强震下深水桥梁垫层隔震基础动力特性与分析方法研究

Recently, advanced construction and design techniques provided by the rapid progress of bridge engineering encourage engineers to design and construct bridge piers using isolated foundations with cushions, especially for sea bridges built in deep water (more than 50 meters in depth). In order to fulfill the significant needs of completing mega bridge projects in our country, studies on the most prominent problems of cushion design for isolated foundations will be conducted comprehensively. The main contents of the present proposal can be addressed as follows: Firstly, build the dynamic stress-strain relationship of sand-gravel cushion and the interface model of cushion-caisson system using large scale dynamic tri-axial tests and shear tests; Secondly, establish the dynamic interaction model of composite foundation-cushion-caisson-water-superstructure system numerically with Opensees; Thirdly, propose a simplified dynamic analysis method based on the macroelements model for isolated foundations with cushions; Fourthly, carry out the dynamic centrifuge model tests for isolated foundations considering hydrodynamic force and inertial response of superstructure; Finally, provide a pseudo-static analysis method of isolated foundations with cushions. As such, present project is aimed at comprehensively analyzing the dynamic interaction in the foundation-cushion-caisson-water-superstructure system, revealing the seismic behaviors of isolated foundations with cushions in deep water during strong earthquakes and providing the reliable analytical method for isolated foundations. All these endeavors are made to provide a thorough guide for the utilization of isolated foundations with cushions in deep water engineering safely and economically.

工程实践表明，垫层隔震基础是一种适宜于水深50m以上的跨海桥梁基础型式。针对我国未来重大跨海桥梁建设的前瞻性需求，围绕垫层隔震基础在设计中存在的一些关键问题，系统地开展以下几个方面的研究。基于大型动三轴试验和大型接触面剪切试验，构建砂石垫层的动应力-应变关系及垫层-沉箱接触面模型；基于开源的OpenSees软件，建立复合地基-垫层-沉箱-水体-上部结构动力相互作用的三维数值模型；构建适用于垫层隔震基础的宏观单元动力简化分析模型；考虑动水力和上部结构惯性响应，开展垫层隔震基础的动力离心模型试验；提出深水桥梁垫层隔震基础的拟静力分析方法。本项目研究旨在深入分析复合地基-垫层-沉箱-水体-上部结构的动力相互作用，揭示强震下深水桥梁垫层隔震基础的动力特性，提出合理可行的垫层隔震基础实用分析方法，便于将垫层隔震基础更为安全和经济地应用于深水桥梁建设中。

作为一种适用于水深50m以上的跨海桥梁基础形式，垫层隔震基础已在工程实践中得到应用。然而，该基础形式在强震下的动力特性及其隔震效应的研究明显滞后于工程实践需求。围绕深水桥梁垫层隔震基础在设计中存在的关键问题，结合我国未来重大跨海工程前瞻性需求和已有研究成果，开展了系统的理论分析和试验研究，取得了如下几方面的成果。.（1）采用大型界面剪切仪，开展单调剪切和循环剪切试验，研究碎石、卵石以及复合垫层与结构界面的静动力学特性及动应力-应变关系，进一步根据垫层-混凝土板接触面特性，构建垫层-结构界面的本构模型；（2）基于OpenSees等有限元软件，建立复合地基-垫层-沉箱-上部结构动力相互作用的三维数值模型，揭示垫层隔震基础的动力特性及其影响机理；（3）采用半数值半解析的方法和基于三维实体单元的数值计算方法，计算垫层隔震基础的动力阻抗，为垫层隔震基础宏观单元模型奠定基础；（4）开展垫层隔震基础的动力离心模型试验，研究了强震下垫层的隔震效应以及桩-箱连接方式对基础动力特性的影响，并通过圆形桥墩和矩形桥墩在不同水深条件下的离心振动台模型试验，研究了地震作用下深水桥墩的动力特性及动水压力分布规律；（5）针对垫层隔震基础刚性桩的受力特点，提出垫层隔震基础刚性桩地震响应拟静力简化分析方法，并采用三维动力有限元数值结果验证所提出的拟静力分析方法的合理性。.上述研究成果系统地揭示了强震下深水桥梁垫层隔震基础的动力特性，提出了适用于工程应用的简化分析方法，对于深水桥梁基础设计理念与分析理论的创新具有重要意义，所提出的拟静力简化方法可为桥梁抗震规范的修订提供参考依据。