Transmission And Substation Foundations - Technical Design Manual (TD06088E)

The required average minimum installation torque (T) is:

T = (T ug x FS) / K t

Equation 7-1

= (24,400 x 2.0) / 10 = 4,900 ft-lbs

where: K t = Empirical torque factor = 10 (default value for Type SS5 series) T = 4,900 ft-lbs is less than the rated torque (5,500 ft-lbs) of the Type SS5 series. (OK). Lower Guywire Helical Anchor The HeliCAP ® summary report for the lower guywire helical anchor is shown in Figure 8-21. This report provides the following information: • Helical Anchor: SS5 (1.5” square shaft, 5500 ft-lbs torque rating, 70 kips ultimate tension rating) • Lead Section: 4 helix (8”-10”-12”-14”) • Installation Angle: 39° • Datum Depth (depth below grade where installation starts): 0 ft • Length: 25 ft (along the shaft at the 39° installation angle) • Recommended Ultimate Capacity (R uc ): 26.6t (kips tension) The Factor of Safety for this tension anchor is R uc / T ug = 26.6 / 12.5 = 2.12 > 2 (OK) Use this helical anchor at each of three lower guywire anchor locations per tower. = Empirical torque factor = 10 (default value for Type SS5 series) T = 2,500 ft-lbs is less than the rated torque (5,500 ft-lbs) of the Type SS5 series. (OK). Helical Pile Given: • Compression Load = 68.0 k • Shear Load = 0.3 k Assume three helical piles installed at 120° intervals in plan view with each pile battered away from vertical at a 10° angle: 68/3 piles = 22.67k ultimate/pile element. Assume entire shear (0.3 k) is taken by one battered pile. Therefore, the resultant axial load (DL) to a battered pile is: DL = (22.67 2 + 0.3 2 ) 0.5 = 22.7k The HeliCAP ® summary report for the helical piles is shown in Figure 8-22. This report provides the following information: • Helical Pile: SS175 (1.75” square shaft, 10,500 ft-lbs torque rating, 100 kips ultimate tension rating) • Lead Section: 4 helix (8”-10”-12”-14”) T = (T lg x FS) / K t Equation 7-2 = (12,500 x 2.0) / 10 = 2,500 ft-lbs where: K t

DESIGN EXAMPLES

• Installation Angle: 80° below horizontal (10° away from vertical) • Datum Depth: (depth below grade where installation starts): 0 ft • Length: 34 ft (along the shaft at the 80° installation angle) • Recommended Ultimate Capacity (R uc ): 50.7c (kips compression)

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