Alternative Support Systems for Cantilever - National Transportation ...

Figure 2-10. Drilled concrete piles for transmission lines
Drilled concrete piles are similar to the current anchor bolt design with the difference being
that the guys are embedded in the cast-in-place foundation instead of anchor bolts (See Figure 2-
10). These foundations handle axial, shear, and biaxial moments by transferring the loading from
the embedded guys to the concrete (9). However, because a transmission line tower is supported
by multiple legs, minimal torsional forces are present in each drilled concrete pile. Even the H-
structures and single pole structures do not introduce much torsional force into the foundation
because there is not a sufficient moment arm to produce significant torsional force. Figure 2-11
demonstrates the typical structural configurations of a lattice tower, H-structure, and single pole
structure as well as a cantilever sign/signal structure (9).
Prestressed and grouted soil anchors are typically not suitable to handle torsional load. As
described in the Institute for Electrical and Electronics Engineers (IEEE) Guide for Transmission
Structure Foundation and Testing, anchors are primarily used to provide resistance to tensile
forces (9). Prestressed anchors are typically expensive and should not be used in soils with time
dependent compressibility (9). These factors make them typically unsuitable to use for cantilever
sign/signal structures. See Figure 2-12 and Figure 2-13 for prestressed and grouted soil anchor
configurations, respectively.
Battered Shaft
Bell
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Straight Shaft