Blast Resistance Performance of CFRP-Concrete-Steel Tube Composite Columns: Numerical Analysis

Literature Overview

Chen Ruilin, Zhang Zhan, Zhou Zhenyu, and Zhou Shengshu (published in Engineering Blasting, Vol. 26, No. 6, 2020, pp. 9–16) present a numerical investigation of the blast response of Carbon Fiber Reinforced Polymer (CFRP)-concrete-steel tube composite columns. Funded by the National Natural Science Foundation of China (51434002) and Hunan Provincial Natural Science Foundation (07JJ6004), this study from Putian University and Xiangtan University employs finite element analysis to evaluate the protective effect of CFRP wrapping on steel tube-concrete composite columns under explosion loading.

Structural Configuration and Analytical Method

The composite column under investigation consists of three concentric layers: an inner concrete core, a middle steel tube, and an outer CFRP wrapping. This configuration leverages the complementary mechanical properties of each material: concrete provides compressive strength and mass, the steel tube provides ductility and confinement, and the CFRP provides high tensile strength with minimal weight addition.

The numerical analysis was conducted using ANSYS/LS-DYNA with the Arbitrary Lagrangian-Eulerian (ALE) algorithm for multi-material fluid-solid coupling. The ALE formulation is essential for accurately capturing the shock wave propagation, air-structure interaction, and large deformation behavior that characterize blast loading scenarios. The shock wave from the explosion is modeled as an air blast load applied to the column surface, with the ALE formulation handling the interaction between the compressible air medium and the deformable solid structure.

Analytical Parameters

Key Findings and Technical Analysis

CFRP contribution: The CFRP wrapping significantly enhances the lateral stiffness and ductility of the composite column compared to a conventional concrete-steel tube column without CFRP. The CFRP effectively delays the onset of cracking and deformation, allowing the column to sustain larger displacements before failure. This is attributed to the high tensile strength of CFRP, which constrains the outward bulging of the steel tube and provides additional confinement to the concrete core.

Steel content ratio: Increasing the steel content ratio effectively reduces both the peak displacement and residual displacement of the column under blast loading. A higher steel content ratio means a thicker steel tube or additional steel reinforcement, which provides greater structural resistance to the blast-induced lateral forces. This parameter is monotonically beneficial within the studied range.

Hollow ratio: The hollow ratio (ratio of hollow section area to total cross-sectional area) exhibits a non-monotonic effect. Within a certain range, increasing the hollow ratio improves blast performance, likely because the hollow section reduces the mass subject to blast loading while maintaining sufficient structural stiffness. However, beyond an optimal value, further increasing the hollow ratio weakens the structural integrity and degrades blast resistance.

Axial compression ratio: Similar to the hollow ratio, the axial compression ratio exhibits a non-monotonic effect. Within a critical range, increasing the axial compression ratio enhances blast performance, possibly due to the pre-stressing effect that increases the column's resistance to lateral deformation. However, beyond the critical value, the increased axial load promotes buckling and reduces the column's capacity to resist lateral blast forces.

Performance Comparison: CFRP vs. Conventional

Engineering Practice and Design Implications

The study provides valuable guidance for the design of blast-resistant columns in critical infrastructure, including military facilities, government buildings, hospitals, and energy installations:

1. CFRP wrapping is an effective retrofit strategy for existing concrete-steel tube columns, providing significant blast resistance enhancement without major structural modifications.
2. The optimal hollow ratio and axial compression ratio must be determined through parametric analysis for each specific application, as both parameters exhibit non-monotonic effects.
3. Increasing the steel content ratio is a straightforward design lever for improving blast performance, though it must be balanced against weight and cost considerations.
4. The numerical methodology (ALE formulation in LS-DYNA) is validated as an appropriate tool for blast analysis of composite columns, though experimental validation is recommended for critical applications.

Design Optimization Strategy

Study Insights

This research contributes to the growing body of knowledge on composite column design for extreme loading conditions. The use of ALE formulation is methodologically appropriate for capturing the complex fluid-solid interaction inherent in blast loading. The identification of optimal ranges for hollow ratio and axial compression ratio is particularly valuable, as these parameters have competing effects that are not intuitive to engineers. The study also highlights the potential of CFRP as a lightweight, high-strength reinforcement for blast protection, offering a practical retrofit solution that does not significantly increase structural weight. However, engineers should note that the study is purely numerical, and experimental validation under actual blast loading conditions would strengthen the confidence in the design recommendations. The parametric study approach is well-suited for identifying design trends, but detailed design of specific columns should incorporate material-specific properties and boundary conditions unique to each application.