCE/SEI 7-10. 
  • FEMA E-74 Example Protection Piping
  • The 2010 edition of NFPA 13 contains prescriptive details and requirements for many aspects of the piping installation, such as hanger size and spacing, clearances between the system and other structural or nonstructural components, and standard bracing installation details. It also contains a simplified method for doing seismic design, based on the concept of “zone of influence,” a method of proportioning forces to bracing elements that has been in use for decades. Most bracing assemblies for fire protection piping must be listed for a maximum load rating .

Retrofit Standard Provisions

Seismic Rehabilitation of Existing Buildings (ASCE/SEI 41-06) classifies suspended fire protection piping as both force controlled and displacement controlled. ASCE/SEI 41-06 requirescompliance with the anchorage provisions of the standard when the performance level is Life Safety or higher. Rehabilitation, if required, is accomplished by prescriptive approaches to support and bracing, in accordance with NFPA 13 .

 Typical Causes of Damage

  • Fire protection piping systems are sensitive to both acceleration and deformation. Vulnerable locations include joints, bends, connections to rigidly mounted equipment and risers subjected to significant relative movement between floors.
  • Older bracing installations may include details that have performed poorly in past earthquakes, including the use of non-seismically rated power actuated fasteners (shot pins) or drop-in type concrete expansion anchors in bracing applications, which have proven unreliable under seismic loads. Many sprinkler system failures in the 1994 Northridge Earthquake were due to failure of poorly designed braces and brace connections.
  • Sprinkler heads are often damaged due to interactions with ceiling systems, especially those with “hard” finishes such as plaster and metal panels. These interactions may also result in impact damage to the ceiling, failure of the sprinkler head, or failure to joints in the piping, with subsequent water damage. Sprinkler heads and sprinkler drops are also damaged by interactions with structural members and other structural braces where inadequate clearance is provided to avoid impact.
  • Older systems may lack lateral restraints on the branch lines, which will make the sprinkler heads more vulnerable to interaction with the ceiling system and adjacent structural members.
  • Fluids may leak from damaged joints or broken pipe; property losses and business outages are often attributed to fluid leaks from fire suppression piping. Facilities may need to be evacuated if the fire suppression system is compromised.
  • Damage to any part of the fire protection system may compromise its functionality. In addition to the piping, pumps, holding tanks, control panels, control sensors, smoke detection equipment, and fire doors must all be operational for the life-safety systems to function correctly. If a fire breaks out following an earthquake and the fire suppression system is not functional, significant property losses may result.

Damage Examples

Figure 6.4.4.1-1 Sprinkler pipe ruptured at the elbow joint due to differential motion within the ceiling plenum. Water leakage from broken fire sprinklers and water lines contributed to the decision to close this hospital for several days following the 1994 magnitude-6.7 Northridge Earthquake (Photo courtesy of Robert Reitherman).


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