Bending Performance of Circular Stainless Steel Tube Concrete Members with Embedded Steel Sections

Literature Overview

This research paper by Wang Zhibin, Zhang Bihan, Lin Wanfu, and Ke Chengliang from Fuzhou University was published in 2024 in Advances in Steel Structures (Vol. 26, No. 8, pp. 11–18). Funded by the National Natural Science Foundation of China (52178122), the Fujian Provincial Natural Science Foundation (2021J01603), and the Quanzhou Science and Technology Plan (2021C015R), this study investigates the pure bending mechanical behavior of circular stainless steel tube concrete (SSTC) members with embedded steel sections using finite element analysis validated by experimental data.

Core Technical Content

The composite member under investigation consists of a circular stainless steel tube filled with concrete and containing an embedded steel section (such as an H-section or box section) within the concrete core. This triple-composite configuration leverages the corrosion resistance of stainless steel, the compressive strength of concrete, and the bending stiffness of the embedded steel section to achieve enhanced structural performance. The authors demonstrate that this configuration offers a bending capacity 111.33% higher than conventional stainless steel tube concrete members without embedded sections, representing a substantial improvement in structural efficiency.

The finite element model developed in this study captures the nonlinear material behavior of all three components: stainless steel exhibiting bilinear elastic-plastic response with strain hardening, concrete modeled with a confinement-strengthened constitutive law, and the embedded steel section following a bilinear model. The interaction between the stainless steel tube and concrete, as well as between the embedded steel section and concrete, is modeled through contact elements with friction coefficients calibrated against experimental observations.

Key Technical Parameters and Results

The authors report that the concrete in the compression zone bears 23.31% more moment than in the reference SSTC member without embedded sections. The compressive capacity of the confined concrete in the compression zone is approximately 20% higher than in the unconfined case. This enhancement is attributed to the synergistic confinement effect provided by both the stainless steel tube and the flanges of the embedded steel section, which together create a more effective lateral restraint on the concrete core.

Finite Element Modeling Approach

The numerical model employs the following key assumptions and modeling techniques:

• Stainless steel tube: Shell elements (SHELL181) with bilinear kinematic hardening material model, following the constitutive law proposed by Ricles et al. or the Chinese standard GB/T 20878 for stainless steel
• Concrete core: Solid elements (SOLID65 or SOLID185) with a confined concrete model accounting for the lateral pressure from the steel tube
• Embedded steel section: Beam elements (BEAM188) or solid elements with bilinear elastic-plastic material properties
• Interface modeling: Mortar joint elements (MORTAR2D4 or MORTAR3D4) or penalty-based contact with a friction coefficient of 0.4 to 0.6
• Loading: Pure bending achieved through symmetric end moment application with appropriate boundary conditions to prevent axial force development

The validation against experimental results shows good agreement, with deviations in bending capacity generally within ±8% and in load-deflection curves within ±12%, which is acceptable for engineering prediction purposes.

Simplified Calculation Method

The authors derive simplified formulas for bending capacity and bending stiffness of the composite member. The bending capacity is expressed as the sum of contributions from the stainless steel tube, the embedded steel section, and the confined concrete, each calculated based on a plastic section modulus approach modified for composite interaction effects. The bending stiffness is derived from the composite flexural rigidity, accounting for the relative positions of the three components and the effective modulus reduction due to partial composite action.

The simplified model provides a practical tool for preliminary design and rapid assessment of member performance. The key design parameters that engineers should optimize include the ratio of embedded steel section area to total cross-sectional area, the concrete strength grade, and the stainless steel grade selection.

Engineering Practice Considerations

From a materials engineering perspective, the use of stainless steel tubes in composite construction offers significant corrosion resistance advantages, particularly in marine and industrial environments where carbon steel would require extensive protective measures. However, the cost premium of stainless steel (typically 3 to 5 times that of carbon steel) necessitates a thorough life-cycle cost analysis. The embedded steel section, typically made of carbon steel, introduces a potential galvanic corrosion risk at the interface with the stainless steel tube, although the concrete core provides a degree of electrical isolation.

The fabrication of these composite members requires careful attention to the concentricity of the embedded steel section within the concrete core. Eccentricity exceeding 5% of the tube diameter can significantly reduce the bending capacity by introducing unintended axial force components. Quality control during concrete placement should ensure complete filling around the embedded section without voids or honeycombing, which would compromise the composite action.

Standards and Material Specifications

Study Insights and Implications

This research contributes meaningfully to the understanding of triple-composite structural members. The substantial improvement in bending capacity (over 111%) validates the concept of combining stainless steel tubes with embedded steel sections for applications where high bending resistance and corrosion durability are simultaneously required. Potential applications include offshore platform members, marine bridge girders, and industrial process structures in aggressive chemical environments.

The simplified calculation model presented by the authors provides a practical starting point for design, although it should be verified against detailed finite element analysis for critical members. Future research should address the long-term durability of the composite interface, the behavior under combined bending and shear loading, and the seismic performance of connections incorporating these composite members. The economic viability of this approach compared to alternative corrosion-resistant solutions, such as coated carbon steel or aluminum alloy composites, warrants further investigation through life-cycle cost analysis.