Dynamic Response of Hollow Box Steel Tube Concrete Composite Columns Under Lateral Impact Loading

Literature Overview

This paper by Jia Zhilu and Wang Rui, published in Journal of Vibration and Shock (2019, Vol. 38, No. 9, pp. 166-172), presents experimental and numerical investigations into the impact resistance of hollow box steel tube concrete composite columns. The research was supported by the National Natural Science Foundation of China (Grant No. 51378290) and the Shanxi Provincial Excellent Youth Fund Project (201701D211006). The authors, from the School of Architecture and Civil Engineering at Taiyuan University of Technology, conducted drop-weight impact tests using a self-developed drop hammer testing machine and performed finite element analysis using ANSYS/LS-DYNA software.

Structural Configuration and Test Setup

The hollow box steel tube concrete composite column combines reinforced concrete (RC) and steel tube concrete (SC) components, where the steel tube is embedded within the RC section in a hollow box configuration. This hybrid structural concept leverages the high ductility and energy absorption capacity of steel tube concrete with the compressive strength of reinforced concrete. The hollow box geometry introduces a void region that affects the load path and energy dissipation mechanism during impact events.

Experimental Parameters

The drop hammer test simulates impact loading conditions that may arise from vehicle collisions, explosion events, or seismic-induced pounding in structural applications. The impact force time-history and mid-span displacement were the primary response quantities measured during testing.

Core Findings and Analysis

Impact Force Time-History Evolution

The experimental results revealed that as impact height increased, the impact force time-history curve evolved from a two-stage pattern to a three-stage pattern. This transition indicates a shift in the energy dissipation mechanism: at lower impact energies, the RC component dominates the response, while at higher energies, the embedded steel tube concrete component progressively engages and contributes significantly to the load-bearing capacity. The three-stage pattern likely corresponds to: (1) initial elastic contact phase, (2) plastic deformation phase involving both RC and SC components, and (3) post-yield hardening or damage phase where the SC component provides sustained resistance.

Energy Absorption Distribution

The finite element analysis using LS-DYNA revealed the internal energy distribution among the structural components. A key finding was that when impact energy was sufficiently large, the steel tube concrete component absorbed approximately one-third of the total impact energy. This is a significant result because it demonstrates that the embedded steel tube concrete functions as an effective energy dissipator under severe impact loading, contributing substantially to the overall impact resistance of the composite column.

Boundary Condition Effects

The comparison between simply supported and fixed-fixed boundary conditions showed that the fixed-fixed configuration provided enhanced deformation resistance. This is consistent with classical structural mechanics, where rotational restraint at the supports increases the effective stiffness and reduces the span deflection under transverse loading. However, the energy absorption capacity may differ between the two configurations, with simply supported conditions potentially allowing greater plastic deformation and hence higher energy dissipation through ductile mechanisms.

Axial Compression Ratio Influence

Contrary to what might be expected from static loading behavior, the axial compression ratio had a relatively insignificant effect on the dynamic response of the composite column. This finding suggests that under impact loading conditions, the dynamic interaction between the steel tube and concrete core, governed by the confinement effect and strain-rate sensitivity of materials, dominates over the influence of pre-existing axial stress. This is an important distinction from quasi-static behavior and has implications for the design of impact-resistant structures that may also carry significant axial loads.

Engineering Practice Integration

FMEA Analysis of Potential Failure Modes

Design Implications

The finding that the steel tube concrete component absorbs up to one-third of the impact energy at high energy levels has direct implications for the design of blast-resistant and impact-resistant structures. Engineers designing critical infrastructure such as bridges, tunnels, and industrial facilities should consider the hollow box steel tube concrete configuration as a viable option for achieving enhanced impact resistance without proportionally increasing material usage. The hollow void region, while reducing overall weight, does not significantly compromise impact performance because the energy is effectively channeled into the steel tube concrete component.

The relatively minor influence of axial compression ratio on dynamic response simplifies the design process, as engineers need not extensively parametrize the interaction between axial pre-stress and impact loading. However, this conclusion should be applied cautiously, as the test conditions may not fully represent all practical scenarios, particularly those involving combined axial and lateral loading at high strain rates.

Key Reflections and Insights

The transition from two-stage to three-stage impact force time-history with increasing impact energy is a particularly insightful observation. It suggests a threshold behavior where the composite action between RC and SC components becomes active only beyond a certain energy level. This threshold energy level is critical for design purposes, as it defines the boundary between elastic and inelastic response regimes. Engineers should determine this threshold for specific structural configurations to ensure that the design provides adequate protection within the expected impact energy range.

The use of a self-developed drop hammer testing machine reflects the dedication of the research team to experimental validation, which is essential for building confidence in numerical models. The agreement between experimental results and LS-DYNA simulations validates the numerical approach and provides a reliable tool for parametric studies that would be impractical to conduct experimentally. Future work should extend this research to include multi-impact scenarios, where a structure may experience repeated impact events, and to investigate the residual capacity after initial impact damage.

The hollow box configuration presents an interesting design philosophy where the void region serves as a controlled deformation zone while the steel tube concrete provides the primary energy absorption mechanism. This concept could be further developed for applications in protective structures, such as blast walls, impact barriers, and seismic isolation systems, where controlled energy dissipation is a primary design objective.