If the Shoe Fits: Design of 765-kV Tower Base Plates

American Electric Power (AEP) recently developed base shoe and standoff anchor bolt designs for their 765-kV lattice tower family. A review of publications from the American Society of Civil Engineers (ASCE), American Institute of Steel Construction (AISC), and American Association of State Highway and Transportation Officials (AASHTO) produced a variety of alternate approaches available for undertaking this design. These included the selection of an effective bend line length, considerations for anchor bolt flexure, and methods for calculating the required anchor bolt area for combined loads. Anchor bolt flexure was included in the final design approach, even though the standoff distance between the concrete and base plate was kept below the two-diameter limit. Finite element analysis used to refine the design approach revealed that assuming a rigid base plate for calculating anchor bolt forces was not always accurate, and that additional design rules for anchor bolt location and minimum base plate and stiffener thickness are required for this assumption to be valid. This paper presents the final design methodology selected to achieve a balance between economy and reliability. It uses a formulation that is consistent with current approaches, and incorporates the findings of the finite element analysis and full-scale installations.