Finite Element Analysis and Full-Scale Testing of Steel Tubular Transmission Tower Structural Strength

Literature Overview

This paper by Wang Meng, Geng Jingdu, Su Zhigang, and Wang Zhangqi (Journal of North China Electric Power University, Vol. 47, Issue 5, 2020, pp. 102-110) presents a comprehensive investigation of the structural strength of ultra-high voltage (UHV) steel tubular towers. Funded by State Grid Corporation of China (Project No. GCB17201800181), the research combines finite element analysis with full-scale tower testing to validate modelling approaches and assess structural performance under extreme loading conditions. This work is directly relevant to engineers involved in the design, fabrication, and quality assurance of large-diameter steel pipe structures used in power transmission infrastructure.

Core Technical Content

The study focuses on a 1000 kV UHV steel tubular transmission tower, which represents one of the largest and most demanding applications of steel tubular structural members in the electrical infrastructure sector. The tower comprises four primary categories of structural members: main materials (主材), diagonal members (斜材), transverse members (横隔材), and auxiliary materials (辅助材), each with distinct loading characteristics and failure modes.

Finite Element Modelling Methodology

The authors developed a hybrid truss-beam finite element model that accounts for the different structural behaviours of the various tower components:

• Main materials are modelled as beam elements to capture their bending and axial stiffness contributions.
• Diagonal and transverse members are modelled as truss elements reflecting their primarily axial force-carrying function.
• Node connections are modelled with appropriate stiffness assumptions to represent the welded or bolted joints.

The modelling principles include proper representation of member cross-sections, material properties (typically Q355 or Q420 grade structural steel per GB/T 1591), and boundary conditions that simulate the tower foundation constraints.

Test Programme and Validation

A full-scale tower test was conducted by applying controlled loads to simulate extreme wind loading and combined ice-wind conditions. The test instrumentation included strain gauges at critical sections, displacement transducers at key nodes, and load cells at the loading points. The comparison between FE model predictions and full-scale test results demonstrated excellent agreement, validating the hybrid truss-beam modelling approach.

Structural Behaviour Under Extreme Loads

The analysis reveals that under wind loading conditions, the tower exhibits a characteristic lateral deflection pattern with the maximum displacement at the tower top. The stress distribution in the main materials shows a non-uniform pattern due to the combined effects of wind pressure distribution and structural geometry. Under combined ice-wind loading, the additional ice weight significantly increases the axial forces in the lower tower sections while the wind-induced bending moments concentrate at the tower mid-height.

Engineering Practice Implications

This research has substantial relevance to the steel pipe and fitting industry for several reasons:

1. Large-diameter pipe quality requirements: UHV transmission towers use large-diameter steel tubes (typically 300-600 mm OD) that must meet stringent quality requirements. The pipe fabrication process—whether seamless, LSAW, or spiral-welded—must ensure uniform wall thickness, consistent mechanical properties, and freedom from surface and volumetric defects.
2. Weld joint integrity: The tower node connections involve complex weld configurations where multiple tubes intersect. The welding process (typically SMAW or FCAW for field fabrication) must achieve full penetration with proper heat input control to avoid excessive HAZ softening or hardening. The residual stress distribution in these multi-plate weld joints directly affects the fatigue life of the tower.
3. Standards compliance: The steel tubular tower fabrication must comply with relevant standards including GB 50017 (Code for Design of Steel Structures), DL/T 5154 (Technical Code for Design of Steel Structures of Overhead Transmission Line Tower), and API 5L for pipe material specifications. The quality control programme should include dimensional inspection, NDT (RT, UT, MT, PT) of welds, and hydrostatic pressure testing of pipe segments.
4. FE model validation approach: The methodology of validating FE models against full-scale test data provides a template for other large-scale steel tubular structures. This approach is particularly valuable for novel or complex structural configurations where analytical solutions are not available.

Key Questions and Reflections

The study demonstrates the effectiveness of the hybrid truss-beam modelling approach but raises questions about its applicability to different tower configurations and loading scenarios. Specifically, the model's accuracy under dynamic loading conditions such as galloping-induced vibrations or ice-induced oscillations has not been examined. Additionally, the long-term effects of corrosion on the structural capacity of the tubular members—particularly at weld zones where the protective coating may be compromised—warrant further investigation.

From a welding metallurgy perspective, I note that the stress concentrations identified in the FE analysis correspond to locations where fatigue cracking is most likely to initiate. The weld HAZ microstructure, residual stress state, and any microstructural defects (such as lack of fusion or porosity) at these critical locations would significantly influence the fatigue performance. A systematic FMEA of the weld joints should be conducted, identifying potential failure modes including fatigue cracking, stress corrosion cracking (SCC), and hydrogen-induced cracking (HIC) in high-strength steel grades.

Study Insights and Implications

This research provides a validated analytical framework for the structural assessment of UHV steel tubular towers. The excellent agreement between FE predictions and full-scale test results gives engineers confidence in using this modelling approach for design optimization and life assessment. For the steel pipe fabrication industry, the study reinforces the critical importance of material quality, dimensional accuracy, and weld integrity in large-diameter tubular structures. The full-scale testing methodology offers a benchmark for quality assurance programmes in similar large-scale steel tubular construction projects.