On the assessment of seismic performance of bridge piers on caisson foundations subjected to strong ground motions

Gaudio Domenico; Rampello Sebastiano

摘要

Substructure method is widely used to evaluate the seismic performance of caisson foundations supporting bridge piers subjected to strong ground motions, mainly because of its simplicity. However, the strongly-simplifying assumption of linear viscous-elastic behaviour for the foundation soil limits its applicability to flexible systems subjected to low-intensity earthquakes, for which irreversible strains and pore water pressure build-up are not anticipated. Furthermore, lumped-parameter models are typically adopted in calculations in which soil-foundation compliance is reproduced via dynamic impedance functions, whose dependency on frequency of excitation is often neglected. Modification of free-field motion leading to foundation input motion (FIM), due to the presence of caisson embedment, is also mostly ignored. The influence of these simplifying assumptions on the seismic performance of bridge piers on caisson foundations is assessed in this paper through a parametric study, where soil-caisson-bridge pier-deck systems differing in geometric and mechanical properties are subjected to real seismic records. Dynamic analyses were carried out in the time domain with the finite element method, using a 3D continuum and a lumped-parameter model for the foundation soil. In the 3D model both the linear viscous-elastic and the nonlinear soil behaviour were assumed, while linear viscous-elastic behaviour was assumed in the lumped-parameter model. The influence of inelastic soil behaviour was assessed by comparing the seismic performance of the systems obtained with the 3D model, while the role of FIM was evaluated by comparing the results of the dynamic analyses computed assimilating the soil to a linear elastic medium.

机译：子方法被广泛用来评价沉箱基础支撑经受强地面运动，它的简单性的，主要是因为桥墩的抗震性能。然而，为基础的土壤线性粘弹性行为的强简化假设限制了其适用性进行低强度地震灵活的系统，不可逆的菌株和孔隙水的压力建立预期不会对哪个。此外，集总参数模型，其中土基础达标通过动态阻抗功能，在激励的频率，其相关性往往被忽视转载的计算通常采用。导致基础输入的运动（FIM），由于沉箱嵌入的存在自由场运动的变形例中，也大多被忽略。上沉箱基础桥墩的抗震性能这些简化假设的影响被在本文中通过一个参数研究，其中几何和机械性质不同的土壤沉箱-桥墩甲板系统受到真实地震记录进行评估。动态分析均与有限元方法中的时域进行的，使用3D连续体和为基础的土壤的集总参数模型。在3D模型中两个线性粘弹性和非线性土壤行为被假定，而线性粘弹性行为被假定在集总参数模型。的非弹性土壤性能的影响通过比较与所述3D模型获得的系统的抗震性能评估，而FIM的作用是通过比较所述动态分析的结果，计算同化土壤线性弹性介质进行评价。

On the assessment of seismic performance of bridge piers on caisson foundations subjected to strong ground motions

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