Advanced Analysis on Transmission Structures

How have we designed transmission structures that can withstand hurricanes, broken conductors, brutal winters and other extreme loads? The Finite Element method has allowed utility engineers to take the next step beyond simple hand calculations to design today’s modern structures. Though this method was originally developed in the 1950’s, computing advancements have enabled what is now known as Finite Element Analysis, or FEA.

FEA started about 40 years ago as a software called NASTRAN which was used by NASA to address the complex structural analysis problems within aerospace and civil engineering. FEA is a programmed method which analyzes elements under applied loads and provides structural design information critical for material member sizing and selection. This has led to increasing reliance on FEA design software in the industry, however, engineers still need to fully understand the fundamentals of structural analysis to be able to verify their results.

For transmission structures, FEA can be used to determine the highest wind speed a structure can theoretically withstand before failure. This software, used in conjunction with the National Electrical Safety Code (NESC) and Design of Latticed Steel Transmission Structures (ASCE 10-15), allows engineers to evaluate towers and poles with more clarity, optimize steel members, predict future trends, and quantify risk and resiliency. To implement this effectively, the design process requires a full layout of the structure including all member sizes, applied load combinations, and other pertinent geometrical constraints (Figure 1). FEA allows the engineer to immediately visualize how the model will deform and displays how loads are distributed throughout the structure.

Often it can be more valuable to model smaller portions of a structure to develop an understanding of how a specific part will react to external loads. For example, modeling software can help design a new temporary support and then the design is issued to the field to use for post leg restoration (Figure 2).

High-level software programs like FEA can solve very advanced structure problems as well as dissect them into finer, more detailed sections than ever before. These programs will continue to evolve and result in future advancements in predicting how structures will respond to catastrophic loads, and how we can further optimize structure restorations.