Dynamic Performance Analysis of 110kV Transmission Steel Tube Poles

Literature Overview

This paper by Li Peipeng, Ren Zhigang, Cheng Shuhuai, and Xu Changwu, published in the Journal of Wuhan University of Technology in 2014 (Vol. 36, No. 5, pp. 106–110), presents a comprehensive dynamic performance analysis of 110kV straight-type transmission steel tube poles. Using ANSYS software, the authors conducted modal analysis, spectral analysis, and transient analysis to evaluate vibration characteristics, seismic response, and pulsating wind response. The study also analyses the influence of cross-arms on the dynamic response of the main pole and provides optimisation recommendations.

Structural Configuration

The 110kV transmission steel tube pole is a tall, slender structure subjected to significant dynamic loading from wind, seismic activity, and electromagnetic forces from transmission line oscillations. The structural configuration includes:

Dynamic Analysis Results

Modal Analysis

The modal analysis identifies the natural frequencies and mode shapes of the steel tube pole under various boundary conditions:

The first natural frequency is critically important for seismic design as it determines the dynamic amplification factor under ground motion. A frequency in the range of 0.3–0.6 Hz indicates a flexible structure with significant dynamic amplification potential during earthquakes.

Seismic Response (Spectral Analysis)

The spectral analysis evaluates the pole response to seismic ground motion using response spectrum methods:

• Deformation increases with height, with the maximum displacement at the pole top.
• Stress levels remain relatively low due to the large strength margin of the steel tube section.
• The pole possesses adequate seismic resistance with displacement as the governing design parameter rather than strength.
• The connection between the main pole and cross-arms experiences locally elevated stresses requiring structural reinforcement.

Wind Response (Transient Analysis)

The pulsating wind load analysis considers the stochastic nature of wind:

• The dynamic wind pressure is decomposed into a mean component and a fluctuating component.
• The fluctuating component is characterised by its power spectral density and correlation function.
• The response includes both quasi-static deflection and dynamic amplification.
• Optimisation of cross-arm cross-section, mass distribution, and position can significantly reduce the dynamic response of the main pole.

Key Technical Findings

Connection with Steel Pipe Manufacturing and Welding

The 110kV transmission steel tube pole presents specific manufacturing and welding requirements driven by its dynamic performance demands:

Steel Pipe Fabrication Requirements

Welding Requirements for Pole Assembly

The welding of cross-arms, base plates, and section transitions is critical for the dynamic performance:

1. Base plate welding – The base plate to pole connection is a full-penetration butt weld or a heavily reinforced fillet weld. This joint experiences the maximum bending moment and must be designed for fatigue resistance per GB 50017 fatigue category. The weld should be ground flush to minimise stress concentration.
2. Cross-arm connections – The locally elevated stress at cross-arm connections identified in the study requires special attention. Weld details should be designed to minimise stress concentration factors. Transition fillets should be ground smooth, and reinforcing plates should be added where the stress concentration factor K_t exceeds 1.5.
3. Section transitions – If the pole is tapered, the section transitions must be smoothly welded to avoid abrupt changes in stiffness that could create stress concentrations and local resonance.
4. Welding process selection – For field assembly, SMAW with low-hydrogen electrodes is commonly used. For shop fabrication, SAW or FCAW may be employed for thicker sections. The welding procedure must be qualified per NB/T 47014 with consideration for the service temperature range and fatigue loading conditions.

Study Insights and Implications

The dynamic performance analysis reveals that 110kV transmission steel tube poles possess significant strength margins, with displacement rather than stress being the governing design criterion. This finding has important implications for economic optimisation—the pole section can potentially be reduced while maintaining adequate dynamic performance, provided that displacement limits are respected. However, the locally elevated stresses at cross-arm connections represent a fatigue vulnerability that must be addressed through detailed design and construction quality control. For steel pipe fabricators, the key requirements are dimensional accuracy to ensure predictable dynamic characteristics, weld quality to prevent initiation of fatigue cracks, and smooth weld details to minimise stress concentrations. The study's recommendation to optimise cross-arm properties for dynamic performance reduction offers a practical approach to improving pole longevity without increasing the main pole section size.