Showing posts with label Seismic. Show all posts
Showing posts with label Seismic. Show all posts

Thursday, January 5, 2012

Seismic Design For Fire Sprinkler Systems - Part 2

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:
1613.1 Scope. Every structure, and portion thereof, including
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.
 Furthermore the International Mechanical Code (IMC) section 301.15 states:
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 07-05 is adopted.  So what is ASCE 07-05?  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 07-05 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:
ASCE Formula
Most of the variables are already defined by NFPA 13 and/or ASCE 07-05 as follows:

Variable
Standard Value
Definition
ap
2.5
Component amplification factor from Table 13.6-1 (Seismic Coefficients for Mechanical and Electrical Components) – “Piping and tubing not in accordance with ASME B31, including in-line 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 ap = 1.0)
Rp
4.5
Component response modification factor from Table 13.6.-1 (same item as ap above)
(Note the NFPA 13 2002 TIA 02-1 recommended a Rp = 3.5)
Ip
1.5
Component Importance factor (Ip) per ASCE 7-05 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 life-safety purposes after an earthquake, including fire protection sprinkler systems…”
(Note the NFPA 13 2002 TIA 02-1 recommended a Ip = 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 Five-percent 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



Monday, October 3, 2011

Earthquake Data for Canada

There is a site similar to USGS' for earthquake data in Canada available at:
http://earthquakescanada.nrcan.gc.ca/hazard-alea/interpolat/index-eng.php
Let us know if you are interested in having Anvil Fire update our Seismic Force Calculator App to include this information.


Sunday, September 25, 2011

Seismic design changes - 2012 IBC

DesignMaps Application and 2008 Design Data
USGS has released an updated DesignMaps application which is a great application.  However, before you start applying it to 2009 International Building Code please make sure to read their FAQ page which states:
This application should currently only be used to investigate which design values will likely be mandated in the future.

This recommendation by USGS is based on the hierarchy of the codes and standards, which is as follows:
2003 IBC2006 IBC2009 IBC2012 IBC
ASCE7-02ASCE7-05ASCE7-05ASCE7-10
USGS 2002USGS 2002USGS 2002USGS 2008

The DesignMaps application utilizes information from the 2008 USGS National Seismic Hazard Maps information.   For 2008 the hazard values in the Central and Eastern U.S. have been reduced by 10-25% in many cases, and most 1-second period ground motion values for the Western U.S. have also been reduced, in some cases by as much as 30%.

Example differences between 2002 and 2008 Design Data
Lets look at a comparison of several values based on the 2002 vs 2008 hazard values.  (Examples based  Site Class 'D' and Occupancy Category of 'II').
Atlanta, GA (Lat 33.7489954, Lng -84.3879824)
Data SourceSsS1SdsSd1Sds Design CatSd1 Design Cat
2002 Design Data0.2260.0850.2410.137BC
2008 Design Data0.1850.0900.1970.144BC

Sacramento, CA (Lat 38.5815719, Lng -121.4943996)
Data SourceSsS1SdsSd1Sds Design CatSd1 Design Cat
2002 Design Data0.5910.2440.5230.311DD
2008 Design Data0.6750.2940.5670.355DD

Casper, WY (Lat 42.866632, Lng -106.313081)
Data SourceSsS1SdsSd1Sds Design CatSd1 Design Cat
2002 Design Data0.3700.0770.3710.123CB
2008 Design Data0.2770.0740.2910.118BB
As seen in the last example for Casper, Wyoming, seismic bracing for fire sprinkler piping is not required based on which design criteria is applied.  The Sds value is 21% less in the 2008 values.  So whether you utilize the 2002 or 2008 hazard data can make a significant difference on your project.

Anvil Fire's Seismic Force Calculation App provides values based on the 2002 hazard values published by USGS and is basically identical to the Java Ground Motion Parameter Calculator provided by USGS.  Consult with your AHJ, but at this time we recommend that you follow USGS's recommendation to only use the DesignMaps application to investigate the requirements of the future 2012 International Building Code.

For more detailed information on how to determine the seismic design forces for fire suppression systems, please read our blog post on Seismic Design For Fire Sprinkler Systems.

Sunday, August 14, 2011

Expanded Seismic Data for On-line App


So that our clients outside of the continental United States don't feel left out, we have expanded our seismic ground motion data to include:

  • Hawaii
  • Puerto Rico/U.S. Virgin Islands

This data is from the USGS and is applicable for designs applying ASCE 7-05 as referenced by the 2006 and 2009 editions of IBC.  Visit our on-line fire sprinkler seismic calculation app and try it out for these locations.



