大体积混凝土防裂和温度控制

大体积砼在施工阶段,它的浇筑温度随着外界气温变化而变化,特别是气温骤降,会大大增加内外层砼温差,这对大体积砼是极为不利的。温差愈大,温度应力愈大。同时,在高温条件下,大体积砼不易散热,并且有较长的延续时间,必须采取措施解决水化热及随之引起的体积变形问题,以最大限度减少开裂。     

寒潮期间大体积混凝土保温研究

大体积混凝土在施工期间不可避免地会发生气温骤降.如果不注重表面保护,大体积混凝土表面极易开裂.通过对混凝土表面放热系数的计算、表面温度的计算以及混凝土表面保温计算原理的研究,为寒潮期间保温措施的采用提供了一定的参考,并计算了温度骤降对某典型坝段的影响.     

金安桥混凝土温度控制施工探讨

由于混凝土温度的不利分布而产生各种裂缝，包括防止最高温度过高引起降温总量过大、内外温差过大及寒潮袭击（气温骤降）产生的不同情况的裂缝，故采用冷却措施，降低混凝土至设计温度，以确保混凝土施工质量。     

筏板基础大体积混凝土施工技术

结合工程实例，将大体积混凝土施工温度、温度差、温度应力控制的计算分析方法，应用到筏板基础混凝土施工中，有效控制了温度应力和收缩应力引起的裂缝，保证了混凝土质量。     

混凝土面板施工期温度及应力分析

温度变化可引起结构内力的变化,导致混凝土裂缝;对结构引起的应力重新分布,随着温变而变化.温度变化引起的应力甚至超过其它荷载应力,尤其是在结构温度急剧变化时,将产生很大的拉应力,而导致混凝土的开裂破坏.因此通过数值模拟计算对大坝面板混凝土进行抗裂分析,依据面板混凝土的浇筑进度计划用方程有限元格式,选择格式中权函数及解的稳定性进行温度应力数值计算,得到不同时段不同工况下面板混凝土的温度场与温度应力值,从而得到降低混凝土面板开裂风险的措施.     

早龄期混凝土结构的温度应力分析

为了分析混凝土在早龄期时温度应力随龄期的发展.通过建立混凝土材料的水化放热模型,引入Arrhenius公式来表征早龄期时混凝土放热速率受温度的影响.采用考虑等效龄期的混凝土弹性模量和抗拉强度CEB-FIP1990计算公式来表征早龄期时温度变化对其力学性能的影响,在应力分析中采用Bazant的双幂函数徐变模型.结果表明:引入Arrhenius公式的混凝土水化放热模型可以用于计算混凝土结构早龄期时的温度场,早龄期时温度应力可以引起混凝土长墙的开裂.早龄期时混凝土结构温度应力的计算为优化混凝土材料的组成提供依据,尽可能减少温度应力引起的开裂.     

暴雨温度骤降下沥青路面有限元分析

基于热弹性层状理论,采用ANSYS建立沥青路面三维有限元模型,对暴雨温度骤降情况下沥青路面温度作用和荷载作用进行耦合分析,研究该环境影响下沥青路面力学响应规律的变化,并将结果与高温作用下沥青路面响应规律比较.结果表明沥青路面结构在受到暴雨作用温度骤降情况下,沥青路面竖向变形值、竖向压应力变小;沥青路面路表由压应力变为拉应力,并使沥青层层底拉应力减小;暴雨骤降使沥青路面最大剪应力增大.     

浅谈混凝土的施工温度与裂缝原因

<正>1裂缝的原因混凝土硬化期间水泥放出大量水化热,内部温度不断上升,在表面引起拉应力。后期在降温过程中,由于受基础或老混凝土约束,又会在混凝土内部出现拉应力。气温的降低也会在混凝土表面引起很大的拉应力。当这些拉应力超出混凝土的抗裂能力时,即会出现裂缝。许多混凝土的内部湿度变化很小或变化较慢,但表面湿度可能变化较大或发生剧     

建筑工程中混凝土裂缝的控制措施

混凝土建筑在施工中,由于结构尺寸大,混凝土用量多,在水泥水化热引起混凝土内部温度变化及外界气温变化的影响下,会产生较大的温度收缩应力,而导致混凝土结构产生裂缝。造成裂缝的产生路径较复杂,受裂缝的破坏而造成的损失费相当高。本文在参考了大量文献资料、总结了建筑工程混凝土温度裂缝产生的原因的基础上,探讨和阐述了混凝土裂缝的控制方法。     

