Spatial Action Influence Coefficient of Single Steel Tube Columns in Fully Integrated Substation Structures

Literature Overview

This study by Yang Jianjiang, Li Chenxi, and Liu Liangliang from Tianjin University and North China Electric Power Design Institute, published in Industrial Construction in 2016 (Vol. 46, No. 12, pp. 146–151), investigates the spatial action influence coefficient of single steel tube columns in fully integrated 500 kV substation structures. Using ANSYS finite element analysis, the authors obtain the force distribution of single steel tube columns with three different connection stiffnesses and their corresponding independent members, derive the spatial action influence coefficients for internal forces and displacements, and compare the results with traditional A-type line-out columns.

Core Technical Content

The study addresses a practical engineering challenge in the design of high-voltage substation structures: the determination of spatial action influence coefficients for single steel tube columns used in fully integrated structures. In substation structures, the columns supporting the line-out equipment are connected to the main structure through various connection types, and the spatial interaction between the columns and the main structure significantly affects the force distribution. The spatial action influence coefficient is a dimensionless parameter that quantifies the effect of spatial interaction on the internal forces and displacements of the column.

Spatial Action Influence Coefficients

The study demonstrates that the spatial action influence coefficient varies significantly with connection stiffness, with rigid connections producing the highest internal forces and the lowest displacements. The comparison with traditional A-type line-out columns shows that the single steel tube column structure has certain advantages in terms of force distribution and structural efficiency.

Interpretation of Technical Points

The concept of spatial action influence coefficient is fundamental to the design of substation structures, as it allows the complex spatial structure to be simplified to a single-member model for analysis. The coefficient is defined as the ratio of the internal force or displacement in the spatial structure to the internal force or displacement in the isolated member, and it accounts for the interaction effects between the column and the main structure.

The study's finding that the spatial action influence coefficient has certain regularity but also uncertainty is important for engineering practice. The regularity allows the coefficient to be estimated based on the connection stiffness and the structural configuration, while the uncertainty highlights the need for detailed analysis in critical cases. The study recommends that different internal forces under different loading conditions should be evaluated separately, as the coefficient for bending moment may differ significantly from the coefficient for axial force or shear force.

The comparison with traditional A-type columns provides a benchmark for evaluating the structural performance of single steel tube columns. The A-type column is a widely used configuration in substation structures, characterized by a triangular frame that provides inherent stability. The single steel tube column, while simpler in form, requires careful consideration of the connection details and the spatial interaction with the main structure to achieve comparable performance.

Process and Standards Analysis

The design of substation structures is governed by several standards, including:

• GB 50059 for the design of 35–500 kV substations
• DL/T 5222 for the design of outdoor substation structures
• DL/T 5092 for the design of indoor substation structures
• GB 50011 for seismic design of building structures

These standards provide general guidance on the design of substation structures but do not specifically address the spatial action influence coefficient for single steel tube columns. The study's findings provide a basis for the development of design guidelines for this specific structural configuration.

From a fabrication standpoint, the steel tube columns used in substation structures are typically fabricated from ERW or HFW welded steel tubes, conforming to standards such as GB/T 8163 or GB/T 9711. The connection details between the steel tube columns and the main structure are critical, as they determine the connection stiffness and hence the spatial action influence coefficient. The connections may be welded, bolted, or a combination of both, and the design of the connection must be carefully considered to achieve the desired stiffness and ductility.

Engineering Practice Integration

The study's findings have direct implications for the design of 500 kV substation structures, where the use of single steel tube columns is becoming increasingly common due to their simplicity, cost-effectiveness, and structural efficiency. The spatial action influence coefficient provides a practical tool for the design of these structures, allowing the complex spatial interaction to be simplified to a single-member model for analysis.

In practice, the following steps can be taken to apply the study's findings:

1. Determine the connection stiffness of the single steel tube column based on the connection type and detail design
2. Select the appropriate spatial action influence coefficient from the study's results or from a detailed finite element analysis
3. Apply the coefficient to the isolated member analysis to obtain the internal forces and displacements in the spatial structure
4. Verify the design by comparing the results with a full spatial model analysis

The study's recommendation that different internal forces under different loading conditions should be evaluated separately is particularly important for seismic design, where the spatial interaction effects can be significant and non-linear. The use of a single spatial action influence coefficient for all internal forces and all loading conditions may be non-conservative and should be avoided.

Key Questions and Reflections

The study raises several important questions for future research. First, how does the spatial action influence coefficient vary with the height of the column and the height of the substation structure? Second, what is the effect of soil-structure interaction on the spatial action influence coefficient, particularly for substation structures located on soft soil? Third, how does the spatial action influence coefficient change under seismic loading, where the non-linear behavior of the connections and the structure may significantly affect the force distribution?

The study's focus on 500 kV substation structures is specific, but the findings may be applicable to other voltage levels and other types of electrical structures. A parametric study covering a wider range of structural configurations and loading conditions would provide more comprehensive design guidance. The study would also benefit from experimental validation of the spatial action influence coefficients, as the finite element analysis results, while validated against isolated member analysis, have not been verified against physical testing.

Study Insights and Implications

This study provides valuable engineering insights into the spatial action influence coefficient of single steel tube columns in fully integrated substation structures, demonstrating that the coefficient varies significantly with connection stiffness and that different internal forces require separate evaluation. The comparison with traditional A-type columns highlights the structural advantages of single steel tube columns, while the identification of regularity and uncertainty in the coefficient provides practical guidance for design. For engineers involved in the design of high-voltage substation structures, the study offers a practical tool for simplifying the analysis of complex spatial structures, while also highlighting the need for careful consideration of connection details and loading conditions. The study reinforces the importance of spatial interaction effects in structural design and provides a foundation for the development of design guidelines for single steel tube columns in electrical structures.