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1.
当前我国预应力混凝土管桩的工程应用发展迅速、量大面广,有关管桩的承载特性、设计、施工、检测等工作应引起重视。总结分析了当前预应力混凝土管桩的发展历史、应用现状及其工程应用中常遇到的问题,结合相关国家规范、行业标准及工程实测资料,针对预应力混凝土管桩的适用条件、承载性状、施工质量控制等问题进行深入对比分析。通过具体工程实例,总结了预应力混凝土管桩工程应用中的注意事项,给出了减少管桩工程质量事故的预防措施,并对工程中如何安全适用、经济合理地应用预应力混凝土管桩提出建议。 相似文献
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根据断裂动力学理论及弹性P波与裂缝相互作用的分析,利用混凝土的动态断裂韧度,研究了大体积混凝土深层或贯穿裂缝在爆炸应力波P波作用下的扩展,得到了含裂缝混凝土的安全质点振动速度,并讨论了P波频率及其入射角对安全质点振动速度的影响。结果表明,频率越低、入射角越大的应力波对混凝土裂缝的扩展作用越大,频率为10 Hz垂直入射条件下,混凝土裂缝不扩展的安全质点振动速度仅为0.95 cm/s,与水利水电工程施工组织设计手册中规定的混凝土重力坝、混凝土闸墩等大体积混凝土结构的安全振速5 cm/s有较大差距,含裂缝混凝土更加容易被破坏。 相似文献
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山砂原材资源丰富、取材便捷,已广泛用于普通强度等级的混凝土。山砂表面粗糙、级配差、含泥量大等特点使其在配制高强度混凝土时具有一定难度。本文采用人工水洗山砂,在固定胶凝材料用量的情况下,考虑砂率、水胶比、 矿物掺和料组合掺量3个因素,每个因素考虑3个水平,找出各因素对混凝土标准龄期抗压强度的影响,利用正交实验设计优选混凝土的配合比设计参数。基于最优配合比设计参数,研究山砂石粉含量对高强混凝土和易性和抗压强度的影响。试验结果表明：最佳配合比方案为A1B2C2,机制山砂中含有7%至10%的石粉能改善混凝土的工作性能和抗压强度。 相似文献
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在浇注混凝土构件时,一般都用木模,既需要木料,又需要请木工制作模具,成本較高。我区登瀛岩水文站,今年在浇注断面觇牌和短电杆(4米长)时,采用“砖模”,成品质量合乎要求,仅表面不及用木模的光滑。这为制作数量少而对表面光洁度要求不高 相似文献
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现浇混凝土空心无梁楼盖是一种无梁、无柱帽、可实现大开间、灵活隔断的水平结构体系。山西医科大学教学楼阶梯教室采用了现浇混凝土空心无梁楼盖。增加结构水平刚度,降低层高,既缩短了工期,又减少了投资。 相似文献
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结合北京一个基坑支护工程,从设计角度就桩锚支护结构在基坑支护中的应用及变形控制进行了阐述。根据受力情况,护坡桩主筋配筋采用不均匀布置方式,结合工程、支护结构特点分段配筋;为了满足基坑安全及现场施工用地,砖墙设计时,在砖墙中部增设混凝土腰梁;护坡桩施工中,运用不同的施工工艺,保证了护坡范围内古树的生命安全。从基坑开挖监测角度,对支护结构顶部水平位移进行了监测,对周边建（构）筑物进行了沉降监测,同时对锚杆进行了检测与监测。结果分析表明,基坑水平及垂直变形量均在设计控制范围内,基坑整体稳定,桩锚支护结构对变形起到了有效的控制作用。 相似文献
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提高渠道衬砌工程质量水平,需要对混凝土衬砌渠道冻胀特性及影响因素进行研究。按照大U形混凝土衬砌渠道断面,利用FEA有限元数学近似分析法,对渠道冻胀特性进行瞬态数值模拟。模拟结果表明：各监测点在冻胀过程中相对外部冻胀量、法向冻胀力、以及切向冻胀力均存在一定的滞后现象,与工程实际中大 U形混凝土衬砌渠道冻胀实际特性相符。 FEA有限元数学近似分析法能够准确模拟渠道冻胀特性,为工程研究提供了一种新的计算机模拟仿真思路。 相似文献
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针对目前多层地基中水平荷载桩计算方法存在的问题,提出了一种基于弹性力学理论,根据桩-土应力应变关系,借助于变分原理和最小势能原理导出桩身位移控制方程,利用有限差分法对方程进行解答的方法,并编制了全桩位移和内力计算程序。算例结果表明,该方法分别同试验结果和有限元计算结果吻合较好,较现行地基系数法具有较高的计算精度和计算效率,对现浇混凝土大直径水平荷载管桩（PCC）的设计计算和分析具有一定的指导意义。 相似文献
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通过厦门某大酒店综合大厦大体积混凝土施工实践,总结大体积混凝土施工技术,特别是对可能产生裂缝的控制,保证了大体积混凝土的施工质量。 相似文献
11.
