Numerical investigation on seismic performance of a shallow buried underground structure with isolation devices

A design procedure for improving the seismic performance of unequal-span underground structures by installing isolation devices at the top end of columns is proposed based on the seismic failure mode of frame-type underground structures and the design concept of critical support columns. A two-dimensional finite element model (FEM) for a soil-underground structure with an unequal-span interaction system was established to shed light on the effects of a complex subway station with elastic sliding bearings (ESB) and lead rubber bearings (LRB) on seismic mitigation. It was found that the stiffness and internal force distribution of the underground structure changed remarkably with the installation of isolation devices at the top end of the columns. The constraints of the beam-column joints were significantly weakened, resulting in a decrease in the overall lateral stiffness and an increase in the structural lateral displacement. The introduction of the isolation device effectively reduces the internal force and seismic damage of the frame column; however, the tensile damage to the isolation structure, such as the roof, bottom plate, and sidewall, significantly increased compared to those of the non-isolation structure. Although the relative slip of the ESB remains within a controllable range under strong earthquake excitation as well as frame columns with stable vertical support and self-restoration functions, the LRB shows a better performance during seismic failure and better lateral displacement response of the unequal-span underground structure. The analysis results provide new ideas and references for promoting the application of seismic isolation technology in underground structures.     

Simulation of the response of base-isolated buildings under earthquake excitations considering soil flexibility

The accurate analysis of the seismic response of isolated structures requires incorporation of the flexibility of supporting soil.However,it is often customary to idealize the soil as rigid during the analysis of such structures.In this paper,seismic response time history analyses of base-isolated buildings modelled as linear single degree-of-freedom(SDOF) and multi degree-of-freedom(MDOF) systems with linear and nonlinear base models considering and ignoring the flexibility of supporting soil are conducted.The flexibility of supporting soil is modelled through a lumped parameter model consisting of swaying and rocking spring-dashpots.In the analysis,a large number of parametric studies for different earthquake excitations with three different peak ground acceleration(PGA) levels,different natural periods of the building models,and different shear wave velocities in the soil are considered.For the isolation system,laminated rubber bearings(LRBs) as well as high damping rubber bearings(HDRBs) are used.Responses of the isolated buildings with and without SSI are compared under different ground motions leading to the following conclusions:(1) soil flexibility may considerably influence the stiff superstructure response and may only slightly influence the response of the flexible structures;(2) the use of HDRBs for the isolation system induces higher structural peak responses with SSI compared to the system with LRBs;(3) although the peak response is affected by the incorporation of soil flexibility,it appears insensitive to the variation of shear wave velocity in the soil;(4) the response amplifications of the SDOF system become closer to unit with the increase in the natural period of the building,indicating an inverse relationship between SSI effects and natural periods for all the considered ground motions,base isolations and shear wave velocities;(5) the incorporation of SSI increases the number of significant cycles of large amplitude accelerations for all the stories,especially for earthquakes with low and moderate PGA levels;and(6) buildings with a linear LRB base-isolation system exhibit larger differences in displacement and acceleration amplifications,especially at the level of the lower stories.     

废轮胎颗粒与黄土混合物压实性能研究

选择废轮胎颗粒以0～50%的掺量与黄土混合,研究了混合土的压实特性,并采用专门设计的环刀击实设备,对环刀击实和标准击实进行了对比分析。试验结果表明,掺量小于20%时混合土的压实特性类似黄土,掺量大于40%时的压实特性类似无黏性土;不同掺量的混合土最大干密度与最优含水率存在幂函数关系,击实能对10%～30%掺量的混合物有效最大干密度影响较小;不同击实能下掺量与最优含水率存在函数关系;混合土存在最佳压实掺量,轻、重型击实能下分别为30%和40%左右。根据室内试验结果,给出了不同掺量混合土击实指标建议值供设计参考。     

铅芯夹层橡胶隔震垫基本力学性能研究

本文详细地研究了中国铅芯夹层橡胶隔震垫的基本力学性能,主要包括隔震垫的竖向,水平特性及极限承载能力,在竖向性能方面研究了隔震垫的竖向刚度及变形特性;水平性能的研究包括水平有效刚度和阻尼特性;极限承载能力的研究包括隔震垫的压缩破坏。     

叠层橡胶支座隔震结构地震响应的突变分析

为全面分析地震破坏过程中由非线性引起的,如突变和滞后效应等某些复杂特性,本文在现有的动力分析模型基础上引入了非线性恢复力,并用突变理论分析方法对改进后的模型进行分析,结果表明叠层橡胶支座参数的微小变化使响应振幅及其突变值、振幅响应的不稳定区域等特性产生明显变化,反映出隔震结构的地震响应特性对参数变化非常敏感。由于支座阻尼的耗能作用,当阻尼较大或激振力、非线性参数较小时,地震响应的突变现象消失,产生"伪线性"特性。     

