柱体碎片撞击事件的解析与数值模拟

摘要

海啸灾后调查一再表明，深入认识碎片荷载十分必要。迄今为止，用于估算碎片撞击荷载的经验公式都建立在单自由度（SDOF）模型之上，然而这类 SDOF 模型估算碎片撞击荷载的有效性一直缺乏充分研究。本文把 SDOF 模型给出的力响应与试验数据以及所建立的多自由度（MDOF）模型相比较，考察以 SDOF 模型预测碎片撞击力的有效性；并就 ASCE 7-22 第 6 章有关碎片撞击荷载的规定与上述替代方法作了对比分析。结果表明，MDOF 方法能够准确刻画试验的力响应数据，而其余各种估算碎片撞击荷载的方法在幅值与频率两方面都高估了力响应；此外，MDOF 模型给出的撞击荷载比 SDOF 模型与 ASCE 7-22 第 6 章给出的持时更长、幅值更小。本文还建立了一个高效的数值模型，用以模拟单碎片与多碎片在柱体上的输移与撞击荷载。该动力数值模型建立在通用有限元程序 LS-DYNA 之中，采用任意拉格朗日-欧拉（ALE）方法模拟溃坝波所致的碎片撞击荷载。模型准确复现了Stolle 等（2019）与 Stolle 等（2020b）给出的水面高程、水动力荷载、碎片输移与碎片撞击力。模型模拟碎片撞击事件的能力表明，它有望成为设计与评估关键基础设施抵御海啸等极端海岸淹没事件韧性的有力工具。

Abstract

Post-disaster surveys of tsunamis have emphasized the need for an in-depth understanding of debris loading. Until now, empirical formulas used to estimate debris impact loads are based on single-degree-of-freedom (SDOF) models. However, the validity of these SDOF models to estimate debris impact loads has not been studied extensively. This study investigates the validity of using a SDOF model to predict debris impact forces by comparing its force response to experimental data and a multiple-degree-of-freedom (MDOF) model developed. Additionally, a comparative analysis was conducted to assess the provisions on debris impact loads in Chapter 6 of ASCE 7-22 against these alternative methods. The MDOF method was shown to model accurately the experimental force response data, while all other methods for estimating debris impact loads overestimated the force response in both magnitude and frequency. Furthermore, the impact loads generated by the MDOF model proved to be longer in duration but smaller in magnitude than loads generated using the SDOF model and Chapter 6 of ASCE 7-22. In addition, a performant numerical model was developed to simulate single and multi-debris transport and impact loads on a column. The dynamic numerical model was developed within the general-purpose finite element program LS-DYNA. Inside this modelling framework, the Arbitrary Lagrangian-Eulerian (ALE) method was used to simulate dam-break wave generated debris impact loads onto the column. The model accurately replicated the water surface elevations, hydrodynamic forces, debris transport, and debris impact forces presented in Stolle et al. (2019) and Stolle et al. (2020b). The model's ability to simulate debris impact events demonstrates its potential as a valuable tool for designing and evaluating critical infrastructure's resilience against extreme coastal inundation events, such as tsunamis.