考虑剪切滞后效应的钢筋混凝土剪力墙单元模型及应用

多垂直杆单元模型是在钢筋混凝土剪力墙非线性分析中较为常用的一种宏观模型。现有的分析方法不能考虑翼板剪滞效应的影响,然而翼板上正应力非均匀分布必然影响剪力墙承载力的充分发挥。其次现有的分析方法大多不能较好地考虑垂直杆中正应力对剪切刚度的影响。本文在多垂直杆单元模型的基础上进行改进,把垂直杆的轴向刚度和剪切刚度相结合,并引入剪滞位移自由度,摒弃平截面假定的限制,对一工程结构模型的静力分析显示其变形状态符合受力机理,对3片短肢剪力墙模型和1片剪力墙模型进行弹塑性静力加载分析,计算结果与试验结果吻合较好,表明该方法应用可行。     

基于OpenSees平台的钢管混凝土结构力学性能数值模拟

基于非线性纤维梁-柱单元理论,以OpenSees为求解平台分别进行了钢管混凝土结构滞回曲线计算和弹塑性动力时程分析等数值模拟,计算结果与试验吻合良好。钢管内核心混凝土采用考虑钢管约束效应的应力—应变关系,钢材采用随动强化本构模型。在传统纤维模型法的基础上,通过直接在截面层次定义非线性剪切恢复力的方法建立了考虑非线性剪切效应的剪力墙结构数值模型,结果表明该模型能较好地模拟组合剪力墙的抗剪承载力、捏缩效应以及刚度退化等力学性能。对输入不同地震波下钢管混凝土框架体系的动力时程分析表明,基于OpenSees求解平台的非线性纤维模型法能够较好地模拟钢管混凝土框架结构的非线性动力特性。     

钢筋混凝土核心简的剪切滞变模型

通过对比评价现有可用于剪力墙的剪切滞变模型,并结合现有国内外钢筋混凝土核心筒体试验结果,选取了带捏缩的修正Takeda模型作为核心筒的剪切滞变模型,并给出了模型的细部滞变规则。     

有限单元柔度法考虑剪切变形的纤维单元模型

基于有限单元柔度法的梁柱单元模型,以单元力的形函数为出发点,其优点是单元内部截面力场的分布总能满足平衡条件。但目前国内外学者提出的梁柱单元模型,还不能考虑剪切变形对构件刚度的影响。建立了基于有限单元柔度法的弹塑性纤维单元模型,考虑了剪切变形和几何非线性的影响,适用于钢筋混凝土短柱、剪力墙等较大截面杆件的分析研究。依据单元模型编制了非线性有限元分析程序,进行了低周反复荷载试验的数值模拟。模拟分析结果反映了结构构件的主要受力特征,并与实验结果具有良好的一致性。     

T形短肢剪力墙弹塑性模型及地震反应分析

根据短肢剪力墙结构的受力和变形特点,对多竖直杆模型进行了改进,建立了截面位移模型,摒弃了杆模型平截面假定的限制,有效地考虑了剪滞效应和翼缘的影响。利用变分原理导出了T形短肢剪力墙的空间单元刚度矩阵,研制了弹塑性时程分析程序,并输入三种不同的地震动进行了算例分析,计算结果表明,短肢剪力墙结构抗震性能较好,适合于在地震区推广使用。     

CRB600H级箍筋混凝土短柱抗震性能研究

为研究高强箍筋混凝土柱抗震性能,通过对CRB600H级高强箍筋混凝土短柱低周往复加载试验展开数值模拟研究。利用OpenSEES中的Nonlinear Beam Column单元、零长度截面转动弹簧单元和零长度剪切弹簧单元,建立了考虑弯-剪耦合效应的抗震数值分析模型。分析轴压比、剪跨比对CRB600H级箍筋柱的滞回性能、刚度退化、延性及耗能性能的影响,并以HRB400级箍筋柱进行对比分析,结果表明：轴压比越大的构件水平抗剪承载力,延性和耗能能力越差;剪跨比越大构件的水平抗剪承载力越低,延性和耗能能力越好;CRB600H级和HRB400级箍筋柱,两者承载力接近,CRB600H级箍筋柱延性和抗震性能更好。     

