农居工程地基砂垫层隔震体系性能试验研究

砂垫层具有取材方便、造价低、施工简便的特点,为了更好地在农居工程建设中推广应用地基砂垫层隔震技术,通过制作农村房屋结构模型,进行地基砂垫层隔震体系与无隔震体系的大型振动台试验,研究了地基砂垫层隔震体系的隔震性能。基于结构加速度反应、结构位移反应和结构应变反应三个方面,对比分析无隔震试验和地基砂垫层隔震试验的结果,研究地基砂垫层隔震体系的隔震性能。结果表明:地基砂垫层隔震体系能够有效地减小上部结构的地震加速度反应、层间位移反应和应变反应,具有良好的隔震效果;输入地震动的量级是影响地基砂垫层隔震体系隔震效果的一个重要因素。     

近断层脉冲型地震动作用下高层摩擦摆基础隔震结构的减震性能研究

近断层地震动中长周期、短持时和高能量的加速度脉冲将对高层摩擦摆基础隔震结构的减震性能产生不利影响,考虑土-结构相互作用（SSI效应）后的隔震结构将产生动力耦合效应,可能进一步放大隔震结构地震响应。为此,通过一幢框架-核心筒高层摩擦摆基础隔震结构的非线性地震响应分析,考察近断层脉冲型地震动作用下框架-核心筒摩擦摆基础隔震结构的层间位移角、楼层加速度和隔震层变形等响应规律,揭示隔震体系的损伤机理。基于集总参数SR （sway-rocking）模型,分析不同场地类别与不同地震动类型对隔震体系动力响应影响规律。结果表明:高层摩擦摆基础隔震结构在近断层脉冲型地震动作用下的减震效果相比普通地震动减震效果变差,楼层剪力、层间位移角和隔震层变形等超越普通地震动作用下的1.5倍;对于Ⅲ和Ⅳ类场地类别,考虑SSI效应使隔震结构的地震响应进一步放大,弹塑性层间位移角随着土质变软增大尤为明显。     

摩擦摆基础隔震结构多维地震反应分析

对摩擦摆基础隔震结构进行了单向、双向和三向地震反应对比分析,表明考虑双向水平地震动时摩擦摆基础隔震结构的支座位移增大,而结构的加速度和楼层剪力减小,其中对支座位移和结构加速度影响较大;考虑竖向地震动时摩擦摆基础隔震结构的支座位移略有减小,而结构的加速度和楼层剪力增大,其中对结构加速度影响较大.因而,在进行摩擦摆基础隔震结构地震反应分析时,应考虑多维地震动的影响.     

滑移摩擦隔震系统在多向地面运动作用下的试验研究

基础隔震通常只考虑隔离水平地面运动，而对竖向地面运动的影响注意不够，本文进行了滑移摩擦隔震系统的振动台房屋模型试验，研究多向地面运动输入时上部结构反应和隔震系统的性能，试验中分别对模型输入了不同方向的地震动，其中包括水平单向、水平双向、水平和竖向及三向地震动输入，对试验结果进行了分析比较，结果表明竖向地震动输入对上部结构的水平地震反应有显著影响，同时在橡胶隔震支座中产生了竖向拉力。     

近断层双向水平地震作用下隔震结构地震反应

近断层地震动脉冲特性在2个水平分量上具有差异,采用平方和开方法分析了近断层脉冲地震动双向地震作用下基础隔震结构和组合隔震结构的隔震层位移,并与近断层脉冲单向地震作用进行了对比分析,结果表明:若仅地震动加速度峰值大的分量或2个方向分量均存在明显速度脉冲,则产生的隔震层位移大于单向地震动;若仅地震动加速度峰值小的分量存在明...     

