Continued from Part 1 of seismic design for fire sprinkler systems.
After you have determined if you need seismic bracing, how do you determine the amount of Horizontal Seismic Force or Fp to apply? (Hint  You can just go to our Seismic Calculator App and have much of the look up work done for you.)
STEP ONE  APPLICABLE STANDARDS AND CODES
Assuming that you are working in a jurisdiction that has adopted the International Building Code (IBC), you would start with section 1613.1 which states:
STEP TWO  DETERMINE THE FORCE FACTOR
ASCE 0705 paragraph 13.3.1 is the applicable section for "nonstructural" components and provides the following formula for determining the horizontal design force (Fp) to be applied:
As you can see the only missing pieces are the Height of Attachment (z), Height of Structure (h), and Fivepercent damped design spectral response acceleration at short periods (Sds).
The calculated design force can be reduced by a factor of 1.4 because ASCE/SEI 7 is based on strength design, whereas NFPA 13 uses allowable stress design. Prior to the 2007 edition, all loads in NFPA 13 were at allowable stress levels with the exception of the buckling loads for brace members. In the 2007 edition, tables that contained the allowable loads on braces have been reduced to add a factor of safety appropriate to the use of allowable stress design
After you have determined if you need seismic bracing, how do you determine the amount of Horizontal Seismic Force or Fp to apply? (Hint  You can just go to our Seismic Calculator App and have much of the look up work done for you.)
STEP ONE  APPLICABLE STANDARDS AND CODES
Assuming that you are working in a jurisdiction that has adopted the International Building Code (IBC), you would start with section 1613.1 which states:
1613.1 Scope. Every structure, and portion thereof, includingFurthermore the International Mechanical Code (IMC) section 301.15 states:
nonstructural components that are permanently attached to
structures and their supports and attachments, shall be
designed and constructed to resist the effects of earthquake
motions in accordance with ASCE 7, excluding Chapter 14 and
Appendix l1A. The seismic design category for a structure is
permitted to be determined in accordance with Section 1613 or
ASCE 7.
301.15 Seismic resistance. When earthquake loads are applicable in accordance with the International Building Code, mechanical system supports shall be designed and installed for the seismic forces in accordance with the International Building Code.Looking in the appendix of the 2009 edition of IBC (page 590), we can see that the 2005 edition of ASCE 07 or ASCE 0705 is adopted. So what is ASCE 0705? The name of the standard is "Minimum Design Loads for Buildings and Other Structures" and is published by the American Society of Civil Engineers (ASCE).
STEP TWO  DETERMINE THE FORCE FACTOR
ASCE 0705 paragraph 13.3.1 is the applicable section for "nonstructural" components and provides the following formula for determining the horizontal design force (Fp) to be applied:
Most of the variables are already defined by NFPA 13 and/or ASCE 0705 as follows:
Variable

Standard Value

Definition

a_{p}

2.5

Component amplification
factor from Table 13.61 (Seismic Coefficients for Mechanical and Electrical
Components) – “Piping and tubing not in accordance with ASME B31, including
inline components, constructed of high or limited deformability materials,
with joints made by threading, bonding, compression couplings, or grooved
couplings”.
(Note the 2002 edition of
ASCE 7 recommended a_{p }= 1.0)

R_{p}

4.5

Component response
modification factor from Table 13.6.1 (same item as ap above)
(Note the NFPA 13 2002 TIA
021 recommended a R_{p }= 3.5)

I_{p}

1.5

Component Importance factor
(Ip) per ASCE 705 13.1.3 “… The component importance factor, Ip, shall be
taken as 1.5 if any of the following conditions apply: 1. The component is
required to function for lifesafety purposes after an earthquake, including
fire protection sprinkler systems…”
(Note the NFPA 13 2002 TIA
021 recommended a I_{p }= 1.5)

z



Height in structure of point
of attachment of component with respect to the base. For items at or below the base, z shall be
taken as 0. The value of z/h need not
exceed 1.0.

h



Average roof height of
structure with respect to base.

As you can see the only missing pieces are the Height of Attachment (z), Height of Structure (h), and Fivepercent damped design spectral response acceleration at short periods (Sds).
The calculated design force can be reduced by a factor of 1.4 because ASCE/SEI 7 is based on strength design, whereas NFPA 13 uses allowable stress design. Prior to the 2007 edition, all loads in NFPA 13 were at allowable stress levels with the exception of the buckling loads for brace members. In the 2007 edition, tables that contained the allowable loads on braces have been reduced to add a factor of safety appropriate to the use of allowable stress design