Uniform fragility spectra for the performance‐based seismic design of structures considering variabilities in structural properties

This paper presents a new methodology based on structural performance to determine uniform fragility design spectra, i.e., spectra with the same probability of exceedance of a performance level for a given seismic intensity. The design spectra calculated with this methodology provide directly the lateral strength, in terms of yield‐ pseudo‐accelerations, associated with the rate of exceedance of a specific ductility characterizing the performance level for which the structures will be designed. This procedure involves the assessment of the seismic hazard using a large enough number of seismic records of several magnitudes; these records are simulated with an improved empirical Green function method. The statistics of the performance of a single degree of freedom system are obtained using Monte Carlo simulation considering the seismic demand, the fundamental period, and the strength of the structure as uncertain variables. With these results, the conditional probability that a structure exceeds a specific performance level is obtained. The authors consider that the proposed procedure is a significant improvement to others considered in the literature and a useful research tool for the further development of uniform fragility spectra that can be used for the performance‐based seismic design and retrofit of structures.     

有限长圆柱体磁异常场全空间正演方法

在经典位场理论中,许多简单形体位场异常难以通过积分得到全空间的解析式.圆柱体是一类很重要的理论模型体,常用于模拟圆柱状地质体或非地质体(如管线),但目前还不能用解析公式正演有限长圆柱体在三维空间里的磁异常,而多是采用近似简化为有限长磁偶极子或线模型代替.对于有限长圆柱体,特别是半径相对于上顶埋深较大时,这种近似的误差不可忽略.本文利用共轭复数变量替换法,推导出有限长圆柱体在全空间的引力位一阶、二阶导数,利用Poisson关系得到磁异常正演公式,进而利用有限长圆柱体磁异常正演公式求解管状体的磁异常,得到不同磁化方向、不同大小的管线产生的磁场的特征,并将其推广到截面为椭圆的情况.最后通过模拟计算定量给出了将圆柱体近似为线模型的条件.     

Simulating monthly streamflow using a hybrid feature selection approach integrated with an intelligence model

ABSTRACT

Streamflow prediction is useful for robust water resources engineering and management. This paper introduces a new methodology to generate more effective features for streamflow prediction based on the concept of “interaction effect”. The new features (input variables) are derived from the original features in a process called feature generation. It is necessary to select the most efficient input variables for the modelling process. Two feature selection methods, least absolute shrinkage and selection operator (LASSO) and particle swarm optimization-artificial neural networks (PSO-ANN), are used to select the effective features. Principal components analysis (PCA) is used to reduce the dimensions of selected features. Then, optimized support vector regression (SVR) is used for monthly streamflow prediction at the Karaj River in Iran. The proposed method provided accurate prediction results with a root mean square error (RMSE) of 2.79 m³/s and determination coefficient (R² ) of 0.92.     

地质异常的有序评价模型及其应用

摘 要　 对有序变量的性质进行了研究‚并按相关性最大准则构造了一个可用于秩序性分析 的线性模型。讨论了该模型的性质和使用条件、可用于地质异常的定量评价和矿产预测中的 成矿规律、控矿因素和找矿标志的研究等问题。给出了一个金矿异常成矿预测的应用实例。     

基于弹塑性损伤单元的RC框架结构的全过程分析

基于损伤力学和塑性理论建立了一种弹塑性损伤单元模型,并编制了基于此单元的RC平面框架非线性分析程序DAMAGE2D。算例表明,弹塑性损伤单元对RC框架非线性分析具有良好的精度。文中根据计算结果对RC框架结构进行了不同损伤阶段的划分。研究成果可用于基于pushover方法的结构抗震分析。     

Variable gain feedback control technique of active mass damper and its application to hybrid structural control

A systematic design procedure and an algorithm are devised for variable gain feedback (VGF) control of buildings with active mass damper (AMD) systems. The limit of the stroke length of the auxiliary mass, which is considered to be one of the most important physical constraints for application of AMD systems to actual structures, is studied. A set of variable feedback gains is designed as a function of a single variable that indicates a trade-off between the reduction of the building response and the amplitude of the auxiliary mass stroke, and this variable is on-line controlled to keep the amplitude of the auxiliary mass stroke constant, and within its limits. A design method of static output feedback controller for modal control of buildings with non-classical damping is also presented. Next, an efficient control method for hybrid structural control is developed, with combined use of the VGF control and the static output feedback control. It is shown through numerical examples that the proposed control method effectively adapts the control performance according to the variation in the intensity level of the external excitations in such a manner that the amplitude of the auxiliary mass stroke is kept within its limits and the control power is restrained as well. The application range of the AMD systems is thereby improved significantly. © 1997 John Wiley & Sons, Ltd.     

