Seismically Rated Fans (FA/125-10)
December 8th, 2010
When a project calls for seismically rated equipment, there are a number of code requirements that need to be considered. This article outlines the methodology of the seismic certification process and considerations involved to properly determine the need for a seismically certified fan.
While the information referenced in this guide is a general overview of the 2009 International Building Code (2009 IBC) and the American Society of Civil Engineers Minimum Design Loads for Buildings and Other Structures (ASCE 7-05), always consult your local building codes for specific requirements. The need for a seismically rated fan is ultimately made by the structural engineer, and should be published in the structural plans.
There are two pertinent mandates for seismic certification of equipment — the International Building Code (IBC) and the Office of Statewide Health Planning and Development (OSHPD).
The International Building Code (IBC)
The International Building Code is a model building code developed by the International Code Council (ICC). The IBC is designed to provide model code regulations that safeguard public health and safety in all communities. The 2009 IBC incorporates standards for the design of nonstructural components subject to seismic events, including HVAC equipment and fans. The code states: 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.
These standards go beyond the need for position retention certification of components and now include certification of the mechanical equipment itself. The IBC has been adopted on the state or local level.
Office of Statewide Health Planning and Development (OSHPD)
The Office of Statewide Health Planning and Development (OSHPD) is one division within the California Health and Human Services Agency with the pertinent objective to ensure the safety of buildings used in providing health care. Though OSHPD enforces building standards for health care facilities per the California Building Code, this code closely reflects the standards presented by the 2009 IBC.
Seismic Certification Methodology
There are three ways in which a component can be seismic certified per the 2009 IBC.
- Shake table test.
- Three-dimensional tests by an analytical method using dynamic characteristics and forces.
- The use of experience data (historical data demonstrating acceptable seismic performance).
For certification of an entire product line represented by the OSP number, OSHPD requires testing of the largest and smallest component of similar construction via shake table. To best encompass the requirements of both the 2009 IBC and OSHPD Special Seismic Certification Preapproval (OSP), seismic certified fans shall be shake table tested. Fans are tested at an independent test facility in accordance with ICC-ES AC 156 and under the responsible charge and review of a California structural engineer.
Seismic Design Category
Each building and structure is assigned a Seismic Design Category (SDC) by the building structural engineer. The Seismic Design Category is a classification assigned to a structure based on its Occupancy Category and the severity of the design earthquake ground motion at the site. The SDC determines whether seismic certified equipment is required by the 2009 IBC. If a piece of equipment is assigned a SDC of C through F, and the importance factor for that piece of equipment is 1.5, the component is to be seismic certified per the 2009 IBC and OSHPD (See table ASCE 7-05 Seismic Design Exceptions.) HVAC components will have the same Seismic Design Category rating as the building unless otherwise noted.
Calculating a Seismic Design Category
The following four steps can be used to determine the Seismic Design Category of a structure:
1. Determine the Occupancy Category of the structure by consulting the 2009 IBC Table 1604.5
-Occupancy Category of Buildings and Other Structures. (See Table 1-1 Occupancy Category of Buildings and Other Structures for Flood, Wind, Snow, Earthquake, and Ice Loads.) The Occupancy Categories are:
- Occupancy Category I – buildings and other structures that represent a low hazard to human life in the event of failure.
- Occupancy Category II - buildings and other structures except those listed in Occupancy Categories I, III and IV.
- Occupancy Category III – buildings and other structures that represent a substantial hazard to human life in the event of failure.
- Occupancy Category IV - buildings and other structures designated as essential facilities.
2. Determine the component’s Importance Factor (Ip). The value for Ip will be 1.5 for any of the following conditions (otherwise it will be 1.0). Note: OSPHD considers fans and air handlers to have an Importance Factor of 1.5.
- The component is required to function for life-safety purposes after an earthquake.
- The component contains hazardous materials.
- The component is in or attached to an Occupancy Category IV structure and it is needed for continued operation of the facility.
3. Determine the designed spectral response acceleration parameters (SDS and SD1).
- Establish the spectral response accelerations based on the building location. Decide the appropriate 0.2 Second Spectral Response Acceleration (Ss) and the 1.0 Second Spectral Response Acceleration (S1) from the 2009 IBC Figures 1613.5(1) through 1613.5(14). Units of Ss and S1 are in percentage of Earth’s gravity (% g). These spectral response accelerations (Ss and S1) can also be determined from USGS Seismic Hazard Curves and Uniform Hazard Response Spectra software. A free version is available via USGS at http://earthquake.usgs.gov/ research/hazmaps/design/.
- Determine the site class based on soil profile. Consult IBC-2009 table 1613.5.2 - Site Class Definitions, shown below, to determine site classification.
