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281.
就服从非关联流动法则软化型砂的临界状态本构模型,在不同应力路径下的分叉进行了理论和数值分析。理论分析表明:分叉现象强烈依赖于应力路径,即当平均应力p一定时,应力路径在洛德角在-25o~15o之间时,均会在应力-应变关系硬化阶段出现分叉现象,而其他应力路径下不会产生分叉。并且分叉时对应的应力比、主应变及剪切带倾角都随洛德角的增加而变化,其值是先增加而后减小。采用回映应力更新算法,编写了该本构模型材料子程序,借助有限元软件ABAQUS及材料子程序,通过数值计算方法预测到了分叉点所对应的应力状态,表明了分叉现象在数值计算中的存在性,并通过数值预测值和理论解的对比,两者结果基本一致。 相似文献
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283.
上埋式钢筋混凝土拱涵受力特性及地基处理研究 总被引:1,自引:0,他引:1
涵洞属于填埋式构造物,其受力状态不同于普通建筑物。对涵-土体系作用机制认识不足和涵洞地基处理不当可能导致涵洞出现各种各样的病害,甚至影响道路运营。通过现场测试和数值模拟分析了上埋式钢筋混凝土拱涵结构与土体的作用机制,得出了涵-土体系的受力状态和变形特性。在此基础上对涵洞地基处理进行了研究,分析了地基处理的宽度、深度以及处理后的地基刚度对涵洞受力状态和变形特性的影响。研究结果表明,涵顶存在明显的应力集中现象,该效应的影响范围为涵洞两侧约3b(b为涵洞宽度);涵顶土压力系数随填土高度的增大而增大,并逐渐趋于稳定;涵顶土压力、基底压力和涵洞结构内力随地基处理宽度的增大而减小,并逐渐趋于稳定,随地基处理深度和地基弹性模量的增加呈非线性增大。实际工程中,涵洞地基处理宽度宜取b+2h(h为涵洞高度)左右,地基处理的深度和处理后的刚度应以允许沉降或差异沉降为控制指标,不应额外增加地基处理深度和提高地基刚度 相似文献
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285.
辽东湾北部浅海区底泥镉元素形态特征 总被引:1,自引:0,他引:1
依据辽东湾浅海区底泥的52件样品中镉元素全量和各形态的测试数据,研究了镉元素存在形态的分布特征和相关性,并探讨了底泥镉形态的环境因素和生态效应.结果表明,底泥中的镉含量为较高水平,非残渣态含量极高,占总量的90%.非残渣态镉主要为离子交换态(44.38%)和碳酸盐结合态(21.38%).镉的全量与各种形态都有极显著的相关性,并且分布特征一致,最高样点都分布在锦州湾.底泥镉的各种形态与底泥的有机质和海水环境中镉存在显著的相关性.底泥的离子交换态镉与脉红螺的镉有正相关关系. 相似文献
286.
EXPERIMENTAL STUDY OF TEMPERATURE EVOLUTION AND IDENTIFICATION OF INSTABILITY POSITION OF PLANAR STRIKE-SLIP FAULT DURING PROCESS OF STICK-SLIP 下载免费PDF全文
Stick-slip of fault in laboratory accompanies change of temperature. Temperature change is not only concerned with sliding friction, but also with the stress state of the sample. In this article, we use infra-red thermal imaging system as wide-range observation means to study the temperature variation of different stages during the deformation of sample. The rock sample for the experiment is made of granodiorite from Fangshan County with a size of 300mm×300mm×50mm. It is cut obliquely at an angle of 45°, forming a planar fault. Two-direction servo-control system was used to apply load on the sample. The load in both directions was forced to 5MPa and maintained constant (5MPa) in the X direction, then the load in the Y direction was applied by a displacement rate of 0.5μm/s, 0.1μm/s and 0.05μm/s successively. The left and below lateral of the sample were fixed, and the right and top lateral of the sample were slidable when loaded. The experiment results show not only the temperature change from increase to decrease caused by conversion of stress accumulation to relaxation before and after the peak stress, but also opposite variation of temperature increase on fault and temperature decrease in rock during instability stage. Most important of all, we have found the temperature precursor identifying the position of instability through the temperature variation with time along the fault. It shows that rate of temperature increase of instability position keeps relative high value since the stage of strongly off-linear stage, and accelerates in stage of meta-instability. After separating the effect of friction and stress, we found that temperature increase occurs in the rock near the fault instead of on the fault, which means the mechanism of temperature increase is stress accumulation. Temperature of fault at the instability position does not increase, which means the position is locked. We speculate that the position of locked area on fault with high stress accumulation near the fault may be the future instability position. It is of significance of studying temperature variation during stick-slip to the monitoring of earthquake precursors. Heat caused by friction of earthquake needs long time to transfer to the surface and could not be detected as a precursor. While the stress of surface rock near the fault would change as the stress of interior rock changes, which could cause detectable temperature variations. The research purpose of this article is to find special change positions before instability. As the temperature variations are caused by stress and slip of fault, the results are also meaningful to analysis of stress and displacement data related to earthquake precursors. 相似文献
287.
