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基于起裂韧度扩展准则和黏聚裂缝模型研究混凝土断裂全过程中的裂缝尖端黏聚区特性;利用不同尺寸的带裂缝三点弯曲梁试件,计算得到了裂缝尖端黏聚区的长度、黏聚力、裂缝张开位移等,并采用现有试验成果和有限元方法计算成果对本文结果进行了验证。分析结果表明:最大黏聚区长度以及峰值时刻对应的临界黏聚区长度随试件尺寸增大而逐渐增大,最大黏聚区长度受拉伸软化曲线影响;裂缝断裂全过程曲线受软化曲线影响较小;当外荷载达到峰值后裂缝张开位移近似为线性分布,黏聚力分布受拉伸软化曲线影响较大。 相似文献
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三点弯曲下的钢纤维高强混凝土断裂能 总被引:2,自引:0,他引:2
通过100个尺寸为100mm×100mm×515mm的不同体积率的钢纤维高强混凝土切口梁三点弯曲试验,探讨了钢纤维体积率和裂缝相对切口深度对高强混凝土断裂能和作用力功的影响。结果表明,钢纤维改善了高强混凝土的断裂性能与延性。钢纤维高强混凝土断裂能增益比、作用力功增益比以及延性指数随着钢纤维体积率的增加而线性增加,随着切口深度的增加而降低;外力功对断裂能的大小起较大作用。在分析试验结果的基础上,建立了钢纤维高强混凝土作用力功和断裂能的计算公式。 相似文献
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试件初始缝长对混凝土双K断裂参数的影响 总被引:1,自引:1,他引:1
本文采用尺寸为400mm×400mm×200mm,初始缝高比分别为0.2、0.4、0.5、0.6的楔入劈拉试件,应用线性渐近叠加原理,利用试验中测得的最大荷载Pmax及对应的裂缝口张开位移CMODc计算了混凝土裂缝的亚临界扩展量Δαc,在此基础上利用虚拟裂缝模型并结合线弹性断裂理论,采用不同的闭合力方程计算了混凝土起裂断裂韧度KiniIc、失稳断裂韧度KunIc及临界裂缝尖端张开位移CTODc.结果表明,采用不同闭合力方程所计算的混凝土KiniIc值有所差异,但当试件缝高比大于或等于0.4时KiniIc及CTODc均与试件初始缝高比无关,而KunIc值则与初始缝高比无关,这表明双K断裂参数及CTODc可以作为描述混凝土裂缝起裂、稳定扩展及失稳破坏全过程的材料常数。 相似文献
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为研究自密实轻骨料混凝土的断裂特性,引入以起裂断裂韧度为参数的裂缝扩展准则,采用数值方法分析了自密实轻骨料混凝土三点弯曲梁裂缝扩展的全过程,得到了不同缝高比的自密实轻骨料混凝土梁在三点荷载下的荷载-裂缝口张开位移曲线,并根据裂缝扩展准则,计算了自密实轻骨料混凝土的断裂过程区长度和裂缝扩展阻力曲线。结果表明:试验和计算的荷载-裂缝口张开位移曲线吻合良好,验证了裂缝扩展准则的正确性;试验断裂过程区长度随着裂缝增长先增大,达到完整断裂过程区长度后减小;自密实轻骨料混凝土的裂缝阻力随着裂缝长度增加而不断增大,初始缝高比对裂缝扩展阻力曲线数值和形状的影响并不明显。 相似文献
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混凝土Ⅰ型裂缝扩展准则及裂缝扩展全过程的数值模拟 总被引:4,自引:1,他引:3
本文将起裂断裂韧度作为材料参数,提出了混凝土Ⅰ型裂缝扩展准则,即当外荷载引起的裂缝尖端应力强度因子与黏聚力引起的裂缝尖端应力强度因子的差值达到起裂断裂韧度时,裂缝开始扩展。在此基础,上采用有限元法对混凝土Ⅰ型裂缝的断裂过程进行了数值模拟,分别计算了不同尺寸混凝土试件的荷载-裂缝口张开位移全曲线、临界裂缝亚临界扩展量、失稳断裂韧度并与应用DIANA软件的数值分析结果及试验结果进行了比较,吻合良好。研究还表明,只要给出混凝土的弹性模量、抗拉强度和起裂断裂韧度,即可用本文提出的方法计算混凝土失稳断裂韧度及裂缝扩展全过程。 相似文献
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混凝土裂缝的稳定扩展过程与临界裂缝尖端张开位移 总被引:18,自引:4,他引:14
本文采用激光散斑照像法并辅以电测法研究观察了2种不同尺寸的混凝土切口梁失稳断裂前微裂缝生成、聚合直到主裂缝发生缓慢的亚临界扩展的全过程以及相应的变形特征和应变场分布。结果表明,混凝土切口梁失稳断裂前存在着明显的主裂缝亚临界扩展过程,其断裂过程区呈不规则的狭长带状形,最大宽度约为最大骨料粒径的1/2。断裂过程区的性状与Dugdale-Barenblatt模型基本相符,因而采用由此衍生发展起来的虚拟裂缝模型和“疵弥”裂缝带方法进行混凝土断裂的数值分析是可行而合理的。实验还表明,在实验范围内临界裂缝尖端张开位移和试件尺寸无关,因而有希望成为判断混凝土失稳断裂的材料参数。 相似文献
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试件初始缝长对混凝民裂参数的影响 总被引:8,自引:2,他引:8
本文采用尺寸为 40 0mm× 40 0mm× 2 0 0mm ,初始缝高比分别为 0 2、 0 4、 0 5、 0 6的楔入劈拉试件 ,应用线性渐近叠加原理 ,利用试验中测得的最大荷载Pmax及对应的裂缝口张开位移CMODc 计算了混凝土裂缝的亚临界扩展量Δac,在此基础上利用虚拟裂缝模型并结合线弹性断裂理论 ,采用不同的闭合力方程计算了混凝土起裂断裂韧度KiniIc、失稳断裂韧度KunIc及临界裂缝尖端张开位移CTODc.结果表明 ,采用不同闭合力方程所计算的混凝土KiniIc值有所差异 ,但当试件缝高比大于或等于 0 4时KiniIc及CTODc 均与试件初始缝高比无关 ,而KunIc值则与初始缝高比无关 ,这表明双K断裂参数及CTODc 可以作为描述混凝土裂缝起裂、稳定扩展及失稳破坏全过程的材料常数 . 相似文献
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混凝土结构在未使用之前往往已经存在裂缝,在外荷载作用下,混凝土内部微裂缝会不断产生、扩展,成为混凝土破坏的根源,因此有必要计算混凝土已有裂缝口的张开位移。应用基于能量理论的裂缝扩展准则和虚拟裂缝模型,通过编程来模拟混凝土梁混合裂缝的扩展,对于混凝土梁裂缝口张开位移的计算是有效的;切口深度增大时,裂缝口张开位移增大;弹性模量增大时,裂缝口张开位移减小,混凝土的抗裂性能得到加强。 相似文献
