沙漠公路风沙土路基风蚀破坏试验研究   总被引：2，自引：0，他引：2  

李驰  高瑜 《岩土力学》2011,32(1):33-38

以沙漠公路风沙土路基为研究对象,通过室内风蚀风洞试验研究路基的风蚀破坏规律,以及路基不同断面对风沙流运动的影响。以路基高度、路基边坡坡率和路基宽度作为路基断面主要设计参数,研究不同路基断面下风沙流扰动、增速、减速、恢复的过程,以及路基周围风速流场的变化特征,分析路基病害较未病害时路基周围流场的变化。试验结果表明：路基高度和边坡坡率对风沙流运动的影响较大。随路基高度增加,路基对风沙流流场扰动增强,迎风坡坡顶处吹蚀破坏和背风坡坡底处堆蚀破坏越显著,在确定的路基边坡坡率下,路基模型高度为250 mm较模型高度为60 mm时,迎风坡坡顶风速增加1.13倍,背风坡坡底风速减小2.53倍,建议沙漠公路路基高度宜小于2.5 m。进一步,在确定的路基高度下,比较不同的边坡坡率对路基沿程风速的影响,发现当路基边坡坡率为1:1.75时,路基沿程风速变化不明显,沙漠公路风沙土路基不宜被风蚀破坏。  相似文献   

离心场中风力电机桩基复杂加载测试设备的研制     

荣冰  张嘎  王富强 《岩土力学》2011,32(5):1596-1600

桩基础是近海风力发电中经常采用的基础形式,承受着包括低频风循环荷载在内的复杂荷载组合。为了采用离心模型试验来研究风机桩基础特性,研制了离心场中风机桩基础复杂加载测试设备。该套设备除了可以施加水平向和竖向静力荷载外,还实现了离心场中长时间低频率的水平循环加载,并能够实现多种荷载同时或者先后施加。通过一系列测试试验,验证了该套设备的有效性,满足离心模型试验中对模拟风机桩基础的复杂荷载要求。初步试验结果表明,桩顶水平位移随着水平荷载循环周数的增加而增大,但增长速率逐渐减小,至一定周数后,桩顶位移趋于稳定,土体变形主要集中在桩周一定区域内  相似文献   

‘Thailand was a desert' during the mid‐Cretaceous: Equatorward shift of the subtropical high‐pressure belt indicated by eolian deposits (Phu Thok Formation) in the Khorat Basin,northeastern Thailand     

Hitoshi Hasegawa  Suvapak Imsamut  Punya Charusiri  Ryuji Tada  Yu Horiuchi  Ken‐Ichiro Hisada 《Island Arc》2010,19(4):605-621

The Tibetan Plateau is a key factor in controlling the present‐day climate and atmospheric circulation pattern in Asia. The pattern of atmospheric circulation after the uplift of the plateau is well known, whereas direct evidence is lacking regarding the nature of the circulation pattern prior to the uplift. The distribution of desert directly reflects the position of the subtropical high‐pressure belt, and the prevailing surface‐wind pattern recorded in desert deposits reveals the position of its divergence axis. Cretaceous eolian sandstone of the Phu Thok Formation is extensively exposed in the northern Khorat Basin, northeastern Thailand. We conducted a sedimentological study on this formation to reconstruct temporal changes in the latitude of the subtropical high‐pressure belt in low‐latitude Asia during the Cretaceous. Spatio‐temporal changes in the paleo‐wind directions recorded in the Phu Thok Formation reveal that the Khorat Basin mainly belonged to the northeast trade wind belt and subtropical high‐pressure belt was situated to the north of the Khorat Basin during the initial stages of deposition, shifted southward to immediately above the basin during the main phase of deposition, and then shifted northward again to the north of the basin during the final stages of deposition. The paleomagnetic polarity sequence obtained for the Phu Thok Formation comprises three zones of normal polarity and two of reversed polarity, correlating to chrons M1n to C34n of the geomagnetic polarity time scale. This result suggests that the Phu Thok Formation is mid‐Cretaceous in age (from c. 126 Ma to c. 99–93 Ma), similar to the age of eolian sandstone in the Sichuan Basin, southern China (the Jiaguan Formation). These results, in combination with paleo‐wind direction data, suggest the development of low‐latitude desert and an equatorward shift of the subtropical high‐pressure belt (relative to the present‐day) in Asia during the mid‐Cretaceous.  相似文献   

Modeling of environmental influence in structural health assessment for reinforced concrete buildings   总被引：2，自引：2，他引：0  

