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Helical Piles Approved for Use in Seismic Zones A-F in Revised AC358
by Bill Bonekemper
Earlier in June the International Code Council Evaluation Services (ICC-ES) voted to include seismic design categories D, E, and F in their acceptance criteria (AC 358) for helical pile manufacturers. Previous to this, helical piles were not pre-approved for new construction applications in those high seismic regions. This omission in the acceptance criteria led a majority of building officials to incorrectly assume that helical piles were not appropriate in those applications, and that lack of understanding has prevented the use of helical piles for new construction in regions with some of the highest levels of seismic activity in the U.S. including Los Angeles, San Diego and San Francisco just to name a few.
This limitation in the criteria has been in place since the very first version of AC358 was published in 2007. Our industry has been trying for thirteen years to convince ICC officials that helical piles are a safe and effective deep foundation solution for use in these high seismic activity regions. Finally, the years of commitment and hard work will now provide the industry with increased opportunities in these potentially lucrative markets.
“ICC-ES engineers were very helpful and worked diligently to assist the Ad Hoc Committee of Helical Pile Manufacturers with developing the parameters and language for the changes to AC358”, said CTL Thompson engineer, Wayne Thompson. CTL Thompson coordinated the efforts of the committee to submit the desired changes and worked with ICC-ES engineers to reach revisions that both parties could agree upon. The Ad Hoc committee members included:
- Cantsink (ESR-1559)
- GoliathTech Inc (ESR-3726)
- Grip-Tite Manufacturing Co.
- Hubbell Power Systems, Inc (ESR-2794)
- Ideal Manufacturing (ESR-3750)
- Maclean Power Systems (ESR-3032)
- Magnum Piering (ESR-2997)
- PierTech Systems (ESR-3969
- Ram Jack Manufacturing (ESR-1854)
- Supportworks, Inc (ESR-3074)
- Techno Metal Post (Techno-Pieux Inc) (ESR-3418)
Addition of International Residential Code
Another notable inclusion in this release of AC358 is the new Appendix A, which specifically allows for the use of helical piles under the International Residential Code. Prior to this, helical piles were used under the direction of the International Building Code. However, some building officials struggled with allowing helical piles in residential applications because of their interpretations of the various codes. One of the concessions in Appendix A is the raising of the factor of safety from 2.0 to 2.5 when there is no geotechnical information available for the project. This safety factor is only applicable in Appendix A, which is limited to residential applications. Although there were concerns about this revision and the impact it will have on material costs on smaller projects, the revision was ultimately agreed upon.