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根据冗各电站地下厂房开挖支护的施工顺序,以隐式杆单元模拟锚杆,以壳单元模拟混凝土喷层,采用三维非线性有限元技术,对洞室群的开挖支护动态过程进行了模拟计算。通过三维非线性有限元计算分析得到:洞室群动态开挖过程中围岩应力变形的分布规律,围岩塑性区的发展规律,锚杆受力变化情况。计算结果表明:整个开挖过程中,洞周围岩位移变化规律正常,量值较小,塑性区主要分布在洞室周边,围岩稳定性较好;但在洞室交叉口处围岩的变形较大,出现较大范围的塑性区,在此基础上提出了支护措施优化方案,并对优化方案的效果进行了评价。 相似文献
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The relocation of unionacean mussels is commonly used as a conservation and management tool in large rivers and streams. Relocation has been used to recolonize areas where mussel populations have been eliminated by prior pollution events, to remove mussels from construction zones and to re-establish populations of endangered species. More recently, relocation has been used to protect native freshwater mussels from colonization by the exotic zebra mussel Dreissena polymorpha. We conducted a literature review of mussel relocations and evaluated their relative success as a conservation and management strategy. We found that 43% of all relocations were conducted because of construction projects that were forced to comply with the Endangered Species Act 1973 and that only 16% were monitored for five or more consecutive years. Most (43%) relocation projects were conducted from July to September, presumably a period when reproductive stress is relatively low for most species and the metabolic rate is sufficient for reburrowing in the substrate. The mortality of relocated mussels was unreported in 27% of projects; reported mortality varied widely among projects and species and was difficult to assess. The mean mortality of relocated mussels was 49% based on an average recovery rate of 43%. There is little guidance on the methods for relocation or for monitoring the subsequent long-term status of relocated mussels. Based on this evaluation, research is needed to develop criteria for selecting a suitable relocation site and to establish appropriate methods and guidelines for conducting relocation projects. 相似文献
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In the lower River Murray, Australia, populations of gastropods have declined markedly over the past 40 years. Of the native fauna of about 18 species, only the ancylid Ferrissia petterdi remains common (but in patches), and another five species feature in sporadic local resurgences. Until recently the viviparid Notopala was thought to be extinct. The introduced physid Physa acuta is widespread, but in low numbers. The decline probably is associated with flow regulation, high turbidity and the introduction of common carp. Snail populations have persisted, however, in irrigation pipelines fed from the river, where they periodically cause blockages. This paper reports the discovery of the only known populaion of Notopala hanleyi in a pipeline where the inner wall accumulates microbial and other organic matter, providing