单层框架建筑模型基础隔震实验研究

对带叠层橡胶隔震基础的钢筋混凝土单层框架模型进行了振动台地震模拟试验,比较了隔震结构与非隔震结构的地震反应,结果表明,用叠层橡胶支座隔震后,框架模型的地震反应比不隔震时大大减小,证明叠层橡胶支座基础隔震技术是一种既有效又很安全的减震措施。     

地震动速度脉冲对巨型结构体系地震响应影响研究

以巨-子结构抗震体系、隔震体系以及智能隔震体系为研究对象,选择4组具有速度脉冲特性的实际地震动加速度记录及人工模拟的具有相同加速度反应谱而无速度脉冲的地震动时程分别作为地震动输入,采用数值分析方法分别计算在有、无速度脉冲的地震动激励下三种结构体系的地震响应,探讨地震动的速度脉冲对巨型结构体系在不同控制策略下地震响应的影响。研究结果表明:三种结构体系在速度脉冲型地震动作用下的地震响应大部分要大于无速度脉冲型的地震响应,近断层地震动的速度脉冲对巨-子结构抗震体系、隔震体系以及智能隔震体系的地震响应均有一定的不利影响。智能隔震体系对速度脉冲地震动较为敏感,但能有效地减小隔震层位移。     

设置抗拔型三重摩擦摆隔震支座框架结构地震响应分析

抗拔型三重摩擦摆隔震支座是一种新型隔震支座。以框架结构为例,利用ANSYS软件建立了6层和10层普通抗震结构和带该支座的基础隔震结构模型;通过模态分析,得到了结构的自振周期;通过地震响应分析,提取了6层框架隔震层和顶层的位移、加速度和剪力时程曲线,并提取了不同层数不同结构类型的各层间位移、加速度幅值。结果表明：与抗震结构相比,基础隔震结构周期显著增大;隔震结构的变形主要集中在隔震层,隔震层以上的结构基本为整体平动,结构的地震位移反应得到了有效的减小;采用抗拔型三重摩擦摆隔震支座能降低结构地震加速度反应;设置抗拔型三重摩擦摆隔震支座的多层数隔震结构的能量衰减不如低层数的隔震结构迅速。     

基于概率密度演化的隔震结构随机地震响应

本文考虑地震动的随机性,运用概率密度演化方法对基础隔震结构的随机响应进行研究.上部结构与隔震层分别采用刚度退化的Bouc-Wen模型与Bouc-Wen模型,建立隔震结构的概率密度演化方程,直接应用四阶龙格-库塔方法迭代求解隔震结构的非线性的响应,得出隔震结构在8度罕遇地震下每层的位移概率.结果显示隔震结构较非隔震结构上部结构的位移大大地减小了,上部结构具有足够的安全性.结构整个概率密度演化过程显示了隔震结构的响应信息,概率密度演化方法能够有效评估隔震结构的抗震性能.     

基础隔震结构抗震可靠度简化分析方法

选用胡聿贤平稳地震地面运动模型作为基础隔震结构的随机地震动输入,采用Bouc-Wen模型描述隔震结构的层间滞变位移,将滞变体系动力特性矩阵随机等效线性化,并建立等价线性状态方程。引入左右特征向量系,对振动微分方程进行解耦,推导了基础隔震结构随机地震响应的统计矩解析解。采用变形失效准则,定义了上部结构和隔震层的功能状态极限函数。在此基础上,采用首次超越破坏模型,基于Possion分布假设和串联系统可靠度模型,建立了从整体上评价基础隔震体系抗震可靠度的简化分析方法。最后,通过一个基础隔震框架结构计算实例,说明了这种方法的运用。     

SCIENCE CHINA Earth Sciences SUBJECT INDEX TO VOLUME 57(2014)

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A Monte Carlo study of rainfall forecasting with a stochastic model

A procedure for short-term rainfall forecasting in real-time is developed and a study of the role of sampling on forecast ability is conducted. Ground level rainfall fields are forecasted using a stochastic space-time rainfall model in state-space form. Updating of the rainfall field in real-time is accomplished using a distributed parameter Kalman filter to optimally combine measurement information and forecast model estimates. The influence of sampling density on forecast accuracy is evaluated using a series of a simulated rainfall events generated with the same stochastic rainfall model. Sampling was conducted at five different network spatial densities. The results quantify the influence of sampling network density on real-time rainfall field forecasting. Statistical analyses of the rainfall field residuals illustrate improvement in one hour lead time forecasts at higher measurement densities.     