基于滞后变量模型的城市群建设用地增长对经济增长的滞后期和效应分析——以京津冀城市群为例

城市群建设用地增长对经济增长存在客观的时间滞后效应,即“用地投入—建设开发—效益产生—效益爬坡—效益稳定”的全周期过程。计算其滞后期长短和总效应大小,并挖掘导致差异的内在机制,对区域建设用地的供给与管理及经济社会的可持续发展具有重要意义。论文以1995—2017年京津冀城市群13个主要城市的统计数据为支撑,提出了建设用地增长对经济增长的滞后变量模型,定量确定了京津冀城市群各城市的滞后期长短、各滞后期的效应以及总效应,并发现了以下规律：① 城市群建设用地增长对经济增长存在普遍的滞后效应,滞后期在0~4 a;② 城市群建设用地增长对经济增长存在显著的正面效应,总效应介于1.66~49.5亿元/km2;③ 城市群建设用地增长对经济增长的滞后期和总效应均呈现出“中心—边缘”的空间分异特征;④ 滞后期主要与城市的等级和功能定位有关,高等级的中心型城市、中等级的副中心型城市和低等级的节点型城市对应的滞后期分别为4 a、2 a和0~2 a;⑤ 总效应主要与产业构成有关,城市产业高、中、低端对应的效应分别为30亿~50亿、10亿~20亿、1亿~10亿元/km2。     

改进权重的迭代最近点算法在点云配准中的应用

针对传统迭代最近点算法不具备抗差性的难题,利用迭代最近点算法配准残差的分布规律,综合M估计及选权迭代思想,提出改进权重的迭代最近点配准算法。根据每个点对配准计算出对应的初始权重,然后在附加点对权重的基础上使用选权迭代法计算出满足条件的权重,以达到抵御粗差的目的。结果表明,选权迭代过程能合理改善三维空间转换参数计算的结果,提出的改进算法较适合含粗差点的点云数据的配准。     

基于三维地图视觉变量理论的三维符号设计

本文首先介绍了三维符号的一种分类方法,然后结合三维态势感知的特点,将三维地图符号视觉变量理论合理的运用到三维符号的设计中去,并从实际应用的角度分析了三维态势表达中符号设计的合理性。     

Effect of variable‐density groundwater flow on nitrate flux to coastal waters

A two‐dimensional variable‐density groundwater flow and transport model was developed to provide a conceptual understanding of past and future conditions of nitrate (NO₃) transport and estimate groundwater nitrate flux to the Gulf of Mexico. Simulation results show that contaminant discharge to the coast decreases as the extent of saltwater intrusion increases. Other natural and/or artificial surface waters such as navigation channels may serve as major sinks for contaminant loading and act to alter expected transport pathways discharging contaminants to other areas. Concentrations of NO₃ in the saturated zone were estimated to range between 30 and 160 mg?L^?1 as NO₃. Relatively high hydraulic vertical gradients and mixing likely play a significant role in the transport processes, enhancing dilution and contaminant migration to depth. Residence times of NO₃ in the deeper aquifers vary from 100 (locally) to about 300 years through the investigated aquifer system. NO₃ mass fluxes from the shallow aquifers (0 to 5.7 × 10⁴ mg?m^?2?day^?1) were primarily directed towards the navigation channel, which intersects and captures a portion of the shallow groundwater flow/discharge. Direct NO₃ discharge to the sea (i.e. Gulf of Mexico) from the shallow aquifer was very low (0 to 9.0 × 10¹ mg · m^?2?day^?1) compared with discharge from the deeper aquifer system (0 to 8.2 × 10³ mg?m^?2?day^?1). Both model‐calibrated and radiocarbon tracer‐determined contaminant flux estimates reveal similar discharge trends, validating the use of the model for density‐dependent flow conditions. The modelling approach shows promise to evaluate contaminant and nutrient loading for similar coastal regions worldwide. Copyright © 2015 John Wiley & Sons, Ltd.