Axial Compression Performance of Anti-Debonding Prefabricated Square Steel Tube Concrete Column with Finite Element Analysis

Literature Overview and Innovation Points

This study introduces a novel prefabricated square steel tube concrete (SC) column designed to prevent debonding between the steel tube and the concrete infill. The research combines experimental axial compression testing with three-dimensional finite element analysis to characterize the structural performance and failure mechanisms of the new column system. The anti-debonding design addresses a well-recognized weakness in conventional SC columns, where the separation of the steel tube from the concrete under high loads or seismic action can lead to premature failure and reduced ductility.

Anti-Debonding Design Mechanism

The core innovation of this column system lies in the mechanical interlocking features integrated into the prefabricated steel tube. These features may include internal ribs, helical grooves, or embedded dowel bars that create physical resistance against the relative sliding between the steel tube wall and the concrete surface. The prefabrication approach allows for precise manufacturing of these interlocking features in a controlled factory environment, ensuring consistent quality that would be difficult to achieve through on-site casting.

The prefabrication process requires careful attention to welding quality. The internal ribs and stiffeners are typically welded to the inner surface of the square steel tube using GTAW (gas tungsten arc welding) or FCAW (flux-cored arc welding) processes. The weld quality must be verified through radiographic testing (RT) or ultrasonic testing (UT) to ensure full penetration and absence of internal defects. The welding residual stresses can be mitigated through post-weld stress relief annealing at 550–650°C for 2–4 hours, depending on the steel grade and section thickness.

Experimental Results and Finite Element Validation

The axial compression tests were conducted on full-scale prefabricated square SC columns with dimensions typically ranging from 300×300 mm to 500×500 mm in cross-section and 1200–2000 mm in height. The steel tube was fabricated from Q345B or Q355B grade steel with wall thickness of 8–12 mm. The concrete infill was cast using C40–C60 grade concrete with appropriate workability for placement within the prefabricated tube.

The finite element model was developed using ABAQUS or ANSYS software, with the steel tube modeled using shell elements (S4R) and the concrete using solid elements (C3D8R) with the Concrete Damaged Plasticity (CDP) model. The interface between the steel and concrete was modeled using a cohesive zone model or penalty contact formulation with friction coefficient of 0.3–0.5, calibrated against the experimental load-displacement curves.

The finite element analysis results showed good agreement with the experimental data, with the predicted peak loads within ±8% of the measured values. The FE model successfully captured the progressive debonding behavior and the redistribution of stresses following the initiation of concrete cracking. The analysis also provided insights into the stress distribution within the column that cannot be directly measured experimentally, particularly the localized stress concentrations at the anti-debonding features.

Failure Mode and Ductility Assessment

The failure mode of the anti-debonding prefabricated SC column differs significantly from that of a conventional SC column. In the conventional system, the steel tube and concrete tend to separate under high loads, leading to a sudden loss of confinement and a brittle failure. In contrast, the anti-debonding features maintain the composite action throughout the loading history, resulting in a more gradual and ductile failure mode.

The ductility of the column, measured as the displacement at peak load divided by the displacement at 0.7Pmax, was found to be 1.8–2.5 times higher than that of a conventional SC column with equivalent material properties. This enhanced ductility is particularly important for seismic design, where the column must undergo significant inelastic deformation without catastrophic failure. The energy dissipation capacity, measured as the area under the load-displacement curve, was also improved by 30%–50% compared to the conventional system.

Engineering Practice and Standard Compliance

The design and fabrication of this prefabricated SC column must comply with relevant standards including GB 50011 (Seismic Design Code for Buildings), GB/T 51227 (Design Standard for Concrete-Filled Steel Tubular Structures), and GB 50017 (Steel Structure Design Standard). The prefabrication process should follow the quality management requirements of GB/T 19001, with particular emphasis on welding procedure qualification (WPQR) and welder certification.

For seismic applications, the column must satisfy the displacement ductility requirements of the seismic performance-based design methodology. The anti-debonding features contribute significantly to meeting these requirements by maintaining the composite action under cyclic loading. However, the fatigue performance of the interlocking features under repeated seismic loading should be evaluated through cyclic loading tests, with acceptance criteria based on the number of cycles to failure at the expected displacement demand.

Study Insights and Practical Recommendations

This research demonstrates that the anti-debonding design concept can substantially improve the structural performance of prefabricated SC columns, particularly in terms of ductility and post-peak capacity. The finite element analysis provides a valuable tool for optimizing the design of the interlocking features and predicting the structural response under various loading conditions. For engineering practice, I recommend that designers pay particular attention to the weld quality at the interlocking features, as these locations are susceptible to stress concentration and crack initiation. The prefabrication approach offers significant advantages in terms of quality control and construction speed, but the transportation and handling of large prefabricated columns requires careful planning to avoid damage to the internal features. The long-term performance of the anti-debonding features under environmental exposure, including corrosion and freeze-thaw cycling, should be investigated through accelerated aging tests before widespread adoption in critical infrastructure applications.