Transmission And Substation Foundations - Technical Design Manual

SECTION 7: DESIGN EXAMPLES Design Example 14 Monopole Foundation with Steel Grillage and RS5500 Helical Piles Provided Design Loads (on entire grillage)

stage is an iterative solution using the design loads from the monopole with the quantity and coordinates of helical piles with Ensoft’s GROUP software. Experience provides best practices to determine the number and coordinates of the helical piles. With these inputs, GROUP software will determine the actual loads on each pile. A model of the grillage can then be developed and analyzed with finite-element analysis (FEA) software to help size structural members within the grillage. With the loads applied to each pile obtained from the GROUP software, Chance® HeliCAP® software is used to design the helical piles. The following information is by no means a complete tutorial on the use of GROUP or HeliCAP software but is provided as an example of this type of solution.

Fx = 34.06 kip (axial) Fy = 49.41 kip (shear) Mz = -35574 kip∙in (moment) Reveal Height: 5.33 feet

These loads require a moment foundation that incorporates multiple helical piles into a steel grillage. Grillages that are mostly moment foundations will be limited in size by what can be transported to the job site. Moment foundations will also have helical piles installed at 5 degrees from vertical. This angle allows the piles to be spaced far enough apart at depth that the helices behave independently. The 5-degree angle also provides a better response to shear load. The first

Group software Inputs

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