Numerical Simulation of Dynamic Response of Slab-Column Structures under Fire-Explosion Coupled Effects
ObjectiveSlab-column structures exhibit inherent vulnerabilities to extreme events due to low structural redundancy. While their response to individual fire or explosion hazards has been studied, the sequential scenario of a fire followed by an explosion presents a complex challenge that is not well...
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| Main Authors: | , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Editorial Department of Journal of Sichuan University (Engineering Science Edition)
2025-01-01
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| Series: | 工程科学与技术 |
| Subjects: | |
| Online Access: | http://jsuese.scu.edu.cn/thesisDetails#10.12454/j.jsuese.202500389 |
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| Summary: | ObjectiveSlab-column structures exhibit inherent vulnerabilities to extreme events due to low structural redundancy. While their response to individual fire or explosion hazards has been studied, the sequential scenario of a fire followed by an explosion presents a complex challenge that is not well understood. This sequence can produce synergistic effects, where the resulting damage significantly exceeds the linear superposition of each isolated event. A critical knowledge gap exists in quantitatively understanding these coupled effects and the governing parameters that influence the structural behavior. This research aims to address this problem by employing high-fidelity numerical simulation to analyze the dynamic response of a full-scale slab-column structure subjected to combined fire-blast loading. The primary objective is to systematically investigate and quantify the influence of crucial parameters—including fire duration, explosive charge mass, scaled distance, and detonation location—on the structural response. The work's necessity lies in providing a validated, data-driven framework for developing more accurate vulnerability assessments and robust protective design strategies for structures facing these complex, multi-hazard threats.MethodsA sequential, uncoupled thermomechanical analysis was conducted using the commercial finite element package ABAQUS. The methodology was bifurcated into three primary stages: individual model validation, coupled model creation, and parametric analysis. In the validation stage, two distinct finite element models were developed and rigorously validated against full-scale experimental data from existing literature. First, a heat transfer and structural fire model was validated against the large-scale RC space frame fire tests conducted by Wang et al. This model incorporated temperature-dependent thermal and mechanical properties for concrete and steel reinforcement as specified by Eurocode standards, utilizing a concrete damage plasticity (CDP) model to capture material degradation at elevated temperatures. The thermal load was applied according to the ISO-834 standard fire curve. Second, a dynamic explosion model was validated against the blast tests on a full-scale two-span slab-column structure reported by López et al. This model utilized material constitutive laws that accounted for high-strain-rate effects, specifically a rate-sensitive CDP model for concrete and the Johnson-Cook material model for steel reinforcement. The blast load was simulated efficiently using the integrated CONWEP (Conventional Weapons Effects Program) algorithm, which applies empirical pressure-time histories without modeling the surrounding air medium. Following successful validation, the coupled fire-explosion model was established. This was achieved through a sequential analysis procedure where the complete results file (containing temperature distributions, material property degradation, stress fields, and deformations) from the thermal-fire simulation was imported as a predefined initial state for the subsequent explicit dynamic blast simulation. This one-way coupling method ensures that the effects of the preceding fire are fully accounted for when the structure is subjected to the explosion. Finally, a comprehensive parametric study was conducted on this coupled model to investigate the sensitivity of the structural response to four key variables: fire duration was varied (0.5 h, 1.0 h, 2.0 h, 3.0 h); TNT equivalent charge mass was altered (5 kg, 10 kg, 20 kg, 40 kg); the scaled distance was adjusted (Z = 0, 0.18, 0.37, and 1.11 m/kg¹/³); and five distinct detonation locations were analyzed to contrast the effects of explosions near columns versus slab centers.Results and Discussions The validation phase confirmed the high fidelity of the numerical models. The fire model accurately reproduced the temperature-time histories and displacement trends observed in the reference experiment. The explosion model showed excellent agreement with blast test data, successfully capturing the acceleration-time history profiles and, most importantly, predicting the final failure mode and damage diameters with a relative error of less than 10%. The core analysis of the coupled model quantitatively confirmed the existence of a severe synergistic effect. Three metrics were proposed to evaluate this: the Damage Superposition Ratio (DSR), the Displacement Amplification Rate (DAR), and the Frequency Attenuation Ratio (FAR). The analysis yielded a DSR of 1.3, a DAR of 1.2, and an FAR of 1.5. As all calculated ratios were significantly greater than 1, it was demonstrated that fire pre-damage nonlinearly amplifies the structural damage, residual displacement, and stiffness degradation caused by a subsequent blast. This is attributed to the thermal degradation of material strength and stiffness creating "pre-paths" for damage propagation under the blast load. The detailed parametric study provided further quantitative insights. It was found that fire duration acts as a critical precursor; increasing the duration from 0 to 2.0 hours led to a modest 5% increase in peak blast-induced displacement, but a further increase to 3.0 hours caused a sharp 20% jump in displacement, indicating a critical threshold for structural integrity at approximately 2 hours. The explosive charge mass exhibited a highly nonlinear influence on the response; an 8-fold increase in TNT mass (5 kg to 40 kg) triggered a nearly 7-fold increase in peak displacement (from -27.9 mm to -221.0 mm) and a 2.3-fold expansion of the damage area diameter. This increase in blast intensity also induced a critical shift in the failure mode towards brittle punching shear at the slab-column connections. The scaled distance showed a non-monotonic relationship with structural damage. A contact explosion (Z=0) was found to be less destructive than a blast at a small standoff distance, with the maximum structural response occurring at a scaled distance of Z ≈ 0.18 m/kg¹/³. Lastly, the detonation location was found to dictate the structural failure mechanism. Explosions initiated directly above columns resulted in concentrated punching shear failure, characterized by high-magnitude, rapidly developing column reaction forces (peak ~64 kN). In contrast, explosions initiated over the slab mid-span led to widespread flexural damage over a larger area, associated with smaller, delayed column reaction forces (peak ~14 kN).ConclusionsThis research successfully developed and validated a numerical framework to investigate the dynamic response of slab-column structures under sequential fire-explosion events. The study quantitatively proves that a significant synergistic coupling effect exists, where prior fire damage nonlinearly amplifies the structural failure caused by a subsequent blast. The damage, deformation, and stiffness loss in the coupled scenario are considerably greater than what would be predicted by a simple superposition of the individual hazards. The key principles established by this work provide a basis for more advanced structural design and assessment. The findings identify a critical fire duration (~2 hours) that can serve as a threshold for vulnerability assessments. A clear, exponential relationship between explosive mass and the onset of brittle punching shear failure was established. Furthermore, the research highlights the critical importance of standoff distance, demonstrating that a small air gap can be more destructive than a contact charge. Finally, a direct correlation between explosion location and the resulting structural failure mode was defined. Collectively, these results provide an essential theoretical foundation and practical quantitative data for enhancing the resilience and protective design of structures against complex, multi-hazard scenarios, moving beyond the limitations of single-hazard analysis. |
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| ISSN: | 2096-3246 |