Civil-structural engineers like to do things by the book. They admittedly tend to be techno geeks who prefer to have automobile owner’s manuals on hand, whether or not they service their own vehicles. They prefer to follow the detailed prescription of a cooking recipe, lest they add too much of an ingredient and spoil a perfectly good meal. In the electrical transmission structures industry, manuals of practice (MoP) and standards have always been important tools for transmission line design and construction. The new renaissance of line development in the U.S. has resulted in a critical need for new and updated MoP and standards.
Whether to provide guidance to new engineers entering the industry or honing seasoned engineers’ expertise, the MoP and standards provide direction for consistent structural designs, which result in safe, reliable and resilient designs in the industry. The MoP and standards are the owner’s manuals and cookbooks in an electrical transmission structural engineer’s everyday working life.
The American Society of Civil Engineers (ASCE) MoP and standards differ from other codes in the industry. They are developed by task or standards committees comprised of individual ASCE members selected by ASCE to the committees based on their personal qualifications and experience. They are typically licensed professional engineers and do not represent any other group, organization or company. Committees are generally balanced, consisting of individuals working in academia, electrical utilities, manufacturing and design sectors within the industry.
The following ASCE MoP and standards are industry consensus- developed documents currently in the process of being created or revised:
• ASCE-74 Guidelines for Electrical Transmission Line Structural Loading. This MoP provides guidance on the development of structural loading from dynamic impact loads as a result of broken conductor to the effects of high-intensity winds and all the special loadings in between. New wind maps from the National Institute of Standards and Technology, as implemented by ASCE-7-16, are referenced, and a new prestandard is introduced with standard formatting and language for industry discussion.
• ASCE-113 Substation Structure Design Guide. This guide provides direction for all equipment inside the fence, as transmission systems cannot function without the substations. This document delves into issues specific to substations such as short-circuit and seismic loads. This revised document is scheduled to be published in 2016.
• ASCE-104 Recommended Practice for Fiber- Reinforced Polymer Products of Overhead Utility Line Structures. Non-steel, non-wood structure technologies will continue to evolve and improve, resulting in lightweight, highstrength fiber-reinforced polymer materials for the industry. Scheduled to be published in 2016, this revised pre-standard discusses design considerations, criteria and suggested guidelines for performance-based designs.
• ASCE–To Be Determined (TBD) Practice for Wood Pole Structures for Electrical Transmission Lines. This brand-new document, currently being developed, provides design information specific to wood poles. The wind blows and ice accumulates on a transmission line the same as on a distribution line, producing the same load; therefore, this design guide can be used for any wood pole line. This MoP is scheduled to be published in 2017.
• ASCE–TBD Aesthetic Design of Transmission Line Structures. Currently being developed, this new ASCE committee report will attempt to address the aesthetics of transmission structures by providing options that can be used in all structure types. While aesthetics are subjective, certain features can be used to enhance the aesthetics of structures yet meet all applicable loading and functionality. This document is scheduled to be published in 2016.
• ASCE-10 Design of Latticed Steel Transmission Structures. Lattice-steel transmission structures have been used for the past 100 years and are still going strong. The newest version includes guidance on the evaluation of existing towers for upgrades or re-rating, and provides information on redundant member design. ASCE-10-15 is now available.
• ASCE-48 Design of Steel Transmission Pole Structures. Tubular-steel poles have been used for line support structures since the 1960s and are now commonly used throughout North America. This revision incorporates 48 change proposals affecting 68 different sections of the document and is scheduled to be published in 2016.
These efforts reflect the increased interest and activity in the industry and are a sign of a healthy, vibrant transmission line engineering community for years to come.
Michael D. Miller is vice president of engineering at SAE Towers in Houston, Texas, U.S. He is chair of the American Society of Civil Engineers’ Electrical Transmission Structures committee. He is a registered professional engineer.
Editor’s note: Visit www.asce.org/templates/publications-bookdetail. aspx?id=7094 to learn about the standards and MoP.