海南橡胶树热带气旋风灾易损性评估

面向橡胶树热带气旋风险评估及保险应用,文章对橡胶树风灾易损性进行了量化评估。基于1971―2010年橡胶树种植及16场热带气旋的橡胶树农场尺度损毁统计数据,计算了每场热带气旋灾害发生时各农场开割、未开割2类橡胶树,倒伏、断主干2 m以下、断主干2 m以上、半倒、全部主枝折断5种类型的损毁率;使用热带气旋参数风场模型,模拟得到1 km栅格分辨率的风速,优选3 s极大风速（V_3s）作为致灾强度指标,建立了6~14级风速区间2类橡胶树5种损毁类型的易损性曲线,并量化表达了损毁率的不确定性。结果表明,开割树（未开割树）自V_3s达6（7）级起开始受到损毁,各类型损毁率在V_3s达到9级后上升速度较快,在V_3s达到14级时,总损毁率达到近70%（55%）;未开割树的易损性低于开割树;易损性的不确定性特征随风速区间、承灾体种类、损毁类型不同而不同。橡胶树易损性曲线的建立及其不确定性的量化为橡胶树热带气旋巨灾风险建模奠定了良好的基础。     

板式支座与铅芯支座连续梁桥振动台试验对比分析

通过对分别采用板式支座和铅芯支座的2座3跨连续梁桥模型进行振动台试验,对比分析了这2类桥梁的动力特性、破坏过程及2种支座对连续梁桥地震反应的影响。研究结果表明：地震波特性对桥梁结构的地震反应有较大影响,在对桥梁结构进行抗震设计时,需选择合理的地震动输入;在地震强度较小时,板式支座的滑动能够起到一定的隔震效果,铅芯支座的隔震性能能得到较好的发挥;在地震强度较大时,铅芯支座的隔震性能不能得到很好的发挥,采用铅芯支座的桥梁地震反应不一定小于普通桥梁;通过合理的设计,2类桥梁都完全可以实现大震不倒的设防目标。     

The Institutional Architecture of Extractive Reserves in Rondônia, Brazil

This paper examines the evolution and development of institutions involved in the establishment of extractive reserves. It focuses on the different actors, organizations and projects concerned with extractive reserves in Rondônia in western Amazonia, Brazil. Extractive reserves are widely seen as a means of integrating forest conservation and local socio-economic development. As such, they have gained the support of the international environmental movement, multilateral and state development organizations, and grassroots community and producer organizations. These institutions represent a vast array of diverse interests which range from conservation of biodiversity, economic and social cohesion, and regional and national development. Whilst the various actors and institutions claim mutual and complementary interests, they form shifting alliances and coalitions in order to further their interests. This paper maps these institutions and interests and describes how alliances have been formed and broken, and how this has contributed to the currently observed implementation of extractive reserves. The paper argues that extractive reserves are constrained by the dissonance or misfit in discourses and underlying worldviews, reflected by the aims and objectives, of the institutions which promote, oppose and lose and benefit from their implementation. This misfit is overcome, in part, by alliances formed between the different institutions, and in part by the creation of new institutions and projects.     

8.5m敞开式硬底橡皮工作艇概念设计

橡皮艇的种类繁多、型号各异,有部队作战用的军用艇、武警防汛救援的防汛艇、专门追求速度的挂机艇、完全手动的皮划艇、体验激流乐趣的漂流艇、用于近海垂钓的钓鱼艇等。中国的橡皮艇业在近几年有着飞速的发展。文章从硬底橡皮工作艇基本特点和生产知识、概念设计目的和意义,以及概念设计对产品设计重要性等方面进行介绍,运用Solidworks软件对橡皮工作艇进行尺寸选择和结构布局设计,从而体现外观设计的人性化。通过对橡皮工作艇基本知识和主要设计理论的介绍,加强对橡皮工作艇设计方面的掌握。     

近断层地震动下设置BRB的双向减隔震桥梁地震反应

在近断层地震动下桥梁结构将发生较大反应,减隔震设计是减轻地震损伤的重要手段。提出了在桥梁双柱墩横桥向设置防屈曲支撑(BRB),在纵桥向设置铅芯橡胶支座(LRB)的双向减隔震体系。利用Midas Civil软件建立3种不同减隔震方式的桥梁结构模型:LRB仅单向,LRB双向与LRB联合BRB,运用非线性时程分析方法计算了桥墩反应(墩顶侧移角、残余位移角和曲率延性)、LRB支座变形和BRB的耗能特性等。结果表明:在近断层地震动输入下联合设置LRB和BRB的双向减隔震桥梁减震效果明显,相比其它2种方式,能有效降低墩柱的塑性变形及起到保护桥墩的作用。在横桥向,桥墩最大侧移角、残余位移角和最大曲率延性系数都显著降低。