钻孔耦合因素对引潮力标定的影响分析   总被引：1，自引：0，他引：1  

田韬  杨军  郝永亮  王维 《内陆地震》2014,(4):312-318

利用多层厚壁筒组合的力学模型,分析介质力学性质变化对钻孔面应变耦合系数的影响。利用引潮力标定方法对观测资料的研究表明,"地层、水泥环和钢筒"模型不能完全反映观测条件,考虑原地应力卸载影响的四层介质耦合模型,与观测环境基本相符,可以对观测结果进行较合理解释,同时发现钻孔面应变耦合系数的大小与台站的背景应力场存在一定关系。  相似文献   

基于分布式光纤测试技术的大直径嵌岩桩承载性能研究     

罗勇  李春峰  邢皓枫 《岩土力学》2014,35(5):1406-1412

采用分布式光纤传感技术对赫章特大桥195 m主墩下的大直径嵌岩桩承载特性进行了系统的研究分析。首先采用室内模型试验验证了光纤技术在桩基测试中应用的可行性;然后通过现场埋设和施工过程中的数据采集、整理与分析,系统研究了大直径嵌岩桩的承载特性及其荷载传递机制;依托工程的实测变形量进一步证明了光纤测试技术的可行性和正确性。基于全分布式光纤传感技术的研究结果对大直径嵌岩桩理论及其工程应用具有参考价值,同时对光纤测试技术在桩基测试中的应用具有借鉴作用。  相似文献   

竖向直排冻结条件水平冻胀力试验研究     

李岩  刘波  张建新 《岩土力学》2014,35(11):3199-3206

竖向直排冻结方式常用于软弱地层中斜井掘进和深基坑止水帷幕的冻结法施工中,目前国内外对该冻结方式下水平冻胀力的分布研究鲜见报导。以某斜井冻结工程为背景,推导出温度场、应力场和水分场等相似模拟准则,设计了竖向直排冻结模型试验并细化具体试验方案,利用大型三维模拟冻结试验系统,对竖向直排冻结条件下不同深度土体的水平冻胀力分布特性进行了试验研究。结果表明,竖向直排冻结过程中埋深对水平冻胀力的影响明显,在其他条件相近的情况下同一水平面中水平冻胀力的大小与温度密切相关;冻胀力的变化率主要受冻结锋面位置的影响,距离冻结锋面较近时冻胀力的变化率逐步达到峰值;已冻土体的冻胀力随冻结锋面向外发展而趋于平稳。  相似文献   

Inelastic spectra to predict period elongation of structures under earthquake loading          下载免费PDF全文

E. I. Katsanos  A. G. Sextos 《地震工程与结构动力学》2015,44(11):1765-1782

Period lengthening, exhibited by structures when subjected to strong ground motions, constitutes an implicit proxy of structural inelasticity and associated damage. However, the reliable prediction of the inelastic period is tedious and a multi‐parametric task, which is related to both epistemic and aleatory uncertainty. Along these lines, the objective of this paper is to investigate and quantify the elongated fundamental period of reinforced concrete structures using inelastic response spectra defined on the basis of the period shift ratio (T_in/T_el). Nonlinear oscillators of varying yield strength (expressed by the force reduction factor, R_y), post‐yield stiffness (a_y) and hysteretic laws are examined for a large number of strong motions. Constant‐strength, inelastic spectra in terms of T_in/T_el are calculated to assess the extent of period elongation for various levels of structural inelasticity. Moreover, the influence that structural characteristics (R_y, a_y and degrading level) and strong‐motion parameters (epicentral distance, frequency content and duration) exert on period lengthening are studied. Determined by regression analyses of the data obtained, simplified equations are proposed for period lengthening as a function of R_y and T_el. These equations may be used in the framework of the earthquake record selection and scaling. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

西北地区30地级市城市区位分析     

陈莉  石培基  焦贝贝 《干旱区地理》2015,38(4):851-857

以西北地区30地级市为研究对象,通过时间距离计算,运用区位偏远度衡量地理区位;采用经济联系强度模型分析其经济区位条件;基于改进的区位优势潜力模型对各市综合区位予以定量化测度。结果表明:(1)对于最邻近省会城市,30地市偏远度都<1,均处于不偏远区位;对北京而言,偏远程度介于0.263~2.446之间,其中12地市处于偏远区域;综合偏远度表明,处于偏远(δ>1)、不偏远(0.5δ≤1)、很不偏远(0<δ≤0.5)区位的城市比重分别为13.33%、53.33%、33.33%。(2)经济联系量表现出如下特点:30地市内部联系远远高于与北京的联系,其联系总量所占比重为99.47%和0.53%;除青海省,其他4省内部联系程度强于外部;以省为单位,经济总量大体沿着自东向西的方向递减。(3)陕西省经济区位明显表现出以西安、咸阳为中心的环形圈层结构,自内而外经济联系强度渐弱。(4)综合地理偏远度、经济区位和综合区位,30地市可大致分为"双优型"、"(偏)地理区位滞后型"、"(偏)经济区位滞后型"和"双滞后型" 4种类型。  相似文献   

