排序方式： 共有11条查询结果，搜索用时 15 毫秒
1.
受明显的层状结构影响,加之材料参数和动荷载的双重随机性,动力条件下碾压混凝土重力坝的层间抗滑稳定可靠度问题值得关注。考虑地震波频谱特性、峰值加速度、坝体材料参数的随机性,统计概化出地震作用下坝体的潜在滑动失效路径;在特定地震动作用下,基于随机有限元分析结果,采用刚体极限状态判断准则和响应面法构建失效路径的动力抗滑稳定功能函数,进而求得其抗滑稳定可靠指标;接着考虑不同失效路径的相关性,用Ditlevsen窄界限公式估算体系的可靠度;最后,考虑地震动荷载的随机性,采用基于全概率公式的数值拟合积分方法求解大坝抗滑稳定体系的动力可靠度。研究结果表明,动力条件下,当水平地震系数大于0.2时,重力坝层间抗滑体系可靠度不再由建基面失效路径决定,而是由下游折坡处层面的失效路径决定。该方法数学意义明确,实用性强。 相似文献
2.
由于切割式横缝的联接作用,切割式横缝碾压混凝土重力坝近似为一个整体结构。当遭遇强震作用时,随着切割式横缝的开裂程度不同,碾压混凝土重力坝的抗震安全性也就有所不同。针对切割式横缝的结构特点,在有限元法动力分析中,利用“生死”单元来模拟切割式横缝的联接单元和切割单元,且以整个横缝联接单元弹性模量的不同折减来模拟切割式横缝的不同开裂程度,并应用到金安桥水电站左岸坡坝段群的抗震安全性分析中。分析结果表明：金安桥水电站左岸坡坝段群在设防烈度为IX度的地震作用下,切割式横缝的开裂对左岸坡单个坝段和坝段群的抗震安全性影响不大,且大坝是安全的。这说明了金安桥水电站碾压混凝土重力坝结构设计合理,能够抵御设防地震。 相似文献
3.
城市的空间格局与社会生活各个方面息息相关,若利用GIS卓越的技术能力,探索城市空间格局的结构性特征、要素关联,挖掘其中的空间关系或其他有意义的结构模式,将为城市经济发展、资源分配、交通规划等社会问题提供知识支撑。此外若将城市空间格局与GIS空间分析相融合,将有助于架起图形与文本之间的桥梁与纽带,提升GIS空间数据挖掘水平。本文总结了城市空间格局的要素体系,并利用RCC8模型和区间代数使之与GIS中的空间关系建立对应关联,实现了由城市规划文本生成城市空间格局意向图。丰富了城市空间格局的规律性、本质性知识,弥补了多种空间关系集成研究的不足,为图形和文本的关联性知识挖掘奠定了基础。 相似文献
4.
基于粗糙集的不确定区域RCC拓扑关系研究 总被引：1，自引：0，他引：1
基于粗糙集定义了粗糙区域和粗糙区域的上、下近似区域,提出两种基于上、下近似区域表示粗糙区域拓扑关系的方法。一种方法用上、下近似区域的连接关系表达粗糙区域拓扑关系,得出两个粗糙区域之间的6种拓扑关系,并进一步利用上、下近似区域的RCC5关系表达粗糙区域之间的拓扑关系,得出两个粗糙区域之间的51种拓扑关系,然后分析两种表达之间的联系。另一种方法扩展RCC5模型,首先定义三值逻辑的部分关系≤和补运算~,然后用三值逻辑三元组(X≤Y,X≤~Y,Y≤X)描述两个粗糙区域X和Y的拓扑关系,并给出可能的8种拓扑关系。 相似文献
5.
Samer?A.?BarakatEmail author Abdallah?I.?Husein?Malkawi Maher?Omar 《Geotechnical and Geological Engineering》2005,23(1):61-78
Parametric study was carried out in this paper using the Finite Element Method (FEM) to study the effects of variations of the two parameters, i.e., variations in batter slope and foundation properties under static and dynamic loading conditions on the distribution of the peak stresses within the dam and foundation soils. The response spectra for the operating basis earthquake (OBE) and the maximum credible earthquake (MCE) were used in the dynamic analysis. It is shown that the distribution of peak stresses across base of dam and the extent of tensile zone on the foundation soils at the foundation level vary with the variations in the batter slope. Generally, as the batter slope increases the extent of the tensile zone at the foundation level decreases but not necessarily the maximum tensile stresses. However, an optimum batter slope could be achieved based on the results of this parametric study. It should be noted that the greatest tension is developed in the rock adjacent to the toe of the batter. For the foundation mechanical properties, it has been shown that the assessment of accurate soil mechanical properties has a great effect on the computed design stresses from finite element analysis. However, the greatest effect of the foundation properties was on the stresses at the base of dam while it has a negligible effect within the dam body. 相似文献
6.
7.
碾压混凝土重力坝全程综合仿真分析与安全评估 总被引：1，自引：0，他引：1
运用有限元方法对光照碾压混凝土重力坝进行施工期温度、渗流、应力应变的综合仿真分析,得出了温度场、渗流场及应力场的分布规律,在此基础上评价整个坝体与坝基系统稳定性的安全度,为坝体与坝基系统的温控、渗控和安全性评价提供参考依据。同时对光照碾压混凝土重力坝进行了不考虑温度、徐变、浇筑过程和蓄水过程的应力-应变和安全度计算,并对两种计算的结果进行了比较,结果表明：对碾压混凝土重力坝而言两者的位移相差最大,达70 mm;应力差别其次,达1.5 MPa;而整体稳定超载安全系数则没有本质区别。由于变形、应力和稳定安全系数在碾压混凝土重力坝设计中都是重要指标,所以综合仿真分析具有意义。 相似文献
8.
介绍了对岷江流域某高拱坝坝体碾压混凝土力学特性，进行的三轴压缩试验和直接剪切试验结果，根据试验资料对碾压混凝土的力学特性进行了分析。 相似文献
9.
《Singapore journal of tropical geography》2018,39(2):215-223
The River Continuum Concept (RCC) is an existing theory regarding the distribution of plant communities along riverbanks. This study is concerned with the pattern of riparian vegetation along the Lower Ogun River (LOR) in relation to the observed downstream variation of various environmental factors (bank height, width, gradient, distance, cross‐sectional area and particle size). The LOR transits between undisturbed and disturbed sections. Forty‐eight cross sections were established at bankfull stage along the river channel stretch of about 90 km. Environmental variables distribution were determined using standard field procedures. Gradient was estimated from a 1:50 000 topographical map. At each corridor along the study sites, a 0.1 ha sampling site was chosen, in which 10 transects of 100 m2 were demarcated. In all, 332 individuals stratified under 80 species were recorded across the transects. The study revealed that total species richness (TSR) downstream decreases exponentially. TSR is significantly correlated with channel width, suggesting that hydraulic variable contributes more to the variation in TSR. The downstream total environmental factors revealed that width is inversely significant with downstream distance, suggesting that the river channel is narrower downstream. This affects plant life form distribution downstream and confirms why there is appearance of anthropogenic induced species downstream as against those in the upper course. 相似文献
10.