high quality food for snails. In the Murray before regulation most of the periphytic biomass was probably microbial, as fluctuating water levels would have maintained littoral communities in a highly productive, early state of succession his postulated that, by stabilizing seasonal water levels, regulation has promoted the production of filamentous green algae, an inferior food source, and so displaced snail populations from the open aquatic environment. 相似文献
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V. K. Konovalov O. V. Yashkin V. V. Ermakov 《Power Technology and Engineering (formerly Hydrotechnical Construction)》2008,42(2):105-109
A system for removal and pneumatic transport of fly ash is examined, in which air pulses act on batches (pistons) of ash formed
in a duct. Studies are made of the effect of several physical parameters on the force required to displace a piston of ash
and these serve as a basis for choosing a system for removal and pneumatic transport of ash simultaneously from several hoppers
of an electric precipitator. This makes it possible to separate the ash particles according to size without introducing additional
components. Formulas are given for calculating the structural and dynamic parameters of this system and measurements of indirect
dynamic parameters are used to calculate the input-output characteristics of the system. In order to optimize the system,
configurations for summing several ducts into a single transport duct for pneumatic ash transport are proposed. Some variants
of dry ash utilization and the advantages of producing of size-separated particles are considered.
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Translated from élektricheskie Stantsii, No. 2, pp. 26–30 (2008). 相似文献
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Peter B. Bayley 《河流研究与利用》1991,6(2):75-86
The ‘flood pulse advantage’ is the amount by which fish yield per unit mean water area is increased by a natural, predictable flood pulse. Evidence for this increase is presented from tropical and temperate fisheries. It is argued that increasing multispecies fish yield by restoring the natural hydrological regime is consistent with increasing production of other trophic levels and with restoration from ecological and aesthetic viewpoints. When applied to a river-floodplain system, this restoration would provide a large, self-sustaining potential for recreation, commercial exploitation, and flood control. An interim ‘natural flood pulse’ restoration approach is proposed for systems modified for navigation. This approach approximates the natural hydrological regime in a river reach and is intended as a first step in the long process of restoring the watershed. 相似文献
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简述天湖水电站投运以来各种故障的表现形式,分析其原因,提出了相应的处理方法及措施,并对合理利用国内外设备提出建议。 相似文献