新型预制预应力混凝土框架结构有限元分析     

颜学渊  周灵哲  祁皑  毛会敏  陈伟宏 《地震工程与工程振动》2020,(2):54-63

为了研究新型预制预应力混凝土框架结构的抗震性能,本文采用ABAQUS软件对试验节点进行有限元分析,验证了建模方法的正确性,并以试验节点为原型,建立相应的两层两跨的新型预制预应力混凝土平面框架模型。采用低周往复加载方式分析了新型预制预应力混凝土框架结构和现浇框架结构的滞回性能,并模拟了新型预制预应力混凝土框架结构在不同的初始荷载、预应力筋数量及控制应力和U形筋配筋率下的滞回性能。结果表明,新型预制预应力混凝土框架和现浇框架的滞回性能非常接近;框架轴压比、预应力筋数量和U形筋配筋率对新型预制预应力混凝土框架的滞回性能有影响,而梁上荷载和预应力筋控制应力的影响较小。  相似文献   

Characterisation of hydroclimatological trends and variability in the Lake Naivasha basin,Kenya          下载免费PDF全文

Vincent Omondi Odongo  Christiaan van der Tol  Pieter R. van Oel  Frank M. Meins  Robert Becht  Japheth Onyando  Zhongbo Su 《水文研究》2015,29(15):3276-3293

Recent hydro‐climatological trends and variability characteristics were investigated for the Lake Naivasha basin with the aim of understanding the changes in water balance components and their evolution over the past 50 years. Using a Bayesian change point analysis and modified Mann–Kendall tests, time series of annual mean, maximum, minimum, and seasonal precipitation and flow, as well as annual mean lake volumes, were analysed for the period 1960–2010 to uncover possible abrupt shifts and gradual trends. Double cumulative curve analysis was used to investigate the changes in hydrological response attributable to either human influence or climatic variability. The results indicate a significant decline in lake volumes at a mean rate of 9.35 × 10⁶ m³ year^?1. Most of the river gauging stations showed no evidence of trends in the annual mean and maximum flows as well as seasonal flows. Annual minimum flows, however, showed abrupt shifts and significant (upward/downward) trends at the main outlet stations. Precipitation in the basin showed no evidence of abrupt shifts, but a few stations showed gradual decline. The observed changes in precipitation could not explain the decline in both minimum flows and lake volumes. The findings show no evidence of any impact of climate change for the Lake Naivasha basin over the past 50 years. This implies that other factors, such as changes in land cover and infrastructure development, have been responsible for the observed changes in streamflow and lake volumes. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

Soil pipe flow tracer experiments: 1. Connectivity and transport characteristics          下载免费PDF全文

G. V. Wilson  J. R. Rigby  M. Ursic  S. M. Dabney 《水文研究》2016,30(8):1265-1279

Much debate has occurred in catchment hydrology regarding the connectivity of flow paths from upslope areas to catchment outlets. This study was conducted in two catchments, one with three upper branches, in a loess soil with a fragipan that fosters lateral flow and exhibits an extensive distribution of soil pipe collapse features. The study aimed to determine the connectivity of multiple soil pipe networks as well as determine pipe flow velocities during storm events. Fluorescein dye was injected directly into soil pipes at the upper most pipe collapse feature of four different hillslopes. Breakthrough curves (BTC) were determined by sampling multiple pipe collapse features downslope. The BTCs were used to determine the ‘average’ (centre of mass) and ‘maximum’ (first arrival) flow velocities. This study confirmed that these catchments contain individual continuous soil pipe networks that extend over 190 m and connect the upper most hillslopes areas with the catchment outlet. While the flow paths are continuous, the individual pipe networks consist of alternating reaches of subsurface flow through soil pipes and reaches of surface flow through gullies formed by pipe collapses. In addition, flow can be occurring both through the subsurface soil pipes simultaneous with surface flow generated by artesian flow from the soil pipes. The pipe flow velocities were as high as 0.3 m/s, which was in the range of streamflow velocities. These pipe flow velocities were also in the range of velocities observed in pinhole erosion tests suggesting that these large, mature soil pipes are still actively eroding. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

土−水特征曲线测量过程中孔隙分布的演化规律探讨     

牛庚  邵龙潭  孙德安  韦昌富  郭晓霞  徐华 《岩土力学》2020,41(4):1195-1202

测量了在宽广吸力范围内原状样和压实样的脱湿持水曲线，对比分析了单双峰结构持水性能的差异；并利用压汞试验测试两种土样在脱湿过程的孔隙分布，分析了两者的差异并探讨了脱湿过程孔隙的演化规律；在考虑收缩变形的基础上，基于孔隙分布曲线确定了土?水特征曲线的基本参数。试验结果表明：原状样在宽广吸力范围内基本上呈单峰孔隙结构；饱和压实样具有单峰孔隙结构，随着吸力的增加，双峰结构越来越明显，当吸力达到很大时，演化成完全双峰孔隙结构。原状样的持水曲线为经典的S形，而压实样的持水曲线在过渡段出现了水平台阶状；低吸力段，压实样的持水曲线低于原状样，而高吸力段，两者的持水曲线基本重合。基于孔隙分布曲线确定了控制持水曲线进气值和残余值的孔径，并计算出对应的吸力值，其值更符合实际物理意义。  相似文献   

