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INSTRUCTORS:
Greg C. Parent P.E., S.E., M.ASCE
Thomas Mara, PhD, P.E., M.ASCE
Josh Sebolt, PE, F.SEI
Michaela Nickell, PE
Jean-Pierre Marais
David Folk
Purpose and Background
These presentations were recorded at the Electrical Transmission & Substation Structures Conference 2025.
Load Categories and Associated MRIs for Overhead Power Line Structures (22 minutes)
This presentation introduces the new ASCE Loading Standard 84 for structures supporting overhead power lines. It explains how the industry is transitioning from deterministic to probabilistic load approaches, ensuring risk-consistent design across different regions. Attendees will learn about mean recurrence intervals (MRIs) for wind and ice loads and how probabilistic maps are developed from historical climatic data. Greg Parent discusses how various load factors, such as those from NESC Rule 250B, compare to MRI-based loads, and how different load categories (1–3) are applied depending on voltage level and structure criticality. The presentation closes with comparisons between ASCE 84 and ASCE 7 to show how the new standard aligns with broader structural reliability concepts.
High Intensity Winds on Overhead Power Line Structures: A New Approach and Case Studies (21 minutes)
This session explores “high-intensity winds” (HIWs), such as downbursts and convective straight-line winds, which can cause localized yet severe damage to overhead power line systems. Dr. Marra outlines a rational, risk-based method to incorporate these wind events into design practice under the new ASCE standard. The presentation discusses regional risk mapping based on thunderstorm occurrence, adjustments to wind load parameters, and considerations for wind correlation and gust structure. Case studies from across the United States illustrate the varying impacts of these winds on lattice, wood, and tubular structures. Participants will come away understanding how to include convective wind events in design without over-conservatism, balancing safety and practicality.
My Insulator Moved, Where Is my Longitudinal Load? (21 minutes)
This engaging presentation breaks down the mechanics of longitudinal loads in transmission structures and the role of “slack” and insulator swing in load development. Through relatable visuals and practical examples, the presenters show how small changes in span length, tension, or structure flexibility can greatly influence load behavior. Attendees will learn why understanding wire tension, sag, and slack relationships is vital, even in an era of advanced design software. The discussion highlights how modeling decisions—such as allowing or restricting insulator swing, affect structural design outcomes. The session encourages engineers to interpret and verify what their modeling tools compute, ensuring informed and reliable design decisions.
Improved Determination of Longitudinal Security Loads (21 minutes)
EPRI researchers present their latest findings on the dynamic behavior of transmission lines during broken wire and cascading failure events. Using full-scale tests and finite element modeling, the team analyzed parameters such as conductor weight, span length, rupture distance, insulator length, and structure stiffness to develop a more accurate predictive algorithm for longitudinal security loads. The session distinguishes between “broken wire” and “anti-cascading” load cases and shows how dynamic load factors can vary from 0.6 to over 2.2 times the installed tension. The findings guide engineers toward more realistic, performance-based load cases that enhance structural resilience while avoiding unnecessary conservatism.
Benefits and Learning Outcomes
Upon completion of this course, you will be able to:
- Describe how the ASCE Loading Standard 84 uses probabilistic loads and MRIs to establish risk-consistent design criteria for overhead power line structures.
- Explain how high-intensity winds differ from standard design wind loads and how they are incorporated into the new ASCE loading framework.
- Identify how slack, span length, and insulator movement influence longitudinal load behavior in overhead line structures.
- Discuss how empirical testing and modeling improve the determination of dynamic longitudinal security loads for overhead line design.
Assessment of Learning Outcomes
Students' achievement of the learning outcomes will be assessed via a short post-test assessment (true-false, multiple choice, and/or fill in the blank questions).
Who Should Attend?
- Utility Engineers
- Structural Engineers
- Consulting Engineers
- Contractors
- Suppliers & Manufacturers
- Researchers & Educators
How to Earn Your CEUs/PDHs and Receive Your Certificate of Completion
To receive your certificate of completion, you will need to complete a short post-test and receive a passing score of 70% or higher within 1 year of purchasing the course.
How do I convert CEUs to PDHs?
1.0 CEU = 10 PDHs [Example: 0.1 CEU = 1 PDH]