Seismic Design For Fire Sprinkler Systems – Part 1a: The Seismic Shift

January 23rd, 2009

Part 1: Using the Seismic Design Category to determine the need for earthquake bracing.

Plumbing Systems & Design Magazine
By now, the majority of jurisdictions across the country is using, or at the very least has had some exposure to, the International Building Code (IBC). Although many of its requirements are identical to the codes that those of us in the engineering disciplines were using prior to
its adoption, a few revisions quietly made their way into mainstream design requirements and unfortunately have made their presence known in very expensive ways. One of those silent revisions concerns seismic design for fire sprinkler systems.

I know many of you in the plumbing and mechanical design disciplines probably are saying to yourselves, “I have been doing this for years. What’s the big deal?” Well, if you read on, you will learn that this seismic stuff is a very big deal.

The Seismic Shift
Seismic design for fire sprinkler systems historically has been governed by building codes that were not very specific regarding the requirements for seismic restraint. In fact, the need for earthquake bracing has been fairly clear and isolated in large part because, up until the last eight to 10 years, the majority of fire sprinkler systems was designed using performance specifications rather than installation specifications. As such, the design criteria were left up to the fire protection contractor.

Almost all performance specifications contain language such as “design and install per NFPA 13;” therefore, fire sprinkler contractors were using NFPA 13: Standard for the Installation of Fire Sprinkler Systems to determine what to include in the design of the system. NFPA 13 never was intended to dictate “if” seismic design was required in a system. It always has been and still is the standard for “how” to install seismic components when they are required. Normally this requirement comes from the adopted building code by which the project is governed. The requirement also can come from the local authority having jurisdiction or the client’s insurance company.

When contractors design and install per NFPA 13, it typically means consulting the seismic map that many contractors use as an indicator of the likelihood of a seismic event taking place in the location in which they are working. Based on this map, contractors decide whether or not to install earthquake bracing. For example, California is a Zone 4, which is the worst case; if a contractor sees that he is in a Zone 0, 1, or even 2, he most likely will decide to do nothing about seismic design. The fact that an earthquake never had occurred in the city and that the AHJ never had required seismic design often confirms the perception that seismic does not need to be included.

For many of you this may seem crazy; for others it may be perfectly logical. How you feel about the process most likely depends on where you live and practice. What is so amazing is that the previous building standards, including the Uniform Building Code and the Building Officials and Code Administrators, never intended for fire sprinkler systems to be exempt from seismic requirements. They were just vague about the extent to which the design was to be implemented. Since the specifications were not giving any definite guidance, the inclusion of seismic design was very isolated.

This is not the case any more. A slow but deliberate metamorphosis has been taking place in the industry, and FS (Fire Sprinkler) sheets are making their way into construction documents across the country. Engineers are beginning to take responsibility for aspects of the installation portion of the design, as well as the criteria, including
seismic, by which the system is to be installed.

Continued at Seismic Design For Fire Sprinkler Systems – Part 1b: IBC Requirements and Exemptions

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