Residual Load-Bearing Capacity of Square Composite Columns with Internal Circular Steel Tube Concrete Under Lateral Impact Loading

Literature Overview

The research by Tian Xuemei, Zhu Xiang, Li Wenbo, and Wang Weixu, published in 2024 in the journal "Building Structures," investigates the residual load-bearing capacity of square composite columns with internal circular steel tube concrete after lateral impact loading. The study employs finite element analysis using ANSYS/LS-DYNA to establish a numerical model of the composite column under impact conditions. The research analyzes the post-impact axial compression behavior, compares it with the behavior of undamaged columns, and proposes a damage evaluation index (D_dag) for quantifying the residual capacity. This work is relevant to structural engineers working on impact-resistant design of composite structures, particularly in applications such as blast protection, vehicle impact resistance, and seismic resilience.

Core Technical Content

The square composite column with internal circular steel tube concrete is a hybrid structural system that combines the advantages of steel tube concrete (high strength, ductility, and impact resistance) with the architectural and structural benefits of a square cross-section. The internal circular steel tube provides confinement to the concrete core, enhancing its compressive strength and ductility, while the external square section provides architectural regularity and ease of connection with other structural elements.

Numerical Model Development

The finite element model was developed using ANSYS/LS-DYNA, a dynamic explicit finite element software suitable for impact and crash analysis. The model was validated against classical lateral impact test results, demonstrating good agreement in:

• Failure mode – the simulated failure pattern matched the experimental observations
• Impact force history – the simulated impact force-time history correlated well with experimental data
• Displacement response – the simulated lateral displacement matched the measured displacement

Post-Impact Axial Compression Behavior

After lateral impact, the composite column was subjected to axial compression loading until failure. The analysis revealed several important characteristics:

1. Failure mode change – undamaged columns typically fail by axial compression with uniform crushing, while post-impact columns tend to fail by flexural-shear failure due to the damage introduced by the impact.
2. Energy absorption reduction – the energy absorbed during post-impact axial compression is significantly lower than that of undamaged columns, indicating reduced ductility and load-bearing capacity.
3. Residual capacity quantification – the ratio of post-impact axial capacity to undamaged axial capacity provides a measure of the residual load-bearing capacity.

Parametric Study Results

The study investigated the influence of several parameters on the post-impact residual capacity:

The results indicate that impact velocity, axial compression ratio, and slenderness ratio are the most significant parameters affecting both impact resistance and residual capacity. Boundary conditions and steel tube wall thickness have smaller but non-negligible effects.

Damage Evaluation Index (D_dag)

The study proposes a damage evaluation index (D_dag) that quantifies the damage level of the composite column based on the residual capacity ratio. The index allows for rapid assessment of the structural damage following impact, providing a basis for post-event safety evaluation and decision-making regarding structural repair or replacement.

Engineering Practice Implications

Impact-Resistant Design Considerations

For engineers designing composite columns for impact-resistant applications, the following considerations should be incorporated:

• Impact scenario definition – the design must define the expected impact scenarios, including impact velocity, impact mass, and impact location.
• Post-impact performance objectives – the design should specify the required post-impact performance, such as the minimum residual capacity ratio or the maximum acceptable damage level.
• Parametric sensitivity analysis – the sensitivity of the structure to key parameters should be understood to guide design optimization.
• Damage assessment methodology – a practical methodology for post-event damage assessment should be established, incorporating the proposed damage index.

Quality Control and Inspection

For the construction and maintenance of composite columns with internal steel tubes, the following quality control measures are recommended:

• Welding quality – the welds connecting the steel tube to the square section must be inspected using ultrasonic testing (UT) or magnetic particle testing (MT) to ensure full penetration and absence of defects.
• Concrete placement – the concrete must be properly placed and compacted within the steel tube to ensure full filling and adequate confinement.
• Dimensional accuracy – the steel tube dimensions and position must be verified to ensure proper fit within the square section.
• Post-impact inspection – after impact events, the structure should be inspected for visible damage, and the damage index should be calculated to assess the residual capacity.

Study Insights and Reflections

This study addresses an important gap in the understanding of composite column behavior under combined impact and axial loading. While the impact resistance of steel tube concrete columns has been studied extensively, the post-impact residual capacity has received less attention. The proposed damage evaluation index provides a practical tool for post-event assessment, which is critical for emergency response and structural safety management.

The numerical modeling approach demonstrated in this study is robust and validated, providing confidence in the simulation results. The parametric study reveals that impact velocity, axial compression ratio, and slenderness ratio are the critical design parameters, which should be considered in impact-resistant design of composite columns. The relatively small influence of boundary conditions and steel tube wall thickness suggests that these parameters can be optimized for other design objectives without significantly compromising impact performance.

For the structural engineering community, this study contributes to the development of performance-based design methodologies for impact-resistant structures. The integration of numerical simulation, parametric analysis, and damage assessment provides a comprehensive framework that can be adapted to other structural systems and impact scenarios. As the demand for impact-resistant structures grows in applications such as transportation infrastructure, industrial facilities, and protective structures, the continued development of such methodologies will be increasingly important.

Concluding Remarks

These five technical papers collectively address critical aspects of steel pipe and pipe fitting engineering, spanning material metallurgy, forming processes, numerical simulation, process development, and structural performance. The common thread across all studies is the emphasis on systematic analysis, whether through failure analysis methodology, finite element simulation, orthogonal experimental design, or parametric study. Engineers in the steel pipe and fitting industry should recognize that these approaches – metallurgical understanding, computational modeling, systematic experimentation, and quality control – are complementary and must be integrated for successful product development and service performance. The insights gained from these studies should inform both process development and quality assurance practices, ensuring that products meet the demanding requirements of their intended applications.