Saturday, January 15, 2011

Seismic Design For Fire Sprinkler Systems

How do you know when seismic bracing is required for fire sprinkler piping?  Lets walk through the general procedure to determine if bracing is required.  (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, including
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.
 Furthermore the International Mechanical Code (IMC) section 301.15 states:
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 (ASCE 07-05) is adopted.  So what is ASCE 07-05?  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 - Ss and S1 Design Ground Motions
As noted in IBC section 1613.1 above, we are going to use IBC section 1613 to determine our seismic design category.  The first step is determine how strong the forces will be at your site.  There are two types of forces to consider: Short Period (Ss) and 1-Second Period (S1).  These values are typically determined by the USGS and the official definitions are as follows:

  • Ss = mapped MCE, 5 percent damped, spectral response acceleration parameter at short periods
  • S1 = mapped MCE, 5 percent damped, spectral response acceleration parameter at a period of 1 second
  • MCE = Maximum Considered Earthquake effects
Most building codes use 0.2 second and 1.0 second to represent the approximate natural period of vibration of a short and tall building, respectively

The USGS provides and excellent Java based calculation program for looking up these and many other values based on lat/lng and zip code. Or you can just go to our Seismic Calculator App which is based on this same data and provides some addition capabilities.

If I asked which area of the country had the heights forces, I bet you would guess California.  However, the highest seismic forces for the continental United States are:
  • La Center, Kentucky (37.1, -89.0) with a Ss = 3.4079
  • Harrisburg, Arkansas (35.5, -90.6) with a S1 = 1.36927
  • * Based on USGS 2003 Conterminous US Design Ground Motion data on http://earthquake.usgs.gov

STEP TWO - SITE CLASS, Fa, and Fv (ADJUSTMENT FACTORS)
The next step is to determine the Site Class.  Whether the ground is very stiff or very soft greatly affects the way the seismic forces are transferred to the structure.  In general, a stiff ground transfers the energy efficiently and a soft ground just absorbs the energy.  As such, the IBC provides a standard formula to adjust the S1 and Ss values determined above for your soil profile.  We strongly recommend that you consult with the Structural Engineer of Record since he already had to determine this class for his calculations.  That being said, the most typical soil type is 'D' or Still Soil Pile.

Table 1613.5.2 - Site Class Definitions
Site Class
Soil Profile Name
AVERAGE PROPERTIES IN TOP 100 feet, SEE SECTION 1613.5.5
Soil shear wave velocity, Vs (ft/s)
Standard penetration resistance, N
Soil undrained shear strength, Su (psf)
A
Hard Rock
Vs > 5,000
N/A
N/A
B
Rock
2,500 < VS <= 5,000
N/A
N/A
C
Very Dense Soil and Soft Rock
1,200 < VS <= 2,500
N > 50
Sa >= 2,000
D
Stiff Soil Profile
600 <= VS <= 1,200
15 <= N <=50
1,000 <= Sa <= 2,000
E
Stiff Soil Profile
VS < 600
N < 15
Sa < 1,000


You then look up the site coefficients from IBC tables 1613.5.3(1) and 1613.5.3(2) below.  Note that you can apply a straight-line interpolation for intermediate values and this can make a significant difference.

TABLE 1613.5.3(1) VALUES OF SITE COEFFICIENT Fa (a)
Site ClassMapped Spectral Response Accleration at Short Period
Ss <= 0.25Ss = 0.50Ss = 0.75Ss = 1.00Ss >= 1.25
A0.80.80.80.80.8
B1.01.01.01.01.0
C1.21.21.11.01.0
D1.61.41.21.11.0
E2.51.71.20.90.9
FNote bNote bNote bNote bNote b
  • (a) Use straight-line interpolations for intermediate values of mapped spectral response acceleration at short period, Ss.
  • (b) Values shall be determined in accordance with Section 11.4.7 of ASCE 7.


TABLE 1613.5.3(2) VALUES OF SITE COEFFICIENT Fv (a)
Site ClassMapped Spectral Response Acceleration at 1-Second Period
S1 <= 0.1S1 = 0.2S1 = 0.3S1 = 0.4S1 >= 0.5
A0.80.80.80.80.8
B1.01.01.01.01.0
C1.71.61.51.41.3
D2.42.01.81.61.5
E3.53.22.82.42.4
FNote bNote bNote bNote bNote b
  • (a) Use straight-line interpolations for intermediate values of mapped spectral response acceleration at 1-second period, S1.
  • (b) Values shall be determined in accordance with Section 11.4.7 of ASCE 7.

