Interface Bonding Performance of Steel Tube Reinforced Concrete Current Research Status and Analysis Progress

Literature Overview

This review paper by Wang Qiuwei and colleagues from Xi'an University of Architecture and Technology, published in Building Structures in 2021, provides a comprehensive summary of the current state of research on the interface bonding performance between steel tubes and concrete in steel tube reinforced concrete (CFST) members. Supported by two National Natural Science Foundation projects (Grant Nos. 51878543 and 51878540) and a Shaanxi Provincial Department of Education research project (20JS078), the study synthesizes both domestic and international research findings on bonding stress composition, bonding strength calculation, bonding-slip constitutive models, and finite element analysis of bonding performance. This review is particularly valuable for engineers and researchers seeking to understand the fundamental mechanisms governing the composite action between steel tubes and concrete, which is critical for the accurate analysis and design of CFST members.

Core Technical Findings

The review identifies three primary components of interface bonding stress: chemical adhesion, mechanical interlock, and friction. Among these, friction is identified as the dominant mechanism responsible for shear resistance at the steel-concrete interface. This finding is consistent with the general understanding of composite interface behavior and has important implications for the design of CFST members, as the frictional resistance depends on the contact pressure between the steel tube and the concrete, which in turn is influenced by the axial load level and the degree of concrete confinement.

Bonding Stress Components

The review also identifies several factors that significantly influence bonding strength, with steel tube shape, steel tube size, and interface roughness degree being the most influential parameters. The effect of steel tube shape is attributed to the difference in confinement effectiveness between circular and non-circular sections, while the effect of steel tube size is related to the scale effect on the concrete confinement and the stress distribution at the interface. Interface roughness degree directly affects the mechanical interlock component of bonding stress and has a significant impact on the overall bonding performance.

A particularly important finding is that existing bonding strength test values do not account for the effect of material self-weight, leading to an underestimation of the actual bonding strength. The authors' calculations indicate that the bonding strength values specified in American codes are relatively reasonable compared to experimental data. This finding has direct implications for code calibration and design practice, as it suggests that current design values may be conservative and that more accurate bonding strength predictions can be achieved by considering the self-weight effect.

Bonding-Slip Constitutive Modeling

The review provides a detailed analysis of the various bonding-slip constitutive models developed in the literature. These models are essential for finite element analysis of CFST members, as they define the relationship between the relative slip at the steel-concrete interface and the corresponding bonding stress. The most common approaches include bilinear models, trilinear models, and nonlinear exponential models, each with its own advantages and limitations.

The selection of an appropriate constitutive model depends on the specific application and the level of accuracy required. For preliminary design and code-based analysis, simpler bilinear models may be sufficient, while for detailed research and advanced finite element analysis, more sophisticated nonlinear models are recommended. The review also highlights the challenges associated with calibrating these models, particularly the need for reliable experimental data on the full range of bonding-slip behavior, including the post-peak softening phase.

Process and Standards Analysis

From a steel pipe manufacturing perspective, the surface roughness of the steel tube interior is a critical factor influencing the bonding performance. The manufacturing process used to produce the steel tube—whether seamless, ERW, HFW, or LSAW—directly affects the internal surface characteristics. Seamless steel tubes produced by the Mannesmann piercing process typically have a relatively smooth internal surface, while welded steel tubes may have a weld seam on the interior surface that can either enhance or degrade bonding performance depending on its quality and geometry.

According to relevant standards such as GB/T 8163 for seamless steel tubes and GB/T 3091 for welded steel tubes, the internal surface of the steel tube should be free from defects such as cracks, folds, and severe oxidation. The surface roughness is typically specified in terms of Ra (arithmetic mean roughness) or Rz (maximum height of the profile), and for CFST applications, a moderate roughness level is generally preferred to enhance mechanical interlock without creating stress concentrations. The use of internal surface treatments, such as shot blasting or mechanical roughening, can be considered to optimize the bonding performance, but must be carefully controlled to avoid damaging the steel tube wall.

The concrete mixture design is also critical for achieving good bonding performance. The aggregate size, concrete slump, and compaction method all influence the quality of the steel-concrete interface. For CFST applications, a concrete with a moderate slump (typically 100 to 160 mm) and a maximum aggregate size of one-third to one-half of the steel tube diameter is recommended. The compaction method—whether by vibration, pumping, or a combination—should be selected to ensure full concrete placement without voids or honeycombing at the interface.

Integration with Engineering Practice

The findings of this review have direct implications for the design and construction of CFST members. The identification of friction as the dominant bonding mechanism suggests that the contact pressure at the interface, which is influenced by the axial load and the degree of concrete confinement, is the primary factor governing bonding performance. Engineers should ensure that the steel tube and concrete are properly bonded during construction, with particular attention to the compaction quality and the avoidance of voids or laitance at the interface.

The finding that existing test values underestimate the actual bonding strength due to the neglect of material self-weight suggests that current design practices may be conservative. While this conservatism provides a safety margin, it also means that the actual performance of CFST members may exceed the predicted performance, which can be beneficial for seismic design where ductility and energy dissipation are important. However, for economic optimization, more accurate bonding strength predictions that account for the self-weight effect could lead to more efficient designs.

The review also highlights the need for further research on the bonding performance of novel CFST configurations, such as those using high-strength steel tubes, ultra-high-performance concrete, or special environmental conditions such as high temperature or corrosive environments. These emerging applications require a deeper understanding of the bonding mechanisms under extreme conditions, and the review provides a valuable roadmap for future research directions.

Key Questions and Reflections

One critical question is the variability of bonding performance in real-world construction environments. While laboratory tests under controlled conditions provide valuable data, the actual bonding performance in the field can be affected by numerous factors, including concrete placement quality, steel tube surface condition, ambient temperature, and construction sequence. Engineers should consider implementing quality control measures, such as internal inspection of the steel tube surface and monitoring of concrete placement parameters, to ensure consistent bonding performance.

Another point worthy of reflection is the long-term durability of the steel-concrete interface. The bonding performance may degrade over time due to factors such as corrosion of the steel tube, carbonation of the concrete, and cyclic loading. The review does not extensively address these long-term effects, and further research is needed to understand the degradation mechanisms and develop strategies for maintaining bonding performance over the service life of the structure.

Study Insights and Implications

This review provides a valuable synthesis of the current state of knowledge on CFST interface bonding performance and identifies key areas for future research. The identification of friction as the dominant bonding mechanism and the quantification of the factors influencing bonding strength provide clear guidance for engineers designing CFST members. The finding that current design values may be conservative due to the neglect of self-weight effects offers an opportunity for more efficient design, while the emphasis on the need for further research on novel configurations and extreme environments highlights the ongoing challenges in the field. For steel pipe manufacturers, the review underscores the importance of controlling internal surface roughness and surface quality to ensure optimal bonding performance, and for concrete contractors, it highlights the critical role of concrete mixture design and placement quality in achieving good interface bonding.