Guidelines for global seismic stability of structures on shallow foundations
Résumé
Current seismic design standards provide guidelines to analyse global stability of structures founded on shallow foundations under earthquake loadings. Such standards consider mainly equivalent linear force based analyses for design purposes, even if the actual behaviour of soil and structures can show low to high non-linearities. Nevertheless, engineers may be required to address specific existing structures on a beyond design basis, or to explore nonlinear behaviour even for new constructions. In that case, the substantiation of global seismic stability requires the use of more advanced analysis methods. To fill the gap between normative and advanced nonlinear analysis methods and propose pragmatic graded approach, the French Association for Earthquake Engineering has established a collaborative framework between design engineers and researchers to develop guidelines for assessing shallow foundation stability under seismic loadings excluding liquefaction effects. This paper introduces a theoretical framework for understanding fundamental mechanisms governing foundation stability during seismic events, including overturning and uplifting, sliding and loss of bearing capacity. It explores the specific actions and criteria on foundations as defined in the ongoing revision of the Eurocode 8 (prEN 1998-5:2024) and other relevant standards, while integrating advanced research approaches, such as full domain finite element methods, macro-element sub-structuring methods along with feedbacks from some reference experimental campaigns. The exposed guidelines propose approaches of increasing physical complexity in line with the graded approach principle, allowing design engineers to adjust efforts, based on project requirements, stakes, and available knowledge and feedback. Additionally, the guidelines incorporate insights from laboratory results (Combescure and Chaudat 2000; Gavras et al. 2020) and post-seismic observations (Morita et al. 2021), along with a state-of-the-art research synthesis.
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