Impact Resistance of Concrete-Filled Steel Tube Members Under Long-Term Sustained Loading

Literature Overview

This paper, published in Explosion and Shock Waves (2021, Vol. 41, No. 8, pp. 89-101) by Wang Wenda, Chen Zhenfu, and Ji Sunhang from Lanzhou University of Technology, investigates the impact resistance of concrete-filled steel tube (CFST) members subjected to long-term sustained axial loads followed by lateral impact. The research was funded by the National Natural Science Foundation (51778274), Gansu Province Higher Education Collaborative Innovation Team Project (2018C-08), and Lanzhou Science and Technology Plan (2019-1-61).

Core Technical Content

The study employs ABAQUS finite element software to establish coupled analysis models for long-term axial loading with lateral impact, as well as post-impact residual compressive load-bearing capacity models. The comparison between single-loading mode and long-term loading mode reveals critical differences in impact behavior.

Dynamic Response Comparison

Response Parameter	Single Loading Mode	Long-Term Loading Mode
Impact force peak value	Higher	Lower
Impact force plateau value	Higher	Lower
Impact duration	Shorter	Longer
Mid-span deflection	Smaller	Larger
Work done by impact force	Baseline	Approximately equal
Axial load work during impact	Lower	Higher

Residual Compressive Load-Bearing Capacity

Condition	Residual Capacity Coefficient
Single loading mode	Higher
Long-Term loading mode	Lower

Key finding: Under identical impact conditions, members that can continue to bear load after impact in the single-loading mode may lose load-bearing capacity when long-term sustained loading is considered.

Influence of Design Parameters

Parameter	Effect on Mitigating Long-Term Load Adverse Effects
Steel ratio increase	Effective mitigation
Steel yield strength increase	Effective mitigation
Long-term load ratio decrease	Effective mitigation

The additional work done by the axial load during impact in the long-term loading mode is primarily dissipated through plastic deformation of the outer steel tube, with minimal contribution from the core concrete.

Engineering Practice Insights

This research addresses a critical but often neglected scenario in structural engineering: the vulnerability of CFST members that have been subjected to long-term sustained loads (such as creep and sustained compressive stresses) when they encounter impact events such as vehicle collisions, falling objects, or blast loads.

From a steel pipe engineering perspective, the findings have several important implications:

Residual capacity degradation: The long-term sustained load pre-conditions the steel tube material through creep deformation and potential microstructural changes (such as stress relaxation and dislocation rearrangement), reducing the material's capacity to absorb impact energy through plastic deformation.
Plastic deformation dominance: The observation that the outer steel tube absorbs most of the additional axial load work through plastic deformation highlights the importance of steel tube material ductility and strain-hardening behavior. For CFST members in impact-critical applications, steel grades with adequate elongation and uniform elongation (such as Q345 with sufficient elongation or high-strength steels with good ductility) should be specified.
Design recommendations: Increasing the steel ratio and steel yield strength, or reducing the long-term load ratio, are effective strategies to mitigate the adverse effects of sustained loading on impact resistance. In practice, this means that CFST members in high-rise building cores, bridge piers, and industrial structures should be evaluated for combined sustained load and impact scenarios.

FMEA Considerations for CFST Members

Failure Mode	Cause	Detection Method	Mitigation
Loss of post-impact load capacity	Long-term creep pre-conditioning	Post-impact NDT (UT, MT)	Increase steel ratio
Excessive mid-span deflection	Pre-existing creep deformation	Visual inspection, laser scanning	Reduce sustained load ratio
Steel tube local buckling	Plastic deformation accumulation	Radiographic testing	Use higher-strength steel
Concrete spalling	Impact-induced cracking	Visual inspection, tap testing	Increase confinement effectiveness

Key Reflections and Implications

This research fills an important gap in the understanding of CFST structural performance under combined long-term and impact loading conditions. The finding that residual load-bearing capacity is significantly reduced under long-term sustained loading has direct implications for the safety assessment of existing CFST structures, particularly those in nuclear facilities, bridge piers, and industrial plants where long-term sustained loads are inevitable and impact events are potential hazards.

Engineers should consider incorporating long-term loading effects into impact resistance design criteria for CFST members, particularly when the service life involves decades of sustained compressive loading. The proposed residual load-bearing capacity coefficient provides a quantitative metric that can be integrated into performance-based design frameworks. Future research should extend these findings to full-scale experimental validation and consider additional factors such as temperature effects, corrosion, and fatigue cycling that may further degrade the impact resistance of CFST members under long-term service conditions.