GIS中的时空数据模型研究 总被引:6,自引:3,他引:3
状态与事件是时态地理信息系统(TemporalGIS ,TGIS)的一对基本概念,目前时空数据模型研究侧重于将两个概念相分离,表现为基于状态模型和基于事件模型,无法兼顾两种模型的优点。本文提出了基于状态-事件的时空数据模型,并系统阐述各时空数据模型之间的相互转换条件。 相似文献
288.
Jennifer L. Rice 《The Professional geographer》2013,65(2):333-344
A survey of local governments participating in two urban climate change programs is presented to determine the mechanisms used to reach emissions reduction goals and the motivations for participation. Results support previous research that shows a preference for policies that rely on changes in individual behavior, while also providing new insights into how mitigation responsibilities are distributed among the public and private sector and the relative importance of scientific consensus, economic incentives, and federal inaction on local government justification for climate-related policies. The article concludes with a discussion of urban climate governance as part of a wider system of neoliberal climate governance. 相似文献
289.
Data resources and assessment frameworks are two keys to ecosystem health assessment (EHA). Application of the land use database together with the Pressure–State–Response (PSR) model in EHA provides better precision relative to traditional data resources and assessment frameworks for EHA at the county scale. The raw data are taken from The Anlu County Annals, The Soil Records of Anlu County, and The Statistical Yearbook of National Economy in Anlu County. The spatial and attribute data are partly extracted from the database of current land use in Anlu City using the MAPGIS platform. Based on the results from principal component analysis (PCA), a total of eleven indicators were selected to build an indicator system designed to assess the ecosystem health at the county scale. According to the PSR model, the scores from three indices (press index, state index, and response index) and a comprehensive assessment index (CAI) were calculated, and an assessment map was constructed. The results from the index scores and spatial analysis display a large range for the state of ecosystem health due to the evolution of natural ecosystems and human activities at the county scale. The precision of the current land use database (scale of 1:10,000) makes it a better candidate for evaluating ecosystem health than the traditional data resources. This study also demonstrates the numerous benefits of combining land use databases with GIS functions to assess ecosystem health at the county scale. 相似文献
290.
Abstract This paper explores the dynamics behind the changing regimes of urban renewal and its social impacts in Taiwan. Before the 1980s, the state was willing to solely shoulder the job of urban renewal with a wholly supportive financial budget and land appropriation law, while in the 1990s it became financially overburdened due to its renewal policy. Around the year 2000, the state turned towards promoting urban regeneration as a key business model. Through this historical exposition, the Taiwanese story of state transformation in urban renewal policy brings two issues to the fore. The first issue is the learning process concerning the policy of public-private partnership (PPP) initiatives. Trans-border policy mobility connects and constitutes cities, such as Taipei, with other places, such as London, through visits and seminars attended by policy makers and experts. However, policy transferred from abroad is “localized” in the learning process and used to prioritize the regeneration of public lands in the urban area. The PPP model is transformed in the face of domestic political struggles. The second issue is the social exclusion as a result of property-led regeneration. Rather than playing the role of an impartial institutional moderator, the state privileged landowners and developers and sacrificed the rights of tenants to stay put. By doing so, the state secures political support from landowner-cum-citizens and initiates a political culture of property in which local citizenship is predicated on ownership. 相似文献