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p 31
Chapter 2
Helical Foundation Systems
CHAPTER 2
HELICAL FOUNDATION SYSTEMS
component of the tieback force will increase
with increasing installation angle, provided the
installed tieback force, T
R
, is held constant.
The vertical force on the wall generated by the
tieback may be calculated by:
T
CV
= T
CH
tanα
or
T
CV
= T
R
sinα
Where,
T
R
= Installed capacity of tieback at angle
α
α
= Angle of tieback installation measured
downward from horizontal
T
CH
= Calculated horizontal tieback capacity
determined from wall analysis
T
CV
= Calculated vertical load on the wall due
to tieback installation
Angled or beveled washers are recommended
at the tieback-to-bearing plate interface to
more uniformly transfer the tension loads.
Beveled washers are especially critical when
the tiebacks are pre-tensioned with a torque
wrench. Uniform bearing of the nut to the
beveled washer to the bearing plate provides
a more accurate reading of resistance and
torque, which in turn is a more accurate
determination of axial force on the tieback.
The design of the tieback system should
consider the structural details of the wall, the
wall reinforcing, present wall condition, and the
effect of any penetrations necessary to install
the tiebacks. Cantilevered concrete retaining
Figure 2.8.1.b
Vector mechanics of tieback forces
Figure 2.8.1.a
Helical tieback
design considerations