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61.
Modelling uncertainty can significantly affect the structural seismic reliability assessment. However, the limit state excursion due to this type of uncertainty may not be described by a Poisson process as it lacks renewal properties with the occurrence of each earthquake event. Furthermore, considering uncertainties related to ground motion representation by employing recorded ground motions together with modelling uncertainties is not a trivial task. Robust fragility assessment, proposed previously by the authors, employs the structural response to recorded ground motion as data in order to update prescribed seismic fragility models. Robust fragility can be extremely efficient for considering also the structural modelling uncertainties by creating a dataset of one-to-one assignments of structural model realizations and as-recorded ground motions. This can reduce the computational effort by more than 1 order of magnitude. However, it should be kept in mind that the fragility concept itself is based on the underlying assumption of Poisson-type renewal. Using the concept of updated robust reliability, considering both the uncertainty in ground motion representation based on as-recorded ground motion and non ergodic modelling uncertainties, the error introduced through structural reliability assessment by using the robust fragility is quantified. It is shown through specific application to an existing RC frame that this error is quite small when the product of the time interval and the standard deviation of failure rate is small and is on the conservative side. 相似文献
62.
Constantinos C. Repapis Petros P. Mimoglou Vicky V. Dimakopoulou Ioannis N. Psycharis Ioannis M. Taflampas 《地震工程与结构动力学》2020,49(5):479-497
The special interest produced by near-field directivity records and their effect on structural response has given a new significance in the velocity time history, its pulse-like content, and relevant parameters and indices. Recent research has shown that directivity pulses inherent in these records govern the linear and the nonlinear response of a wide range of structures. Based on this observation, it is suggested in this paper that a truncated ground motion, limited to the duration of the predominant velocity pulse, can be efficiently used to predict the structural response, instead of the base motion with the total duration, reducing significantly the required runtimes. The proposed methodology is verified for a series of medium to high rise reinforced concrete buildings, for which nonlinear time-history analyses are performed for a vast suite of pulse-like near-field records applied as base excitations with their total duration and the proposed truncated one. Comparison of the results for the response displacements and forces shows very good agreement, permitting the acceptance of the pulse duration as the efficient strong motion time interval of the original record, which determines the response and, thus, it can be used for nonlinear structural analyses. 相似文献
63.
Zeng Zhou Luying Chen Jianfeng Tao Zheng Gong Leicheng Guo Mick van der Wegen Ian Townend Changkuan Zhang 《地球表面变化过程与地形》2020,45(3):590-604
Salinity difference between terrestrial river discharge and oceanic tidal water plays a role in modifying the local flow field and, as a consequence, estuarine morphodynamics. Although widely recognized, recent numerical studies exploring the long-term morphological evolution of river-influenced estuaries with two-dimensional, depth-averaged models have mostly neglected salinity. Using a three-dimensional morphodynamic model, we aim to gain more insight into the effect of salinity on the morphodynamics of fluvio-deltaic systems. Model results indicate that the resultant estuarine morphology established after 600 years differs remarkably when a salinity gradient is included. A fan-shaped river-mouth delta exhibits less seaward expansion and is cut through by narrower channels when salinity is included. The inclusion of salinity tends to generate estuarine circulation, which favours landward sediment transport and hence limits the growth of the delta while enhancing the development of intertidal areas. The formation of deltaic channel–shoal patterns resulting from morphodynamic evolution tends to strengthen salinity stratification, which is characterized by an increased gradient Richardson number. The direction of the depth-averaged residual sediment transport over a tide may be opposite to the direction of residual velocity, indicating the significant influence of baroclinic effects on the net sediment transport direction (and hence morphological change). The effect of salinity on morphological evolution becomes less profound when the strength of tidal or fluvial forcing is dominant over the other. The effects of sediment type and flocculation, which are particularly important when salinity gradients are present, are also discussed. Overall, this study highlights that neglecting salinity to simulate long-term estuarine morphodynamics requires more careful justification, particularly when the environment is characterized by fine sediment types (favouring suspended transport), and relatively large river discharge and estuarine depth (favouring baroclinic effects). © 2020 John Wiley & Sons, Ltd. 相似文献
64.