高强混凝土剪力墙地震损伤模型分析

在分析比较现有钢筋混凝土结构的地震损伤模型的基础上,根据高强混凝土剪力墙的滞回曲线特性及刚度退化规律,采用能量耗散系数和最大变位处的卸载刚度的退化为破坏参数,提出了适用于高强混凝土剪力墙构件的双参数地震损伤模型。依据已有的高强混凝土剪力墙构件试验研究结果,对损伤模型进行非线性回归分析,确定了相应的地震损伤模型参数,提出了高强混凝土剪力墙各性能水平的损伤指数以及相应于三水准抗震设防的损伤指数允许值。分析结果表明,按本文所提出的损伤模型计算得到的剪力墙构件最终破坏时对应的损伤指数,其平均值在合理范围内,标准差较小;损伤指数计算值对应的损伤程度基本符合试验结果,计算结果离散程度较低。     

OPENSEES中纤维模型的研究

详细介绍了OPENSEES[2]和CANNY[1]中各种纤维模型的计算原理，并用OPENSEES中的纤维模型分别模拟了一个钢筋混凝土柱试件和一个钢筋混凝土剪力墙试验模型。通过计算结果与试验结果的对比，显示此模型能够比较准确地模拟钢筋混凝土柱构件和钢筋混凝土剪力墙构件在大变形下的非线性反应。     

考虑轴-弯-剪耦合效应的钢筋混凝土柱滞回性能研究

试验研究及震害调查发现:由于配箍不足或箍筋间距过大,地震作用下钢筋混凝土柱易发生剪切破坏,继而发生轴向破坏。采用纤维截面的钢筋混凝土梁柱单元及与之串联的剪切弹簧以及轴向弹簧考虑钢筋混凝土柱的轴-弯-剪耦合效应,其中纤维梁柱单元用于模拟柱的弯曲机制,与梁柱单元串联的剪切弹簧和轴向弹簧用于模拟剪切机制和轴向机制,并利用单轴材料模型中的Limit State Material及其相应的Shear Limit Curve和Axial Limit Curve确定材料的剪切破坏与轴向破坏失效点,最终从单元层次上定义轴-弯-剪耦合效应。为验证该数值模型的合理性,选取不同破坏形式、轴向力与水平循环往复荷载共同作用下拟静力试验的钢筋混凝土柱,借助Open Sees分析软件模拟其滞回性能。模拟结果与试验结果的对比分析表明:考虑轴-弯-剪耦合的串联模型能较好地模拟钢筋混凝土柱的强度、刚度退化及捏拢效应等,且能够反映钢筋混凝土构件在复杂应力条件下的受力性能。     

型钢高性能混凝土剪力墙恢复力模型研究

在前人研究成果的基础上,本文通过对6个型钢高性能混凝土剪力墙荷载-位移滞回曲线的分析,得出了简化的三折线型恢复力模型,并提出各个特征参数的计算公式,计算值与与试验值较为吻合。滞回规则采用考虑刚度退化和强度退化的剪切滞变模型,为型钢混凝土剪力墙的弹塑性分析提供了依据。     

Forward model nonlinearity versus inverse model nonlinearity

The issue of concern is the impact of forward model nonlinearity on the nonlinearity of the inverse model. The question posed is, “Does increased nonlinearity in the head solution (forward model) always result in increased nonlinearity in the inverse solution (estimation of hydraulic conductivity)?” It is shown that the two nonlinearities are separate, and it is not universally true that increased forward model nonlinearity increases inverse model nonlinearity.     

Combining climate model output via model correlations

In climate science, collections of climate model output, usually referred to as ensembles, are commonly used devices to study uncertainty in climate model experiments. The ensemble members may reflect variation in initial conditions, different physics implementations, or even entirely different climate models. However, there is a need to deliver a unified product based on the ensemble members that reflects the information contained in whole of the ensemble. We propose a technique for creating linear combinations of ensemble members where the weights are constructed from estimates of variation and correlation both within and between ensemble members. At the heart of this approach is a Bayesian hierarchical model that allows for estimation of the correlation between ensemble members as well as the study of the impact of uncertainty in the parameter estimates of the hierarchical model on the weights. The approach is demonstrated on an ensemble of regional climate model (RCM) output.     

