Steel Pole Design

During Factory Acceptance Testing (FAT) of 69kV steel poles in China 2019.
Photo Courtesy of Poleman Energy Systems Corp and Yixing Futao Metal Components Co., Ltd.

Steel poles are receiving increased attention from utilities as they look for alternatives to the wood poles they have used in the past. The advantages of steel poles include:

  1. Design flexibility
  2. High strength
  3. Relatively light weight
  4. Long life
  5. Factory pre-drilling
  6. Reduced maintenance costs
  7. Predictability and enhanced reliability
  8. No damage due to woodpeckers, pole rot, or fires
  9. Aesthetically pleasing
  10. Manufactured from recycled steel
  11. Superior Life Cycle Cost

This page will cover the basic concepts and example calculations of steel pole design based on my experience. Optimization of the design using PLS-POLE will be presented.

Note that this is still work in progress. Once articles are completed, it will be linked below.

1. Loading Analysis

Loading Analysis Based on NESC 2017

Loading Analysis Based on ASCE

These are forces that the pole may be subjected to. These are classified into based on their direction:

  1. Vertical Loads
  2. Transverse Loads
  3. Longitudinal Load

2. Calculation of Tip Load

Tip load is a single equivalent force applied 2 feet below the tip of the pole. Its groundline moment is equal to the summation of all ground line moments of the forces applied to the pole.

3. Design Factors/Parameters

Design factors include the following:

  • Cross-section geometry (examples: octagonal, hexagonal, dodecagonal, etc.)
  • Length of segment or shaft
  • Number of segments or shaft
  • Slip Joint Length
  • Market availability of steel thicknesses and yield strengths
  • Bottom and Top Diameters
  • Installation ( anchor bolts or direct burial )
  • Allowable Overload Capacity Factor or simply Safety Factor
  • Limits in deflection
  • Others

4. Design Optimization Using PLS-Pole Software

PLS-POLE has the capacity to directly calculate the usage that will determine if the design passed or failed. Also, optimization can be easily carried out. PLS-POLE will try different combinations of (1) available thicknesses and (2) top and bottom diameters.

The optimized pole design is the one with the lightest weight. Weight is directly related to the cost of steel poles.

5. How Steel Poles are Made

The step-by-step process of manufacturing steel poles will be presented here.

6. Types of Surface Protection

Corrosion protection and finish are important considerations when designing a line using steel structures. The most commonly used corrosion protection and finish options used for steel poles include (1) paint and coating systems, (2) galvanizing, (3) weathering steel, and (4) metalizing.

7. Full-Scale Load Testing

Based on my experience, I will present the process in full-scale testing as well as the common Factory Acceptance Criteria.