钢筋-沥青隔震层非线性震动特性研究          下载免费PDF全文

尚守平  刘水 《世界地震工程》2019,35(1):001-8

为了研究钢筋-沥青隔震层的材料与几何非线性震动特性，对钢筋-沥青隔震结构进行了振动台试验，分析了结构在不同加速度幅值输入时的隔震性能。同时，在钢材的应力-应变关系基础上，考虑构件竖向力的二次矩效应，提出了钢筋-沥青隔震层骨架曲线的计算方法，并结合双线型恢复力模型的滞回规则，建立了相应的恢复力模型。利用建立的恢复力模型，编制程序进行了弹塑性时程分析，并与试验结果作对比。结果表明:当钢筋-沥青隔震层的受力钢筋进入弹塑性阶段时，隔震层能够吸收大部分地震能量，显著降低上部结构的地震反应；弹塑性时程分析结果与试验结果吻合较好，由此建立的恢复力模型准确并且适用，可为钢筋-沥青隔震层的工程设计与非线性地震反应分析提供参考。  相似文献   

非迁移潮作用下的电离层赤道异常区单峰现象及其经度分布          下载免费PDF全文

田耀宇  郝永强  张东和  肖佐 《地球物理学报》2019,62(11):4067-4081

当喷泉效应较弱而双峰结构发展不充分的时候，可能在赤道异常区仅能够观测到一个电子密度的峰值，称之为单峰现象.本文利用CHAllenging Minisatellite Payload卫星在2001-2010年的电子密度数据给出了单峰的发生规律，单峰在地方时早上08：00-10：00和下午16：00-19：00发生率高，发生位置在经度上呈现多波数分布，尤其在10：00-18：00明显：在分季时多呈现四波，而在冬至季时以三波为主.单峰发生多的经度，正好对应着双峰的结构特征较弱之处.究其原因，是非迁移潮的DE2和DE3分量调制了背景风场和大气发电机电场，在电场和喷泉效应减弱的经度，双峰结构难以形成时，就会表现为单峰结构.本文扩展了对单峰现象的地方时、季节和经度分布等规律的了解，明确了非迁移潮在其中施加的影响，由此，单峰同双峰现象一样可以用于研究非迁移潮对热层-电离层的作用.  相似文献   

Study of Fractal Characteristics of the Cementation Index in Shale Gas     

LIU Hongqi  LIU Shiqiong  LUO Xingping  SUN Yangsh  TIAN Jie  LIANG Lixi  LIU Xiangjun 《《地质学报》英文版》2020,94(2):456-466

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基于VG模型确定土水特征曲线基本参数     

潘登丽  倪万魁  苑康泽  张镇飞  王熙俊 《工程地质学报》2020,28(1):69-76

土水特征曲线基本参数(进气值、残余吸力值和反弯点的斜率等)在非饱和土的强度理论、渗流理论以及体变特性等方面都是非常重要的参数,常常通过传统画图法来确定,其精确度难以保证。以洛川标准剖面4层原状黄土为研究对象,基于VG模型提出单峰和双峰SWCC基本参数的确定方法;采用滤纸法测得SWCC数据点,基于VG模型进行最优化拟合,获取拟合参数,利用单峰和双峰SWCC数据点验证该方法的可行性;进行自然状态下的水分蒸发试验,根据质量含水率与蒸发时间的关系确定蒸发残余饱和度Srzf,依据Sr1、Sr2(Sr1和Sr2分别由确定残余状态的两种方法得到)与Srzf的相对误差值,比较了两种确定残余状态的方法。结果表明:对于单峰和双峰SWCC曲线,该方法都可以得到合理的基本参数并有效地确定其残余状态。  相似文献   

1927年古浪8级大震区小震重新定位及问题讨论          下载免费PDF全文

董宗明  刘白云 《地震工程学报》2017,39(4):692-697

联合利用甘肃及周边测震台网记录的古浪及周边地区4 592次地震的P波绝对到时和相对到时资料，采用双差地震定位方法对古浪震源区小震进行重新定位后发现，皇城-双塔断裂带东、西两段表现出不同的力学运动性质，西段以逆冲运动为主，地震主要发生在断裂的下盘；而东段地震却主要发生在上盘，断层活动以局部拉张为主。还首次发现在皇城-双塔断裂带的中段与主破裂呈垂直方向存在一条主震发生时新产生的共轭断层，基于小震的断层面参数反演显示该断裂是一高倾角运动性质以右旋为主兼具正断的断裂。  相似文献   

THE INVERSION OF S-WAVE VELOCITY STRUCTURE IN NINGXIA AND ITS ADJACENT AREA USING BACKGROUND NOISE IMAGING TECHNOLOGY          下载免费PDF全文

XIE Hui  MA He-qing  JIAO Ming-ruo  MA Xiao-jun  ZHANG Nan  LI-Qing-mei 《地震地质》2017,39(3):605-622

In this paper, we use seismic waveform data of 90 seismic stations in Ningxia and its adjacent areas recorded between January 2012 and December 2013 to obtain the Rayleigh surface wave group velocity dispersion of the study area according to the noise imaging method and the 3-D S-wave velocity structure of the crust and upper mantle in Ningxia and its adjacent regions. The results show that within the depth range of 10~40km in Yinchuan graben and Liupanshan fault belt there exists a slow anomaly body, and with the increase of the depth this slow anomaly becomes an abnormal slow zone surrounding Lanzhou Basin between the massif arcuate structure of northeastern margin of Tibet Plateau and Alxa block. The 3-D S-wave velocity structure of the crust and upper mantle of the study area presents obvious lateral inhomogeneity. These results have important significance for the study of the dynamics of active tectonic zones and mechanism of strong earthquakes in Ningxia and its adjacent areas.  相似文献