两层两跨方钢管混凝土框架抗震性能试验研究

为了研究采用穿芯高强螺栓-端板节点的方钢管混凝土框架的抗震性能,对一榀两层两跨的方钢管混凝土柱-钢梁框架进行了竖向荷载和低周反复水平荷载作用下的抗震性能试验研究,观测了框架的破坏形态,得到了框架试件的荷载-位移滞回曲线、骨架曲线,分析了方钢管混凝土框架的破坏机制、滞回性能、延性、耗能能力、强度及刚度退化等力学性能。结果表明:框架试件基本实现了梁铰破坏机制,具有良好的变形性能和耗能能力,位移延性系数为5.86~6.42,等效黏滞阻尼系数达到0.454,均满足延性框架的抗震要求。框架试件的强度和刚度退化较为平缓,具有较强的抗侧移能力。     

增设节点阻尼器的外附钢框架结构抗震性能试验研究

提出一种组合型减震结构,由钢框架、节点阻尼器和原结构连接组成,外附钢框架将节点阻尼器连接在原混凝土框架结构上形成的增设节点阻尼器的外附钢框架结构,节点阻尼器的剪切滞回变形可以减小结构自身需要消耗的能量,从而提高原结构抗震性能。对原混凝土结构和增设节点阻尼器的组合型结构进行了的振动台试验。通过分析结构在不同地震波激励下的加速度和位移响应,得出楼层加速度和层位移的减震效果。研究结果表明:该结构体系在小震作用下通过提高结构刚度来增强其抗震性能;在大震作用下则可借助节点阻尼器的变形耗能来提升结构耗能能力,结构加速度减震系数达到53%,层间位移减震系数高达72%,验证了增设节点阻尼器的外附钢框架结构的减震效果。     

强震下框架-剪力墙结构损伤破坏量化指标研究

为了探究能够全面评估钢筋混凝土结构抗震性能的量化指标,借助有限元软件ABAQUS对一拟建的10层框架-剪力墙结构进行了大量的非线性动力时程数值计算,对比分析了不同地震作用下最大层间位移角与滞回耗能的分布情况,从结构滞回耗能的角度揭示了破坏机制,得到主要结论如下:结构层间位移角最大的位置不一定是损伤破坏最严重或者薄弱的部位,以层间位移角作为整体结构抗震性能的判别指标离散性较大,计算结果易受所选地震波的方法及数量影响;结构滞回耗能沿楼层的分布受地震波选取方法和数量的随机性影响较小,结构底层耗能对结构整体耗能贡献最大,约占结构总耗能的60%,其余各楼层滞回耗能约占结构总滞回耗能的1%~8%;梁和柱滞回耗能主要集中于结构底部1层,总的框架梁滞回耗能仅占结构总滞回耗能的18%~22%,绝大部分地震输入能由框架柱吸收,总的框架柱滞回耗能占结构总滞回耗能的80%左右,该计算结果与实际震害中结构主要形成"柱铰"破坏机制的现象较为一致。     

梁铰型屈服RC框架结构地震弹塑性位移增大系数研究

本文通过弹性和弹塑性时程分析,研究了水平地震作用下梁铰型屈服RC框架模型结构的楼层屈服剪力系数、基本自振周期、楼层数3个因素对弹塑性位移增大系数的影响,通过非线性回归分析给出了弹塑性层间位移增大系数经验公式;通过分析滞回耗能沿楼层高度的分布,初步确定了梁铰型屈服RC框架结构的薄弱楼层位置;基于结构损伤分析,讨论了抗震规范中RC框架结构弹塑性层间位移角限值的水准。     

