Bond-Slip Behavior in Concrete-Filled Steel Tubes: A Comprehensive Review

Literature Overview

The review paper by Kang Xiliang, Zhao Hongtie, Xue Jianyang, and Chen Zongping from Xi'an University of Architecture and Technology, published in Journal of Xi'an University of Architecture and Technology (Vol. 38, No. 3, 2006, pp. 321-326), provides a systematic analysis of the bond strength and bond-slip behavior between the steel tube and concrete in concrete-filled steel tube (CFST) members. Funded by the National Natural Science Foundation of China (Project No. 50478044), this review synthesizes international and domestic research findings to identify existing gaps and provide guidance for future investigation.

Fundamental Bond-Slip Mechanism

The bond between the steel tube wall and the confined concrete core is the primary mechanism through which composite action is achieved in CFST members. This interfacial bond transfers shear stresses between the two materials, enabling them to act as a unified structural element rather than as independent components. The bond-slip relationship is nonlinear and evolves through several stages: initial elastic adhesion, progressive debonding, and eventual frictional sliding.

Bond Strength Development Stages

Stage	Bond-Slip Behavior	Dominant Mechanism
Initial loading	Linear elastic bond	Adhesion and mechanical interlock
Peak bond stress	Maximum bond strength reached	Combined adhesion and friction
Post-peak	Descending bond stress with increasing slip	Frictional sliding and aggregate interlock
Residual	Constant residual bond stress	Pure friction

Factors Influencing Bond Strength

The review identifies several critical factors that influence the bond strength between the steel tube and concrete:

Factor	Influence on Bond Strength	Engineering Significance
Concrete strength	Higher strength generally increases bond	Material selection for high-performance CFST
Steel tube diameter-to-thickness ratio	Larger D/t ratio may reduce bond efficiency	Affects design of large-diameter columns
Concrete casting method	Centrifugal casting produces denser interface	Manufacturing process selection
Tube surface roughness	Rougher surface increases mechanical interlock	Surface treatment considerations
Axial compressive stress	Pre-compression enhances bond through friction	Residual stress effects in service
Concrete moisture content	Affects adhesion and shrinkage	Quality control of concrete placement

Bond-Slip Constitutive Models

The review critically examines existing bond-slip constitutive models and identifies limitations in current approaches. Most models adopt a simplified bilinear or trilinear relationship, which may not adequately capture the complex interfacial behavior under cyclic or impact loading. The review highlights that the transition from adhesion to friction is not abrupt but gradual, and that the residual frictional bond stress is often underestimated in conventional models.

Quality Control Implications for Steel Pipe Manufacturing

For steel pipe manufacturers producing tubes intended for CFST applications, the internal surface condition of the tube is a critical quality parameter. Excessive surface roughness from the welding seam (in welded tubes) or from manufacturing scale (in hot-rolled tubes) can affect the bond strength in unpredictable ways. The review implicitly suggests that a controlled surface finish is beneficial, though the optimal roughness profile remains an area requiring further research.

Concrete Placement and Filling Quality

The quality of concrete placement within the steel tube is equally critical. Inconclusive filling, void formation, or segregation during placement can create weak zones at the interface that compromise the composite action. For large-diameter tubes, the use of self-compacting concrete or vibrated placement with internal access is recommended. The review emphasizes that the current understanding of bond-slip behavior is insufficient to establish reliable quality control criteria for concrete filling, which represents a significant challenge for engineering practice.

Key Reflections

This review, while published in 2006, remains relevant as the fundamental bond-slip mechanisms in CFST members have not changed. The identified research gaps—particularly regarding the bond behavior under cyclic loading, the effect of different concrete casting methods, and the development of more sophisticated constitutive models—have seen partial progress in subsequent literature but remain active areas of investigation. For steel pipe manufacturers and structural engineers, the practical takeaway is that the bond-slip interface is a critical but often overlooked aspect of CFST design. The design codes (such as GB 51248, JGJ/T 70, and AISC 360) provide simplified approaches for composite action, but the underlying bond mechanism warrants more attention in performance-based design, particularly for applications involving seismic or impact loading where the bond may be the governing failure mechanism.