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APPENDIX 2F
MODEL SPECIFICATIONS
Chapter 2
Helical Foundation Systems
3.1.4 Design Loads: A generic and ambiguous term used to describe any load used in design.
It is not specific to factored or unfactored loads or any particular design methodology.
It is a term; therefore, that should be avoided when specifying load requirements. FSI
recommends using the term service load, nominal load or factored load, as described
herein, where applicable.
3.1.5 Design Strength: A term used in structural design which is defined as the product of the
nominal strength and the applicable resistance factor. An equivalent term typically used
in geotechnical design is, also sometimes referred to as factored resistance (Load and
Resistance Factor Design).
3.1.6 Extension Section: Helical pile shaft sections connected to the lead section or other
extension sections to advance the helix plates to the required bearing depth. Plain
extensions (without helix plates) or helical extensions (with one or more helix plates)
may be used depending upon soil conditions or project requirements.
3.1.7 Factor of Safety: The ratio of the ultimate pile capacity or nominal resistance (strength)
to the nominal or service load used in the design of any helical pile component or
interface (Allowable Stress Design).
3.1.8 Factored Load: The product of a nominal load and an applicable load factor (Load and
Resistance Factor Design).
3.1.9 Factored Resistance: The product of a nominal resistance and an applicable resistance
factor (Load and Resistance and Factor Design).
3.1.10 Geotechnical Capacity: The maximum load or the load at a specified limit state, that can
be resisted through the piles interaction with the bearing soils (see also Ultimate Pile
Capacity).
3.1.11 Helical Pile: Consists of a central steel shaft with one or more helix-shaped bearing
plates and a load transfer device (bracket) that allows attachment to structures. Helical
piles are installed into the ground by application of torque and axial compressive force
(“crowd”).
3.1.12 Helix (Helical) Plate: Generally round steel plate formed into a helical spiral and welded
to the central steel shaft. When rotated in the ground, the helix shape provides thrust
along the pile’s longitudinal axis thus aiding in pile installation. The plate transfers axial
load to the soil through bearing.
3.1.13 Helix Pitch: The distance measured along the axis of the shaft between the leading and
trailing edges of the helix plate.
3.1.14 Lead Section: The first helical pile shaft component installed into the soil. It consists of
one or more helical plates welded to a central steel shaft.
3.1.15 Limit State: A condition beyond which a helical pile component or interface becomes unfit
for service and is judged to no longer be useful for its intended function (serviceability
limit state) or to be unsafe (ultimate limit state (strength)).
3.1.16 Load and Resistance Factor Design: A structural and geotechnical design methodology
that states that the Factored Resistance (Design Strength) must be greater than or equal
to the summation of the applied factored loads.
