seismic design for fire sprinkler systems - part 1b_ ibc requirements and exemptions

2/21/13 Seismic Design For F ire Sprinkler Sy stems - Part 1b: IBC Requirements and Exemptions

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Seismic Design For Fire Sprinkler Systems – Part 1b: IBCRequirements and Exemptions

January 23rd, 2009

Steven Scandaliato, SET, CFPS

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

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

IBC Requirements and ExemptionsNow that we are working in this new era, you must understand the “if” of the requirement before discussing the

“how.” The information used to determine design standards includes data that is collected and tested by theNational Earthquake Hazard Reduction Program (NEHRP). IBC, NFPA 5000: Building Construction and

Safety Code, and others all use the data collected by this organization to create the criteria that should befollowed.

Let’s first take a look at how the IBC deals with seismic. The text about earthquake protection in the IBC is

based in large part on criteria found in ASCE 7. This separate document is published by the American Society of

Civil Engineers. It includes design criteria for seismic restraint of architectural, mechanical, and electrical

components and systems. The first edition of IBC in 2000 introduced the requirement for seismic design for fire

sprinklers but did not directly reference ASCE 7 at that time. IBC Section 1614.1 states, “Every structure, and

portion thereof, shall as a minimum, be designed and constructed to resist the effects of earthquake motions and

assigned a Seismic Design Category as set forth in Section 1616.3. Structures determined to be in Seismic

Design Category A need only comply with Section 1616.4.” The 2003 edition kept this requirement in place but

revised the exemptions that followed.

The first exemption says, “Structures designed in accordance with the provisions of Sections 9.1 through 9.6,

9.13 and 9.14 of ASCE 7 shall be permitted.” This exemption allows the use of ASCE 7 in lieu of IBC.



The referenced sections that deal specifically with fire sprinklers are found in the body of Section 9.6. Within this

section are six exemptions that detail when seismic is not required. It is within these six exemptions that the “if”

can be determined. The first exemption allows you to exclude all aforementioned components if the Seismic

Design Category is A. The second allows architectural components that are in a Seismic Design Category B with

some exceptions concerning parapets and wall types. The third exemption is where fire sprinkler systems are

addressed. This exemption allows mechanical and electrical components that are a Seismic Design Category Bto be excluded. This section will prove to be the most referenced section in the process. After several years of

dealing with this process, I have found that the majority of the country will be classified as a Seismic Design

Category B. The fourth exemption appears to affect fire sprinkler systems as well. It allows mechanical and

electrical components that have a Seismic Design Category C to be excluded; however, they must have an

Importance Factor (Ip) that is equal to 1.0. Fire sprinkler systems have been assigned an Ip of 1.5 (ASCE 7-9.6

1.5) because they are considered life safety systems. Therefore, this exemption cannot be applied. The fifth and

sixth exemptions, while applying to mechanical and electrical components, both include a requirement for an Ip

equaling 1.0, meaning fire sprinklers are not allowed to be excluded.

Five other exemptions in IBC Section 1614.1 can be applied if the first one does not apply. The second

exemption states, “Detached one- and two-family dwellings as applicable in Section 101.2 in Seismic Design

Categories A, B and C, or located where the mapped short-period spectral response acceleration, Ss, is less

than 0.4g, are exempt from the requirements of Sections 1613 through 1622.” No specific language in NFPA13D: Standard for the Installation of Sprinkler Systems in One- and Two-Family Dwellings and Manufactured

Homes requires seismic design for structures of this type; however, be advised, this does not include multifamilystructures. NFPA 13R: Standard for the Installation of Sprinkler Systems in Residential Occupancies Up to and

Including Four Stories in Height requires systems to follow the requirements of NFPA 13 in their entirety. Thereare no exceptions to this. If your project is a one- or two-family detached dwelling, seismic design is not

required. However, if you are working on a multifamily structure that most likely falls into a R1 type ofoccupancy, it will be subject to seismic design if it cannot meet any of the other exemptions.

The third IBC Section 1614.1 exemption states, “The seismic-force-resisting system of wood frame buildingsthat conform to the provisions of Section 2308 are not required to be analyzed as specified in Section 1616.1.”

This exemption deals more with the structure itself rather than the portions thereof. I doubt this section ever couldbe applied in an effort to exempt fire sprinkler systems. The fourth exemption states, “Agricultural storage

structures intended only for incidental human occupancy are exempt from the requirements of Sections 1613through 1623.” The reasoning behind this exemption seems self-explanatory. Obviously these types of structures

would have a very low occupancy load and most likely would not require very extensive life safety systems.Hence, it stands to reason that system protection would be minimal.