预应力混凝土箱梁桥的温度效应分析

介绍国内外几种典型规范的温度梯度计算模式,并根据箱梁常用截面尺寸范围,推导出相应的温度梯度解析表达式.以广州某预应力混凝土箱梁桥为工程实例,根据现场试验测试数据的分析,对3种折线模式的温度梯度提出相应的曲线型改进模式.根据国内外几种典型规范的温度梯度计算规定和本文提出的相应改进温度模式分别计算实例桥梁结构在各种温度梯度作用下引起的内力分布和变形.对比分析与计算结果表明:提出的温度模式可以简化计算程序,计算所得的截面最大拉应力略大于规范模式的相应结果,这有利于箱梁的裂缝控制;截面的最大拉应力出现在箱梁顶板的底面位置;桥墩边缘截面的温度应力大于跨中截面的温度应力;在现行设计规范的温度梯度作用下,箱梁截面的最大拉应力可能大于混凝土的抗拉强度,设计中应采取裂缝预防措施.     

Characterization of Ordovician carbonate reservoirs, southeastern Saskatchewan, Canada

The discovery of the prolific Ordovician Red River reservoirs in 1995 in southeastern Saskatchewan was the catalyst for extensive exploration activity which resulted in the discovery of more than 15 new Red River pools. The best yields of Red River production to date have been from dolomite reservoirs. Understanding the processes of dolomitization is, therefore, crucial for the prediction of the connectivity, spatial distribution and heterogeneity of dolomite reservoirs.The Red River reservoirs in the Midale area consist of 3～4 thin dolomitized zones, with a total thickness of about 20 m, which occur at the top of the Yeoman Formation. Two types of replacement dolomite were recognized in the Red River reservoir: dolomitized burrow infills and dolomitized host matrix. The spatial distribution of dolomite suggests that burrowing organisms played an important role in facilitating the fluid flow in the backfilled sediments. This resulted in penecontemporaneous dolomitization of burrow infills by normal seawater. The dolomite in the host matrix is interpreted as having occurred at shallow burial by evaporitic seawater during precipitation of Lake Almar anhydrite that immediately overlies the Yeoman Formation. However, the low δ18O values of dolomited burrow infills (-5.9‰～ -7.8‰, PDB) and matrix dolomites (-6.6‰～ -8.1‰, avg. -7.4‰ PDB) compared to the estimated values for the late Ordovician marine dolomite could be attributed to modification and alteration of dolomite at higher temperatures during deeper burial, which could also be responsible for its 87Sr/86Sr ratios (0.7084～0.7088) that are higher than suggested for the late Ordovician seawaters (0.7078～0.7080). The trace amounts of saddle dolomite cement in the Red River carbonates are probably related to "cannibalization" of earlier replacement dolomite during the chemical compaction.     

A computer generator for randomly layered structures

AcomputergeneratorforrandomlylayeredstructuresYUJia shun1,2,HEZhen hua2(1.TheInstituteofGeologicalandNuclearSciences,NewZealand;2.StateKeyLaboratoryofOilandGasReservoirGeologyandExploitation,ChengduUniversityofTechnology,China)Abstract:Analgorithmisintrod…     

An Index mechanism for multi-scale view in spatial databases

There are numerous geometric objects stored in the spatial databases. An importance function in a spatial database is that users can browse the geometric objects as a map efficiently. Thus the spatial database should display the geometric objects users concern about swiftly onto the display window. This process includes two operations:retrieve data from database and then draw them onto screen. Accordingly, to improve the efficiency, we should try to reduce time of both retrieving object and displaying them. The former can be achieved with the aid of spatial index such as R-tree, the latter require to simplify the objects. Simplification means that objects are shown with sufficient but not with unnecessary detail which depend on the scale of browse. So the major problem is how to retrieve data at different detail level efficiently. This paper introduces the implementation of a multi-scale index in the spatial database SISP (Spatial Information Shared Platform) which is generalized from R-tree. The difference between the generalization and the R-tree lies on two facets: One is that every node and geometric object in the generalization is assigned with a importance value which denote the importance of them, and every vertex in the objects are assigned with a importance value,too. The importance value can be use to decide which data should be retrieve from disk in a query. The other difference is that geometric objects in the generalization are divided into one or more sub-blocks, and vertexes are total ordered by their importance value. With the help of the generalized R-tree, one can easily retrieve data at different detail levels.Some experiments are performed on real-life data to evaluate the performance of solutions that separately use normal spatial index and multi-scale spatial index. The results show that the solution using multi-scale index in SISP is satisfying.     

