Analyse By Fea of Helical Piles and Grillages - Case Study From Brazilian Transmission Lines-Paper

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The paper evaluates steel grillages supported by helical piles as an alternative to concrete-block foundations for transmission towers in Brazil. The case study concerns an approximately 850-km, 500-kV transmission line between Manaus and Boa Vista.<br /><br />Finite element analyses examine grillages connected to groups of three, four, five, and seven 8⅝-inch-diameter helical piles, with and without stiffeners. The study considers structural response—including shape, nodal displacement, and von Mises stress—and highlights the importance of accounting for soil-support stiffness and soil–structure interaction. It also discusses the behavior of pile components and connections under tension, compression, torsion, and construction-related eccentricities. These analyses are intended to help identify quality-control and design improvements in manufacturing, assembly, and installation.<br /><br />The authors emphasize that transmission-line foundation design involves significant uncertainty, arising from variable soil conditions, limited site investigations and full-scale tests, and imperfect prediction models. Finite element analysis can support a more detailed assessment of structural stresses and deformations and help reduce uncertainty.<br /><br />A cost comparison found steel grillages to be 23% less expensive than concrete blocks. The authors conclude that the proposed grillage-and-helical-pile systems are technically and economically viable, while offering shorter construction schedules, lower indirect costs, and environmental benefits. They also suggest that better knowledge of steel stresses may enable more reliable numerical analysis and reduce safety margins associated with uncertainty.

Keywords

steel grillages

helical piles

transmission towers

finite element analysis

soil-structure interaction

von Mises stress

foundation design

structural response

Brazil transmission line

cost comparison