Ka-Veng Yuen  Sin-Chi Kuok 《地震工程与工程振动(英文版)》2010,9(2):295-306

One branch of structural health monitoring (SHM) utilizes dynamic response measurements to assess the structural integrity of civil infrastructures. In particular,modal frequency is a widely adopted indicator for structural damage since its square is proportional to structural stiffness. However,it has been demonstrated in various SHM projects that this indicator is substantially affected by fluctuating environmental conditions. In order to provide reliable and consistent information on the health status of the monitored structures,it is necessary to develop a method to filter this interference. This study attempts to model and quantify the environmental influence on the modal frequencies of reinforced concrete buildings. Daily structural response measurements of a twenty-two story reinforced concrete building were collected and analyzed over a one-year period. The Bayesian spectral density approach was utilized to identify the modal frequencies of this building and it was clearly seen that the temperature and humidity fluctuation induced notable variations. A mathematical model was developed to quantify the environmental effects and model complexity was taken into consideration. Based on a Timoshenko beam model,the full model class was constructed and other reduced-order model class candidates were obtained. Then,the Bayesian modal class selection approach was employed to select the one with the most suitable complexity. The proposed model successfully characterizes the environmental influence on the modal frequencies. Furthermore,the estimated uncertainty of the model parameters allows for assessment of the reliability of the prediction. This study not only improves the understanding about the monitored structure,but also establishes a systematic approach for reliable health assessment of reinforced concrete buildings.  相似文献   

Running safety analysis of a train on the Tsing Ma Bridge under turbulent winds     

Weiwei Guo  He Xia  Youlin Xu 《地震工程与工程振动(英文版)》2010,9(3):307-318

The dynamic responses of the Tsing Ma suspension bridge and the running behaviors of trains on the bridge under turbulent wind actions are analyzed by a three-dimensional wind-train-bridge interaction model. This model consists of a spatial finite element bridge model, a train model composed of eight 4-axle identical coaches of 27 degrees-of-freedom, and a turbulent wind model. The fluctuating wind forces, including the buffeting forces and the self-excited forces, act on the bridge only, since the train runs inside the bridge deck. The dynamic responses of the bridge are calculated and some results are compared with data measured from Typhoon York. The runnability of the train passing through the Tsing Ma suspension bridge at different speeds is researched under turbulent winds with different wind velocities. Then, the threshold curve of wind velocity for ensuring the running safety of the train in the bridge deck is proposed, from which the allowable train speed at different wind velocities can be determined. The numerical results show that rail traffic on the Tsing Ma suspension bridge should be closed as the mean wind velocity reaches 30 m/s.  相似文献   

Near‐fault effects on residual displacements of RC structures          下载免费PDF全文

Eftychia Liossatou  Michael N. Fardis 《地震工程与结构动力学》2016,45(9):1391-1409

Residual displacements of single‐degree‐of‐freedom systems due to ground motions with velocity pulses or fling step displacements are presented as a function of period T and of its ratio to the pulse period T_p. Four hysteretic behaviors are considered: bilinear elastoplastic, stiffness‐degrading with cycling, stiffness‐cum‐strength degrading, with or without pinching. When expressed in terms of T/T_p, peak inelastic and residual displacements due to motions with a pulse or fling appear similar to those due to far‐fault motions, if the response to far‐field records are expressed in terms of the ratio of T to the record's characteristic period. However, as the latter is usually much shorter than the pulse period of motions with fling, the range of periods of interest for common structures becomes a short‐period range under fling motions and exhibits very large amplification of residual and peak inelastic displacements. Similar, but less acute, are the effects of motions with a velocity pulse. Wavelets of different complexity are studied as approximations to near‐fault records. Simple two‐parameter wavelets for fling motions overestimate peak inelastic displacements; those for pulse‐type motions overestimate residual displacements. A more complex four‐parameter wavelet for motions with a velocity pulse predicts overall well residual and peak displacements due to either pulse‐ or fling‐type motions; a hard‐to‐identify parameter of the wavelet impacts little computed residual displacements; another significantly affects them and should be carefully estimated from the record. Even this most successful of wavelets overpredicts residual displacements for the periods of engineering interest. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

Soil–pile–structure interaction: experimental outcomes from shaking table tests          下载免费PDF全文

Maria Giovanna Durante  Luigi Di Sarno  George Mylonakis  Colin A. Taylor  Armando Lucio Simonelli 《地震工程与结构动力学》2016,45(7):1041-1061