海南岛地体及其毗邻陆缘晚中生代—新生代古地磁研究和构造演化

本文叙述了对海南岛及其毗邻大陆边缘白垩纪到第四纪地层岩石进行古地磁研究的全部工作过程。通过分析岩石中剩余磁矢量的磁偏角及磁倾角的变化,提出海南岛白垩纪以来经历的构造演化模式如下:早期伴随顺时针旋转而向南迁移,后期伴随逆时针转动并向北运移。联系该地区及邻区的地质、地球物理资料,对海南岛上述的构造地体运动提出以下认识:北部湾内早期有一拉张作用,主要是该作用使湾内地壳显著伸长减薄,形成北部湾盆地。从而导致了海南岛的早期构造运动,而海南岛后期的构造运动则主要是受南海海底扩张的影响。海南地体运动规律的阐明对于了解北部湾油气盆地的形成演化有重要的理论和实际意义。     

Exciton Seebeck in Molecular Systems

Various applications relevant to the exciton dynamics,such as the organic solar cell,the large-area organic light-emitting diodes and the thermoelectricity,are operating under temperature gradient.The potential abnormal behavior of the exicton dynamics driven by the temperature difference may affect the efficiency and performance of the corresponding devices.In the above situations,the exciton dynamics under temperature difference is mixed with     

Achieving Unusual States of Matter Under High Pressure

The elongation method,originally proposed by Imamura was further developed for many years in our group.As a method towards O(N)with high efficiency and high accuracy for any dimensional systems.This treatment designed for one-dimensional(ID)polymers is now available for three-dimensional(3D)systems,but geometry optimization is now possible only for 1D-systems.As an approach toward post-Hartree-Fock,it was also extended to     

《Chinese Science Bulletin》SUBJECT INDEX TO VOLUME 59(2014)

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An on-line scaling method for improving scalability of a database cluster

The explosive growth of the Internet and database applications has driven database to be more scalable and available, and able to support on-line scaling without interrupting service. To support more client's queries without downtime and degrading the response time, more nodes have to be scaled up while the database is running. This paper presents the overview of scalable and available database that satisfies the above characteristics. And we propose a novel on-line scaling method. Our method improves the existing on-line scaling method for fast response time and higher throughputs. Our proposed method reduces unnecessary network use, i.e. , we decrease the number of data copy by reusing the backup data. Also, our on-line scaling operation can be processed parallel by selecting adequate nodes as new node. Our performance study shows that our method results in significant reduction in data copy time.     

An improved R-tree based on childnode''s probability

R-Tree is a good structure for spatial searching. But in this indexing structure,either the sequence of nodes in the same level or sequence of traveling these nodes when queries are made is random. Since the possibility that the object appears in different MBR which have the same parents node is different, if we make the subnode who has the most possibility be traveled first, the time cost will be decreased in most of the cases. In some case, the possibility of a point belong to a rectangle will shows direct proportion with the size of the rectangle. But this conclusion is based on an assumption that the objects are symmetrically distributing in the area and this assumption is not always coming into existence. Now we found a more direct parameter to scale the possibility and made a little change on the structure of R-tree, to increase the possibility of founding the satisfying answer in the front sub trees. We names this structure probability based arranged R-tree (PBAR-tree).     

Integrating GIS Web services based on mediating architecture

The geographic information service is enabled by the advancements in general Web service technology and the focused efforts of the OGC in defining XML-based Web GIS service. Based on these models, this paper addresses the issue of services chaining,the process of combining or pipelining results from several interoperable GIS Web Services to create a customized solution. This paper presents a mediated chaining architecture in which a specific service takes responsibility for performing the process that describes a service chain. We designed the Spatial Information Process Language (SIPL) for dynamic modeling and describing the service chain, also a prototype of the Spatial Information Process Execution Engine (SIPEE) is implemented for executing processes written in SIPL. Discussion of measures to improve the functionality and performance of such system will be included.