Blast Dynamic Response of Steel Tube RPC Columns After Fire Exposure

Literature Overview and Research Context

This paper by Zou Huihui, Chen Wanxiang, Guo Zhikun, and Zhou Zixin from the State Key Laboratory of Explosion Shock Disaster Prevention and Mitigation at Army Engineering University and the School of Civil Engineering at Sun Yat-sen University investigates the blast dynamic response of steel tube confined reactive powder concrete (RPC) columns after fire exposure. Published in 2019 in the journal Vibration and Shock (Vol. 38, No. 21, pp. 155-163), the study was supported by the National Natural Science Foundation of China (51378498, 51578541) and the Jiangsu Provincial Natural Science Foundation (BK20141066). The research addresses the critical challenge of multi-hazard structural protection, where engineering structures must be designed to withstand sequential or concurrent threats such as fire followed by blast loading.

Numerical Simulation Methodology

The study employs a two-stage numerical simulation approach using LS-DYNA and ANSYS software. The first stage involves thermal analysis in ANSYS to determine the temperature field distribution within the steel tube RPC column under ISO-834 standard fire exposure. The second stage involves dynamic blast analysis in LS-DYNA using the residual strength data obtained from the thermal analysis. The steel tube is modeled using an elastic-plastic constitutive model, while the RPC core is modeled using the Kim & Card (K&C) concrete damage model, which captures the nonlinear behavior of concrete under dynamic loading.

Simulation Parameters and Variables

Core Findings and Technical Interpretation

The numerical simulation results show good agreement with experimental data, validating the proposed simulation methodology for capturing the blast dynamic behavior of fire-exposed steel tube RPC columns. The key findings include: after fire exposure, the steel tube still effectively confines the core RPC under blast loading, and the column failure mode is predominantly bending failure, indicating good blast resistance performance. The high-temperature exposure causes strength degradation and stiffness reduction of the steel tube concrete column, resulting in significantly increased deformation under blast loading. Reducing the scaled distance causes more pronounced deformation at the mid-span of the column, with a tendency toward shear failure at the supports.

Effect of Load Parameters

The fire duration directly influences the degree of strength degradation and stiffness loss of the column. Longer fire exposure results in lower residual strength and greater deformation under subsequent blast loading. The scaled distance, which represents the ratio of the charge weight to the distance from the explosion source to the column, has a significant effect on the blast response. A smaller scaled distance corresponds to a more intense blast loading, which causes more severe deformation and potential shear failure at the supports. The axial load level affects the initial stress state of the column, which influences the post-fire blast response through the interaction between axial compression and blast-induced bending.

Effect of Geometric and Material Parameters

The steel ratio, defined as the ratio of the steel tube cross-sectional area to the total cross-sectional area, has a significant influence on the blast resistance performance of the column. A higher steel ratio provides greater confinement and load-carrying capacity, which improves the blast resistance after fire exposure. The length-to-diameter ratio affects the slenderness and bending capacity of the column, with more slender columns exhibiting greater deformation under blast loading. The steel strength grade influences the residual strength after fire exposure, with higher-strength steels generally retaining more strength at elevated temperatures compared to lower-strength grades.

Engineering Practice Implications

For engineers involved in the design of structures that must withstand multi-hazard scenarios, the findings of this study provide important guidance. The validation of the numerical simulation methodology offers a practical tool for predicting the post-fire blast response of steel tube RPC columns, which can be used in the design phase to optimize the structural configuration. The emphasis on the steel ratio as a key parameter suggests that engineers should carefully consider the trade-off between structural efficiency and blast resistance when selecting the steel tube thickness and diameter. The observation that shear failure at the supports becomes a concern at smaller scaled distances highlights the need for adequate shear reinforcement at the column supports, particularly in structures designed for blast resistance.

From a materials engineering perspective, the use of RPC as the core material offers advantages over conventional concrete due to its higher strength, stiffness, and post-fire residual strength. The combination of RPC with a steel tube confinement provides a synergistic effect that enhances the overall structural performance under multi-hazard loading. Engineers should also consider the effect of fire protection systems, such as intumescent coatings or fire-resistant enclosures, which can reduce the peak temperature exposure of the steel tube and RPC core.

Study Insights and Professional Reflection

This research addresses an important and increasingly relevant topic in structural engineering, as the threat of multi-hazard scenarios becomes more prevalent in urban environments. The integration of thermal analysis and dynamic blast simulation provides a comprehensive framework for evaluating the structural performance of steel tube RPC columns under sequential fire and blast loading. The finding that the steel tube still effectively confines the core RPC after fire exposure is encouraging, as it demonstrates the robustness of the composite system under extreme conditions. The identification of shear failure at the supports as a potential failure mode at small scaled distances is a critical finding that should be incorporated into design practices. Engineers should adopt a multi-hazard design approach that considers the interaction between different threat scenarios and optimizes the structural configuration to provide adequate performance under the most severe expected loading conditions.