An effective way to study the complex seismic soil‐structure interaction phenomena is to investigate the response of physical scaled models in 1‐g or n‐g laboratory devices. The outcomes of an extensive experimental campaign carried out on scaled models by means of the shaking table of the Bristol Laboratory for Advanced Dynamics Engineering, University of Bristol, UK, are discussed in the present paper. The experimental model comprises an oscillator connected to a single or a group of piles embedded in a bi‐layer deposit. Different pile head conditions, that is free head and fixed head, several dynamic properties of the structure, including different masses at the top of the single degree of freedom system, excited by various input motions, e.g. white noise, sinedwells and natural earthquake strong motions recorded in Italy, have been tested. In the present work, the modal dynamic response of the soil–pile–structure system is assessed in terms of period elongation and system damping ratio. Furthermore, the effects of oscillator mass and pile head conditions on soil–pile response have been highlighted, when the harmonic input motions are considered. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

黏土中两种不同直径单桩水平循环加载模型试验与分析     

俞剑  黄茂松  张陈蓉 《岩土力学》2016,37(4):973-980

为探讨海上风机在风、浪等水平往复循环荷载下大直径单桩基础的循环弱化特性,设计了稳定输出长期循环荷载的机械加载装置,开展了软黏土中长期水平循环荷载下海上风电大直径单桩基础和传统长桩基础的模型试验对比研究。根据API给出的骨干曲线和Masing二倍准则构建循环荷载下的p-y（荷载-位移）曲线,并借鉴前人工作,采用累积塑性应变描述软黏土的不排水抗剪强度弱化,提出了分析大周数水平循环荷载下单桩基础循环弱化的理论方法。该方法将循环荷载次数、幅值等外界条件与桩周土体的循环弱化特性建立联系,以适应海洋环境复杂多变的水平循环荷载形式。通过模型试验和理论研究认为,大直径单桩基础因刚度较大,在同样的水平力循环荷载条件下,其抵抗循环荷载的能力明显优于传统长桩。在海上风机大直径单桩的设计中采用基于黏土残余强度的循环后稳定水平承载力更为合理。  相似文献   

基于高斯曲线拟合-FFT方法的南海风场反演     

田斯妤  黄晓霞  李红旮  汪昊  李霞  程鹏 《地球信息科学学报》2016,18(11):1544-1550

海面风场是海洋学的基本参量,获取海面风场对了解海洋的物理过程以及海洋与大气之间的相互作用至关重要。宽阔的海域面积及复杂的海面状况通常使南海海面上的风场信息很难被及时获取。ENVISAT ASAR是一种全天候全天时监测海面的微波雷达传感器,可实时获取海面风场数据。本文基于已有ASAR数据对南海海面风场进行反演实验,首先将结合高斯曲线拟合的FFT风向反演方法应用于南海风向反演,并参考Cross-Calibrated Multi-Platform （CCMP）风场数据去除180o方向模糊获得海面风向。然后,将高斯曲线拟合-FFT风向与传统的峰值-FFT风向进行对比,最后将准确率较高的高斯曲线拟合-FFT风向分别输入CMOD4模型和CMOD5模型获得海面风速大小。实验结果与CCMP参考数据的比较结果表明,在风条纹不明显的情况下,利用结合高斯曲线的FFT风向反演方法和CMOD4模型风速反演方法可有效地进行南海海面风场反演。该成果对利用SAR数据实时获取南海大面积海面风场信息,尤其是观测点缺乏海域的风场信息,具有重要的指导意义。  相似文献   

科尔沁沙地春季冷锋过境的地面风况特征     

韩广  尤莉  程玉琴 《中国沙漠》2016,36(4):1087-1096

对13个气象台站2014年5月上旬逐时风况的分析发现：（1）受高空槽和地面低压的影响,科尔沁沙地冷锋过境时瞬时风速8h内快速增加到10m·5s^-1以上,风向转为西北风;（2）上风向锡林郭勒草原的冷锋推进速度约为12.5m·5s^-1,科尔沁沙地主体部分则降到9.21m·5s^-1,总体推进速度因地而异;（3）风速的功率谱以大兴安岭东麓的林西县幅值最大,科尔沁左翼后旗最小;（4）沙地和草原两地区分别存在区域性10h、25h和2h、4h周期性,而冷锋过境引起的强风周期性不明显;（5）常年稳定而频繁的冷锋过境,不仅造成了沙丘的形态变化和不同程度的位移,而且还塑造和维持着该区沙丘群的多种空间格局。  相似文献