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251.
戈壁地表沉积物组分呈多峰态分布的特征,研究其全粒径分布模式是认识戈壁成因及形成过程的基础。目前粒度分布模式(对数正态分布、Weibull分布等)难以正确表达呈多峰态的沉积物粒度分布特征,本文利用单调递减函数P(d_i)=Cd_i-μexp(-d_i/Dc),对戈壁地表沉积物粒度的全粒径分布模式进行解析。结果表明:(1)该函数能够反映出戈壁地表沉积物组分的全粒径分布特征,拟合优度R^2>0.99,参数C值范围为52.64~166.75,μ为-0.083~0.108,Dc为0.103~2.336;(2)在分选作用下,以富沙组分为主的戈壁地表,跃移组分含量高,μ值、Dc值偏小,以富砾组分为主的戈壁地表,蠕移及风蚀残余组分含量高,μ值、Dc值偏大;(3)全粒径分布模式参数值可以揭示洪积扇戈壁的分选沉积特征,为解析戈壁地表的成因以及风蚀风积作用提供新的指标参数。 相似文献
252.
本文对中国台湾海峡鱼类寄生线虫幼虫的形态特征进行了聚类分析和主成份分析。针对目前鱼类寄生线虫形态分类中存在的问题,尤其是难以区分是形态学差异还是个体间变异,以及主成份分析在分类学中运用应注意的问题进行探讨 。 相似文献
253.
254.
为了提高铁路房屋的抗震能力,分析地震动竖向分量对铁路房屋的地震响应性能,提出基于荷载—变形关系联合评估的地震动竖向分量对铁路房屋的地震响应评估模型。构建地震动竖向分量的力学响应评估模型,识别铁路房屋的地震屈服响应参数,采用荷载—变形关系和极限荷载结合的方法进行铁路房屋的地震屈服响应应力评估,分析地震动竖向分量对铁路房屋的响应。建立动量平衡方程和弯矩平衡方程,构建铁路房屋的地震响应的三阶段荷载—变形模式,实现地震动竖向分量对铁路房屋的地震响应性能评估模型的优化设计。测试结果表明,采用该模型能有效分析地震动竖向分量对铁路房屋的地震响应性能影响,Simulink仿真结果和有限元模拟结果的准确性较高,力学参数辨识性能优越,计算结果准确可靠。 相似文献
255.
《地震工程与结构动力学》2018,47(6):1566-1588
An experimental program was performed for evaluating the seismic response and fragilities of nonstructural lightweight steel drywall partitions, also considering the interaction with structural elements and other nonstructural building components, ie, outdoor façade walls. Therefore, in‐plane quasi‐static reversed cyclic tests were carried out on 8 specimens of indoor partition walls infilled in a frame and on 4 specimens of indoor partition walls connected at its ends with transversal outdoor façade walls. Constructive parameters under investigation include type of connections used for connecting the indoor partition walls to the surrounding elements, stud spacing, type of sheathing panels, and type of jointing finishing. The effect of the constructive parameters on the lateral response in secant stiffness and strength is examined. Furthermore, the main damage phenomena observed during the tests are reported and associated to 3 damage limit states distinguished for the required repair level for the tested partition walls. Fragility curves are used for the experimental assessment of seismic fragility of the tested specimens, in accordance with the interstorey drift limits required by the European code. Finally, the quantitative estimation of the repair action costs starting from the damage observation is also developed. The obtained results could be considered a starting point for developing the in‐plane seismic design assisted by testing of lightweight steel drywall partition walls. 相似文献
256.
