Hysteretic Performance of Square Composite Stainless Steel Tube Concrete Columns

Literature Overview and Research Context

The paper by Zheng Yongqian, Lai Pengsong, and He Chunxia from Fujian University of Technology and Fuzhou University, published in the China Civil Engineering Journal in 2019, investigates the hysteretic performance of square composite stainless steel tube concrete (SCSCC) columns. Funded by the National Natural Science Foundation of China (51678151), the Fujian Provincial Science and Technology Department Guidance Project (2016H0004), and the Fujian Provincial University Research Special Fund (JK2015029), this study introduces a novel composite column type that combines the corrosion resistance of stainless steel with the structural efficiency of composite construction. The research is particularly relevant given the increasing demand for durable, low-maintenance structural elements in aggressive environments such as marine, industrial, and chemical settings.

Core Technical Findings

The experimental program comprises 8 compression-bending specimens tested under reversed cyclic loading, with three primary parameters varied: axial compression ratio (0.05, 0.3, and 0.6), inner-to-outer tube dimension ratio (0.42 and 0.67), and column type (composite stainless steel tube concrete, hollow夹层 stainless steel tube concrete, and stainless steel tube concrete). A finite element model was developed to complement the experimental results and investigate the influence of additional parameters including outer tube yield strength, interlayer concrete compressive strength, outer tube width-to-thickness ratio, slenderness ratio, and inner tube diameter-to-thickness ratio.

The hysteretic curves of square composite stainless steel tube concrete columns are characterized as relatively full and well-shaped, indicating good energy dissipation capacity. Compared to hollow interlayer stainless steel tube concrete columns and conventional stainless steel tube concrete columns, the composite columns exhibit higher ultimate load capacity, ductility, and plastic energy dissipation capacity. This demonstrates that the composite configuration, which incorporates both an outer and inner stainless steel tube with concrete in between, provides superior structural performance over single-tube configurations.

The influence of various parameters on the ultimate load capacity is systematically documented. The ultimate load capacity increases significantly with increasing outer tube yield strength and interlayer concrete compressive strength, and decreases with increasing outer tube width-to-thickness ratio, axial compression ratio, and slenderness ratio. The inner-to-outer tube dimension ratio and inner tube diameter-to-thickness ratio have a moderate positive effect on the ultimate load capacity, but the increase is relatively modest. In most cases, the square composite stainless steel tube concrete columns exhibit ultimate load capacities 2% to 20% higher than composite ordinary steel tube concrete columns of comparable geometry.

Technical Parameters and Test Configuration

Interpretation from a Steel Pipe and Stainless Steel Perspective

From a steel pipe manufacturing perspective, the use of stainless steel tubes in composite columns introduces several unique considerations. Stainless steel exhibits a fundamentally different stress-strain behavior compared to carbon structural steel. Most austenitic stainless steels, such as those conforming to ASTM A270 or EN 10216-5, do not exhibit a distinct yield plateau but instead show a gradual transition from elastic to plastic behavior. The 0.2% proof stress (Rp0.2) is typically used as the yield strength, which is generally 200 to 300 MPa for common grades such as 304 and 316 stainless steel. This is significantly lower than the yield strength of carbon structural steel (typically 235 to 460 MPa), but stainless steel offers superior corrosion resistance, fatigue performance, and post-yield ductility.

The square geometry of the composite columns introduces additional challenges compared to circular columns. Square stainless steel tubes are more susceptible to local buckling of the flat panels, particularly under combined axial and bending loads. The width-to-thickness ratio of the outer tube is identified as a critical parameter, with larger ratios leading to reduced ultimate load capacity due to premature local buckling. This is consistent with the general principles of steel tube design, where the local buckling resistance of flat panels is governed by the width-to-thickness ratio and the material's elastic modulus.

The composite configuration with both inner and outer stainless steel tubes creates a multi-layer confinement system. The outer tube provides the primary structural resistance and corrosion protection, while the inner tube provides additional confinement to the interlayer concrete and contributes to the overall shear capacity. The interlayer concrete, confined by both tubes, experiences a biaxial or triaxial stress state that enhances its compressive strength and ductility. This multi-layer confinement is analogous to the double-confined concrete concept, where multiple layers of confinement provide progressively enhanced confinement pressure.

Engineering Practice Implications

The findings of this study have several important implications for engineering practice:

• Stainless steel tube concrete columns offer a compelling solution for structures in aggressive environments where corrosion resistance is paramount, such as marine platforms, chemical processing facilities, and coastal infrastructure.
• The composite configuration with both inner and outer tubes provides superior performance over single-tube configurations, justifying the additional material cost in critical applications.
• The width-to-thickness ratio of the outer tube should be carefully controlled to prevent premature local buckling, particularly for square sections where the flat panel buckling resistance is lower than for circular sections.
• The axial compression ratio should be limited to ensure adequate ductility, as higher axial compression ratios reduce the energy dissipation capacity and increase the risk of brittle failure.

Key Questions and Reflections

Several important questions warrant further investigation. First, the long-term corrosion behavior of the interlayer concrete in the composite configuration needs to be studied, as the concrete may be exposed to aggressive environments through any cracks that develop during service. Second, the fatigue performance of square composite stainless steel tube concrete columns under cyclic loading is not addressed in this study, but is critical for applications such as offshore platforms and wind turbine foundations. Third, the cost-effectiveness of the composite configuration needs to be evaluated against single-tube configurations and alternative structural systems, considering both initial material costs and long-term maintenance savings.

The use of stainless steel in composite columns represents a significant advancement in structural engineering, combining the durability of stainless steel with the structural efficiency of composite construction. For steel pipe manufacturers, this opens up specialized markets for high-quality stainless steel tubes with precise dimensional tolerances and controlled surface finishes, as the performance of the composite column is sensitive to the quality and consistency of the steel tube material.

Summary

The research by Zheng et al. establishes the square composite stainless steel tube concrete column as a high-performance structural element with superior hysteretic behavior, ductility, and energy dissipation capacity compared to conventional steel tube concrete and hollow interlayer configurations. The systematic parametric study provides clear design guidelines for optimizing the column geometry and material properties. For steel pipe engineers, this study highlights the growing demand for specialized stainless steel tubes in composite structural applications, with critical attention to dimensional accuracy, surface quality, and material consistency to ensure optimal composite performance.