基于褶积模型的地球物理反演模型增强

地球物理数据在采集和处理过程中,由于存在噪声、模型误差、以及数据离散化误差等系统误差,导致了异常体边界模糊和模型分辨率降低等一些不可避免的不良系统退化效应的产生.本文提出了一种新的地球物理反演模型增强方法,通过消除反演估计模型中的系统误差,压制模型中的不良系统退化效应,增强反演模型的分辨率.文章从理论上分析了数据中存在的系统误差对模型求解的影响,提出了一个新的系统误差褶积退化模型,并根据该模型提出了一种基于混合范数总变分正则化的盲反褶积模型增强算法.最后,文章通过1D线性反演增强试验和2D大地电磁反演增强试验,验证了所提出的地球物理系统退化模型的正确性,以及盲反褶积增强算法的有效性.试验结果表明,方法可以有效地提高反演参数模型的分辨率.     

Patuxent landscape model: 1. Hydrological model development

We developed a spatially explicit, process-based model of the 2352 km² Patuxent river watershed in Maryland, and its subwatersheds to integrate data and knowledge over several spatial, temporal and complexity scales, and to serve as an aid to regional management. The model was developed using the Library of Hydro-Ecological Modules (LHEM, http://giee.uvm.edu/LHEM), which was designed to create flexible landscape model structures that can be easily modified and extended to suit the requirements of a variety of goals and case studies. The LHEM includes modules that simulate various aspects of ecosystem dynamics. In this paper we consider modules that represent the physical conditions in the environment (climatic factors, geoporphology), and hydrologic processes, both locally and spatially. Where possible the modules are formulated as Stella(R) models, spatial transport processes are presented as C++ code.     

Developing land use scenario dynamics model by the integration of system dynamics model and cellular automata model

Models of land use change are useful tools for un-derstanding the analysis of the cause and conse-quences of land use changes, assessing the impacts of land use system on ecological system and supporting land use planning and policy[1,2]. Modeling land use scenario changes and its potential impacts on the structure and function of the ecosystem in the typical regions are regarded as one of the good ways to un-derstand the interactive mechanism between land use system and ecological system[3―10…     

A complementary relationship evaporation model referring to the Granger model and the advection–aridity model

A complementary relationship evaporation model has been proposed and verified based on evaluations of the advection–aridity model and the Granger's complementary relationship model (Granger model) in dimensionless forms. Normalized by Penman potential evaporation, the Granger model and the advection–aridity model have been transformed into similar dimensionless forms. Evaporation ratio (ratio of actual evaporation to Penman potential evaporation) has been expressed as a function of dimensionless variable based on radiation and atmospheric conditions. Similar dimensionless variables for the different functions have been used in the two models. By referring to the dimensionless variable from the advection–aridity model and the function from the Granger model, a new model to estimate actual evaporation was proposed. The performance of the new model has been validated by the observed data from four sites under different land covers. The new model is an enhanced Granger model with better evaporation prediction over the aforementioned different land covers. It also offers more stable optimized parameters in a grassland site than the Granger model. The new model somewhat approximates the advection–aridity model under neither too wet nor too dry conditions, but without its system bias. Copyright © 2011 John Wiley & Sons, Ltd.     

A synthetic Earth gravity model based on a topographic-isostatic model

The Earth??s gravity field is related to the topographic potential in medium and higher degrees, which is isostatically compensated. Hence, the topographic-isostatic (TI) data are indispensable for extending an available Earth Gravitational Model (EGM) to higher degrees. Here we use TI harmonic coefficients to construct a Synthetic Earth Gravitational Model (SEGM) to extend the EGMs to higher degrees. To achieve a high-quality SEGM, a global geopotential model (EGM96) is used to describe the low degrees, whereas the medium and high degrees are obtained from the TI or topographic potential. This study differes from others in that it uses a new gravimetric-isostatic model for determining the TI potential. We test different alternatives based on TI or only topographic data to determine the SEGM. Although the topography is isostatically compensated only to about degree 40?C60, our study shows that using a compensation model improves the SEGM in comparison with using only topographic data for higher degree harmonics. This is because the TI data better adjust the applied Butterworth filter, which bridges the known EGM and the new high-degree potential field than the topographic data alone.     

