Describe what spiral is doing here as per PCI std 142Eriksson Pile uses PCI BDM Chapter 20 and PCI Standard 142, as well as, AASHTO LRFD 9th Edition when determining the minimum requirements for the enclosing spiral or hoops. A given pile is divided into two zones, the ductile zone and the non-ductile zone. Both PCI and AASHTO specify different requirements based on what zone of the pile the user is in.
The Ductile Regions for a given pile are defined under:
PCI BDM Section 20.5.4.2.5
AASHTO LRFD
Article 5.11.3.2.3
Article 5.11.4.5.2
Article 5.11.4.5.5
Transverse reinforcement is divided into 3 zones which vary from PCI BDM to AASHTO LRFD. PCI BDM defines these zones as Ordinary, Intermediate, and Special. AASHTO LRFD defines these zones as “Seismic Zone 1”, “Seismic Zone 2”, and “Seismic Zones 3 and 4”.
AASHTO
AASHTO is considered to be overly conservative as stated by in seismic loads the PCI BDM Chapter 20, below is a brief breakdown of the zones found in the AASHTO code.
Seismic Zone 1 [LRFD Art. 5.12.9.4.3]
Seismic Zone 1 requires no special consideration for seismic forces and only requires the prescriptive reinforcement as shown in Figure 1 or Figure 2 depending on the pile width.
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Seismic Zone 2 [LRFD Art. 5.11.3.2.3]
Seismic Zone 2 requires the full length of the prestressing strands be enclosed in steel spirals or equivalent ties. The
Seismic Zone 3 & 4 [LRFD Art. 5.11.4.5.5]
Seismic Zone 3 & 4 requires the full length of the prestressing strands be enclosed in steel spirals or equivalent ties. In addition minimum volumetric ratios are defined at:
LRFD Eq. 5.6.4.6-1
LRFD Eq. 5.11.4.1.4-1
LRFD Eq. 5.11.4.1.4-2
LRFD Eq. 5.11.4.1.4-3
PCI
PCI defines their zones to be more aligned with ACI 318-19 and the 2018 IBC. The equations are based on ductility considerations which, according to the PCI BDM, are more appropriate for use with prestress piles in seismic regions.
Ordinary Concrete Piles [PCI Std. 142 4.7.3]
Ordinary Concrete Piles are a pile designation used for seismic design of piles with an expected curvature ductility capacity of at least 6. Ordinary Concrete Piles require no special consideration for seismic forces and only requires the prescriptive reinforcement as shown in Figure 1 or Figure 2 depending on the pile width.
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Intermediate Concrete Piles [PCI Std. 142 4.7.4.2]
Intermediate Concrete Piles are a pile designation used for seismic design of piles with an expected curvature ductility capacity of at least 12.
Special Concrete Piles [PCI Std. 142 4.7.4.3]
Special Concrete Piles are a pile designation used for seismic design of piles with an expected curvature ductility capacity of at least 18.