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采用虚拟激励法,以一大跨度弦支穹顶结构—济南奥体中心体育馆为研究对象,考虑结构静力初始状态的影响,分析大跨度弦支穹顶结构多点激励随机地震响应。研究结果表明：大跨度弦支穹顶结构受行波效应与部分相干效应影响显著,考虑地震动空间变化效应使径向杆、环向杆、环索及竖向撑杆控制构件内力增幅约分别达到了50%、39%、27%及150%;其中结构不同类型、不同位置构件提升程度不同,需对具体响应具体分析;考虑地震动多维输入相比单维输入增大达到30%;行波效应与部分相干效应对结构轴力响应的影响程度存在差异;单独考虑行波效应和部分相干效应不能得到结构的最不利响应。由此得出结论：为确保大跨度弦支穹顶结构的安全,必须根据场地条件选取多种可能的地震波视波速,同时考虑部分相干效应的影响进行多维多点随机地震响应分析。 相似文献
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为了模拟脉冲地震作用下简支梁桥的倒塌过程，基于LS-DYNA平台建立了简支梁桥的三维有限元模型，并人工合成了不同脉冲幅值和脉冲周期的地震动，研究了脉冲幅值和脉冲周期对简支梁桥倒塌过程和地震响应的影响，总结了地震作用下简支梁桥的灾变过程。研究表明：脉冲幅值对简支梁桥的倒塌模式影响显著，脉冲幅值较小时桥墩发生倒塌，脉冲幅值较大则会导致梁体落梁；脉冲幅值对桥梁位移响应影响较小，对内力响应和碰撞效应影响较大，增大脉冲幅值会加重梁间的碰撞效应，从而消耗大量地震能量；位移响应随脉冲周期的增大而增大，梁间碰撞力则与之相反；桥梁开始出现损伤的时间点与脉冲周期的大小有关，脉冲周期越小，开始出现损伤的时间越靠近地震加速度峰值时刻；脉冲地震作用下简支梁桥的倒塌表现为三个阶段：分别为正常运行阶段、损伤演变阶段和倒塌阶段。 相似文献
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行波效应对大跨度空间结构随机地震响应的影响 总被引：1，自引：0，他引：1
深入研究了行波效应对大跨度空间结构随机地震响应的影响,进一步完善了大跨度空间结构随机地震响应分析理论。推导了双支座、单自由度体系地震响应功率谱密度函数的解析表达式,研究了不同频率体系的响应峰值随地面视波速的变化规律,分析了多支撑点、多自由度体系的地震响应功率谱矩阵的特点,发现多自由度体系地震响应随地面视波速的变化规律与单自由度体系相似。数值模拟了某体育馆网壳结构在不同地面视波速情况下的随机地震响应,结果表明,考虑地震动行波效应后,结构地震响应随地面视波速的变化而显著变化,当视波速较低时其变化规律很复杂;且支撑点附近、受拟静力位移影响较大的部分杆件的地震响应明显增大,远离支撑点处、受拟静力位移影响较小的部分杆件的地震响应稍有减小。由此得出结论,对于大跨度空间结构的随机地震响应分析,必须考虑地震动的行波效应,尤其当受拟静力位移影响较大的部分杆件对结构抗震设计起控制作用时;且应对可能出现的地面视波速进行全面分析,作为结构抗震设计依据。 相似文献
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结合多跨连续梁桥的结构特点,提出了一种能模拟联间碰撞行为的连续梁桥碰撞分析模型.用非线性时程方法对行波输入下连续梁桥的地震碰撞反应进行了参数分析.结果表明:相邻联的周期比对短周期联位移的碰撞效应较大,考虑地震行波输入时伸缩缝处的碰撞效应可能会大幅度增大墩梁的相对位移,从而增大了地震作用下发生落梁的风险;墩梁相对位移随滑动支座摩阻系数的增大而减小.最后提出用一个碰撞效应增大系数来考虑连续梁桥相互碰撞对墩梁相对位移的影响,利用碰撞效应增大系数的概念为连续梁桥防止落梁的设计提供了一个新的思路. 相似文献
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《世界地震工程》2017,(2)
