MATERIALS - Prestressed Concrete Transmission Pole Structures - page 26

Fig. 3-2. Material properties for prestressing steel
Source: Illustration courtesy of University of Alabama at Birmingham.
Reproduced with permission.
capacity. Deformed steel reinforcing bar (ASTM 2012) or nonprestressed
strand (ASTM 2010b) is commonly used and should conform to the appli-
cable ASTM standards. This supplemental longitudinal steel reinforcement
is usually placed at the critical sections only and does not typically extend
throughout the entire length of the pole. Consideration of the strength of the
nonprestressed longitudinal reinforcing steel may be important, because
mild steel will yield at strains much less than prestressed reinforcement. If
deformed steel reinforcing bar is used and the structure undergoes large
defl ection, the pole may have nonrecoverable deformation.
Spiral Reinforcement
Spiral reinforcement surrounding the longitudinal reinforcement
(strands and bars) helps to resist radial stresses caused by the wedging
effect of the strand at release. It also can have a signifi cant role in control-
ling or minimizing cracks attributable to torsion, shear, shrinkage, or
temperature-induced stresses.
The wedging effect from the release of the pretensioning forces causes
tensile stresses at every cut-off strand location throughout the pole. Thus,