Tubular 3D Frames for Long Span Transmission Structures

Some transmission lines require very long span crossings over rivers and other obstacles. The increased height and heavy loading may make lattice towers and tubular H-frames inefficient designs for these structures. This paper presents an innovative tubular 3D frame design as an effective solution for tall, long span transmission structures. The design of tubular 3D frames follows the requirements in ASCE 48 Standard Design of Steel Transmission Pole Structures. The three-dimensional configuration significantly increases the structural capability in resisting heavy longitudinal loads due to broken wire or unbalanced wire tensions. While the overall configuration may appear similar to lattice towers, all main members in this type of frame are tubular sections that provide much higher loading capacities. This paper discusses general structure configuration, geometry optimization to improve design efficiency, typical connection joints, Finite Element Analysis (FEA) for static loadings, and full-scale load testing. Examples of installed tubular 3D frames in operation are presented as well.