动力UH模型

针对砂土在动力荷载作用下所表现出的应力诱导各向异性,以改进后的UH超固结土模型为基础,采用旋转硬化规则将其扩展为可考虑与砂土应力应变关系的动本构模型。主要改进有3方面:(1)将形状固定的椭圆屈服面改变为可变屈服面,椭圆的形状由β来刻画,而β本身是椭圆旋转轴的大小,表示应力诱导各向异性程度的大小;(2)引入旋转硬化规则,使椭圆屈服面可围绕原点旋转以反映反向加载条件下的本构响应;(3)对统一硬化参数进行了修正,首先对潜在强度公式增加了一个参数α用来调节超固结应力比参数R对于潜在强度值的影响,其次针对应力诱导各向异性建立起能反映旋转硬化与等向硬化相协调的扩展统一硬化参数。模型预测与试验结果的对比以及有限元模拟表明:提出的动力统一硬化(DUH)模型能够简单、合理的描述与砂土在动力载荷下的本构关系,验证了所提模型的合理性。     

A newF-layer model

Summary The model originally constructed for theF1-layer is adapted to enable an investigation of both theF-layers. Essential premises are: The ionization of a single constituent of atmosphere by monochromatic radiation. A positive temperature gradient in theFl-region, a temperature—independent from height—in theF2-region and a negative temperature gradient above the height of theF2-electron-peak; furthermore during the daytime strong heating in theF2-region. It is further assumed that the rate of electron loss in theF1-layer is proportional to the square of the density of the electrons, and in theF2-layer is in simple proportion to this density. It is also assumed that this electron loss stands in proportion to the powerk of the pressurep, and to the powern of the absolute temperatureT, as assumed in the originalF1-layer model.The above mentioned assumption as to temperature conditions are essential to an understanding of the transition from static to dynamic conditions observed in theF2-layer. During the night and in the morning theF2-layer can be treated as a static problem, movement of air-masses being of no great importance. Later in the day however an labile stratification of air-masses gives rise to such movement that theF2-layer can only be handled as a dynamic problem, particular attention being paid to the movement of the air.Numerous observational data are referred to in order to prove the practicability of the new model and, with the help of this model, to justify new assertions. It has been possible for example, to calculate the yearly temperature variation at a constant level in theF1-layer.A critical report upon the models published recently by other authors concludes this paper.

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Zusammenfassung Das seinerzeit nur für dieF1-Schicht aufgestellte Modell wird so erweitert, daß eine Deutung beiderF-Schichten möglich wird. Wesentliche Voraussetzungen sind: Ionisierung eines einzigen Bestandteiles der Luft durch eine monochromatische Strahlung. Ein positiver Temperaturgradient im Bereich derF1-Schicht, eine höhen-unabhängige Temperatur im Bereich derF2-Schicht und ein negativer Temperaturgradient oberhalb des Ionisationsmaximum, derF2-Schicht. Weiters wird vorausgesetzt, daß der Elektronenvernichtungsprozeß in derF1-Schicht dem Quadrat der Elektronendichte proportional sei, in derF2-Schicht soll er dagegen der Elektronendichte einfach proportional sein. Eine Abhängigkeit dieses Prozesses von derk-ten Potenz des Druckes,p und von dern-ten Potenz der absoluten TemperaturT wird hier vom ursprünglichenF1-Schicht-Modell übernommen.Erst die genannten Annahmen über die Temperaturverhältnisse machen den beobachteten Übergang von statischen zu dynamischen Verhältnissen in derF2-Schicht verständlich. Während der Nacht und am Morgen bis in die ersten Vormittagsstunden kann dieF2-Schicht als statisches Problem behandelt werden, die Bewegungsvorgänge der Luftmassen spielen eine nur untergeordnete Rolle. Darnach aber ruft eine labile Schichtung der Luftmassen kräftige Luftbewegungen hervor, sodaß dieF2-Schicht nur mehr als dynamisches Problem mit besonderer Berücksichtigung von Luftmassenverschiebungen behandelt werden kann.Zahlreiche Beobachtungsdaten werden herangezogen, um die Anwendbarkeit des neuen Modells zu beweisen und um mit Hilfe des Modells zu neuen Aussagen zu gelangen. Es gelingt so z. B., den Jahresgang der Temperatur in einem konstant gehaltenen Druckniveau derF1-Schicht anzugeben.Eine kritische Betrachtung der Modelle, die in letzterer Zeit von anderen Autoren veröffentlicht wurden, beschließt die Arbeit.

     

Blaney-Morin-Nigeria evapotranspiration model

An evapotranspiration model which parallels that proposed earlier by Blaney and Morin has been developed for application in Nigeria. The model, designated as the Blaney-Morin-Nigeria evapotranspiration model, predicts potential evapotranspiration with accuracy and consistency that are better than the Penman model, under Nigerian conditions. It is suggested that the Blaney-Morin evapotranspiration concept may have similar potential elsewhere when given specific form with appropriate constants derived to reflect climatic peculiarities.