中美巴印过去300年耕地时空变化的比较研究   总被引：1，自引：0，他引：1  

李美娇  何凡能  肖冉 《地理科学进展》2015,34(1):64-72

本文利用长时间序列数据,对中、美、巴、印四国过去300 年耕地时空变化特征及驱动因素进行了比较分析。结果表明:①四国耕地总量在过去300 年均呈持续增长态势。中国和印度土地垦殖历史悠久,其中,中国在1700-1980s 耕地面积增加了68.21×10⁴ km²,印度在1700-2000 年增加了131.28×10⁴ km²,为中国的1.92 倍;美国和巴西虽然农业起步较晚,但发展迅猛,其中,美国在1700-1950 年的250 年间耕地面积增长了190.87×10⁴ km²,分别是中国、印度增量的2.80 倍和1.46 倍;巴西在1700-2000 年增加了64.57×10⁴ km²,其中近百年的增量为62.82×10⁴ km²,超过了同期其他三国的增加量。②从空间格局变化特征看,近300 年来,中国和印度均是在已有耕地分布格局的基础上向高原及山地丘陵地区扩展;而美国在“西进运动”的影响下,耕地大规模向中西部拓殖;巴西随着向北西部开发的推进,北部、西部地区的耕地急剧增加。③过去300 年推动四国土地垦殖发展最直接的驱动因素是国家政策,但就根本驱动因素而言,中国和印度是人口,而美国和巴西则是国家财政;在农技发展取向方面,中国和印度选择了精耕细作以提高土地生产率;而美国和巴西则选择了机械化以提高劳动生产率。  相似文献   

Force–displacement mixed control for collapse tests of multistory buildings using quasi‐static loading systems          下载免费PDF全文

Peng Pan  Gang Zhao  Xinzheng Lu  Kailai Deng 《地震工程与结构动力学》2014,43(2):287-300

In quasi‐static tests for structures with multi‐DOF, the forces exerted to the structures commonly follow a prescribed force profile, for example, triangular pattern and/or uniform pattern. Therefore, force control is the natural choice. However, force control is no longer applicable when the specimens sustain significant stiffness and strength degradation, particularly in collapse tests. To solve this problem, a force–displacement mixed control algorithm is proposed, which is able to achieve stable control in quasi‐static tests following prescribed force profiles. On the basis of the FlexTest IIm platform of the MTS Systems Corporation (14000 Technology Dr, Eden Prairie, MN 55344 United States), a test program named Tsinghua University mixed control test program, which uses a mixed control algorithm, was developed. The algorithm was initially applied to an elastic test of a cantilever column to verify its accuracy and stability and then to a collapse test of a multistory RC frame to investigate its effectiveness. In the collapse test, the effects of major control parameters, that is, the number of iterative rounds and the loading time of each round on the control accuracy, were also studied. The test results show that the test program applying the mixed control algorithm can achieve stable control of the collapse tests maintaining the expected force profile. Increasing the number of iterative rounds and the loading time of each round can improve the control accuracy. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Seismic behavior and strength capacity of steel tube‐reinforced concrete composite columns          下载免费PDF全文

Xiaodong Ji  Hongzhen Kang  Xingchen Chen  Jiaru Qian 《地震工程与结构动力学》2014,43(4):487-505

The steel tube‐reinforced concrete (ST‐RC) composite column is a novel type of composite column, which consists of a steel tube embedded in RC. In this paper, the seismic behavior of ST‐RC columns is examined through a series of experiments in which 10 one‐third scale column specimens were subjected to axial forces and lateral cyclic loading. The test variables include the axial force ratio applied to the columns and the amount of transverse reinforcement. All specimens failed in a flexural mode, showing stable hysteresis loops. Thanks to the steel tube and the high‐strength concrete it is filled with, the ST‐RC column specimens had approximately 30% lower axial force ratios and 22% higher maximum bending moments relative to the comparable RC columns when subjected to identical axial compressive loads. The amount of transverse reinforcement made only a small difference to the lateral load‐carrying capacity but significantly affected the deformation and energy dissipation capacity of the ST‐RC columns. The specimens that satisfied the requirements for transverse reinforcement adopted for medium ductile RC columns as specified by the Chinese Code for Seismic Design of Buildings (GB 50011‐2010) and EuroCode 8 achieved an ultimate drift ratio of around 0.03 and a displacement ductility ratio of approximately 5. The design formulas used to evaluate the strength capacity of the ST‐RC columns were developed on the basis of the superposition method. The predictions from the formulas showed good agreement with the test results, with errors no greater than 10%. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

月球引潮力振动与大气潮汐的周期变化     

张明初  彭义峰  张敏  胡宇峰 《气象与减灾研究》2010,33(2):54-59

在天气学中,当复杂而开放的气候系统处于远离平衡的临界状态时,任何微小的外力扰动都有可能带来一场雪崩式的"蝴蝶效应";而天气系统的演变尽管错综复杂,其实质却主要是冷暖气团的强弱与进退,再就是月球引潮力的周期变化还能引发周期大气潮。据此推想,在月球的周期运行过程中,是交点月南、升、北、降水平引力拐点所产生的引潮力振动(方向、大小的改变),通过大气内部的动力过程,对不稳定气团可产生激发作用,从而引导冷暖空气南北进退和天气系统演变,便出现了周期大气潮和转折天气周循环。  相似文献   

新疆且末绿洲土地利用变化机制与驱动力分析   总被引：11，自引：0，他引：11  

王让会  孙洪波  赵振勇 《干旱区地理》2005,28(6):849-855

土地利用与覆盖变化是全球变化研究的重要组成部分,干旱区土地利用与覆盖变化的机制与驱动力又是干旱地区相关问题研究的核心。新疆且末绿洲特殊的MODS背景,制约着LUCC的一系列过程及其规律。LUCC是各种自然、社会、政治、经济和文化因素相互作用的结果。驱动力类型与特征受绿洲时空特征的制约而表现出不同的特征。在区域尺度上,且末绿洲LUCC的自然驱动力,包括了相关区域地壳运动、冰川变化、风沙活动等自然作用过程,热量、降水、温度变化等的气候过程以及地表径流、冰川进退等引起的水文过程的作用。在特定生产力发展水平下,人类的社会经济活动直接影响了LUCC的演变过程及演变趋势。  相似文献