入模温度对框架桥温度场及应力场的影响

为了控制混凝土浇筑后所产生大量的水化热量,消散混凝土内部聚集的热量,采用数值模拟的方法,设置4种不同的工况,来分析入模温度对框架桥温度场及应力场的影响,并结合现场试验进行论证。结果表明:入模温度直接制约了由水化热导致的混凝土内部的最高温度。底板处受影响最大,入模温度平均每升高5℃,养护期底板处混凝土最高温度就升高2.4℃;顶板处受影响最小,入模温度平均每升高5℃,养护期顶板处混凝土最高温度升高1℃。当入模温度降低时,温度峰值向后偏移,温度区间延长,有利于水化热量及应力释放,减小温差,减少裂缝,达到控制裂缝的目的。     

混凝土水化热对井筒外壁受力变形影响分析

为了解决深厚冲积层冻结井筒外壁易产生环向裂缝难题,以杨村煤矿主井冻结段外壁为研究对象,采用现场实测、理论分析和实验室试验相结合的方法,进行了混凝土水化热对外壁受力变形影响分析.研究结果表明,在外壁混凝土入模后,受水泥水化放热反应的影响,混凝土温度快速上升,外壁峰值温度高达55.5℃.随后又开始降温,混凝土产生收缩,由于...     

大体积混凝土墙水化放热温度场分析

为有效进行大体积混凝土施工温度控制，对大体积混凝土施工过程中温度场分布规律进行研究．针对混凝土水化放热过程中内热源随时间变化的问题，采用杜哈美尔定理推导出第三类边界条件下大体积混凝土墙水化放热温度场的解析解．由大体积混凝土墙水化放热温度场解析解可知，混凝土水化放热过程中，混凝土内某一点温度随时间增加先增大后减小，且温度变化近似符合指数函数之和；某一时刻混凝土内温度从核心到表面逐渐降低，且温度分布近似符合三角函数．结合解析解与数值分析方法研究发现，随着混凝土厚度、入模温度、混凝土绝热温升和单方胶凝材料对应系数的增大，混凝土养护阶段核心最高温度升高，导致混凝土里表温差增大；随着表面传热系数增加，混凝土养护阶段核心最高温度和表面温度降低，但是混凝土里表温差增大．混凝土内最大自约束应力正比于里表温差，因此通过分层浇筑、降低混凝土的入模温度、减小混凝土表面传热系数、降低混凝土绝热温升值和单方胶凝材料对应系数等方式可以减小混凝土内最大自约束应力，降低大体积混凝土开裂风险．     

温度变化下围岩参数对隧洞喷层结构温度和应力的影响

在高地温环境下,地下洞室气温及围岩温度的变化会导致围岩应力、混凝土喷层温度和应力的改变,为了研究围岩参数随温度变化时对混凝土喷层温度和应力的影响,结合新疆某电站引水隧洞工程,研究高地温对围岩力学参数的影响,分析围岩参数随温度变化时对混凝土喷层温度和应力的影响机制,分别对围岩和喷层的热力学参数随温度变化时对喷层的温度和应力的影响进行了分析。研究结果表明,当温度从20℃升高至100℃时,围岩弹模、比热、导热系数和线膨胀系数随温度变化时对喷层应力影响不超过5%;混凝土弹模、比热、导热系数和线膨胀系数参数随温度变化时对喷层受力影响不超过5%,温度升高对喷层应力的影响较小。该问题的研究,为高地温区围岩喷层结构的设计和施工中采取合理的温控措施提供了理论依据。     

