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IBC Compliance for Seismic and Wind
Baltimore Aircoil Company
What is the International Building Code®?
The International Building Code® (IBC) is a model code developed by the International
Code Council (ICC)® and available for adoption by jurisdictions internationally.Various
editions of the IBC are the basis for nearly all US state and local building codes. Once
adopted, the IBC provisions become enforceable regulations.
The IBC includes structural design requirements for buildings and structures. Cooling
towers are parts of buildings and other structure types, and as such, the structural
design falls within the scope of the IBC.The design provisions contain requirements
for towers subjected to wind and seismic loads. For these design requirements, the
IBC refers extensively to ASCE/SEI 7, the consensus standard published by the
American Society of Civil Engineers.
Seismic Design Requirements for Cooling Towers
Several key variables are provided in the project design documents to determine the
seismic design requirements for factory assembled cooling towers.
Seismic Design Category (SDC) – A building classification ranging from A to F
(low to high) that is based on the Occupancy Category and the severity of the design
ground motion at a building site.
Occupancy Category – A classification ranging from I to IV for buildings and other
structures based on the level of occupancy and the nature of use. Category I buildings
represent a low hazard to life in the event of failure. Category IV buildings are
considered essential facilities and include hospitals and emergency response centers.
Component Importance Factor (Ip) – All cooling towers are assigned a
component factor of either 1.0 or 1.5. Towers needed for continued operation of an
essential facility (Occupancy Category IV), or required to function after an earthquake
are assigned an Ip of 1.5. Air conditioning is needed for operation of most essential
facilities, meaning cooling tower operation after an event will be required.
Design Spectral Acceleration (SDS) – The design spectral acceleration is dependent
on soil characteristics and maximum ground shaking intensity at a given location.
The ground shaking intensity can be obtained from probabilistic seismic hazard maps
provided in the IBC or by using software tools provided by the ICC® or the U. S.
Geological Survey. The specific acceleration that cooling towers are required to resist
is the design spectral acceleration at short period, SDS.
Tower Attachment Location – The height of the cooling tower structure
within a building affects the design seismic acceleration.
QUALIFICATION METHODS
Manufacturers must provide certification to confirm that their towers have been
qualified by at least one of the following methods:
Testing – A full-scale cooling tower is subjected to a simulated seismic event in a test
laboratory.Typically, the test method is a shake-table test conducted in accordance with
a code-recognized test procedure, such as the AC156.
Analysis – A cooling tower is analyzed to determine if it can resist the code-prescribed,
seismic design forces.Typically, an analysis of this type focuses on the anchorage only or
on the anchorage and main structural components.The analysis usually does not address
the non-structural portions of a tower that affect functionality and cannot be used for
cooling towers with an importance factor of 1.5.
Experience Data – A cooling tower is qualified using actual earthquake performance
data collected in accordance with a nationally recognized procedure.Though this method
is used to some extent in the nuclear power industry, its use in commercial mechanical
equipment applications is extremely limited.
The methods are not equally suitable for verification of all aspects of cooling tower
seismic performance.The suitability of each method is summarized in the following table.
Suitability of Qualification Methods for Cooling Towers
Qualification Method
Characteristic
Anchorage integrity
Structural integrity
Non-structural
component integrity
Functionality
Testing
Anaylsis
4
4
4
4
4
4
Experience Data
Seismic Hazard Map
Highest
Hazard
64+
48-64
32-48
%g
16-32
8-16
4-8
0-4
Lowest
Hazard
BAC’S DESIGN & QUALIFICATION PHILOSOPHY
BAC has developed and implemented a
comprehensive approach for qualifying all
new products for seismic and wind loads,
using multiple methods. BAC’s comprehensive
seismic and wind load design and qualification
approach includes:
Testing:
• Full-size towers are tested at independent
test laboratories in accordance with AC156
• Tests are conducted on tri-axial shake tables
Reliability:
• Functional tests are conducted before and
after testing to verify functionality and certify
towers for use in applications where the
component importance factor is 1.5
Insist on shake table
• Wind loading tests
Analysis:
• Products are analyzed using the latestgeneration, three-dimensional finite element
analysis (FEA) software packages
• Computer models are validated using
full-scale test data as described above
• Computer models are used to optimize
tower design for various loading conditions
and product configurations
Certification:
• Certificate of Seismic and Wind
Compliance provided on every order
testing based verification
of operability after an
event. According to
ASCE/SEI 7 (American
Society of Civil
Engineers), which is the
basis for much of the
IBC code, analysis only
cannot be used to verify
functionality.
• Analysis and testing conducted under the
supervision of an independently registered
Professional Engineer
Baltimore
Baltimore Aircoil
Aircoil Company
Company
Insist on IBC Compliant Construction
for your next evaporative cooling equipment project.
Contact your local BAC Representative for more information
or contact:
Baltimore Aircoil Company
P.O. Box 7322, Baltimore, MD 21227 USA
Phone: 410.799.6200 • Fax: 410.799.6416
Web: www.BaltimoreAircoil.com
Baltimore Aircoil Company
...because temperature matters™
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