钢筋混凝土框架柱的变形能力及基于性能的抗震设计方法

框架柱的变形能力主要取决于轴压比和约束箍筋用量,本文建立了柱塑性铰区配箍特征值λcv,轴压比n及塑性铰极限转动量θplc^u之间的函数关系,即λcv-n-θplc^u关系式,并与柱试验数据进行了对比,计算公式与试验结果在平均意义上吻合很好。文中推导了柱截面λcv-n-μcφ关系式,建立了配箍特征值λcv、轴压比n、柱曲率延性μcφ之间的关系。在本文公式的基础上,讨论了按现行抗震设计规范最小配箍要求的RC框架柱所达到的最大变形能力,同时指出规范的构造要求并不总满足特定的变形要求。文中提出了框架柱的性能设计方程,给出了框架柱在指定性能目标DI下基于性能的抗震设计方法的基本过程。     

高轴压比密配箍筋框架柱抗震性能研究

为研究高轴压比下箍筋强约束钢筋混凝土柱的抗震性能,完成了3根配箍特征值0.22~0.44的钢筋混凝土柱的拟静力试验。试验表明:配置加密箍筋能有效提高高轴压比钢筋混凝土柱的抗震性能,水平承载力有一定提高,延性有较大程度改善,配置加密箍筋的RC框架柱的耗能能力明显高于未加密箍筋的柱。基于Msc.marc的THUFIBER程序对试件进行模拟,模拟结果与试件结果吻合较好。同时,对不同轴压比、不同配箍特征值构件的延性进行分析,通过对计算数据的回归分析,得出了框架柱位移延性系数随配箍特征值、轴压比变化的计算公式。通过与已有试验数据、美国规范ACI318-08、欧洲规范Eurocode 8的比较,论证了本文回归计算公式的合理性,并通过该公式给出了配箍特征值的建议值。     

高强钢筋混凝土短肢剪力墙抗震性能试验研究

通过对采用高强钢筋的6片T形混凝土短肢剪力墙和采用高强钢筋高强混凝土的6片L形短肢剪力墙进行低周往复加载试验,研究了T形和L形的破坏形态与性能差异,分析了高厚比、轴压比、配箍间距等参数对构件破坏形态、滞回耗能、骨架曲线、延性及耗能等抗震性能的影响,对比分析了构件与普通短肢剪力墙的抗震性能差异。试验结果表明:采用腹板端部箍筋加密的方式可减轻构件端部的损伤和降低正负向加载时承载力和延性的不对称性;T形构件中高厚比为5的试件表现为弯曲破坏,其他构件表现为弯剪破坏;试验中高厚比小的构件相对于高厚比大的试件延性耗能更好,轴压比增大,构件承载力提高但延性降低;与普通短肢剪力墙相比,T形短肢剪力墙承载力和变形能力提高,耗能增加,L形短肢剪力墙承载力提高较大,极限位移增大,构件后期变形能力略有降低,但可以满足抗震性能要求。     

碳纤维布加固钢筋混凝土柱的剪力-位移关系及其破坏位移增大系数分析

编制了碳纤维布加固钢筋混凝土柱的剪力-位移关系全过程分析程序,通过对多种工况下碳纤维布加固钢筋混凝土柱的剪力-位移关系进行大量计算分析,较全面地探讨了碳纤维布配箍特征值、轴压比、剪跨比、箍筋配箍特征值、纵筋配筋率、混凝土强度等参数对碳纤维布加固钢筋混凝土柱的剪力-位移关系及其破坏位移增大系数的影响。在此基础上,给出了碳纤维布加固钢筋混凝土柱破坏位移增大系数的回归计算公式,统计建立了碳纤维布加固钢筋混凝土柱的剪力-位移关系三折线模型中各无量纲特征参数的确定方法。     

轻钢骨混凝土剪力墙延性的非线性有限元分析

轻钢骨混凝土剪力墙结构作为新型结构在工程界要得到认同并推广使用,必须对该结构的各项性能指标进行系统的试验研究和理论分析。本文应用ADINA有限元软件对轻钢骨混凝土剪力墙延性进行非线性有限元分析,根据不同的高宽比、轴压比、轻钢骨配筋率以及端部配筋模型的计算结果,对该结构体系的延性及其破坏形态进行综合分析,并对轻钢骨混凝土剪力墙轴压比设计提出建议。分析结果表明,高宽比主要控制轻钢骨混凝土剪力墙的破坏形态,轴压比对其结构的延性的影响最为显著,而端部配筋对其延性影响不大。     