The fifth and sixth exemptions are really the only other viable exemptions where seismic design for fire sprinkler

systems is allowed to be excluded. Exemption five allows you to use the seismic maps that are included inSection 1615. “Structures located where mapped short-period spectral response acceleration, Ss, determined in

accordance with Section 1615.1 is less than or equal to 0.15g and where the mapped spectral responseacceleration at 1-second period, S1, determined in accordance with Section 1615.1 is less than or equal to0.04g shall be categorized as Seismic Design Category A. Seismic Design Category A structures need only

comply with Section 1616.4.” The contour lines shown on these maps are based on two different time periods.Without delving too deep into the world of seismology, we will accept these maps as a guide to determining the

anticipated g-forces that are expected over a given time period.



Finally, exemption number six allows you to use a calculation procedure to determine the values to be compared

with the allowed minimums. It states, “Structures located where the short-period design spectral responseacceleration, SDS, determined in accordance with Section 1615.1, is less than or equal to 0.167g and the design

spectral response acceleration at 1-second period, SD1, determined in accordance with Section 1615.1, is lessthan or equal to 0.067g, shall be categorized as Seismic Design Category A and need only comply with Section

1616.4.”

According to these two exemptions, if you look at the two different maps—short period and long period—andinterpolate your location on each, and the values you determine are less than those listed in these exceptions

respectively, then you do not have to provide seismicrestraint for the system.

For example, consider a single-story office building being built in Tampa, Fla. You would look at the short and

long-term spectral response maps, IBC Figures 1615-1 and 1615-2, and interpolate as exactly as possible theclosest g-force percentage. (Keep in mind that these values are presented as percentages. This will becomeuseful when we actually do the calculations.)

The maps in the code book itself are very small

and somewhat difficult to read. Several resourcesare available that provide these maps as .dwf files,

which are a type of AutoCAD viewing file similarto a .pdf or Acrobat file. Most manufacturers that

provide components that are listed for seismicrestraint have these files available. A software

program available through the International CodeCouncil also provides a more useful and accurateway to evaluate these maps. You also can

purchase the maps as one large foldout that has theshort-term period on one side and the long-term

period on the other. I highly recommendthis investment.

Figure 1 is an enlargement from the electronic version of the map that came from ICC. It helps you better

determine the short- and long-term values for our example. Figure 1 is the short-term map. The upper contourline is 10 (the number is not visible) and the lower contour line is 5 as shown.

As you can see, Tampa, which is in Hillsborough County, falls nearly between the short period responsepercentages lines of 5 and 10. Depending on the project’s location in the county, you can further define, or

interpolate, between these two lines; however, for the sake of this example we are going to assume a value of

7.5.

The long-period map (Figure 2) has contour lines 2 and 4 showing in the same area (2 is the lower contour line

and 4 is the upper contour line). Here again, you can interpolate between the contour lines or simply choose the

higher of the two.

Keep in mind that you must satisfy both the short- and long-term values in order to use the fifth exemption.



Continued at Seismic Design For Fire Sprinkler

Systems – Part 1c: Determining the Seismic

Design Category of a Building

Comments (4) Leave a comment

1.

Joseph KeltosJanuary 22nd, 2010 at 14:54 | #1

Reply | Quote

Stephen,Does your conclusion that structures with a

Seimic Design Category B do not require

seismic braces continue to be applicable

when the 2006 edition of the IBC is used.Section 1613.1 stills references ASCE 7 so

I presume the exception to mechanical

systems still applies.

Thank you in advance for your response.

2.

StevenJanuary 24th, 2010 at 08:34 | #2

Reply | Quote

Yes…fire protection is exempt in categoriesA and B through IBC 2009…

3.

Chris Freshcoln

February 6th, 2010 at 11:35 | #3Reply | Quote

It appears this exemption applies to the piping component – do you also apply this to the structure holding

up the pipe? For instance, if you have a piperack inside a building carrying pipes that are exempt does thismean the piperack does not have to be designed for seismic forces or just that the pipe does not? There is

another section in the code specifically for pipe supports and non building structures similar to buildings.

There has been considerable debate in our office whether you do or do not have to consider seismicforces on the support structure if the component is exempt per the requirement you listed. Just looking for

another opinion.

4.



Ver

July 28th, 2011 at 08:45 | #4

Reply | Quote

Hi

If the project is categorize as A what is there any exemption about annular space around the sprinkler

pipe?

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

Seismic Design For Fire Sprinkler Systems – Part 1c: Determining the Seismic Design Category of a Building

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