A: Hard rock
C: Very dense soil and soft rock
D: Stiff soil
E: Soft clay soil
F: Sandy clays
Unknown, use D.
Site Class Definitions (IBC 2009)
Table 1613.5.3 (1)
Values of Site Coefficient Faa
Table 1613.5.6 (1)
Seismic Design Category Based on Short-Period Response Accelerations
Table 1613.5.6 (2)
Seismic Design Category Based on 1-Second Period Response Acceleration
ASCE 7-05 Seismic Design Exceptions
Greenheck’s Seismic Certification
Greenheck’s tests incorporated the most severe seismic conditions anywhere in the United States including the most severe spectral response accelerations (SDS = 2.28), an Importance Factor of 1.5, all Site Classes (F being the most severe), all Occupancy Categories (IV- essential facilities), and all Seismic Design Categories (F being the most severe).
Testing equipment for the worst case scenarios allows Greenheck to supply a seismic certified fan to a job anywhere in the United States regardless of location. For projects presided over by OSHPD, please reference OSP-0105-10 and OSP-0113-10 for a listing of Greenheck equipment that meets Special Seismic Certification Pre-approval.
The 2009 International Building Code (IBC) and the Office of Statewide Health Planning and Development (OSHPD) both require seismic certification of nonstructural mechanical equipment, including fans. Fans assigned to a seismic design category (SDC) of C through F and to an Importance Factor of 1.5 (Ip=1.5), shall be seismic certified to comply with the 2009 IBC and OSHPD. To best encompass both standards, the equipment shall be tested on a shake table by an accredited laboratory. In addition to referencing the structural plans to determine the seismic design category of a fan, you can use the above steps to calculate the SDC value. Greenheck has achieved seismic certification through shake table testing for worst-case conditions in the United States on a number of its products. The certification process allows for its fans to be used anywhere in the United States.
- 2009 International Building Code
- American Society of Civil Engineers. Minimum Design Loads for Buildings and Other Structures
Table 1-1 Occupancy Category of Buildings and Other Structures for Flood, Wind, Snow, Earthquake, and Ice Loads
|Nature of Occupancy||Occupancy Category|
|Buildings 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
|All buildings and other structures except those listed in Occupancy Categories I, III, and IV||II|
|Buildings and other structures that represent a substantial hazard to human life in the event of failure, including, but not limited to:
• Buildings and other structures where more than 300 people congregate in one area
• Buildings and other structures with day care facilities with a capacity greater than 150
• Buildings and other structures with elementary school or secondary school facilities with a capacity greater than 250
• Buildings and other structures with a capacity greater than 500 for colleges or adult education facilities
• Health care facilities with a capacity of 50 or more resident patients, but not having surgery or emergency treatment facilities
• Jails and detention facilities
Buildings and other structures, not included in Occupancy Category IV, with potential to cause a substantial economic impact and/or mass disruption of day-to-day civilian life in the event of failure, including, but not limited to:
• Power generation stations
• Water treatment facilities
• Sewage treatment facilities
• Telecommunication centers
Buildings and other structures not included in Occupancy Category IV (including, but not limited to, facilities that manufacture, process, handle, store, use, or dispose of such substances as hazardous fuels, hazardous chemicals, hazardous waste, or explosives) containing sufficient quantities of toxic or explosive substances to be dangerous to the public if released.
Buildings and other structures containing toxic or explosive substances shall be eligible for classification as Occupancy Category structures if it can be demonstrated to the satisfaction of the authority having jurisdiction by a hazard assessment as described in Section 1.5.2 that a release of the toxic or explosive substances does not pose a threat to the public.
|Buildings 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, ambulance, 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 in an emergency
• Ancillary structures (including, but not limited to, communication towers, fuel storage tanks, cooling towers, electrical substation structures, fire water storage tanks or other structures housing or supporting water, or other firesuppression material or equipment) required for operation of Occupancy Category IV structures during an emergency
• Aviation control towers, air traffic control centers, and emergency aircraft hangars
• Water storage facilities and pump structures required to maintain water pressure for fire suppression
• Buildings and other structures having critical national defense functions
Buildings and other structures (including, but not limited to, facilities that manufacture, process, handle, store, use, or dispose of such substances as hazardous fuels, hazardous chemicals, or hazardous waste) containing highly toxic substances where the quantity of the material exceeds a threshold quantity established by the authority having jurisdiction.
Buildings and other structures containing highly toxic substances shall be eligible for classification as Occupancy Category II structures if it can be demonstrated to the satisfaction of the authority having jurisdiction by a hazard assessment as described in Section 1.5.2 that a release of the highly toxic substances does not pose a threat to the public. This reduced classification shall not be permitted if the buildings or other structures also function as essential facilities.
|Cogeneration power plants that do not supply power on the national grid shall be designated Occupancy Category II.|