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2009 IBC alt. all heights method explained
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7/21/2019 2009 IBC Section 16096 Alternate All-Heights Method
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2009 IBC Section 1609.6: Alternate All-Heights Method cenews.com /article/6551/2009_ibc_section_1609.6__alternate_all_heights_method
June 2009 » Columns
This Code Simple addresses a new provision in the 2009 International Building Code (IBC), which becameavailable in March 2009. One of the most significant revisions to the structural provisions in this edition of the IBC is the introduction of the Alternate All-Heights Method of wind design in Section 1609.6.
By S. K. Ghosh, Ph.D., and Susan Dowty, S.E.
This Code Simple addresses a new provision in the 2009 International Building Code (IBC), which becameavailable in March 2009. One of the most significant revisions to the structural provisions in this edition of the IBC is the introduction of the Alternate All-Heights Method of wind design in Section 1609.6.
The Alternate All-Heights Method is a welcome simplification to the American Society of Civil Engineers’Minimum Design Loads for Buildings and Other Structures’ (ASCE 7) Method 2-Analytical Procedure. Thetitle of this new method implies that it applies to structures of all heights; however, that is not exactly so.The method applies only to structures with height not exceeding 75 feet and the height-to-least-width rationot exceeding 4. Alternatively for a structure to be eligible to be designed by this method, its fundamentalnatural frequency must be no less than 1 Hz, making it a rigid structure.
There is a rather lengthy checklist of other conditions that must be met in order to use this new method.See Table 1 on the opposite page for an explanation of this checklist in order to facilitate the use of thismethod whenever possible.
7/21/2019 2009 IBC Section 16096 Alternate All-Heights Method
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Answers to FAQsOne may question why this new method is in the IBC and not in ASCE 7, especially since the other designmethods (Method 1—Simplified Procedure, Method 2—Analytical Procedure, and Method 3—Wind TunnelProcedure) are found in ASCE 7-05.
The reason for this is really an issue of timing. The 2009 IBC, just like the 2006 IBC, references ASCE 7-05, which does not include this method. The Alternate All-Heights Method was only developed during thelast couple of years and incorporated into the 2009 IBC as a modification to ASCE 7-05, through the ICCcode-development process.
It is expected that the next edition of ASCE 7, scheduled to be published in 2010, will include a simplifiedversion of Method 2 in Chapter 6, and at that time the Alternate All-Heights Method will be deleted from thenext issue of the IBC, which is expected to be the 2012 IBC.
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S.K. Ghosh Associates Inc., is a structural seismic, and code consulting firm located in Palatine, Ill., and Aliso Viejo, Calif. President S.K. Ghosh, Ph.D. , and Susan Dowty, S.E. , are active in the developmentand interpretation of national structural code provisions. They can be contacted at [email protected] [email protected] , respectively, or at www.skghoshassociates.com .