受控摇摆式钢筋混凝土框架抗震机理研究

受控摇摆式钢筋混凝土框架结构(controllable rocking reinforced concrete frame,简称CRRCF)是一种新型减震耗能结构。通过对摇摆节点及整体框架进行的低周反复加载试验,研究其滞回特性。根据整体摇摆框架的滞回曲线得到了受控摇摆式钢筋混凝土框架的等效黏滞阻尼比。通过摇摆节点试验及理论分析,提出了摇摆节点的恢复力模型。利用有限元软件ABAQUS对受控摇摆式钢筋混凝土框架结构进行数值模拟,得到了不同节点刚度水平下结构的地震动力响应,并分析得出摇摆节点刚度的合理弱化程度。通过受控摇摆式钢筋混凝土框架和常规钢筋混凝土框架(RCF)的动力响应对比,可以发现CR-RCF结构可以有效降低结构的层间剪力与加速度响应。与RCF结构相比,CR-RCF结构的剪力与位移响应沿楼层分布较为均匀,这有利于防止层间变形过于集中,使各层材料都能得到充分利用。在受控摇摆式钢筋混凝土框架结构中设置耗能阻尼器,进行时程分析可以发现结构的位移响应可以得到有效的控制。     

高强轻骨料混凝土框架抗震性能试验研究与数值模拟

以一个3层高强轻骨料混凝土高铁站房框架结构的底部两层为研究对象,通过一榀1∶5比例的两层两跨高强轻骨料混凝土框架低周反复荷载试验,系统研究了框架的受力过程、破坏形态、破坏机制、滞回曲线、骨架曲线、刚度退化及耗能能力等。同时,运用有限元软件ABAQUS,建立了该框架的三维非线性有限元模型,分析了高强轻骨料混凝土框架在低周反复荷载作用下的工作性能,并与试验结果进行了对比分析。研究表明:框架破坏机制为混合机制,试件以柱脚混凝土压溃为破坏标志。有限元模拟得到的滞回曲线、骨架曲线和破坏形态,与试验结果符合良好。     

新型外廊式钢筋混凝土框架结构抗震性能试验研究

为改善带填充墙外廊式框架结构的抗震性能,尝试将采用高阻尼砂浆阻尼层的阻尼填充墙和PVA-ECC材料应用于外廊式框架结构中。以5.12汶川地震中倒塌的漩口中学综合教学楼为原型,选取最具代表性的中间榀较大跨满布填充墙框架的底层,设计制作了2个缩尺比例为1/4的单层两不等跨试验模型,并进行了低周反复加载试验,得到了其裂缝发展情况、破坏形态、承载能力、滞回曲线、骨架曲线、位移延性、刚度退化以及耗能性能。结果表明:采用高阻尼砂浆阻尼层的阻尼填充墙较普通填充墙具有更强的变形能力,对主体框架变形约束更弱,能延缓主体框架的破坏;采用PVA-ECC柱的组合框架较普通混凝土框架具有更强的承载力、更高的延性、更好的刚度退化与耗能性能。     

装配式预制混凝土框架结构拟动力试验研究

本文对2个采用橡胶垫螺栓连接梁柱节点的单层两跨的装配式预制混凝土框架结构进行拟动力试验,考察结构的破坏模式,研究结构的强度、刚度、滞回、耗能等抗震性能。试验结果表明:此类装配式预制混凝土框架结构具有较好的抗震性能,当层间位移角达到1/25时,结构仍具有一定的承载能力,采用橡胶垫螺栓连接的梁柱节点抗震性能良好,结构体系破坏模式为柱底弯曲破坏。     

低周反复荷载下两跨两层轻钢框架抗震性能试验研究

本文通过两跨两层轻钢框架试件的低周反复加载试验,研究了轻钢框架结构在地震作用下的滞回性能、耗能机制、耗能能力、刚度退化和破坏形态,结果显示轻钢框架具有很好的抗震性能,节点域耗能能力强。论文结论可为多层轻钢框架的抗震设计提供依据。     

高强钢筋高强混凝土框架结构滞回耗能分析

本文研究配有高强钢筋的高强混凝土框架结构的耗能性能与抗震能力.对2层2榀1/2比例的模型结构进行了拟动力试验,分析了高强钢筋的高强混凝土框架结构在地震作用下的滞回反应和耗能能力,探讨了结构在地震作用下的破坏机理,滞回特性及薄弱环节或部位.结构的延性系数达到4.0以上,等效阻尼系数达到0.055以上.试验结果表明,此类结...     

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

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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.     

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.     

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.