The impact of adopting different dynamic soil–structure interaction (SSI) models on the assessment of seismic fragility functions for buildings with pile foundations is studied herein. Given the importance on seismic response of the coupling of structure, foundation and soil, and the challenges posed on modelling dynamic SSI, especially when soil nonlinearity plays a significant role, the linear substructure approach is initially adopted by implementing two different models, followed by the use of a nonlinear pile-head macro-element. The first model is one-dimensional and includes, between the foundation node and the ground, only a translational elastic spring and a dashpot, whose stiffness and viscous damping are retrieved from the real and imaginary parts of the dynamic impedance at the first natural frequency of the structure. The second and more refined model is a Lumped-Parameter Model accounting for frequency dependence of the coupled horizontal and rotational impedances in a two-dimensional response. A nonlinear pile-head macro-element model is introduced afterwards to explore the sensitivity of fragility functions to the linearity assumption. This approach models the soil nonlinear behaviour at near-field, as well as the far-field dynamic impedance and energy dissipation through radiation damping, by condensing the entire soil-foundation system into a single nonlinear element at the base of the superstructure. In all models, the superstructure is represented in a simplified way as a nonlinear single-degree-of-freedom system. The comparison between the adopted approaches is evaluated in terms of their effects on the characterisation of fragility functions for unreinforced masonry buildings with pile foundations.

中文翻译：

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基于桩的URM建筑的地震易损性分析：动态土-结构相互作用模型的影响

本文研究了采用不同的动态土-结构相互作用（SSI）模型对具有桩基础的建筑物的地震脆性函数评估的影响。考虑到结构，地基和土体耦合对地震响应的重要性以及对动态SSI进行建模所带来的挑战，尤其是在土壤非线性起重要作用的情况下，线性子结构方法最初是通过实施两个不同的模型而采用的，使用非线性桩头宏单元。第一个模型是一维模型，在基础节点和地面之间仅包含一个平移弹性弹簧和一个减震器，它们的刚度和粘性阻尼是在第一自然频率下从动态阻抗的实部和虚部中获得的。结构。第二个更完善的模型是集总参数模型，该参数模型考虑了二维响应中耦合的水平和旋转阻抗的频率依赖性。随后引入非线性桩头宏单元模型，以探索脆弱性函数对线性假设的敏感性。该方法通过将整个土壤基础系统压缩为上部结构基础中的单个非线性元素，对近场的土壤非线性行为以及通过辐射衰减的远场动态阻抗和能量耗散进行建模。在所有模型中，上部结构都以简化的方式表示为非线性单自由度系统。