Zhuojin Pipe Fitting Co., LtdFull-Scale Test of UHV Double-Circuit Steel Tube Tower
Literature Overview
This paper published in Proceedings of the CSEE (2009, Vol. 29, Issue 34, pp. 102-107) by Li Maohua, Dong Jianyao, Yang Jingbo, Geng Jingdu, Li Xilai, and Fu Pengcheng from China Electric Power Research Institute and China Power Engineering Consulting Group East China Electric Power Design Institute reports on the full-scale test of the SZT2 steel tube tower, the first 1000 kV AC ultra-high voltage (UHV) double-circuit full-scale test tower in China. The tower has a total height of 93.4 m and a mass of 132 t. The test was conducted in accordance with the standard DL/T 899-2004 "Overhead Line Tower Structure Load Test," under nine test conditions including strong wind, ice verification, anchor line, and conductor break scenarios.
Test Conditions and Results
The full-scale test was designed to verify the structural safety and performance of the SZT2 tower under realistic loading conditions. The nine test conditions covered the most critical load combinations that the tower would experience during its service life.
| Test Condition | Load Type | Key Result |
|---|---|---|
| Strong wind | Wind load | Displacement within acceptable limits |
| Ice verification | Ice load | Strain within allowable limits |
| Anchor line | Unbalanced tension | Structural integrity maintained |
| Conductor break | Sudden load release | No structural failure |
| Combined loads | Multiple load combinations | Safe performance verified |
The test results demonstrated that the displacement measurements met the deformation requirements, and the strain measurements did not exceed the component load-bearing capacity, indicating that the overall structure is safe. The test also verified that forged necked flanges can safely and reliably transmit forces in UHV double-circuit steel tube towers.
Forged Necked Flange Performance
One of the significant findings of this test was the verification of forged necked flanges as a reliable connection method for UHV steel tube towers. The forged necked flange offers several advantages over traditional welded connections:
- Reduced welding workload, which decreases the risk of welding defects.
- Improved processing efficiency, leading to shorter construction times.
- Reliable force transmission, as verified by the full-scale test.
- Reduced need for post-weld inspection and repair.
The recommendation to promote the use of forged necked flanges in practical engineering is well-founded, as the test demonstrated their structural adequacy under the most severe loading conditions. This finding has important implications for the design and construction of future UHV transmission line towers.
Node Plate Connection Scheme
The SZT2 tower employed a node plate connection scheme, which was also verified through the full-scale test. The test confirmed the feasibility and safety of the following node plate types:
- U-shaped insert plate
- Cross-shaped insert plate
- C-shaped insert plate
The connection plate end tube local yielding was identified as a weak point in the design. The study recommends strengthening the structural measures to prevent local failure at these locations. This finding highlights the importance of detailed design considerations for connection details in large-scale steel structures.
Engineering Practice Implications
The full-scale test of the SZT2 tower provides valuable data for the design and construction of future UHV transmission line towers. The following recommendations are derived from the test results:
- Forged necked flanges should be considered as a preferred connection method for UHV steel tube towers, given their proven performance and manufacturing advantages.
- Node plate connection schemes, including U-shaped, cross-shaped, and C-shaped insert plates, are feasible and safe for UHV tower applications.
- Local yielding at connection plate end tubes should be addressed through strengthened structural measures, such as increased plate thickness, additional stiffeners, or improved connection geometry.
- Full-scale testing should be conducted for critical UHV towers to verify the design assumptions and ensure structural safety.
Study Insights and Reflections
The full-scale test of the SZT2 tower represents a significant milestone in the development of UHV transmission line technology in China. The successful verification of the tower's structural performance under realistic loading conditions provides confidence in the design and construction methods employed.
The identification of local yielding at connection plate end tubes as a design weak point is a valuable finding that should be incorporated into future design guidelines. Engineers should pay particular attention to the detailed design of connection details, as these are often the critical locations for structural failure. The use of forged necked flanges, which reduces the reliance on welding, is a positive development that can improve the overall quality and reliability of steel tube towers.
The test also demonstrates the importance of full-scale testing for critical infrastructure. While analytical methods and component testing provide valuable information, full-scale testing under realistic conditions is the ultimate verification of structural safety. For future UHV projects, full-scale testing should be considered as a standard practice for critical towers, particularly those with novel design features or connection details.
The findings of this study contribute to the development of design standards and construction practices for UHV transmission line towers. The verified performance of forged necked flanges and node plate connection schemes provides a technical basis for their wider adoption in future projects. Engineers should carefully review the test results and incorporate the lessons learned into their design and construction practices to ensure the safe and reliable performance of UHV transmission infrastructure.