Transmission And Substation Foundations - Technical Design Manual (TD06088E)

DESIGN EXAMPLE 2 SELF SUPPORT TOWER DESIGN WITH FIXED HEAD GRILLAGE DESIGN SYMBOLS USED IN THIS DESIGN EXAMPLE

T-Z CURVE.......................AXIAL DISPLACEMENT VS LOAD PLOT 7-13 Mp................................................................................. PLASTIC MOMENT 7-14 FS..............................................................................FACTOR OF SAFETY 7-14 K t ........................................................... TORQUE TO CAPACITY RATIO 7-15

Purpose This design example is intended to assist with the design of Self Support Structure foundations using Chance® RS3500.300 Helical Piles and Can Grillages where reveal is required. The basic principles used in this example can be used for any Self Support Structure. In this example, each leg of the Self Support Structure will be supported by a grillage on helical piles. This type of structure will generally have tension, compression, and shear loads that will need to be calculated or provided by the tower manufacturer. Generally all moment loads are transferred to the structure by Tension/Compression force couples (One side has a tension load while the other side is compressed). After the loads for the structure have been determined, it is possible to design the piles. Loads For This Example • Compression: 130 kip • Tension: 100 kip • Shear: • Transverse: 11 kip • Longitudinal: 10 kip Soils • Layers • 0-15ft: 500 psf clay (500 psf is the cohesion of the clay)

DESIGN EXAMPLES

• 15-30ft: 1000 psf clay • >30ft: 2000 psf clay • Water Table: 10 ft below surface • Required Reveal Height: 1 ft.

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