Axial Compression Test Study on Double-Skin Stainless Steel Tube Concrete

Literature Overview

This paper by Ye Bin, Zhang Xudong, and Qiao Qiyun from Tongji University and Beijing University of Technology investigates the axial compression behavior of double-skin stainless steel tube confined concrete (DSSTCC) specimens. The research addresses a critical gap in the structural engineering field, as ordinary carbon steel has limitations in extreme environments such as marine or corrosive industrial settings. Double-skin stainless steel tube concrete combines the mechanical advantages of conventional CFST with the corrosion resistance of stainless steel, making it suitable for special engineering applications. The study was funded by the Shanghai Science and Technology Committee project (16DZ1202204).

Core Technical Parameters and Test Results

The experimental program systematically varied the inner tube thickness and strength to evaluate their effects on the ultimate axial load-bearing capacity and ductility of the specimens. The key finding is that when the strain reaches 0.07, the specimens can still maintain more than 80 percent of their peak load-bearing capacity, demonstrating excellent ductility.

The study also found that increasing the inner tube thickness clearly slows down the decline of ultimate axial bearing capacity, although its overall influence remains limited compared to the outer tube. Both increasing the inner tube thickness and strength can significantly improve the compressive stiffness of the specimens. Importantly, current design codes can provide reasonably accurate estimates of the axial compression capacity of double-skin stainless steel tube concrete.

Interpretation of Key Technical Points

From a metallurgical perspective, the selection of stainless steel grades for the inner and outer tubes is critical. Common grades used in structural applications include austenitic stainless steels such as SUS304 and SUS316, or duplex stainless steels such as 2205. The choice of grade directly affects the mechanical properties, corrosion resistance, and weldability of the tubes. The welding of stainless steel tubes requires careful control of the heat input to prevent sensitization and intergranular corrosion in the heat-affected zone. According to standards such as ASTM A269 for stainless steel welded tube and ASME B31.3 for process piping, the welding procedures must be qualified with appropriate filler metals to maintain the corrosion resistance of the weld metal.

The double-skin configuration creates a unique load-sharing mechanism between the inner and outer tubes through the confined concrete core. The inner tube provides additional confinement and lateral support to the concrete, while the outer tube serves as the primary load-bearing element. The interaction between the two tubes is mediated by the concrete, which must be properly compacted to avoid voids that could compromise the structural integrity. The concrete mixture design should consider the workability constraints imposed by the confined space between the two tubes, which is typically narrow.

Integration with Engineering Practice

The practical implications of this research are significant for engineers designing structures in corrosive environments such as offshore platforms, marine structures, chemical processing facilities, and nuclear power plants. The double-skin stainless steel tube concrete system offers an alternative to carbon steel CFST with cathodic protection or to fully stainless steel structures, potentially achieving a favorable balance between cost and performance. During fabrication, the concentricity of the inner and outer tubes must be maintained within tight tolerances to ensure uniform concrete confinement. The welding connections between the inner and outer tubes at the ends of the specimens require special attention to prevent misalignment and ensure proper load transfer.

Quality control during manufacturing should include hydrostatic testing per ASTM A269, dimensional inspection, and non-destructive testing of welds using methods such as ultrasonic testing (UT) or magnetic particle testing (MT) in accordance with applicable standards. The corrosion resistance of the completed structure should be verified through immersion testing or salt spray testing per ASTM B117 to ensure long-term durability in the intended service environment.

Study Insights and Implications

The finding that current codes can reasonably estimate the axial compression capacity of DSSTCC is encouraging for the practical adoption of this structural system, as it means that engineers do not need to develop entirely new design methods. However, the research also highlights areas where further investigation is needed, particularly regarding the long-term behavior under cyclic loading, the effect of concrete curing conditions on the confinement effectiveness, and the weld quality requirements for the double-skin configuration. The excellent ductility demonstrated at high strain levels (0.07) is particularly valuable for seismic applications, as it indicates that the specimens can undergo large inelastic deformations without catastrophic failure. This research opens new possibilities for the application of stainless steel tube concrete in demanding environments where corrosion resistance and structural performance are both critical requirements.