Advanced Seismic Fragility: Diverse Structures and Factors

Isabelle Martin^*
*Correspondence: Isabelle Martin, Department of Structural and Seismic Engineering, University of Grenoble, Grenoble 38000, France, Email:

Introduction

A fundamental aspect of earthquake engineering involves understanding the seismic fragility of various structures to ensure their resilience and public safety. This goal drives extensive research, such as the investigation into existing reinforced concrete bridges. One study specifically accounts for the complex effects of spatially variable ground motions. It highlights how variations in ground motion across a bridge's span can significantly alter its seismic performance and damage probability, leading to more accurate assessments than traditional uniform ground motion assumptions [1].

Another critical area involves assessing the vulnerability of steel frame buildings, particularly when subjected to mainshock-aftershock sequencesâ??a scenario often overlooked yet highly impactful. Research in this domain integrates machine learning techniques to efficiently model and predict structural damage probabilities, clearly demonstrating that aftershocks can substantially increase fragility compared to considering mainshocks alone [2].

Beyond modern structures, the seismic fragility assessment of older or specialized buildings is equally vital. For example, a method was presented for unreinforced masonry buildings, combining incremental dynamic analysis (IDA) with machine learning. This innovative approach enhances the efficiency of fragility curve generation and provides insights into the vulnerability of these older structures, showcasing how Machine Learning can accelerate complex seismic evaluations [3].

The analysis of base-isolated structures under seismic loads is another key focus, especially concerning their response to spatially varying ground motions. It reveals that the effectiveness of base isolation can be significantly influenced by the non-uniformity of ground excitation, offering crucial insights for the design and performance assessment of such critical infrastructure [4].

Underground infrastructure also faces unique challenges. Research has performed a seismic fragility analysis for shield tunnels situated in soft soil environments, specifically addressing the spatial variability of ground motion. This work demonstrates that neglecting this variability can lead to an underestimation of damage probabilities, underscoring the need for more sophisticated seismic design approaches for these essential underground structures [5].

The interaction between soil and structure is a persistent factor in seismic performance. A specific study focused on the seismic fragility of gravity retaining walls, explicitly integrating soil-structure interaction effects into the analysis. Its findings reveal that ignoring the dynamic interaction between the wall and the surrounding soil can lead to inaccurate fragility assessments, providing critical insights for geotechnical earthquake engineering design [6].

Similarly, in high-stakes environments, such as nuclear power plants, robust seismic analysis is paramount. Research conducted a seismic fragility analysis of a standard reactor building within a nuclear power plant, incorporating detailed soil-structure interaction effects. This highlights the importance of accurately modeling these interactions to derive reliable fragility curves, which are essential for assessing the safety and resilience of such critical nuclear facilities [7].

Aging infrastructure presents its own set of vulnerabilities. One paper investigated the seismic fragility of buried pipelines, uniquely considering the combined impacts of corrosion and various failure modes. It demonstrates that pre-existing corrosion significantly increases the vulnerability of pipelines to seismic events, providing a comprehensive framework for assessing and mitigating risks in aging infrastructure networks [8].

Urban development introduces challenges like structural pounding. Research conducted a seismic fragility analysis of high-rise buildings, specifically examining the detrimental effects of structural pounding during earthquakes. It quantifies how adjacent buildings colliding can dramatically increase damage probability, emphasizing the need for adequate separation gaps in urban seismic design [9].

Finally, the integrity of renewable energy infrastructure also relies on accurate seismic assessment. A study presented a seismic fragility analysis for onshore wind turbines, integrating the critical aspect of soil-structure interaction. It reveals that the dynamic coupling between the turbine foundation and the soil significantly influences the overall seismic response and damage susceptibility, offering vital data for the resilient design of wind energy infrastructure [10].

Description

Seismic fragility analysis is a crucial field within earthquake engineering, focusing on understanding and predicting the damage probability of structures when subjected to seismic events. A significant recurring theme across various studies is the impact of spatially variable ground motions. For instance, the seismic fragility of existing reinforced concrete bridges is notably affected by how ground motion varies across a bridge's span, altering performance and damage probability compared to uniform assumptions [1]. Similarly, the effectiveness of base isolation in structures can be influenced by the non-uniformity of ground excitation, providing insights for critical infrastructure design [4]. Even underground structures, such as shield tunnels in soft soil environments, show that neglecting this spatial variability can lead to an underestimation of damage probabilities, underscoring the need for sophisticated design approaches for these vital systems [5].

