Pile groups under cyclic horizontal loading

根据EA-Pfähle（EA-P）（DGGT 2012），循环荷载定义为桩的重复荷载，其中不需要考虑作用在桩土系统上的惯性力。桩基的循环荷载在土木工程的各个领域都很重要，例如海上和陆上风力涡轮机或运输基础设施的结构。对于海上风力涡轮机，主要建造桩柱（即大直径的单桩）或具有大桩间距的导管架结构（即桩之间的相互作用不太重要）。然而，桥台经常建立在桩间距相对较小的群桩上。这种由多个相互作用的桩组成的基础，以后称为桩群。循环荷载是由风和波浪（海上风力涡轮机）或温度引起的约束（没有接头和支座的整体桥梁）引起的。根据EA-P，对于循环荷载下的桩，只有有限的知识。为了考虑整体式和半整体式桥梁的循环温度诱导约束，在设计过程中经常或多或少地应用任意选择的折减系数。因此，该项目的主要目标是对循环水平荷载下群桩的承载性能进行基础研究，并对结果进行定性和定量评估。在这项研究中，参数的影响，如地基条件，群桩几何形状和载荷条件进行了实验和数值研究。桩群几何形状和荷载条件应基于整体式和半整体式桥梁的典型配置。具体而言，应处理以下主题：-确定影响循环水平荷载下桩群承载性能的主要参数。-审查EA-P中记录的桩荷载分布折减系数和静态荷载下桩群内的Winkler模量，并调整这些系数以适应显著的循环荷载。基于Tasan（2011年）的增强应变楔模型（ESWM）开发的分析模型允许确定以下参数：+桩头水平位移的累积。 + 各种桩的Winkler模量沿着桩身的分布 在桩组内。 + 桩身弯矩和剪力沿着分布 桩组内的各种桩。

According to EA-Pfähle (EA-P) (DGGT 2012) cyclic loading is defined as a repetitive loading of piles where forces of inertia acting on the pile-soil-system do not need to be considered. Cyclic loading of pile foundations is of importance in various fields of civil engineering such as offshore- and onshore- wind turbines or structures for transport infrastructure. For offshore wind turbines mainly monopiles (i.e. single piles with large diameters) or jacket-structures with large pile spacing (i.e. interactions between piles are of minor importance) are constructed. However, bridge abutments are frequently founded on groups of piles with relatively small pile spacing. Foundations of this type comprising a number of interacting piles subsequently will be termed pile groups. Cyclic loadings are caused for example by wind and waves (offshore wind turbines) or temperature induced constraints (integral bridges without joints and bearings).According to EA-P there is only limited knowledge available for piles under cyclic loading. To consider cyclic temperature induced constraints for integral and semi-integral bridges, frequently more or less arbitrarily chosen reduction coefficients are applied in the design process. It is therefore the main objective of the project to carry out a fundamental study on the bearing behaviour of pile groups under cyclic horizontal loading and to evaluate the results qualitatively as well as quantitatively. Within this study the influence of parameters such as subsoil conditions, pile group geometry and loading condition are to be investigated experimentally and numerically. Pile group geometries and loading conditions are to be based on configurations typical for integral and semi-integral bridges.In detail the following topics are to be treated:- Identification of the main parameters influencing the bearing behaviour of pile groups under cyclic horizontal loading.- Review of the reduction coefficients documented in the EA-P for the distribution of pile loads and Winkler modulus within a pile group under static loading and adjustment of these coefficients for significant cyclic loading.- Development of an analysis model based on the Enhanced Strain Wedge Model (ESWM) by Tasan (2011) which allows the determination of the following parameters: + Accumulation of the horizontal displacement at the pile head. + Distribution of the Winkler modulus along the pile shaft for the various piles within the pile group. + Distribution of bending moment and shear force along the pile shaft for the various piles within the pile group.