Transmission And Substation Foundations - Technical Design Manual

SECTION 7: DESIGN EXAMPLES

Design Example 4

Traditional Monopole Helical Foundation Design Purpose This design example is intended to assist with the design of a small Monopole Structure. It will go through the basic design using hand calculations/L-pile. GROUP® can also be used for this eample. The leg of the Monopole Structure will be supported by a concrete pile cap. This type of structure will generally have compression, shear, and moment loads that will need to be calculated or provided by the tower manufacturer After the loads for the structure have been determined, it is possible to design the piles. For this example the loading is as follows:

Loads • Compression: 50 kip • Shear: 40 kip • Moment: 200 ft-kip

Soils • Layers

• 0-15 ft: 1000 psf clay • 15-30 ft: 1500 psf clay • >30ft: 2000 psf clay • Water Table: Surface (0 ft)

Helicap Printout Figure 7-15

Pile Capacity: The first step in the design is to look at the soil profile and estimate a maximum ultimate axial capacity that can be attained. This is done by putting the boring into Helicap® and selecting the product line and helix configuration you wish to use. This value is generally the maximum capacity for the pile (the axial capacities of shafts can be found in the Drawings and Ratings section), but can be lower if the soils are not very good.

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