Beyond standard single-event analyses, research extends to more complex seismic scenarios and advanced analytical methods. The seismic fragility of steel frame buildings under mainshock-aftershock sequences represents a critical, yet often overlooked, scenario. Integrating machine learning techniques helps efficiently model and predict structural damage probabilities, demonstrating that aftershocks can substantially increase fragility compared to mainshocks alone [2]. Machine Learning also proves valuable in assessing the seismic fragility of unreinforced masonry buildings. Combining incremental dynamic analysis with Machine Learning enhances the efficiency of fragility curve generation, offering insights into the vulnerability of these older structures and accelerating complex seismic evaluations [3].

Another key aspect that significantly influences seismic response is soil-structure interaction. Studies explicitly integrate these effects into their analyses to achieve more accurate fragility assessments. For gravity retaining walls, for example, ignoring the dynamic interaction between the wall and the surrounding soil can lead to inaccurate fragility assessments, which are vital for geotechnical earthquake engineering design [6]. The importance of accurately modeling these interactions is also evident in critical facilities like nuclear power plants, where a detailed seismic fragility analysis of a typical reactor building revealed that reliable fragility curves are contingent on precise Soil-Structure Interaction modeling for safety and resilience [7]. Similarly, the seismic fragility analysis for onshore wind turbines reveals that the dynamic coupling between the turbine foundation and the soil profoundly influences the overall seismic response and damage susceptibility, providing essential data for resilient wind energy infrastructure design [10].

The vulnerability of different types of infrastructure to seismic events also varies based on unique characteristics and potential failure modes. For buried pipelines, investigations uniquely consider the combined impacts of corrosion and various failure modes. Findings indicate that pre-existing corrosion significantly increases pipeline vulnerability to seismic events, thus establishing a comprehensive framework for assessing and mitigating risks in aging infrastructure networks [8]. In urban settings, high-rise buildings face specific risks such as structural pounding during earthquakes. A detailed seismic fragility analysis quantifies how adjacent buildings colliding can dramatically increase damage probability, emphasizing the need for adequate separation gaps in urban seismic design to prevent such detrimental effects [9].

Collectively, these studies highlight a comprehensive approach to seismic fragility analysis, moving beyond simplified assumptions to account for complex factors like spatial variability of ground motion, mainshock-aftershock sequences, soil-structure interaction, and specific material or structural vulnerabilities. The integration of advanced computational methods, including Machine Learning, further refines the accuracy and efficiency of these assessments. This ongoing research is vital for designing safer, more resilient infrastructure globally, ensuring better preparedness for future seismic events across a diverse range of civil engineering applications.

Conclusion

Research across a decade has profoundly advanced the field of seismic fragility analysis, encompassing diverse structural types and complex influencing factors. Studies have moved beyond uniform assumptions to address critical aspects like spatially variable ground motions, which significantly impact reinforced concrete bridges, base-isolated structures, and shield tunnels [1, 4, 5]. The effects of successive seismic events, such as mainshock-aftershock sequences, on steel frame buildings have been rigorously explored, often leveraging machine learning to predict damage probabilities [2]. Machine learning also enhances the efficiency of fragility curve generation for structures like unreinforced masonry buildings [3]. A significant focus lies on the intricate dynamics of soil-structure interaction, proving crucial for accurately assessing the fragility of gravity retaining walls, nuclear reactor buildings, and onshore wind turbines [6, 7, 10]. Furthermore, specific vulnerabilities inherent to certain infrastructure types, such as corrosion in buried pipelines and structural pounding in high-rise buildings, have been investigated to provide comprehensive risk mitigation frameworks [8, 9]. This body of work collectively underscores the importance of detailed, context-specific analyses for robust seismic design and resilience planning across modern and aging infrastructure, ensuring more accurate damage probability assessments and informed engineering decisions.

Acknowledgement

None.

Conflict of Interest

None.

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