时间域激发极化法是应用于金矿勘查的一种重要地球物理勘探手段,以往主要采用中梯扫面和激电测深组合的方法获取激电异常。中梯扫面受限于单一固定供电极距,仅能反映某一深度的激电异常分布;常规对称四极激电测深由于需要对固定测点布设不同极距的供电电极,工作效率较低,并且不适合三维探测。近些年随着大功率、阵列观测技术发展起来的类中梯激电装置可在观测区布设多组不同极距的供电电极,兼顾了激电测深与激电剖面二者的特点,为常年干旱的戈壁滩地区金属矿深部勘查提供了一种可能的探测手段。本文基于类中梯装置大功率三维激电测量技术在甘肃花牛山金矿区开展时间域激发极化法实验工作。实验结果表明：类中梯装置大功率三维激电观测能快捷高效获得研究区不同深度的激电异常;采用与类中梯装置相适应的三维反演方法对激电数据进行三维反演,可获取研究区地下三维精细电性结构;基于矿区的三维电性结构并结合相关地质资料构建的三维地质-地球物理模型,与矿区已知金矿点位置吻合,并发现了三处潜在成矿点;类中梯装置大功率三维激电测量技术在供电困难的戈壁滩地区金属矿勘查中应用效果明显。 相似文献
12.
华北地区奥陶系灰岩岩溶研究的几点思考 总被引：8，自引：0，他引：8
讨论了华北地区奥陶系马家沟灰岩岩溶研究中的几个问题，包括沉积期岩溶、暴露期岩溶，埋藏期岩溶，现代岩溶及本区特殊的岩溶现象“陷落柱”等，指出了沉积岩溶，暴露岩溶洞穴不要存或保存甚少，但对后期的岩溶发育具有重要控制作用，埋藏岩溶可分为完全埋藏和局部埋藏两个阶段，其中后者是现今奥灰岩溶面貌的定形期，陷落柱是该期岩溶的典型标志，最后提出了今后奥灰岩溶研究的思路。 相似文献
13.
This study evaluates the impact of Pakistan's development policies on regional development, using multi-variate statistical techniques of analysis. Regional economic development policies were inspired by the growth pole theory, but the centralized sectoral planning processes, relying on the market mechanism on the one hand and controlled fiscal and monetary policies on the other, have increased interregional development inequalities. The growth pole planning strategies have stimulated very little development in the lagging areas, especially agricultural development. Future planning strategies need to be divised that will assure development advances in Pakistan's backward regions. 相似文献
14.
计算机技术的不断发展为古大陆的复原与再造提供了有力的支持,特别是GIS强大的数据管理和数据分析功能为古大陆再造系统的研发提供了良好的平台。在分析和总结了国内外常见古大陆再造软件的特点的基础上,设计开发了以古地磁和欧拉旋转为基本模型的古大陆再造系统,通过对古地磁极、欧拉极等一些地质与几何要素的计算来定量描述板块的位置、运动轨迹、运动速度等属性,同时能对这些地质要素的数据和板块的数据进行管理,方便查询、检索、分析与展示,并以羌塘、拉萨、喜马拉雅3个地块为例对古陆再造系统的应用进行了说明。 相似文献
15.
A numerical–analytical approach is used to investigate irregular effects in oscillations of the Earth’s pole related to variations in the Chandler and annual components. An approach to studying oscillations in the motion of the Earth’s pole based on a joint analysis of the Chandler and annual components of this motion is proposed. A transformation to a new coordinate system in which the motion of the pole is synchronous with the precession of the lunar orbit can be found in this approach. Estimates of the precision of predictions of the coordinates of the Earth’s pole taking into account additional terms due to lunar perturbations are presented.
