Stability Analysis of Super-Large Cooling Tower Steel Tube Concrete Double-Cross Support System

Literature Overview

The paper by Chen Dejin, Zha Xiaoxiong, and Hou Xian'an (2022), published in the Journal of Huazhong University of Science and Technology (Natural Science Edition), investigates the stability performance of a steel tube concrete double-cross support system for a super-large cooling tower. Using the finite element software ABAQUS, the authors established nonlinear models to analyze the full-process axial compression behavior of individual steel tube concrete columns, obtained buckling modes and ultimate stability bearing capacity, and analyzed the overall stability of the double-cross support system under combined gravity and wind loads.

Core Technical Findings

The study analyzes both the local stability of individual columns and the overall stability of the double-cross support system. The authors compare two scenarios: tower shell reinforcement and unreinforced conditions, obtaining the ultimate stability bearing capacity for each case. A simplified calculation method based on elastic buckling analysis and code formulas is proposed, yielding results close to the nonlinear analysis results with a safety bias.

Buckling Mode and Stability Analysis

Analysis Level	Loading Condition	Key Finding	Method
Individual Column	Axial Compression	Buckling modes identified	Nonlinear FE analysis
Individual Column	Axial Compression	Ultimate stability capacity determined	Nonlinear FE analysis
Overall System	Gravity + Wind (reinforced shell)	Higher ultimate stability capacity	Nonlinear FE analysis
Overall System	Gravity + Wind (unreinforced shell)	Lower ultimate stability capacity	Nonlinear FE analysis
Overall System	Simplified Method	Results close to nonlinear analysis, safety-biased	Elastic buckling + code formula

Nonlinear Analysis Methodology

The nonlinear finite element analysis encompasses several critical aspects:

Geometric nonlinearity: Large deformation effects during buckling are captured through the use of appropriate element formulations and convergence criteria.
Material nonlinearity: The constitutive behavior of both steel and concrete is modeled with appropriate nonlinear material models, including the confinement effect of the steel tube on the concrete core.
Contact nonlinearity: The interaction between the steel tube and concrete core, as well as between structural components, is modeled using contact algorithms.
Load nonlinearity: The combined gravity and wind loading is applied incrementally to capture the progressive stability degradation.

Tower Shell Reinforcement Effect

The comparison between reinforced and unreinforced tower shell conditions demonstrates the significant role of the tower shell in providing lateral restraint to the double-cross support system. The reinforced shell increases the effective buckling length reduction, thereby enhancing the overall stability capacity.

Condition	Effective Buckling Length	Ultimate Stability Capacity	Safety Margin
Reinforced Shell	Reduced	Higher	Larger
Unreinforced Shell	Longer	Lower	Smaller

Simplified Calculation Method

The proposed simplified calculation method combines elastic buckling analysis with code formulas to provide a practical design tool. The method yields results close to the nonlinear analysis results with a safety bias, making it suitable for preliminary design and code verification purposes.

The simplified method is particularly valuable for engineering practice because:

It reduces computational complexity while maintaining acceptable accuracy.
The safety bias provides an inherent margin against modeling uncertainties.
It can be easily implemented in standard structural analysis software or even manual calculations for preliminary design stages.

Engineering Practice Implications

For steel pipe manufacturing and structural engineering practice, this study has several important implications:

The double-cross support system requires high-precision steel tube fabrication, as geometric imperfections can significantly reduce buckling resistance in slender columns.
Welding quality is critical for the stability performance, as weld defects can act as stress concentrations and initiate buckling.
The tower shell reinforcement strategy should be considered early in the design phase to optimize the overall stability performance.

Steel Tube Manufacturing Quality Requirements

Quality Parameter	Tolerance Requirement	Impact on Stability
Ovality	Within 1-2% of nominal diameter	Affects local buckling resistance
Wall Thickness Variation	Within ±10% of nominal thickness	Affects stiffness and buckling capacity
Straightness	Within 1/1000 of column length	Affects initial imperfection amplitude
Weld Quality	Full NDE (UT/RT) inspection	Prevents stress concentration initiation

Study Insights and Outlook

This research provides comprehensive stability analysis for a critical structural component of super-large cooling towers. The nonlinear finite element analysis captures the complex stability behavior accurately, while the simplified calculation method offers practical utility for engineering design. The finding that tower shell reinforcement significantly enhances stability performance highlights the importance of integrated structural design, where the interaction between different structural components must be carefully considered. Future research should investigate the effect of dynamic loading (such as wind gusts and seismic excitation) on the stability performance, as well as the long-term stability degradation due to material aging and environmental exposure. For steel pipe manufacturers, the study reinforces that dimensional accuracy and weld quality are not merely compliance requirements but critical factors in the structural stability of large-scale cooling tower support systems.