L形高强钢筋高强混凝土短肢剪力墙抗震性能试验研究

L形短肢剪力墙由于其肢短的特点,已经广泛应用于民用建筑的外围结构。为研究使用高性能材料加强后的新型L形短肢剪力墙的抗震性能,本文基于不同轴压比、高宽比和配箍率,设计制作了六片短肢剪力墙试验模型,对其进行了低周往复荷载试验,根据试验结果,对试件的滞回性能、刚度退化、破坏形态、耗能能力等抗震性能指标进行分析与研究。结果表明:高强材料的使用提高了试件的整体承载能力;在满足最小配箍率的前提下适当增大配箍率有利于提高试件的承载力和延性;轴压比大小是影响试件破坏形态的主要因素,随着轴压比逐渐增大,试件趋于脆性破坏;高厚比大小是影响试件抗震性能的次要因素,其影响程度主要根据工程实际情况来确定,但可以肯定的是,较大高厚比有利于提升墙体的稳定性和承载能力。     

钢管混凝土叠合柱受力性能研究

为研究钢管混凝土叠合柱受力性能,本文首先根据叠合柱截面上的应变发展对其管内外混凝土轴力重分布机理及截面塑性变形能力进行了分析,然后采用条带法编制MATLAB计算程序得到了钢管混凝土叠合柱弯矩-曲率及荷载-位移关系曲线。将理论计算值与试验结果进行对比,验证了条带法分析模型的有效性。在此基础上,分析了名义轴压比n、叠合比m、管外混凝土纵筋配筋率ρ、套箍系数θ、管外混凝土配箍特征值λ各主要参数对钢管混凝土叠合柱管内外混凝土部分轴力重分配关系及构件延性的影响,同时讨论了叠合比、配箍特征值等参数对轴力-水平荷载(n-p)曲线的影响。最后根据参数分析的结果,建议了在满足叠合柱延性需求(u△≥3)的基础上,叠合柱名义轴压比限值及相应的最小配箍特征值,为叠合柱的工程设计提供参考。     

内置钢板钢筋混凝土组合剪力墙数值模拟

内置钢板钢筋混凝土组合剪力墙具有良好的抗震性能,目前已在超高层建筑中得到越来越多的应用。采用OpenSees程序对普通钢筋混凝土剪力墙和钢板组合剪力墙试验构件进行模拟分析,验证了建模与分析方法的合理性与准确性,分析结果表明,该方法能够较好地模拟组合剪力墙的弹塑性行为。分析了轴压比和配钢率这两个关键参数对内置钢板组合剪力墙抗震性能的影响。计算结果表明,与普通钢筋混凝土剪力墙相比,内置钢板可以明显提高构件的承载力、延性和滞回耗能;轴压比和配钢率对组合剪力墙的抗震性能有较大影响。     

中国规范钢筋混凝土抗震墙延性和位移角的量化研究

分析了中国、美国、新西兰规范三种不同钢筋混凝土剪力墙约束箍筋设计方法的内在机理,讨论了三国规范存在的问题。结果表明,中国规范仅按照轴压比判断是否加约束箍筋的设计方法不合理,使同一抗震等级剪力墙的位移和延性指标不平衡。美国和新西兰规范是基于位移和延性的设计方法,但其没有考虑剪力墙钢筋拉断的受拉破坏,导致混凝土高度很小时高估了位移和延性能力,而实际位移和延性不能满足要求。提出了基于修正后的美新规范位移角和延性计算方法,评估了现行中国规范不同的抗震等级、烈度下剪力墙具有的位移和延性能力。按照中国规范设计剪跨比为4的剪力墙在抗震等级为一级(9度)、一级(6、7、8度)、二三级时,延性指标平均值分别能达到5.1、3.6和2.6,位移角指标能达到1/81、1/129和1/175。     

边缘约束构件对钢筋混凝土剪力墙抗震性能的影响

钢筋混凝土剪力墙是高层建筑中的主要抗侧力构件，边缘约束情况是影响剪力墙抗震性能的一个重要因素。为研究边缘约束构件对钢筋混凝土剪力墙抗震性能的影响，本文进行了三片边缘约束情况不同的钢筋混凝土剪力墙的低周反复试验，并对试验结果进行了分析，分析内容包括：破坏形态、水平承载力、位移延性系数、刚度退化、抗震耗能能力等方面。研究结果表明，合理地设置边缘约束能够扩大塑性破坏区域，提高试件的水平承载力，改善其抗震耗能性能。研究进一步发现，边缘纵筋配筋率在提高试件的水平承载力，改善其抗震耗能性能和刚度退化程度方面影响显著，而边缘配箍率对抗震性能的贡献在本次试验分析中表现得并不明显。     

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.