Heel or Toe? The Transmission Engineer’s Guide to Single Angles in Flexure

The analysis and design of new and existing latticed steel structures are essential engineering tasks for transmission line projects. Optimization of the structural system to meet the expected weather-related and construction loads is especially important in today’s very competitive environment. Engineers must efficiently perform thorough analyses, both productively and accurately, using methods and tool sets currently available. One design responsibility required of the structural engineer is to check the flexural capacity of redundant and other structural members that are climbing-accessible. While performing this task for multiple projects, AEP studied the current methods for calculating the flexural capacity of equal and unequal single angle sections. This study included comparing simple elastic beam theory to alternate methods provided by AISC and ASCE-10, which consider lateral torsional buckling. Interpreting these resources for computations related to specific angle leg orientation and limit states such as yielding, lateral torsional buckling, and local leg buckling can be laborious. So what’s best-“heel” or “toe”? And how does “equal” leg or “unequal” leg impact the flexural capacity? This paper will convey the results of the flexural capacity comparison, along with providing guidance for applying these recommendations to latticed transmission structures.