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横向撞击下短梁的剪切破坏研究 被引量:2
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作者 郝志明 陈裕泽 +2 位作者 陈刚 颜怡霞 徐友钜 《爆炸与冲击》 EI CAS CSCD 北大核心 2002年第1期52-55,共4页
应用实验和数值模拟手段研究了 2 0 # 钢梁在横向撞击下的双剪破坏问题。实验中通过测量加速度 ,分析了梁破坏需要吸收的能量 ;数值分析中采用Cauchy应力对数应变Cowper Symonds过应力本构方程模拟材料率相关行为 ,累积塑性应变破坏准... 应用实验和数值模拟手段研究了 2 0 # 钢梁在横向撞击下的双剪破坏问题。实验中通过测量加速度 ,分析了梁破坏需要吸收的能量 ;数值分析中采用Cauchy应力对数应变Cowper Symonds过应力本构方程模拟材料率相关行为 ,累积塑性应变破坏准则与单元死活技术结合模拟材料弱化行为 ,数值分析给出的结构破坏吸收能量与实验结果基本吻合 ,由计算得到的剪切塑性铰长度与S .B .Menkes等的实验结果基本一致。 展开更多
关键词 短梁 剪切破坏 横向撞击 Cauchy应力 单元死活技术 材料弱化 结构塑性动力响应
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白鹤滩拱坝谷幅变形预测及不同计算方法变形机制研究 被引量:14
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作者 钟大宁 刘耀儒 +3 位作者 杨强 徐建荣 何明杰 张伟狄 《岩土工程学报》 EI CAS CSCD 北大核心 2019年第8期1455-1463,共9页
中国已建成的特高拱坝如溪洛渡、锦屏一级等,在初期蓄水过程中均表现出了谷幅收缩的异常现象。而拱坝是高次超静定结构,对坝基变形尤其是不均匀变形非常敏感。从有效应力改变和岩体材料泡水弱化这一谷幅变形机制和边界施加位移这一计算... 中国已建成的特高拱坝如溪洛渡、锦屏一级等,在初期蓄水过程中均表现出了谷幅收缩的异常现象。而拱坝是高次超静定结构,对坝基变形尤其是不均匀变形非常敏感。从有效应力改变和岩体材料泡水弱化这一谷幅变形机制和边界施加位移这一计算手段出发,利用弹塑性有限元方法,计算并预测白鹤滩拱坝在初期蓄水过程中可能产生的谷幅变形,并分析了谷幅变形对大坝位移和应力的影响。结果表明:两种方法的计算结果相差很大;从有效应力改变和岩体材料弱化角度出发,白鹤滩拱坝两岸山体可能产生的最大谷幅收缩不大于40mm,且该谷幅变形不会很大程度上降低拱坝的整体稳定性,只是使坝体产生了新的应力集中区。而拱坝对施加边界位移具有很强的超载能力,但谷幅收缩对坝体应力的影响极小。对比发现,坝基不均匀变形是影响拱坝应力的关键因素。 展开更多
关键词 谷幅变形 有效应力 材料弱化 边界加位移 不均匀变形
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Potential Effects of Global Change to Urban Vegetation: Vulnerability and Adaptations
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作者 Robert Saye Felicidad de Herralde Xavier Arand Carmen Biel 《Journal of Life Sciences》 2012年第2期194-199,共6页
An urban area is a space with high population density which develops new, major and complex structures in comparison to the areas surrounding it. In order to develop these structures and maintain population and its ac... An urban area is a space with high population density which develops new, major and complex structures in comparison to the areas surrounding it. In order to develop these structures and maintain population and its activity, the metabolism of urban areas needs a lot of external sources of energy and nutrients (water, food, materials...), which produces heat waste, garbage, sewage and pollution which are some of the major problems for urban sites, and the related areas from it. This metabolism promotes major environmental changes in the urban areas, which promote stress on vegetation used in gardening. The main environmental factors that affect vegetation in urban areas are the same that have been defined in literature from long time ago, but now they are acting as the sum of complementary and synergic effects of these classical stresses at the same moment, in the same place, which happen due to the incredibly amount of energy that we place in the systems. This is called global change. Ecophysiological studies can provide objective information to be used as a tool to improve the vegetation management in urban areas from design to process, and consequently avoiding the potential vulnerabilities associated with global change. Present paper tries to show several examples about the plant response, measurement tools and vulnerabilities and adaptations to global change under urban conditions. It can be concluded that the large availability of vegetal material and the great technical development can be highlighted as strong points of gardening and urban landscaping while, as weak points, it could be mentioned the changing taste of consumers, which can force the introduction of new vegetal material with no time for adaptation, Urban gardening and landscaping can be considered to be exposed to global change, but in our opinion it is necessary to carry out more studies to determine the real degree of vulnerability of this activity to this complex kind of stress. 展开更多
关键词 ECOPHYSIOLOGY water-use efficiency plant water relations biotic and abiotic stresses.
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