Distribution of throughfall and stemflow in multi‐strata agroforestry,perennial monoculture,fallow and primary forest in central Amazonia,Brazil

The partitioning of rain water into throughfall, stemflow and interception loss when passing through plant canopies depends on properties of the respective plant species, such as leaf area and branch angles. In heterogeneous vegetation, such as tropical forest or polycultural systems, the presence of different plant species may consequently result in a mosaic of situations with respect to quantity and quality of water inputs into the soil. As these processes influence not only the water availability for the plants, but also water infiltration and nutrient leaching, the understanding of plant effects on the repartitioning of rain water may help in the optimization of land use systems and management practices. We measured throughfall and stemflow in a perennial polyculture (multi‐strata agroforestry), monocultures of peach palm (Bactris gasipaes) for fruit and for palmito, a monoculture of cupuaçu (Theobroma grandiflorum), spontaneous fallow and primary forest during one year in central Amazonia, Brazil. The effect on rain water partitioning was measured separately for four useful tree species in the polyculture and for two tree species in the primary forest. Throughfall at two stem distances, and stemflow, differed significantly between tree species, resulting in pronounced spatial patterns of water input into the soil in the polyculture system. For two tree species, peach palm for fruit (Bactris gasipaes) and Brazil nut trees (Bertholletia excelsa), the water input into the soil near the stem was significantly higher than the open‐area rainfall. This could lead to increased nutrient leaching when fertilizer is applied close to the stem of these trees. In the primary forest, such spatial patterns could also be detected, with significantly higher water input near a palm (Oenocarpus bacaba) than near a dicotyledonous tree species (Eschweilera sp.). Interception losses were 6·4% in the polyculture, 13·9 and 12·3% in the peach palm monocultures for fruit and for palmito, respectively, 0·5% in the cupuaçu monoculture and 3·1% in the fallow. With more than 20% of the open‐area rainfall, the highest stemflow contributions to the water input into the soil were measured in the palm monocultures and in the fallow. Copyright © 1999 John Wiley & Sons, Ltd.     

Anthropogenic Eutrophication and Red Tide Outbreak in Lacustrine Systems of the Kashmir Himalaya

Red tide, a recurrent phenomenon has become conspicuous in several Kashmir lake ecosystems since 1991. The responsible organism (Euglena pedunculata), a rare flagellate rediscovered in the Kashmir Himalaya (Khan 1993) caused first and unprecedented red tide outbreak, constituting a maximum of 96% of resident numerical phytoplankton density in Dal Lake. At present, conflicting hypotheses exist on the generation of causal assemblage(s) imparting redness to waters: Jeeji Bai (1991) linked its origin to acid precipitation – a fallout of burning oil‐fields during the Gulf War – whilst Khan (1993) holds local factor(s) responsible. Field/experimental studies support the latter contention that the influx of untreated sewage, in unison with warm temperatures, high levels of PhAR, iron and interruption to hydrological flow‐pattern together with absence/or reduction in grazing activity created conducive environmental milieu for red tide outbreak. Dal Lake “red tide” drifted the bloom‐inoculum to other waters, including Lake Wular, where additional ecological niches were carved out, threatening the aesthetic value and biological diversity of Kashmir lakes. Ecological monitoring indicates frequent seasonal red tide occurrence in Dal Lake (including summer‐autumn event of 1998) which testifies its unabated eutrophication status. Further studies are needed on ecological adaptability and biogeographic distribution of this rare and unique red tide‐causing flagellate.