MATERIALS - Prestressed Concrete Transmission Pole Structures - page 25

Table 3-1. Material Properties for Prestressing Steel.

Nominal
diameter of
stand (in)

Breaking
strength of
stand (min lb)

Nominal
steel area of
stand (in 2 )

Nominal weight
of stands (lb
per 1,000 ft)

Minimum
Load at 1%
extension (lb)

Seven-Wire Strand GRADE 250, f pu = 250 ksi

1/4 (0.250) 9,000 0.036 122 7,650

5/16 (0.313) 14,500 0.058 197 12,300

3/8 (0.375) 20,000 0.080 272 17,000

7/16 (0.438) 27,000 0.108 367 23,000

1/2 (0.500) 36,000 0.144 490 30,600

3/5 (0.600) 54,000 0.216 737 45,900

Seven-Wire Strand GRADE 270, f pu = 270 ksi

3/8 (0.375) 23,000 0.085 290 19,550

7/16 (0.438) 31,000 0.115 390 26,350

1/2 (0.500) 41,300 0.153 520 35,100

3/5 (0.600) 58,600 0.217 740 49,800

Modulus of Elasticity = 27,500,000 to 28,500,000 psi

Source: Table courtesy of University of Alabama-Birmingham. Reproduced with
permission.

low relaxation and stress relieved seven-wire strand (ASTM [2010b],
grade 250 or 270). The steel is placed inside the form and stressed to the
required tension.
Strand is also available with coatings, such as epoxy, in accordance with
ASTM A882 (ASTM 2010a).
Galvanizing may also be used to provide protection in extremely cor-
rosive environments. However, the galvanizing process may result in the
prestressing steel having lower breaking strengths and a slightly lower
modulus of elasticity.
Increased development length should be considered for both epoxy
coated and galvanized strands because of the reduction in bond strength.
Mechanical properties of commonly used prestressing steel are pre-
sented in Table 3-1. Load-elongation curve for a strand is limited to 1%
elongation as shown in Fig. 3-2.

Supplemental Longitudinal Steel Reinforcement

Additional nonprestressed longitudinal steel reinforcement may be needed
at points along the length of the pole to increase the ultimate moment