Double Stainless Steel Tube High-Strength Recycled Aggregate Concrete Short Column Axial Compression Study

Research Context and Innovation

The paper by Wang Weihua et al., published in Advances in Engineering Science (2022, Vol. 54, No. 3, pp. 180-191), presents a comprehensive experimental study of double stainless steel tube (D-SSCF) short columns filled with high-strength recycled aggregate concrete. The research was supported by the National Natural Science Foundation of China and Quanzhou Science and Technology Support Program. The innovation lies in combining the corrosion resistance and fire resistance of stainless steel with the sustainability of recycled concrete, creating a composite column system that addresses multiple engineering challenges simultaneously.

Experimental Program and Test Parameters

Sixteen double stainless steel tube recycled aggregate concrete short columns were tested, investigating the effects of recycled aggregate replacement ratio, confinement effectiveness coefficient, and strength difference between old and new concrete on axial compression performance.

Key Experimental Findings

The axial compression bearing capacity of double stainless steel tube recycled aggregate concrete short columns decreases with increasing recycled aggregate replacement ratio. At a 20% replacement ratio, the maximum reduction in bearing capacity is 6.8%, which is relatively modest and suggests that recycled aggregate can be used at moderate replacement levels without significant structural penalty.

The failure process and failure modes of the double stainless steel tube recycled aggregate concrete columns are similar to those of conventional double stainless steel tube concrete columns. This similarity is important for design purposes because it means that existing understanding of D-SSCF column behavior can be extended to recycled concrete applications.

The internal circular steel tube concrete exhibits two types of failure: barrel-shaped (鼓型) and shear-type. The barrel-shaped failure indicates uniform confinement and good composite action, while the shear-type failure suggests localized stress concentration that may require design attention.

Confinement Effectiveness and Design Methodology

The authors propose a simplified method for calculating the confinement effect of the steel tube cross-section on the core concrete in double stainless steel tube concrete sections. This simplification is valuable for practical design because it reduces the complexity of calculating the confinement effect, which is typically difficult for non-circular or composite sections.

Four bearing capacity calculation methods were compared with test results. The assumption that the bearing capacity of the circular section portion is multiplied by a reduction factor showed good applicability, with calculated results in good agreement with experimental results.

Engineering Practice and Fabrication Considerations

From a steel pipe manufacturing perspective, the use of stainless steel tubes in double-tube columns introduces specific fabrication challenges. Stainless steel has different welding characteristics compared to carbon steel, including higher susceptibility to sensitization and intergranular corrosion. The welding of the outer square stainless steel tube and the inner circular carbon steel tube must be carefully controlled to ensure structural integrity.

The incorporation of recycled aggregate concrete into the column core requires careful attention to concrete placement and compaction, particularly around the inner circular steel tube. The interface between the inner and outer concrete, and between the concrete and the steel tubes, must be properly bonded to ensure composite action. From a quality control standpoint, ultrasonic testing and radiographic inspection should be used to verify concrete density and detect voids.

The fire resistance advantage of stainless steel is significant for practical applications. Stainless steel maintains higher strength at elevated temperatures compared to carbon steel, which means that D-SSCF columns can maintain structural integrity longer during fire events. This reduces or eliminates the need for fireproofing coatings, simplifying construction and reducing maintenance costs.

Study Insights and Future Directions

The most significant finding is that double stainless steel tube recycled aggregate concrete columns maintain excellent post-peak behavior, with residual bearing capacity exceeding 63% of peak load for all specimens. This is remarkable and suggests that these columns have significant reserve capacity, which is particularly valuable for seismic design and for structures where redundancy is important.

The modest reduction in bearing capacity with recycled aggregate replacement (6.8% at 20% replacement) suggests that recycled aggregate can be used at relatively high replacement levels in D-SSCF columns without significant structural penalty. This finding supports the use of recycled materials in structural applications and contributes to sustainable construction practices.

Future research should focus on the long-term durability of D-SSCF columns with recycled aggregate concrete, particularly the corrosion resistance of the inner carbon steel tube when surrounded by recycled aggregate concrete. The chloride permeability and carbonation resistance of recycled aggregate concrete may be inferior to ordinary concrete, which could affect the service life of the inner steel tube. Additionally, the seismic performance of these columns under cyclic loading should be investigated to establish design guidelines for earthquake-prone regions.

The proposed simplified method for calculating the confinement effect and the recommended bearing capacity calculation method with a reduction factor for the circular section portion represent practical advances that can be readily adopted by engineers. However, these methods should be validated through additional testing with different geometries, material properties, and loading conditions before being applied to critical structures.