Eccentric Compression Performance of Irregular Section Multi-Chamber Steel Tube Concrete Mega Columns

Literature Overview

This comprehensive study by Cao Wanlin, Wang Ruwei, Yin Fei, Wang Zhihui, and Dong Hongying from Beijing University of Technology investigates the eccentric compression behavior of irregular section multi-chamber steel tube concrete (SC) mega columns. Published in the Journal of Harbin Institute of Technology in 2020, the research was supported by the National Natural Science Foundation of China (Grant No. 51578020). The study was inspired by mega columns in two iconic Chinese skyscrapers: the China Zun Tower in Beijing and the Tianjin 117 Tower. Four large-scale model specimens were tested under unidirectional repeated eccentric loading, including one octagonal thirteen-chamber China Zun mega column model, one octagonal thirteen-chamber model with circular steel tubes in the corner chambers, and two hexagonal six-chamber Tianjin 117 mega column models.

Core Technical Findings

The China Zun mega column models were scaled at 1/13 and the Tianjin 117 models at 1/12. The specimens exhibited excellent mechanical performance under eccentric loading, with good damage evolution, bearing capacity, deformation recovery ability, and stiffness degradation characteristics. A key finding was that placing circular steel tubes within the corner chambers of the octagonal thirteen-chamber mega column effectively slowed damage progression and significantly improved both bearing capacity and deformation capacity.

The theoretical analysis employed multiple international codes and the fiber model method to calculate N-M interaction curves and load-deformation curves. The code-based calculations were found to be conservative compared to test results. The authors then proposed a simplified correction method for calculating the unified compressive strength fsc of multi-chamber SC columns, based on the N-M calculation method in GB 50936 and Han Linhai's SC constitutive relationship.

Theoretical Analysis and Code Comparison

The study compared calculations from multiple international codes including GB 50936, ACI 408, Eurocode 4, and Han Linhai's unified strength model. The code-based results were generally conservative, which is acceptable from a safety perspective but may lead to uneconomical designs. The proposed simplified correction method for fsc calculation provided results that agreed well with experimental data for both N-M interaction curves and bearing capacity.

The fiber model method was found to be particularly effective for analyzing the complex cross-sectional behavior of multi-chamber SC mega columns. This method divides the cross-section into multiple fibers, each assigned appropriate material constitutive relationships, allowing for the simulation of the nonlinear behavior of the entire cross-section under combined axial and bending loads.

Engineering Practice Integration

The findings have direct implications for the design of mega columns in super-tall buildings. The octagonal thirteen-chamber configuration of China Zun and the hexagonal six-chamber configuration of Tianjin 117 represent innovative structural systems that require careful engineering analysis. The addition of circular steel tubes in corner chambers is a practical measure that can be implemented during fabrication to enhance the seismic performance of these complex columns.

From a welding and fabrication standpoint, multi-chamber SC mega columns present significant challenges. The welding of multiple internal partition plates within the mega column requires precise alignment, adequate access for welding operations, and rigorous non-destructive testing. The internal welds are particularly critical because they transfer loads between chambers and must maintain integrity under cyclic loading. Standards such as GB 50017, GB 50936, and ASME B31.3 provide relevant guidance, but the specific requirements for mega column fabrication may require additional engineering specifications.

Key Questions and Reflections

The research raises several important questions for future investigation. First, how does the presence of corner steel tubes affect the long-term fatigue behavior of the mega column under cyclic loading? Second, what are the optimal dimensions and wall thicknesses for the corner tubes to maximize their beneficial effect? Third, how does the multi-chamber configuration affect the thermal expansion behavior of the mega column, which is critical for tall buildings subject to temperature variations?

The parametric analysis also suggests that the eccentricity ratio plays a significant role in determining the failure mode and deformation characteristics. For small eccentricities, the column behaves more like an axially loaded member with high bearing capacity but limited ductility. For large eccentricities, the column exhibits better deformation recovery but lower bearing capacity. This behavior must be carefully considered in the design of seismic-resistant mega columns.

Study Insights and Implications

This study provides a comprehensive understanding of the eccentric compression behavior of irregular section multi-chamber SC mega columns through large-scale experimental testing and theoretical analysis. The proposed simplified correction method for fsc calculation offers a practical tool for engineers designing multi-chamber SC columns. The experimental results demonstrate that the addition of circular steel tubes in corner chambers is an effective measure for enhancing the seismic performance of these complex structural members. For engineers involved in the design and construction of super-tall buildings, this research underscores the importance of rigorous experimental investigation, validated numerical analysis, and code-based design procedures that account for the unique characteristics of multi-chamber SC mega columns. The findings contribute to the advancement of mega column design technology and provide valuable reference data for future research and engineering practice.