Experimental research and finite element analysis of bridge piers failed in flexure-shear modes

In recent earthquakes, a large number of reinforced concrete （RC） bridges were severely damaged due to mixed flexure-shear failure modes of the bridge piers. An integrated experimental and finite element （FE） analysis study is described in this paper to study the seismic performance of the bridge piers that failed in flexure-shear modes. In the first part, a nonlinear cyclic loading test on six RC bridge piers with circular cross sections is carried out experimentally. The damage states, ductility and energy dissipation parameters, stiffness degradation and shear strength of the piers are studied and compared with each other. The experimental results suggest that all the piers exhibit stable flexural response at displacement ductilities up to four before exhibiting brittle shear failure. The ultimate performance of the piers is dominated by shear capacity due to significant shear cracking, and in some cases, rupturing of spiral bars. In the second part, modeling approaches describing the hysteretic behavior of the piers are investigated by using ANSYS software. A set of models with different parameters is selected and evaluated through comparison with experimental results. The influences of the shear retention coefficients between concrete cracks, the Bauschinger effect in longitudinal reinforcement, the bond-slip relationship between the longitudinal reinforcement and the concrete and the concrete failure surface on the simulated hysteretic curves are discussed. Then, a modified analysis model is presented and its accuracy is verified by comparing the simulated results with experimental ones. This research uses models available in commercial FE codes and is intended for researchers and engineers interested in using ANSYS software to predict the hysteretic behavior of reinforced concrete structures.     

Tethered Balloon Observations Of The Nocturnal Stable Boundary Layer In A Valley

Detailed measurements of profiles of mean and turbulent variablesthrough the nocturnal stable boundary layer over a valley arepresented. Two nights of data are analysed in detail, one with only aweakly stable boundary layer and one with a strongly stable boundarylayer. The weakly stratified night shows high levels of turbulence inwhich the flow remains attached to the valley and the boundary layeracts as a single coherent layer. On the strongly stratified night, twoflow regimes are identified: attached flow, as on the weaklystratified night, and decoupled flow in which the air in the valleybecomes so dynamically stable that there is no turbulent interactionwith the mean flow aloft. Because the valley is sloping, the decoupledlower stagnant air then forms a drainage current. We find that theFroude number evaluated at the hill height, F_H = U(H)/N(H) H,diagnoses the flow regime: when F_H = 2, the flow remainsattached and when F_H 2 the flow in the valley becomesdecoupled from the flow aloft. The dynamics of the flow regimes areshown to be understandable in terms of the gradient Richardson number,which indicates the turbulent mixing. We show that the gradientRichardson number is a key parameter in diagnosing each flow regime.     

北太平洋海温与江淮流域汛期流量的关系研究

利用自然正交函数分解法,对北太平洋海温与江淮流域汛期流量的关系进行了研究。结果表明,赤道东人平洋（10°S-10°N、180°-80°W）和西北太平洋（35°—45°N、150°E-140°W及30°N、170°-140°W）的海温变化与江淮流域汛期流量关系密切。当赤道东太平洋海温升高时,江淮流域汛期流量减少,反之则增加。依据这两个关键区的典型场时间系数所建立的流域预报模型,试报效果较为理想,除汉口8月流量预报误差为-10．7％外,其他要素流量预报误差均在±5％左右。     

CINRAD/CD雷达方位伺服系统驱动电源故障分析及处理

对遵义CINRAD/CD新一代多普勒天气雷达运行6年多来发生的8次方位伺服系统驱动电源故障维修工作进行归纳总结。根据故障现象细微差别,将其归纳为3类,并对应分析故障原因,找出具体维修措施,以便于本站维修经验的积累和国内其他同型号雷达维修技术人员参考。     

细网格非静力二维高阶闭合模式对山体流场特征的模拟分析

本文采用二阶矩湍流闭合方案，分别就非静力和准静力两种条件建立ＰＢＬ数值模式，并模拟了二维山脊流场的结构，计算了二维山体对气流平均场和湍流场的影响。计算结果表明，无论是平均场还是湍流场，采用准静力假设都会造成模拟结果的较大偏差，且对平均场的影响比对湍流场的影响更为显著。两种模式计算结果的差别还随地形坡度和背景风增大而增大。     

Flow field visualization of sediment-laden flow using ultrasonic imaging

This investigation concerns the application of particle image velocimetry (PIV) to ultrasonic images of sediment-laden flow in order to obtain accurate, quantitative, two dimensional vector maps of the flow field within the sediment suspension. Experiments were carried out using a medical ultrasound scanner to obtain ultrasonic images in a kaolin/salt water suspension of mean concentration 16 g/l and to compare results obtained with the ultrasound scanner in clear water with those from established measurement techniques. Measurements of mud were obtained, and the comparison with established methods indicated that the application of PIV to the analysis of ultrasound images yields velocity information accurate to within ±15%. This measurement technique will be of great value in furthering the understanding of the behavior of sediment-laden flows.     

用改进的十进制遗传算法确定土质边坡最危险滑面

基于瑞典圆弧法和简化Bishop条分法分析土质边坡的稳定性,以圆弧滑裂面与边坡面的左右交点的两个横坐标和以滑裂面圆心的纵坐标作为优化变量,采用了一种改进的十进制遗传算法对优化变量进行优化。这种改进的遗传算法是以简单的十进制遗传算法为基础,结合优体克隆操作、子体优生操作和多代调环操作。通过计算ACADS考核题验证,该方法有较强的自适应能力,具有收敛速度快、解的精度高和避免出现早熟等优点。     

典型冰水堆积体浪蚀作用下变形破坏机制研究

大渡河中游沿岸中海拔地区广泛分布的一层冰水堆积体大多具有较为密实的结构和一定程度的胶结, 在风浪作用下的变形破坏机制与其他堆积体存在较大差别。通过对某电站库区高速公路冰水堆积路基岸坡调查和试验分析认为, 该冰水堆积体属级配良好的含细颗粒的粗粒～巨粒混合土, 颗粒之间嵌合紧密, 一般呈中密～密实状, 具有不同程度的泥质、钙质胶结, 其强度明显较其他松散堆积体高。通过采用地质过程定性分析和有限元半定量评价相结合的手段对该冰水堆积体在风浪作用下的变形破坏机制进行了分析和研究, 认为该类冰水堆积体在风浪作用下主要表现为淘蚀- 坍塌型失稳模式。     

土层抗浮锚杆试验破坏标准选取的建议

因抗浮锚杆试验没有统一的破坏标准，测出的抗拔参数差异大，不能正确指导设计，文中根据几个典型试验实例，分析了现有相关规范中破坏标准的局限性，并对一些条款的修改提出了建议。     

层状结构岩体顺层斜坡失稳机理的力学分析

本文从力学方面研究了层状结构岩体顺层斜坡的失稳机理，通过能量平衡法，求出了层状结构岩体顺层斜坡溃屈破坏的均布临界载荷，临界波长，并经实际计算验核，对工程评估，灾害防治有一定参考价值。