Optimal Control of Structures under Earthquakes Including Soil-Structure Interaction

It is well known that the soil-structure interaction (SSI) changes the dynamic response of a structure supported on flexible soil. The analysis of optimally controlled SSI systems has certain difficulties due to the nature of the SSI and the optimal control problem. In this paper, a two-step iteration-based numerical algorithm is proposed to handle optimally controlled SSI systems under earthquakes. First, the optimal control forces are obtained by using a fixed-base system. Then, the optimal control forces are converted to the frequency domain by the Fourier transform technique to be used in the equations of the SSI system. The lateral displacement and the rocking of the foundation are obtained from the equations of the SSI system containing the optimal control forces in the frequency domain. The lateral displacement and rocking of the foundation are then converted to the time domain by the inverse Fourier transform technique, and the lateral accelerations and the rocking accelerations of the foundation are obtained by the forward finite difference method. During the second step, the optimal control forces are calculated again by using the lateral acceleration and the rocking acceleration of the foundation along with the earthquake ground motion. Using the method explained above, the optimal control forces obtained in the time domain are used in the equations of the soil-structure system from which the behavior of foundation and structure is obtained. In the final section of the paper, a numerical study is conducted for a controlled structure supported on flexible soil.     

Estimation of the Displacement of Viscously Damped Pinching Hysteretic Structures Subjected to Near-fault Ground Motions

To fulfill a displacement-based design or response prediction for nonlinear structures, the concept of equivalent linearization is usually applied, and the key issue is to derive the equivalent parameters considering the characteristics of hysteretic model, ductility level, and input ground motions. Pinching hysteretic structures subjected to dynamic loading exhibit hysteresis with degraded stiffness and strength and thus reduced energy dissipation. In case of excitation of near-fault earthquake ground motions, the energy dissipation is further limited due to the short duration of vibration. In order to improve the energy dissipation capability, viscous-type dampers have been advantageously incorporated into these types of structures. Against the viscously damped pinching hysteretic structure under the excitation of near-fault ground motions, this study aims to develop a seismic response estimation method using an equivalent linearization technique. The energy dissipation of various hysteretic cycles, including stationary hysteretic cycle, amplitude expansion cycle, and amplitude reduction cycle, is investigated, and empirical formulas for the equivalent damping ratio is proposed. A damping modification factor that accounts for the near-fault effect is introduced and expanded to ensure its applicability to structures with damping ratios less than 5%. An approach for estimating the maximum displacement of a viscously damped pinching hysteretic structure, in which the pinching hysteretic effect of a structure and the near-fault effect of ground motions are considered, is developed. A time history analysis of an extensive range of structural parameters is performed. The results confirm that the proposed approach can be applied to estimate the maximum displacement of a viscously damped pinching hysteretic structure that is subjected to near-fault ground motions.     

篇章结构:谋篇之形,结构之象

本文通过对篇章结构理论的解读,诠释了篇章结构理论作用下的谋篇之形和结构之象;讨论了谋篇之形是文章实现主题的设计蓝图;剖析了结构之象的具体组合形态及其对结构理论的意义;研究了篇章结构的延承发展和组合法则。指出它们的构象组合是一个完美的统一的整体,是谋篇布局的思维成果,是写作过程中对材料组织安排的思维轨迹的实现。     

区域旅游:空间结构及其研究进展

区域旅游的空间结构涉及内容复杂。文章在对国内外研究进行综述的基础上,首先导入了区域旅游的概念,从旅游空间要素的识别与分析入手,接受了Pearce Douglas的观点,认为区域旅游供给的五大空间影响要素:吸引物、交通、住宿、支持设施和基础设施。从旅游规划、基本距离、旅游地区位等角度对旅游空间结构及其研究进展进行了阐释。指出由于缺乏范式的指引,国内外对区域旅游规划的研究体系较为松散,绝大多数研究者被实践性问题或者潮流牵着走。对区域旅游活动发生地的区位进行考查,显示出对城市这一空间经济实体的极大依赖。同时,指出旅游地宏观区位因子和可进入性是衡量旅游地发展潜力的主要因素。运用TDD理论对西安旅游目的地区域的空间结构进行了解释。     

重庆城市体系的结构研究

本文讨论了重庆城市建设发展的总特征,分析了城市体系发展中规模结构工业职能的空间结构所存在的主要问题,提出了进一步推动重庆城市体系建设发展的战略研究。     

北阴阳营新石器时代墓地分析与探讨

北阴阳营新石器时代墓地由于其特殊的埋葬方式、随葬品极其复杂等原因,从器物形态的角度进行文化的分期较困难,但若从墓地结构与布局变迁的角度进行考察,并结合器物形态变化的程度,则可以大致以第三、第二墓层之间为界,将墓葬区代表的新石器时代文化分为早、晚两个期(段)。笔者认为从空间关系上看墓地上存在着分群、群内分组而葬的现象,这表现在各墓群随葬的陶器与石制品的比重上也有明显的差别,说明墓地有不同的社群组织构成并且社群间的生产经济方面的职能分化已见端倪。另外,本文还指出墓地所代表的社会存在陶器制作分散、自由化的特点,整个社会缺乏统一的生产系统,社会没有被有机地整合,这可能是北阴阳营类型文化最终消融在崧泽——良渚文化系统中的一个重要原因。     

散文美教学谈

散文的美着重表现在它的结构美、意境美、语言美。这也就是我们在散文教学中要解决的重点、难点。     

云南剑川兴教寺木构技术研究

云南剑川兴教寺的大殿和中殿为明永乐十三年(1415年)之遗构,作为全国现存唯一的阿吒力密宗寺院,兴教寺建筑群具有特殊的历史地位和社会文化价值。本文通过剖析兴教寺大殿及中殿的构件尺度及其构架结构特征,可见其木构技术所表达的"滞后"现象,既带有技术的独创性、体现云南木构殿堂建筑的地域特色,又保留了一些古老的中原木结构建筑技术手法,是研究云南现存早期殿堂建筑营造技艺的珍贵遗存。     

北京南部“浙江村”的结构、定位和特征研究

本文采用文献分析法,对北京南部“浙江村”进行了探讨。介绍了“浙江村”的分布及地理位置特点,指出“浙江村”居民是指来京务工经商的浙江个体工商户,阐述了“浙江村”的规模和结构;分三个层次讨论了“浙江村”内部的地域结构,并分析了其主要成因;着重讨论了“浙江村”的定位机理;最后分析了“浙江村”的系统特点,归纳为“低层次自我服务与外向型服装加工相结合的开放系统”     

The key role of zinc,tin and lead in copper-base objects from medieval Talgar in Kazakhstan

Metallurgical examination of brass and bronze objects from the medieval (AD 9th–13th century) site at Talgar in Kazakhstan shows that they were mostly cast from the quaternary copper–zinc–tin–lead system with some exceptions that were forged from binary copper–zinc alloys. Evidence is found that brass was produced in the cementation process and that the addition of tin and lead to the parent brass was considered beneficial in casting but was strictly avoided in forging. The mutual effect of zinc, tin and lead for better casting and the advantages of the binary copper–zinc alloys in forging seem to have been the major factors driving the establishment of this unique brass tradition in a society with probably limited access to tin.