This study evaluated the spatial variability of streambed vertical hydraulic conductivity (Kv) in different stream morphologies in the Frenchman Creek Watershed, Western Nebraska, using different variogram models. Streambed Kv values were determined in situ using permeameter tests at 10 sites in Frenchman, Stinking Water and Spring Creeks during the dry season at baseflow conditions. Measurements were taken both in straight and meandering stream channels during a 5 day period at similar flow conditions. Each test site comprised of at least three transects and each transect comprised of at least three Kv measurements. Linear, Gaussian, exponential and spherical variogram models were used with Kriging gridding method for the 10 sites. As a goodness-of-fit statistic for the variogram models, cross-validation results showed differences in the median absolute deviation and the standard deviation of the cross-validation residuals. Results show that using the geometric means of the 10 sites for gridding performs better than using either all the Kv values from the 93 permeameter tests or 10 Kv values from the middle transects and centre permeameters. Incorporating both the spatial variability and the uncertainty involved in the measurement at a reach segment can yield more accurate grid results that can be useful in calibrating Kv at watershed or sub-watershed scales in distributed hydrological models. 相似文献
65.
66.
桩基础在水平荷载或地震作用下的承载力计算一直是工程界的一个研究难点,近年来随着建筑、桥梁桩基础的规模大幅增加,基于小规模、小比例尺群桩基础水平承载力试验得出来的结论和计算方法可能会不适应新的计算要求,相关的认识和计算方法需要重新论证和更新。本文针对大规模群桩基础水平承载力效应系数的计算问题,首先对国内外研究进展进行调研,发现现有的规范计算方法可能会高估群桩基础的水平承载力。针对这些问题,对大规模群桩基础的水平承载力效应系数进行有限元数值计算分析,探讨水平承载力效应系数的规律,给出相应的计算方法,并与规范计算方法结果进行对比。本文的研究结果可为相应的工程设计问题提供依据,结果的适用性需要今后进一步的检验。 相似文献
67.
为研究抗滑桩合理桩间距以及荷载传递机制,首先以桩侧摩阻力为拱脚时的破裂面推导出以桩身为拱脚时的破裂角计算公式;然后引入对数螺旋线法确定桩间土体的滑移深度,以土拱效应为基础建立计算模型,求解考虑桩间土体滑移深度的合理桩间距表达式;最后对桩间净距的主要影响因素进行分析,包括滑坡推力、黏聚力、桩截面宽度以及高度。研究结果表明:由桩身和桩侧摩阻力同时作为土拱拱脚更符合实际受力状态,同时求得的土拱拱圈厚度和矢高小于以桩身为拱脚条件下相应值而大于以桩侧摩阻力为拱脚条件下的相应值,并且随桩埋深的增加而增大。 相似文献
68.
69.
为了得出雾霾气象成因机制、影响因素和时空分布特征,以石家庄市区与郊县为研究区域,将2013年9月至2016年12月石家庄市各市区、郊县的PM2.5历史监测数据中的有效数据进行了数据分析处理得到雾霾浓度数据,还有温度、降水、风速、地形和人口密度等数据,运用GIS分析的方法,模拟绘制石家庄雾霾的时空分布图、雾霾与各影响因子的专题对比图,得到雾霾形成机制的因子、雾霾的时空分布规律、雾霾季节变化特征、雾霾与地形间的关系等;运用数据分析软件OriginPro8.SR3分析雾霾浓度与风速数据、降雨数据、温度数据间的相关性。 相似文献
70.
对建筑物进行高精度的变形监测是后期信息提取,预防安全隐患的基础。针对GPS变形监测中存在的多径误差问题,本文提出一种基于CLEAN算法的GPS多径提取方法,首先对多径信号理论模型进行分析,结果表明多径信号可以作为直达信号的谐波分量,在此基础上利用CLEAN算法在频域对多径信号进行提取,基于仿真和实测数据的实验结果表明,所提方法相对于小波方法和经验模态分解(Empirical Mode Decomposition,EMD)方法具有更高的提取精度和更好的多径抑制性能。 相似文献