sprinklernotes
Seismic Requirements for a Seismic Design Category B Building
You asked the following questions: “We have a project that has been assigned a Seismic Design Category B. We have annotated and referenced IBC section 1613, and ASCE 7 sections 13.1.3 and 13.1.4(4) “Mechanical and electrical components in seismic design category B” are exempt from the minimum design criteria. We have also referenced ASCE 7 13.6.8 and 13.6.8.2 to correlate the fire sprinkler systems to a nonstructrual building mechanical component. However, the local AHJ has stated "ASCE 7 13.1.4 gives mechanical and electrical components an exemption from seismic bracing. Fire sprinkler systems are fire life safety systems and thus not included in this exemption. Seismic bracing shall be required per NFPA 13." Are fire sprinkler systems allowed to use the exemption called out in ASCE 7, 13.1.4 (4) as a fire life safety system that is also considered a nonstructrual mechanical component even though the exemption does not spell out "Fire Sprinkler System," and even though it appears that ASCE 7 section table 13.2-1 which references ASCE 7 sections 13.6.3, 13.6.8, seems to separate non-structrual Mechanical components into sub components one of which is piping and fire sprinkler systems?” In response to your question, we have reviewed NFPA 13, 2016 edition and ASCE 7-10 as the applicable standards. Our informal interpretation is that seismic protection is not required. There is confusion related to this issue, in part because NFPA 13 is a prescriptive-based standard, which tells us how to install the system, not when to provide a system. When and where systems are required are provided by building and/or fire codes. The same is true for seismic protection. NFPA 13 provides installation requirements for seismic protection of fire sprinkler systems where required to be provided. It should also be noted that project specifications may require seismic protection in regions where other buildings were not required to be provided with such protection. An example of this includes federal government buildings throughout the USA. NFPA 13 requirements for seismic protection have been revised in the recent past, in order to continue to be in compliance with ASCE 7, and these rules apply where required by applicable codes, specifications, or where required by a local AHJ through adopted policies. To address your specific situation, ASCE-7, section 13.1.4 – Exceptions explicitly identifies what nonstructural components are not required to provide seismic protection. Exception No. 4 states: “Mechanical and electrical components in Seismic Design Category B.” This means all mechanical systems regardless of the importance factor. This is confirmed by exception No. 5 which is the next higher risk level SDC-C, where systems with a lower importance valve of 1.0 are exempted but sprinklers are not. This allowance for a mechanical system in an SDC-B category makes sense since the building itself is effectively not seismically protected. It should also be noted that the use of the phrase “mechanical systems” has generated questions as to whether it applies to sprinkler systems. This is a broad reference addressing all mechanical systems including piping systems like drain and sprinkler systems. As indicated above, the mechanical systems are sub-divided based on their function as indicated by their importance factor. This also supports the fact that they all fall into the family of mechanical systems. As for the old IBC text: “automatic sprinkler systems designed in accordance with NFPA 13 shall be deemed to meet the requirements of section 13.6.8 of ASCE 7," it, too, is simply saying how to install it, not when. This text was previously required because there was a difference in the methods for assigning the applicable force between NFPA 13 and ASCE-7. Without this text in the IBC, NFPA 13 could not be applied on how the bracing is installed. The conflict has since been resolved by many changes to NFPA 13 so the IBC no longer needs such text. In conclusion, seismic protection, whether it be clearance from structural elements, flexible couplings, or bracing should not be required for a building with an SDC of a B classification.
