4.22 Seismic Design Requirements for Sprinkler Systems

Reference: CBC 2007 Section 1613; ASCE 7-05, chapter 13; NFPA 13-2002, Section 9.3 with Tentative Interim Amendments (TIA) 02-1, NFPA 13-2007.

Due to the complexity of implementing the seismic design requirements outlined in the California Building Code, the San Francisco Fire Department will allow either of the two options below to be used to justify the sprinkler system sway bracing design for new buildings. Fire Department staff engineers have the opinion that either method provides equavilent protection.

Option 1:

Except where allowed in Section 1613 of the 2007 CBC, the Civil or Structural Engineer of Record for the project shall prepare construction documents for plan review of the design of supports and attachments for seismic sway bracing. Seismic Design Category for a structure shall be determined by CBC 1613 or ASCE 7-05. All plans and calculations required for permit submittal documentation shall be wet signed and wet stamped by the responsible design professional, no copies or facsimiles are allowed.
The construction documents submitted for permit review, in addition to the above requirements, shall include documentation of all steps necessary to determine seismic demands, including but not limited to the following:

Items 1 through 8 are required for site permit approval.

1. Project specific seismic ground motion map(s).
2. A summary of certified soil reports.
3. The site classification.
4. Seismic ground motion values.
5. The seismic design category.
6. A ASME B31 compliance statement, if applicable.
7. Basis of determining values of ap, Rp, Ip
8. Anchorage data and approvals (concrete and masonry anchors, Rp=1.5 unless exceptions in ASCE 7-05, section 13.4.2 are met. Note, exception  c' is not allowed per CBC 2007, 1613.1)

Items 9 through 17 are required for fire sprinkler permit.

9. Calculation of seismic design forces.
10. Basis of values used in calculating seismic relative displacements.
11. The calculation of seismic relative displacements
12. An analysis of seismic relative displacements effects.
13. A summary of seismic design criteria.
14. The pertinent material specifications.
15. The strength of structural elements where attachments/anchors connect.
16. The plans and documents (11 x 17 minimum) of supports and
attachments.
17. Fire sprinkler plans accompanied by copy of approved site permit documents

Loads calculated for lateral braces shall include the weight of the branch lines located within the zone of influence. Loads calculated for longitudinal braces shall include the weight of the branch lines located within the zone of influence, if branch line restraints are farther than 2-feet from the main pipe.

Option 2:

1. Design per NFPA 13, 2007 section 9.3 et al, (except as modified in 4 below) including all Tentative Interim Amendments.
2. A minimum value of Cp=0.50 shall be used.
3. The Ss value shall be obtained from one of the following: a qualified design professional, a letter PE stamped and wet signed; USGS website, with printout of project specific data, C-16 stamped and wet signed, and included on the submitted plans.
4. Insert the following three tables, A, B and C to replace the corresponding tables in NFPA 13-2007 edition, titled: "Wedge Anchors in Normal Weight Concrete," "Wedge Anchors in Lightweight Concrete Filled Metal Decking," and "Undercut Anchors in Normal Weight Concrete".

Table A

Wedge Anchors in 3000 psi Lightweight Concrete-Filled Metal Decking

Table B

Wedge Anchors in 3000 psi Normal Weight Cracked Concrete

Table C

Undercut Anchors in 3000 psi Normal Weight Concrete

5. The following new tables D, E, and F are to be used as field circumstances dictate as specified by their respective titles:

Table D

Wedge Anchors in 3000 psi Lightweight Cracked Concrete

Table E

Wedge Anchors in 4000 psi Normal Weight Cracked Concrete

Table F

Wedge Anchors in 6000 psi Normal Weight Cracked Concrete

Seismic Design: The following two options are for existing fire protection systems:

Option 1. Comply with requirements for new fire protection systems.

Option 2:
1. Design for the worst case, most demanding seismic demands using the following:
a. Fp=1.6 SDS Ip Wp
i. Importance Factor, Ip=1.5
ii. Weight of piping and components, Wp
iii. Spectral Amplification Factor, SDS= 1.23
iv. Therefore, Fp=2.95 Wp
2. Provide items 8, 9, 13, 14, 15, and 16 as required for new systems
3. Applicable sections of NFPA 13, 2002: 9.3.5 'Sway Bracing', including TIA 02-1; 9.3.6 Restraint of Branch Lines. Section 9.3.7.9 is not allowable.
4. NFPA 13, 2002 table 9.3.5.9.1 values are not acceptable for concrete anchors; IBC approved anchors values shall be used. Refer to ASCE 7-05, section 13.4.2, exception  c' not allowed per CBC 2007, 1613.1
5. Wp shall be calculated by totaling the weight of piping, W, in the zone of influence and adding an additional 15%, i.e. Wp=1.15 W.
6. Loads calculated for lateral braces shall include the weight of the branch lines located within the zone of influence. Loads calculated for longitudinal braces shall include the weight of the branch lines located within the zone of influence, if branch line restraints are farther than 2-feet from the main pipe
7. Pipe used for braces shall be minimum schedule 40.