sprinklernotes
When Seismic Protection is Required
You have asked the following question: “We have a building that has an assigned seismic design category (SDC) of B. The AHJ is saying that seismic protection is required for the sprinkler system for the following two reasons: 1 - ASCE 7, 13.1.4 Exception 4 does not apply due to sprinklers having an importance factor of 1.5 2 – IBC, 1613.6.3: “automatic sprinkler systems designed in accordance with NFPA 13 shall be deemed to meet the requirements of section 13.6.8 of ASCE 7" means in order for bracing to be in compliance with NFPA 13, it must be installed. It should be noted that the IBC text is from the 2009 edition and the 2015 edition is the adopted version (which does not contain this text). Do any of the codes and standards, including ACSE7, require seismic protection regardless of the SDC category?” In response to your question, we have reviewed the 2013 edition of NFPA 13, 2015 edition of the IBC, and 2010 edition of the ASCE-7 as the applicable codes and standards. Our informal interpretation is seismic protection is not required. There is a lot of confusion on this issue so let’s start with the sprinkler system itself. NFPA 13 only tells us how to install the system, not when to provide a system. That is dictated by the building code. The same is true for seismic protection. NFPA 13 only tells us how to install the bracing and other features required for seismic protection. The building code tells us when to install a system. Let’s now discuss the two reasons identified as deficiencies. There are many portions of the country that require no protection for the building itself due to the potential acceleration from a seismic event being so low. There are other portions where protection is provided for everything due to the potential for such high levels of acceleration. Then there is much of the country that is a mix where some buildings are being protected and others are not. Additionally, when in a protected building there is a mix whereby some mechanical systems are protected, and others are not. One of the primary variables in determining what is protected is the SDC. It is based on the potential acceleration and the type of soil. It’s a progressive category of A through F with A having the lowest level of risk. As shown by Table 12.2-1 of the ASCE-7, a SDC B building has no limits or restrictions on any of the typical structural elements (only cantilevered column systems). In other words, this building does not require seismic protection. To ensure there is no confusion on whether systems within the building must be protected, 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 in 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. 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 is not required for a building with a SDC of a B classification.