高速铁路T构桥墩顶块水化热效应控制和浇筑方案优化

T构桥墩顶块具有混凝土体积大、应力状态复杂等特点,有效控制混凝土浇筑时的水化热效应是保障全桥工程质量的关键。依托渝黔高铁石梁河特大桥主桥墩顶块混凝土施工,采用数值仿真和现场监测的方法,研究一次性浇筑方案的可行性,对比不同措施对混凝土水化热效应的控制效果,提出墩顶块混凝土浇筑优化方案并应用于实桥施工。提出石梁河大桥墩顶块优化浇筑方案。研究结果表明：原定一次性浇筑方案由于混凝土浇筑体积过大、所采取的降温散热措施很少,导致混凝土水化热温度峰值、最大内表温差和名义拉应力均大幅超出规范限值,不具可行性;分层浇筑、埋设冷却水管是缓解混凝土整体水化热效应的关键措施,调整混凝土入模温度是控制水化热温度峰值和内表温差的重要措施;表面热交换系数与混凝土养护覆盖措施密切相关,对混凝土内表温差有显著影响;所提出的石梁河大桥墩顶块优化浇筑方案为分两层浇筑+底板埋设冷却水管+混凝土入模温度调整至15℃+混凝土表面采用6 mm厚钢板+2 cm厚聚乙烯泡沫覆盖,采用该方案进行现场施工,实测混凝土水化热温度峰值为58℃,最大内表温差22.74℃,最大表面名义拉应力为1.76 MPa,均小于规范限值,说明混凝土水化热效应...     

大体积混凝土施工裂缝控制技术

分析研究了大体积混凝土裂缝的成因,提出了优选混凝土原材料、降低水泥水化热、减小混凝土收缩变形;削减温度应力,提高混凝土极限拉伸强度;降低混凝土骨料温度、入模温度、浇筑温度,加强测温工作控制内外温差;掺外加剂和外掺料,主动控制混凝土绝热温升等施工防裂技术措施,结合工程实例探讨了大体积混凝土施工裂缝控制技术。     

风环境对大体积混凝土桥塔施工水化热的影响分析

采用数值模拟结合现场监测的方法研究了复杂风环境对跨江、跨海大桥大体积混凝土桥塔施工水化热的影响.首先,提出了风环境下混凝土水化热的理论计算方法,并基于实际背景工程考虑风环境,对大体积混凝土桥塔施工过程中的水化热效应进行数值模拟;然后,利用现场实际监测数据,对模拟的准确性进行验证;最后,利用此数值模型,针对风特征及结构参数进行分析.分析结果表明:环境平均风速增大会使混凝土桥塔节段内的水化热温度极值降低,但其表面温度梯度增加,开裂可能性也相应增大;结构尺寸的增大会削弱风环境对混凝土水化热的影响,但由尺寸增大引起的刚度增加会导致水化热最大主拉应力明显增大,从而引起混凝土开裂;同一风环境下,桥塔截面形式的改变对浇筑过程中结构内部温度梯度、极值分布以及主应力大小影响明显.     

地下室底板大体积混凝土裂缝的原因及控制措施

为了确保地下室底板大体积混凝土的浇筑质量,增强混凝土密实度,防止有害裂缝的产生与发展,改善结构抗渗防水能力,必须从各个环节着手,制定行之有效的具体措施。实践证明降低水化热、掺加膨胀剂、控制混凝土的入模温度、分段和分层施工、采取养护措施、温度监测措施等,编制科学的施工方案,可以控制混凝土裂缝的产生。     

考虑水化度对热学参数影响的早期混凝土温度场分析

为了更加准确地模拟早期混凝土的温度场,通过试验研究了早期混凝土温度的变化规律,同时基于ABAQUS二次开发平台,考虑早期混凝土热学参数(导热系数和比热容)随水化度的变化规律,开发了温度场子程序UMATHT和用于模拟温度场第3类边界条件的FILM子程序.在此基础上,采用不同的温度场计算模型对试验进行数值模拟,通过实验结果与数值模拟结果的对比得出:考虑比热容及导热系数随水化度的变化过程,数值模拟结果与实测值基本一致,最大误差控制在1.5%以内,达到温度峰值的时间误差控制在0.5 h以内;当不考虑这2个参数随水化过程的变化,数值模拟与实测值存在较大误差,峰值温度误差均在4.6℃以上,达到峰值温度的时间均延长5 h以上.因此在对早期混凝土的温度场分析时有必要考虑导热系数和比热容随水化度的变化.     

弧形底梯形渠道混凝土衬砌板下温度与气温间的关系研究

基于弧形底梯形渠道混凝土板衬砌冻胀观测试验,分析讨论了气温对衬砌板下温度的影响及其两者间数量关系。研究结果表明:初冻期板下20 cm地温稳定通过0℃,冻结期及融化期内板下20 cm处地温始终小于日平均气温;冻结期内负积温是影响板下温度的最关键因素;大气与土壤间的热量交换值在初冻期、冻结期、融化期依次增大;负积温与板下地温及冻深间均很好地符合二次多项式相关关系。     

Markedness and its Interpretation in Language Use

Language markedness is a common phenomenon in languages, and is reflected from hearing, vision and sense, i.e. the variation in the three aspects such as phonology, morphology and semantics. This paper focuses on the interpretation of markedness in language use following the three perspectives, i.e. pragmatic interpretation, psychological interpretation and cognitive interpretation, with an aim to define the function of markedness.     

