Development of Servo-Hydraulic Earthquake Actuators for use on Geotechnical Centrifuges

地震对基础设施造成严重破坏。虽然英国对地震相对安全，但英国的建筑行业在全球范围内开展业务，经常在地震易发地区进行设计，包括东南亚、台湾、印度次大陆和其他国家。此外，英国的保险业和风险管理行业经常需要对工程基础设施的性能进行预测。近年来，利用动态离心机建模来研究地震岩土工程领域的各种问题，已经成为一种有吸引力的工具，既可以理解工作中的基本力学，也可以建立给定抗震设计的性能。在世界范围内，能够在离心机模型上进行地震测试的离心机中心的数量正在增加，加州大学戴维斯分校、纽约RPI和香港科技大学升级了他们的地震致动器，法国南特LCPC和韩国水力研究实验室最近在他们的离心机设施上增加了地震致动器。剑桥大学在20世纪70年代末开始用离心机模拟地震，著名的“颠簸的道路”系统于1979年投入使用。1994年研制了一种基于存储角动量（SAM）的地震致动器，它可以在单音爆发时传递强震。这个驱动器在剑桥非常成功，导致了大量的研究，包括对土壤液化现象的基础研究，以及对特定边界值问题的研究，并产生了10个博士学位，以及大量的期刊和会议出版物。SAM地震执行器系统虽然非常成功，但需要升级。目前我们研究能力的真正需要是能够产生多频地震运动，这是实地记录的真实地震的更真实的表示。由于小波分析方法的发展，剑桥大学的分析能力得到了显著提高，小波分析方法使我们能够分析时频空间中的多频输入。这种能力为我们跟踪复杂的非线性土壤-结构系统的动态响应提供了明显的优势。这些理论的发展和当前研究界和英国实践工程师的需求都融合到伺服液压地震驱动系统的要求中。剑桥大学的中期目标是开发一种强大的二维伺服液压地震执行器，能够产生离心机模型的水平和垂直振动。然而，这样一个系统是相当复杂的，它被认为是谨慎的处理这一发展阶段。这对我们获得快速动作伺服液压阀的经验是必要的。本课题旨在开发一维伺服液压地震致动器，作为开发二维地震致动器的第一步。这将有助于我们获得在高重力场中使用快速动作伺服阀的必要经验，进行辅助系统如液压动力组，控制系统，系统安全装置的设计和实施。这些系统需要纳入剑桥离心机设施的相当专业的要求，该设施的有效载荷限制为1吨（振动系统+离心机模型），以及特殊的摆动和锁定机制。该项目将以1-D地震执行器的形式确定交付，其震动力约为7吨，并将单独用于触发强烈地震，并使我们能够模拟真实的地震载荷。

Earthquakes inflict severe damage to infrastructure. While UK is relatively safe from earthquakes the UK based Construction Industry operates worldwide often performing designs in earthquake prone areas including South-East Asia, Taiwan, Indian sub-continent and other countries. Also the UK based Insurance industry and Risk Management industries often need predictions on the performance of engineered infrastructure. In recent years the use of dynamic centrifuge modelling to investigate various problems in the earthquake geotechnical engineering area has established itself as an attractive tool both to understand the fundamental mechanics at work as well as establishing the performance of a given earthquake resistant design. Worldwide the number of centrifuge centres that are able to carryout earthquake testing on centrifuge models is on the increase with University of California, Davis, RPI in New York and Hong Kong University of Science and Technology upgrading their earthquake actuators and LCPC in Nantes, France and Korean Hydraulic Research Labs recently adding earthquake actuators to their centrifuge facilities. Earthquake modelling on centrifuges started at Cambridge in late 1970's with the famous 'bumpy road' system coming into operation in 1979. In 1994 a Stored Angular Momentum (SAM) based earthquake actuator was developed which could impart strong earthquakes at single tone bursts. This actuator was very successful at Cambridge leading to significant amount of research both fundamental research looking at liquefaction phenomena of soils as well as investigating specific boundary value problems and produced 10 PhD's and significant number of journal and conference publications. The SAM earthquake actuator system though very successful needs to upgraded. The real need in our research capabilities at this time is to have the ability to produce multi-frequency earthquake motions which are a more realisitc representations of the real earthquakes recorded in the field. The analytical ablities in Cambridge have been significantly boosted by the development of Wavelet analyses methods that allow us to analyse multi-frequency inputs in time-frequency space. This ability gives us the distinct advantage to follow the dynamic respone of complex non-linear soil-structure systems. These theorectical developments and the needs of the current research community and the UK based practicising engineers all confluence into the requirement of a servo-hydraulic earthquake actuation system. The medium term aim at Cambridge is to develop a powerful 2-D servo-hydraulic earthquake actuator that is able to generate horizontal and vertical shaking of centrifuge models. However such a system is quite complex and it is considered prudent to approach this development in stages. This is necessary for us to gain experience with fast acting servo-hydraulic valves. This proposal aims to develop a 1-D servo-hydraulic earthquake actuator as the first stage in the development of a 2-D earthquake actuator. This will help us gain the necessary experience in the usage of fast acting servo-valves in the high gravity field, carrying out design and implementation of the appurtant systems such as hydraulic powerpacks, control systems, system safety devices. These systems need to be incorporated into rather specialist requirements of the Cambridge Centrifuge facility which has a limit of 1 ton on the payload (shaking systems + centrifuge model) and the special swing up and lock mechanisms. The project will have a definite deliverable in the form of 1-D earthquake actuator with a shaking force of about 7 tons and will be used in its own right to trigger powerful earthquakes and gives us the ability to model realistic earthquake loading.