相似文献16.
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郑州地下水均衡试验场的改建,是由中国地质环境监测院主持的国家地下水监测工程中地下水均衡试验场的改建项目之一,由河南省环境地质监测院具体负责实施。科学技术的发展,为试验场观测数据采集的自动化奠定了良好基础。试验场数据采集需要自动化的有:3m高主杆气象站测试系统;太阳全辐射、太阳净辐射、太阳直射观测仪,E—601蒸发仪,5TM含水率、温度传感器,自动补水仪,负压测量仪。除后两项外,其他需要数据采集仪器已经市场化。后两项是作者的发明与实用专利。自动补水仪是用来模拟地下水位埋深的设备,它是以传统的马里奥特瓶补水原理为基础,采用控制电路使其可以自动补给因蒸发而消耗的水量,同时还可以记录降水的历时过程。负压测量是利用空气运动黏度约大于水运动黏度的15倍这一特性,即当水刚通过多孔瓷头时,气体不能通过多孔瓷头,据此设计了在包气带中能测定负压的传感器。数据采集则应用了惠斯登电桥平衡的补偿原理。由于控制、供电、采集数据的电缆过多,因此数据自动化采集系统应用了三级采集、逐级集成的方案。 相似文献
18.
System dynamics assessment of mitigation strategies for power distribution poles subjected to hurricanes 总被引：1，自引：1，他引：0
This paper presents a system dynamics-based method to evaluate the cost-effectiveness of mitigation strategies for the replacement of power distribution poles subjected to hurricanes. The method demonstrates how the performance of poles distributed over a certain region, as well as the cost of maintenance and replacement, varies with time. Compared to a static assessment, the dynamic analysis provides more information for decision-making about replacement strategies, e.g., the changing trend of cost and performance in a period, and thus a potential trade-off between short-term and long-term benefits. Also, some variables and features that play an important role in cost-effectiveness are examined using sensitivity analysis, so that refinement of pole replacement strategies can be made. The model depicts the systemic and dynamic natures of long-term cost-effectiveness of pole maintenance and assists in the development of a better replacement strategy for multipole systems. In a case study, the model was applied to a typical region subjected to hurricanes, i.e., Miami-Dade County in Florida, USA. The simulation results from the model led to a maintenance strategy optimization that included both selection of class of poles and ways of replacement. 相似文献
19.
The spatial distribution of joint orientations features self-similarity. Based on the fractal theory, a new method for meshing of Schmidt pole diagram has been established to study the fractal dimension of the orientation pole distribution of joint. Meshing of Schmidt pole diagram by equal area is performed in both circumferential and radial directions. When the cycle number n is set, the circle is evenly divided with n diameter lines to obtain 2n sectors of equal area; meanwhile the radius R is divided n times to obtain n rings, and specific ring radii are set to perform meshing of Schmidt pole diagram by equal area, thus obtaining different side lengths of cells and corresponding number of cells occupied by poles; on this basis the fractal dimension of joints was calculated. This method is applied to the research on the fractal dimension of joints in rock mass of mine. The results of the research showed that the method with fewer parameters made the process in which the fractal dimension of the orientation pole distribution of joint was solved simply and easy to operate, and calculating the fractal dimension of the orientation pole distribution for joint by this method could better describe the dispersity and complexity of the orientation distribution of joint. 相似文献
20.
Based on a system dynamics (SD) model of long-term cost-effectiveness of power pole maintenance over 50 years, the influence of factors that affect cost-effectiveness was examined. Taking a typical region subjected to hurricanes (i.e., Miami-Dade County, USA) as a case, the SD model was established and tested with scenarios of power poles maintenance strategies. Factors such as wind speed variation (due to climate change), regional annual growth rate of the pole population, and discount rate were explored. It was shown that changing the parameters for these factors results in the following: The variation of wind speed due to climate change produces a negative impact on cost-effectiveness under the given replacement strategy; the factors of wind speed and annual growth rate of poles have a significant influence on the replacement ratio of poles particularly in the later period such as later 30 years; similarly, the discount rate has a marked impact on cumulative cost in the later decades. The difference between the contribution of factors is more significant in the later stages of the design life. The simulation results indicate how the change of these factors can lead to an impact on cost-effectiveness over time. The results have meaningful strategy implications, allowing an optimization of the timing of maintenance and a focus on different critical factors at various time periods. 相似文献