为揭示河谷场地"钢管混凝土空间组合桁架连续梁桥"地震响应规律,以京昆高速公路"干海子特大桥"为工程背景,建立其三维有限元动力计算模型;采用有限元与间接边界积分方程耦合法(FEM-IBIEM耦合法)进行场地反应计算,并通过多点激励(改进LMM法)方式进行地震动输入,研究行波效应、局部场地效应对其地震响应影响,并和一致激励进行比较,结果表明:该类桥梁低墩较高墩对地震动更敏感,且在墩高突变区域最为明显;较一致激励和高墩和对应梁跨,行波效应增大其墩底轴力、跨中下弦杆和斜腹杆轴力,但减小其它量测值;低墩和对应梁跨,行波效应减小其墩底弯矩、墩顶位移和跨中位移;较一致激励和行波效应,局部场地效应显著增大了大多桥墩和梁跨的位移和内力,且对墩高突变处低墩、梁跨的放大作用最为明显,因此对于河谷场地中"钢管混凝土空间组合桁架连续梁桥"抗震设计,特别是墩高突变区的低墩和梁跨,必须重点考虑局部场地效应的影响。 相似文献
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大跨度空间网格结构在地震行波作用下的响应 总被引：11，自引：4，他引：11
本文对地震行波三向正交分量分别独立作用和联合作用下的大跨度空间网格结构的地震响应（包括结构控制点的位移，杆件内力，柱底弯矩等）进行了数值分析，结果表明，与一致地震振动相比，地震动的行波效应可使大跨度空间网格结构的控制点位移增大21%，柱脚弯矩增大79%，杆件内力增大100%，因此，在大跨度空间结构的抗震分析中必须进行详细的抗震分析。 相似文献
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《地震工程与工程振动》2016,(2)
为研究行波效应对大跨度钢筋混凝土拱桥地震响应的影响,以绵竹市金花大桥为工程实例,结合该桥实际震害。基于SAP2000建立金花大桥结构模型,采用汶川地震动分析了行波效应对金花大桥非线性地震响应的影响。结果表明:行波效应对金花大桥地震响应影响较大,特别是对拱肋拱脚截面和拱上短立柱影响显著,其计算结果与实际震害一致,对同类型桥梁的抗震评估提供了有益的参考。 相似文献
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本文对某特大跨上承式铁路钢管混凝土拱桥建立“V”型河谷场地有限元动力计算模型,结合时空解耦的时域动力有限元方法,研究“V”型河谷场地效应对其地震响应的影响,并考虑地震入射角、行波速度及地震动峰值等因素对场地效应的影响。结果表明:海拔高且坡度均匀的地形使地震波在反射过程中能量增大,海拔较低且坡度下陡上缓的地形使地震波在反射过程中能量减少,“V”型河谷场地效应使大部分钢管混凝土拱圈截面内力测量值放大作用明显;“V”型河谷场地地形效应与地震波的入射角、行波速度及加速度峰值等因素均有关联,且CFST拱肋面外受弯抗震性能受行波速度的影响较大。因此,钢管混凝土拱桥抗震设计中应注意场地地形效应及行波速度的影响。 相似文献
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M. N. French R. L. Bras W. F. Krajewski 《Stochastic Environmental Research and Risk Assessment (SERRA)》1992,6(1):27-45
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. 相似文献
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Gtz Schroth Luciana Ferreira Da Silva Marc‐Andree Wolf Wenceslau Geraldes Teixeira Wolfgang Zech 《水文研究》1999,13(10):1423-1436
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. 相似文献
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M. A. Kahn 《洁净——土壤、空气、水》2000,28(2):95-101
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. 相似文献