Features of Women's language

Language is a means of verbal communication. People use language to communicate with each other. In the society, no two speakers are exactly alike in the way of speaking. Some differences are due to age, gender, statue and personality. Above all, gender is one of the obvious reasons. The writer of this paper tries to describe the features of women＇s language from these perspectives： pronunciation, intonation, diction, subjects, grammar and discourse. From the discussion of the features of women＇s language, more attention should be paid to language use in social context. What＇s more, the linguistic phenomena in a speaking community can be understood more thoroughly.     

低渗透非均质砂岩油藏启动压力梯度研究

理论推导与室内实验相结合,建立了低渗透非均质砂岩油藏启动压力梯度确定方法。首先借助油藏流场与电场相似的原理,推导了非均质砂岩油藏启动压力梯度计算公式。其次基于稳定流实验方法,建立了非均质砂岩油藏启动压力梯度测试方法。结果表明:低渗透非均质砂岩油藏的启动压力梯度确定遵循两个等效原则。平面非均质油藏的启动压力梯度等于各级渗透率段的启动压力梯度关于长度的加权平均;纵向非均质油藏的启动压力梯度等于各渗透率层的启动压力梯度关于渗透率与渗流面积乘积的加权平均。研究成果可用于有效指导低渗透非均质砂岩油藏的合理井距确定,促进该类油藏的高效开发。     

On Tragic Consciousness In The Works By Ernest Hemingway

As an American modern novelist who were famous in the literary world, Hemingway was not a person who always followed the trend but a sharp observer. At the same time, he was a tragedy maestro, he paid great attention on existence, fate and end-result. The dramatis personae's tragedy of his works was an extreme limit by all means tragedy on the meaning of fearless challenge that failed. The beauty of tragedy was not produced on the destruction of life, but now this kind of value was in the impact activity. They performed for the reader about the tragedy on challenging for the limit and the death.     

Achieving Unusual States of Matter Under High Pressure

正The periodicity of the elements and the non-reactivity of the inner-shell electrons are two related principles of chemistry,rooted in the atomic shell structure.Within compounds,Group I elements,for example,invariably assume the+1 oxidation state,and their chemical properties differ completely from those of the p-block elements.These general rules govern our understanding of chemical structures and reactions.Using first principles calcula-     

Exchange-Correlation and Electronic Excitation Energies from Pairing Matrix Fluctuations

We have developed an adiabatic connection to formulate the ground-state exchange-correlation energy in terms of pairing matrix linear fluctuations.This formulation of the exchange-correlation energy opens a new channel for density functional approximations based on the many-body perturbation theory.We illustrate the potential of such approaches with an approximation based on the particle-particle Random Phase Approximation(pp-RPA).This re-     

Density Functional Theory for the Response of Periodic Systems to Electric Fields Based on the Vector Potential Approach

正The electronic and nuclear(structural/vibrational)response of 1D-3D nanoscale systems to electric fields gives rise to a host of optical,mechanical,spectral,etc.properties that are of high theoretical and applied interest.Due to the computational difficulty of treating such large systems it is convenient to model them as infinite and periodic(at least,in first approximation).The fundamental theoretical/computational problem in doing so is that     

On the Thermodynamic Limit for Responses to Static Electromagnetic Fields

For molecular systems,the quantum-mechanical treatment of their responses to static electromagnetic fields usually employs a scalar-potential treatment of the electric field and a vector-potential treatment of the magnetic field.Although the potential for each field separately is associated with the choice of an(unphysical)origin,the precise choice of the origin for the electrostatic field has little consequences for the results.This is different for the     

Call for Papers

<正>"The Journal of Shanghai Normal University:Mathematics"is published by Shanghai Normal University as regular issues of The Journal of Shanghai Normal University each year from 2014 in English.The editors-in-chief of the issues are professors Yuhao Cong and Maoan Han.The Journal of Shanghai Normal University was started in 1958 with     

Journal of Donghua University ( English Edition) Contents of Volume 31

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