DESIGN - Prestressed Concrete Transmission Pole Structures - page 33

• specifi ed loading conditions (including load factors and applicable
code requirements);
• foundation behavior (expected translations and rotations);
• height and geometric confi guration;
• defl ection limitations, if applicable;
• other limitations, such as diameter restrictions and length and
weight restrictions; and
• special material requirements affecting pole durability that can be
specifi ed (i.e., unique environmental conditions), if applicable.
Loading may include wind pressure distributed over the projected area
of the pole and arms, or loading may be represented by forces applied to
the attachment points or loads translated to the pole via member reac-
tions. When translating forces, it may be important that some accommo-
dation of the geometric displacement of the members be considered. This
is especially true when multipart insulators, hinged braces, and arms are
specifi ed.
It is preferable that when forces are provided at the attachment points,
the loads be provided in the form of load trees, using a single orthogonal
coordinate system as shown in Fig. 4-2.
Foundation and Boundary Conditions
Typically, concrete poles are designed as direct embedded structures.
However, socketed piles and base plated foundations are feasible and
have been used (see Fig. 4-3).
Socketed pile foundations are typically multisided steel or cylinder
concrete piles. The socketed joint (the length of the pile that engages the
pole) is a relatively short length, typically 8 ft. to 10 ft. to fully develop
the prestress strand.
It should be noted that cylinder concrete piles are commonly used for
bridge supports, wherein they are used in pairs or clusters with pile caps
poured in place, thus strengthening the open end that is in contact with
the imposed loads. However, when used singly as a socketed pole support,
the pile becomes an extension of the pole itself and, as such, must transfer
the full reactions coming into the cylinder from the base of the pole. The
internal resisting moment couple required will produce extremely high
shears that are then imparted to the wall of the concrete cylinder, causing
an elevated hoop stress to be developed in the spiral reinforcement within
the pile. This stress must be accounted for in the design of the concrete
cylinder pile to prevent longitudinal cracks.
Variation in soil conditions will infl uence the type of foundation
selected. Those soil variances also infl uence the degree of fi xity