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采用三维有限元法对陆水蒲圻宽缝重力坝闸墩尾墩纵缝下端出现的裂缝进行了分析计算。利用混凝土单元的开裂特性来模拟闸墩的开裂,结果表明裂缝是由温度荷载、水荷载及坝体本身自重的共同作用造成的,在现有荷载状况下,闸墩裂缝有进一步发展的趋势。因此提出了粘贴钢板的加固处理措施,结果表明能有效控制混凝土的进一步开裂;同时对钢板的布置进行了优化分析,得出加固处理优化方案。 相似文献
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混凝土结构裂缝成因复杂,年代已久的水利枢纽工程混凝土裂缝处理更为繁琐,因此,选择经济、合理、适用的处理方案极为重要.陆水蒲圻水利枢纽运行30多年后,主坝闸墩中部原垂直永久缝下端开裂,裂缝向下延伸至溢流面.经检测,裂缝贯穿闸墩,并有继续发展趋势.通过计算分析,经多方案比较,采用了粘贴钢板方案进行加固处理.简要介绍了陆水主坝闸墩裂缝粘钢板加固施工过程,对类似工程缺陷处理具有借鉴作用. 相似文献
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以江西省某水电枢纽工程为例,基于abaqus有限元分析软件,采用弹塑性本构分析模型,对4种不同工况下的闸墩受力情况进行了分析,结果表明:当闸墩在自重应力和静水压力作用情况下,所承受的应力—应变值大致接近;当闸门关闭后,在牛腿附近产生较为明显的高拉应力区,超过了混凝土的抗拉强度极限,导致混凝土开裂,需及时采取措施对闸墩进行加固,防止闸墩裂缝宽展和延伸进而导致结构的整体破坏;根据分析结果,提出闸墩采取粘贴钢板+裂缝环氧灌浆的加固补强方案,并对加固后的效果进行了模拟分析,论证加固方案的合理性。 相似文献
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水闸普遍存在着可见和不可见的裂缝,带裂缝工作是水闸的常态,当受到寒潮的影响时,已有的细微裂缝会连通、扩展,甚至贯穿整个闸墩,严重影响结构的安全性和耐久性。扩展有限元法(XFEM)通过富集非连续位移模式,使得非连续位移场的表征独立于单元边界,可有效描述混凝土中的裂纹扩展。基于XFEM并结合热力耦合,研究了水闸在不同初始温度下,遭遇不同降温幅度及历时的寒潮作用时的渐进开裂破坏过程,并与某实际工程的开裂情况进行对比,数值模拟结果与现场情况基本吻合。研究结果表明,水闸遭遇寒潮时,靠近闸墩表面的温度与外界温度变化基本一致,靠近闸墩中心的温度变化较小,闸墩内外温差随着寒潮强度的增强而增大;闸墩混凝土的内表温差和约束是导致闸墩开裂的根本原因;裂缝分布在上下游墩头与底板相交的位置,随着寒潮强度的增强,裂缝与底板的夹角、长度及深度也随之增大,对水闸结构的不利影响也越大。因此,寒潮来临时应做好安全监测及混凝土防护工作,控制闸墩的温降以防止裂缝的开展。 相似文献
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闸墩开裂是水闸建设的关键问题之一,为了分析闸墩开裂的真正原因,找出具有针对性的加固措施,采用全过程仿真粘弹性空间有限单元法,对混凝土闸墩浇筑过程的因素进行了敏感分析,共计算了7个闸墩长度、7个闸墩厚度、3种地基情况下的全部应力分量,计算结果表明闸墩的长度、厚度和地基情况对闸墩应力均有一定的影响,但闸墩长度不是闸墩温度应力的控制因素。在岩石地基上,当闸墩厚度超过2.0 m时,第一温度主应力超过混凝土的抗拉强度,温度应力成为控制闸墩开裂的绝对关键因素;在岩土地基上闸墩的开裂不仅仅只是由温度应力引起的,其它因素如外加荷载和地基的不均匀变形等也起很大的作用。 相似文献
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应用三维有限元方法对太平哨水电站溢流坝闸墩竖向开裂的原因进行数值分析,计算中主要考虑了温度作用、静水压力、自重及冰压力的影响。通过对裂缝实际发生位置的应力变化规律进行分析,发现大坝在正常挡水情况下,冰压力对闸墩应力的影响很小,不足以使闸墩混凝土开裂;冬季温降荷载对闸墩应力影响很大,很多典型位置拉应力已经超过混凝土抗拉极限值,从而认为温度荷载是闸墩出现裂缝的主要因素。 相似文献
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木兰溪江东水闸闸墩0~2. 6 m高程混凝土浇筑后,出现了细微竖向裂缝。该文通过分析混凝土裂缝成因,从混凝土材料和混凝土施工养护等两方面提出预防措施,闸墩后续2. 6~8. 0 m高程混凝土浇筑后未再出现裂缝。采用裂缝内部化学灌浆补强加固结合表面涂刷单组份聚脲柔性涂层封闭的处理方法进行裂缝修补,恢复了结构混凝土的整体性,提高了水闸闸墩混凝土的耐久性。混凝土裂缝预防及处理措施可供类似工程参考。 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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Samples were taken year-round at eleven sites along the altitudinal profile (2900-1400 m a.s.l.) of the Gunnison River, a 329 km tributary of the Colorado River, to document the distribution of the Plecoptera and to evaluate responses to hypolimnial-release dams in the headwaters and middle reaches. Twenty-two species were present, with the greatest species richness occurring in an unregulated segment upstream of the middle reach dams; average nymphal biomass over the study period (175 organisms, 395 mg dry mass m?2) was also greatest in this segment. Only four species (58 organisms, 48 mg m?2) were present in the tailwaters of the headwater dam and values were greatly reduced (nine species; 35 organisms, 180 mg m?2) below the middle reach dams. The stonefly community recovered ca. 80 km downstream from the last dam (15 species; 244 organisms, 250 mg m?2), apparently in response to natural resetting of environmental conditions corresponding to those above the middle reach dams. At the most downstream site (11) only four species (four organisms, 16 mg m?2) were present. The observed distributional pattern is a classic serial discontinuity in response to hypolimnial stream regulation in a temperate latitude river. 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