桩基础抗震性能的简易评价方法

Simplified Method for Evaluating Seismic Performance of Pile Foundation

摘要:

桩基础的抗震性能可从承载力和变形两方面来评价。承载力可考虑地震时作用于结构上的荷载组合,多采用拟静力法进行分析,不同因素变异的影响可用概率分析或可靠度方法予以考虑。变形分析多为按承载力设计之后的校核,其中地震力和土体参数以及地质条件等因素影响可分别加以评估。本文着重阐明基于一维波动方程和概率分析的桩基抗震性能实用分析方法,并以桥梁桩基础为例进行讨论,其中考虑的关键因素为设计地震加速度、测站记录、基桩尺寸及其配筋率。研究表明,当土层液化可忽略时最大弯矩会发生在桩顶,故增加桩顶延性可有效提升桩基础的抗震性能。

Abstract:

Performance based design for pile foundations can be analyzed on bearing capacities and deformations.The foundation capacities are often computed knowing the superstructural loads and their combinations.The design needs to consider ordinary and special conditions.Conventional calculation methods or other reliable methods can be adopted.Influence factors are assessed by probability and/or reliability analyses to match the PBD requirements.On the other hand,foundation deformations can be analyzed further.The effects of seismic forces,soil parameters and geological structure could be evaluated independently.This paper introduces the seismic PBD analysis on piles using one-dimensional wave equation analysis and the so called PBEE analysis.A case study is discussed on the bridge pile foundations.The key issues in the analysis are design PGA,accelerogram,pile dimensions and the amount of steel bars in use.It is found that if the soil liquefaction influence could be negligible,then the maximum bending moment would occur at pile head,in which to increase the ductility of the pile at the pile head will help the seismic performance of the piles.