Selection of Calculation Models for UHV Steel Tube Transmission Towers

Literature Overview

This paper, published in Power System Technology in 2010 by Yang Jingbo, Han Junk, Li Maohua, Li Feng, and Yang Fengli from the China Electric Power Research Institute, addresses the selection of calculation models for ultra-high voltage (UHV) steel tube transmission towers. The study uses the 1000 kV Huainan-Shanghai (Anhui-East Power Transmission) UHV double-circuit steel tube tower as the analysis object and compares three calculation models: member element model (from the general tower design program), beam-member hybrid element model (from ANSYS finite element software), and beam element model (from ANSYS). The research evaluates the static and dynamic performance of the tower under each model and provides recommendations for the most appropriate calculation approach.

Technical Background

UHV steel tube transmission towers are large-scale space truss structures used for 1000 kV AC or ±800 kV DC transmission lines. These towers are typically 100–200 meters in height and carry extremely heavy conductor bundles, insulator strings, and hardware. The structural members are fabricated from steel tubes (typically rectangular or circular cross-sections) rather than conventional angle steel or lattice section members, which provides higher structural efficiency and improved aerodynamic performance.

Structural Characteristics of UHV Steel Tube Towers

Characteristic	Description	Typical Range
Tower height	Total height of the tower	100–200 m
Steel tube diameter/width	Cross-section dimension of main members	200–600 mm
Wall thickness	Thickness of steel tube walls	6–16 mm
Steel grade	Material specification	Q345, Q390, Q420
Span length	Distance between adjacent towers	500–1000 m
Conductor weight	Weight per conductor bundle	5000–15000 N
Wind load	Design wind pressure	0.75–1.5 kN/m²

Comparison of Calculation Models

Model 1: Member Element Model (Truss Model)

The member element model treats each structural member as a pin-jointed truss element that carries only axial forces (tension or compression). This is the traditional approach used in tower design programs and is based on the assumption that the joints are idealized as frictionless pins.

Aspect	Description
Element type	2D or 3D truss member
Degrees of freedom	Axial only
Joint behavior	Pin-jointed (no moment transfer)
Software	General tower design program (e.g., PTDS)
Strength	Simple, fast, suitable for preliminary design
Limitation	Ignores end moments, may underestimate member stresses

Model 2: Beam-Member Hybrid Element Model

The beam-member hybrid element model uses a combination of beam elements (for main members that carry significant bending moments) and truss member elements (for secondary members that primarily carry axial forces). This approach recognizes that the main members of the tower experience bending moments due to the semi-rigid nature of the joints.

Aspect	Description
Element type	Beam elements for main members + truss members for secondary
Degrees of freedom	Axial + bending (beam) or axial only (truss)
Joint behavior	Semi-rigid (partial moment transfer)
Software	ANSYS finite element software
Strength	Captures end moments in main members
Limitation	Requires judgment in element selection, more complex

Model 3: Beam Element Model

The beam element model treats all structural members as beam elements that can carry axial forces, shear forces, and bending moments. This is the most comprehensive model but may overestimate the stiffness of the structure if the joints are not truly rigid.

Aspect	Description
Element type	3D beam elements for all members
Degrees of freedom	Axial + shear + bending
Joint behavior	Rigid (full moment transfer)
Software	ANSYS finite element software
Strength	Most comprehensive, captures all load effects
Limitation	May overestimate stiffness, computationally more intensive

Analysis Results and Comparison

Static Analysis Comparison

Parameter	Member Element Model	Beam-Member Hybrid Model	Beam Element Model
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