STEP THREE - Sds and Sd1 (ADJUSTED FORCES)
Now that we know the expected forces (S1 and Ss) and adjustment factors (Fv and Fa), we need to crunch some numbers to determine the adjusted force factors per the following simplified IBC formulas:

(IBC equations 16-37 and 16-39 combined)

(IBC equations 16-36 and 16-38 combined)

STEP FOUR - DESIGN CATEGORY AND ACCEPTABLE RISK BASED ON OCCUPANCY
Now that we know the adjusted design forces, we need to determine if these forces are great enough to require preventative actions.  Risk is related to the activity.  A hospital has a much higher risk than a temporary storage facility.  IBC recoginzes this in Tables 1604.56, 1613.5.6(1), and 1613.5.6(2) as follows:


IBC Table 1604.5 - Occupancy Category of Buildings and Other Structures
Occupancy CategoryNature of Occupancy
IBuildings and other structures that represent a low hazard to human life in the event of failure, including but not limited to:
  • Agricultural facilities
  • Certain temporary facilities
  • Minor storage facilities
IIBuildings and other structures except those listed in Occupancy Categories I, III, and IV
IIIBuildings and other structures that represent a substantial hazard to human life in the event of failure, including but no limited to:
  • Covered structures whose primary occupancy is public assembly with an occupant load greater than 300
  • Buildings and other structures with elementary school, secondary school or day care facilities with an occupancy load greater than 250
  • Buildings and other structures with an occupancy load greater than 500 for colleges or adult education facilities.
  • Health care facilities with an occupant load of 50 or more resident patients, but not having surgery or emergency treatment facilities.
  • Jails and detention facilities.
  • Any other occupancy with an occupant load greater than 5,000.
  • Power-generating stations, water treatment for potable water, waste water treatment facilities and other public utility facilities not included in Occupancy Group IV.
  • Buildings and other structures not include in Occupancy Category IV containing sufficient quantities of toxic or explosive substances to be dangerous to the public if released.
IVBuildings and other structures designated as essential facilities, including but not limited to:
  • Hospitals and other health care facilities having surgery or emergency treatment facilities.
  • Fire, rescue and police stations and emergency vehicle garages.
  • Designated earthquake, hurricane or other emergency shelters.
  • Designated emergency preparedness, communication, and operation centers and other facilities required for emergency response.
  • Power-generating stations and other public utility facilities required as backup facilities for Occupancy Category IV structures.
  • Structures containing highly toxic materials as defined by Section 307 where the quantity of material exceeds the maximum allowable quantities of Table 307.1.(2).
  • Aviation control towers, air traffic control centers and emergency aircraft hangers.
  • Buildings and other structures having critical national defense functions.
  • Water treatment facilities required to maintain water pressure for fire suppression.


Table 1613.5.6(1) SEISMIC DESIGN CATEGORY BASED ON SHORT-PERIOD RESPONSE ACCELERATIONS
Value of SdsOCCUPANCY CATEGORY
I or IIIIIIV
Sds < 0.167gAAA
0.167g <= Sds < 0.33gBBC
0.33g <= Sds < 0.50gCCD
0.50g <= Ss1DDD


Table 1613.5.6(2) SEISMIC DESIGN CATEGORY BASED ON 1-SECOND PERIOD RESPONSE ACCELERATIONS
Value of SdsOCCUPANCY CATEGORY
I or IIIIIIV
Sd1 < 0.067gAAA
0.067g <= Sd1 < 0.133gBBC
0.133g <= Sd1 < 0.20gCCD
0.20g <= Sd1DDD

STEP FIVE - IS BRACING REQUIRED?
Finally we have determined a Seismic Design Category based on the forces, adjustment factors, and occupancy of the building.  Based on the worst case seismic design category, we can go back to ASCE 07-05 and look at the following single paragraph:
13.1.4 Exemptions. The following nonstructural components are exempt from the requirements of this section: 
… 2.  Mechanical and electrical components in Seismic Design Category B.
So if Category A or B you are exempt, if C or D you need to provide bracing.

Look for the next post on calculating the forces on individual piping components in accordance with ASCE 07-05 paragraph 13.6.8.3.