This study aims to consider the effect of soil–structure interaction (SSI) on the ductility and hysteretic energy demands of superstructures and propose empirical equations for demand prediction in soil–structure systems. To this end, the FEMA 440 procedure was considered to develop nonlinear single-degree-of-freedom oscillators with a period range of 0.1–3.0 s, as the representative of superstructures. The elastic-perfectly plastic and a moderate pinching degrading hysteretic models were considered for the nonlinear response of the superstructure. The model of the nonlinear soil–foundation system was developed through the Winkler method. In this regard, the type of soil beneath the foundation was assumed as D category, according to the site classification in ASCE 7-10. A wide range of key parameters, including the strength reduction factors (2 ≤ R_μ ≤ 8), the foundation safety factor (3 ≤ SF ≤ 7), the foundation-to-structure height aspect ratio (1 ≤ h/b ≤ 5), and the foundation length-to-width ratio (3 ≤ L_f/B_f ≤ 20) was introduced into the analytical models to conduct parametric studies. Results show the considerable effect of SSI on reducing the ductility and hysteretic energy demands in superstructures with short fundamental periods. More demand reduction can be achieved by providing the lateral sliding of the foundation on the soil surface, especially for systems with a small aspect ratio. The pinching–degrading hysteretic behavior of the superstructure remarkably modifies the level of demands. Moreover, predictive models were proposed for estimating the ductility and hysteretic energy demands in flexible base systems. These models modify demands in the rigid base structures based on their physical and mechanical properties. The developed models consider the effects of structural hysteretic behavior as well as foundation flexibility. The efficiency of the proposed model was assessed on a multi-story frame. Finally, the required ductility capacity of the systems was determined through the Park–Ang damage index and by using the developed predictive models. Results show the efficiency of the empirical models to reasonably estimate the required ductility capacity.

这项研究的目的是考虑土-结构相互作用（SSI）对上层建筑的延性和滞后能量需求的影响，并提出经验公式来预测土-结构系统的需求。为此，FEMA 440程序被认为可以开发周期范围为0.1–3.0 s的非线性单自由度振荡器，作为上层建筑的代表。考虑到上层建筑的非线性响应，采用了弹性完美的塑料和适度的收缩降解滞后模型。非线性土壤基础系统的模型是通过Winkler方法开发的。在这方面，根据ASCE 7-10中的场地分类，将地基以下的土壤类型假定为D类。多种关键参数，包括强度折减系数（2≤ ř _μ  ≤8），基础安全系数（3≤  SF  ≤7），基础到结构的高度的纵横比（1个≤  ħ / b  ≤5），和基础长度与宽度的比率（3≤ 大号_f / B _f ≤20）被引入分析模型以进行参数研究。结果表明，SSI在降低基本周期短的上层建筑的延性和滞回能量需求方面具有显着效果。通过在土壤表面提供基础的横向滑动，可以实现更多的需求减少，尤其是对于纵横比较小的系统。上部结构的收缩降解滞后行为显着改变了需求水平。此外，提出了预测模型以估计柔性基础系统的延性和滞后能量需求。这些模型根据其物理和机械特性修改了刚性基础结构中的要求。所开发的模型考虑了结构滞后行为以及基础柔性的影响。在多层框架上评估了提出的模型的效率。最后，通过Park-Ang破坏指数并使用已开发的预测模型确定了系统所需的延性能力。结果表明，经验模型可以有效地估计所需的延展性。