Correction factors for SSI effects predicted by simplified models: 2D versus 3D rectangular embedded foundations 下载免费PDF全文
The effects of soil‐structure interaction (SSI) are often studied using two‐dimensional (2D) or axisymmetric three‐dimensional (3D) models to avoid the high cost of the more realistic, fully 3D models, which require 2 to 3 orders of magnitude more computer time and storage. This paper analyzes the error and presents correction factors for system frequency, system damping, and peak amplitude of structural response computed using impedances for linear in‐plane 2D models with rectangular foundations, embedded in uniform or layered half‐space. They are computed by comparison with results for 3D rectangular foundations with the same vertical cross‐section and different aspect ratios. The structure is represented by a single degree‐of‐freedom oscillator. Correction factors are presented for a range of the model parameters. The results show that in‐plane 2D approximations overestimate the SSI effects, exaggerating the frequency shift, the radiation damping, and the reduction of the peak amplitude. The errors are larger for stiffer, taller, and heavier structures, deeper foundations, and deeper soil layer. For example, for a stiff structure like Millikan library (NS response; length‐to‐width ratio ≈ 1), the error is 6.5% in system frequency, 44% in system damping, and 140% in peak amplitude. The antiplane 2D approximation has an opposite effect on system frequency and the same effect on system damping and peak relative response. Linear response analysis of a case study shows that the NEHRP‐2015 provisions for reduction of base shear force due to SSI may be unsafe for some structures. The presented correction factor diagrams can be used in practical design and other applications. 相似文献
257.
The performance of nonstructural components has attracted attention, and previous large earthquakes have resulted in widespread damage to expansion joints. In contrast to the main structural components, for which ductility beyond the design tolerance is ensured, the safety margin of nonstructural components classified as the product of mechanical engineering, such as expansion joints, is uncertain. This paper investigates the damage sequence and safety margin of expansion joints through shake table testing. The expansion joints were installed to connect 2 rigid steel frames with short and long natural periods. Four commonly used types, high-performance and standard-performance floor and wall expansion joints, were tested. Seven damage patterns of the 4 expansion joints were observed, and most of the damage patterns were considered displacement dependent. The damage mechanisms and relative displacements at the moment of damage were identified by using strain gauges attached near collision and damage locations. The high-performance expansion joints showed only minor damage beyond the design motion range, whereas the standard-performance expansion joints exhibited minor damage below the design motion range and failure at the design motion range or slightly beyond. For each damage state, repair information was obtained through a questionnaire to an expansion joint manufacturer, and the sum of the initial cost and repair cost for high-performance and standard-performance expansion joints was compared. The results will be useful for the selection of expansion joints in the design process. 相似文献
258.
尺度叠加高斯相关模型在GRAPES-RAFS中的应用 总被引:1,自引:0,他引:1
背景误差水平相关模型影响着分析增量的结构,同时也决定着不同尺度上分析增量信息的多少.为了提高中小尺度系统的分析质量,研究尺度叠加高斯相关模型的特征及其在三维变分同化系统中的应用效果.通过分析高斯模型和尺度叠加高斯模型的空间特征,以及它们的拉普拉斯算子和谱响应函数的特征,同时依据统计的背景误差特征来改进背景误差水平相关模... 相似文献
259.
In this contribution, the regularized Earth’s surface is considered as a graded 2D surface, namely a curved surface, embedded
in a Euclidean space . Thus, the deformation of the surface could be completely specified by the change of the metric and curvature tensors, namely
strain tensor and tensor of change of curvature (TCC). The curvature tensor, however, is responsible for the detection of
vertical displacements on the surface. Dealing with eigenspace components, e.g., principal components and principal directions
of 2D symmetric random tensors of second order is of central importance in this study. Namely, we introduce an eigenspace
analysis or a principal component analysis of strain tensor and TCC. However, due to the intricate relations between elements
of tensors on one side and eigenspace components on other side, we will convert these relations to simple equations, by simultaneous
diagonalization. This will provide simple synthesis equations of eigenspace components (e.g., applicable in stochastic aspects).
The last part of this research is devoted to stochastic aspects of deformation analysis. In the presence of errors in measuring
a random displacement field (under the normal distribution assumption of displacement field), the stochastic behaviors of
eigenspace components of strain tensor and TCC are discussed. It is applied by a numerical example with the crustal deformation
field, through the Pacific Northwest Geodetic Array permanent solutions in period January 1999 to January 2004, in Cascadia
Subduction Zone. Due to the earthquake which occurred on 28 February 2001 in Puget Sound (M
w > 6.8), we performed computations in two steps: the coseismic effect and the postseismic effect of this event. A comparison
of patterns of eigenspace components of deformation tensors (corresponding the seismic events) reflects that: among the estimated
eigenspace components, near the earthquake region, the eigenvalues have significant variations, but eigendirections have insignificant
variations. 相似文献
260.