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1.
一、荷载引起的裂缝
直接应力裂缝是指外荷载引起的直接应力产生的裂缝,原因有:
1.设计计算阶段,结构计算时不计算或部分漏算;计算模型不合理;结构受力假设与实际受力不符;荷载少算或漏算;内力与配筋计算错误;结构安全系数不够。结构设计时不考虑施工的可能性;设计断面不足;钢筋设置偏少或布置错误;结构刚度不足;构造处理不当:设计图纸交代不清等。 相似文献
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浅谈水库土坝裂缝及渗流稳定的处理措施 总被引:1,自引:0,他引:1
水库土坝裂缝是一种较为常见的现象。一般来说,水库土坝裂缝产生的原因有以下几种:一是因筑坝土料失水干缩而导致的干缩裂缝。这种裂缝大都发生在坝体表面,多呈现不规则分布。二是因坝体和坝基的不均匀沉降而引起的裂缝。这种不均匀沉降产生的裂缝又有三种表现形式:即坝体表面可见的、裂缝呈垂直或斜交于坝轴线的横向裂缝;坝体表面可见的、裂缝走向与坝轴线平行的裂缝;产生于坝体内部、在坝体表面没有明显表现的裂缝(这种内部裂缝是坝体的内部隐患,须通过对土坝变形的长期观测资料进行分析和计算,或者根据蓄水期对土坝渗漏水量和水的浑浊度观测才会得知)。三是因滑坡引起的裂缝。这种因滑坡引起的裂缝对土坝坝体的危害较大,应格外引起重视。 相似文献
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文章介绍了黑尔水库混凝土面板裂缝的情况及分析裂缝产生的原因,即混凝土原材料引起的裂缝、塑性裂缝、温度应力裂缝、干缩裂缝、施工工艺产生的裂缝;通过采用中热硅酸盐水泥降低水泥水化热、掺入粉煤灰改善混凝土和易性并补充细小颗粒、控制混凝土出机入仓和易性;喷洒DH10表面养护剂等措施减少面板混凝土裂缝;裂缝处理的方法,采用LW-水溶性聚氨酯化学灌浆对裂缝进行处理。 相似文献
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介绍了常见的土石坝防渗墙的布置方式,采用应力分析法分析了裂缝产生的原因,指出:防渗墙成槽施工过程中,进入槽段两侧的渗流水引起孔隙水压力上升是造成纵向裂缝的主要原因;布置在坝顶的混凝土防渗墙在施工期容易产生纵向裂缝;出现纵向裂缝或发现泥浆液面急剧下降现象时,在槽孔内回填干土或水泥干土混合物,能有效防止裂缝的延伸和加宽。 相似文献
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混凝土裂缝的预防与处理 总被引:1,自引:0,他引:1
<正>混凝土裂缝产生的原因很多,有变形引起的裂缝,如温度变化、收缩、膨胀等原因引起的裂缝;有养护环境不当和化学作用引起的裂缝,等等。目前人们遇到的主要是施工中产生的温度裂缝。本文对混凝土施工中裂缝的成因和处理措施作初步探讨。一、裂缝的成因混凝土产生裂缝的原因有多种,主要因素有温度和湿度的变化、混凝土的脆性和不均匀性、结构不合理、 相似文献
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混凝土裂缝的成因、预防及处理 总被引:2,自引:0,他引:2
在工程施工中,混凝土裂缝是一个普遍存在而又较难解决的问题.混凝土裂缝产生的原因很多,有变形引起的裂缝,如温湿度变化、收缩、膨胀、基础不均匀沉陷等原因引起的裂缝;有外载作用引起的裂缝;有养护环境不当和化学作用引起的裂缝;有混凝土的脆性和不均匀性、结构不合理、原材料不合格(如碱骨料反应)、模板变形引起的裂缝等等.对混凝土工程中常见的一些裂缝问题进行了探讨分析,并针对裂缝成因提出了预防及处理的措施. 相似文献
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西南岔水库位于黑龙江省虎林市境内,是一座中型平原水库,总库容2 700万m~3,控制流域面积158.5km~2,该水库于1991年动工兴建,1995年竣工,投入使用以来,发现溢洪道的混凝土工程部分,有多处裂缝:①溢流堰的堰体上、下都有裂缝,并且是贯通的;②溢洪道下游圆弧翼墙有倾斜状裂缝;③消力池上部交通桥的两根桥墩中部也有裂缝。 一、原因分析 经专家分析,产生裂缝主要原因如下: (一)施工中出现不均衡施工现象,如相关工程的施工不及时; (二)施工的不协调,不一致,例如回填土不及时; (三)设计中未考虑施… 相似文献
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西北口堆石坝面板裂缝成因的研究 总被引:20,自引:1,他引:20
通过对西北口堆石坝面板的应力计算,研究面板产生裂缝的原因.坝体的变形按邓肯E-B模型采用非线性有限元增量法计算,并模仿施工加载过程,分层累计;面板混凝土的干缩应力采用欧洲混凝土委员会建议的CEB/FIB方法计算;混凝土面板温度场和温度应力的计算采用有限元方法,模仿施工过程,并考虑混凝土徐变的影响.经计算、对比和分析,得出结论:温度应力和干缩应力是引起面板裂缝的主要原因.由此进一步提出防止堆石坝面板出现裂缝的一些建议. 相似文献
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砼路面施工中,路枯面板常常出现裂缝,归其原因不外是:底层强度、基层表面平整土达不到设计要求;所选水泥砂石水及填缝材料不符合质量标准以及施工工艺中出现问题,因此,要把握好引起砼路面产生裂缝的各项环节,加以及时的适当处理 相似文献
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1 裂缝形成原因综述混凝土是一种由砂石骨料、水泥、水及其它外加材料混合而形成的非均质脆性材料。混凝土的裂缝问题是一个普遍存在而又难于解决的工程实际问题。混凝土裂缝产生的原因很多:有变形引起的裂缝,有外载作用引起的裂缝,有养护环境不当和化学作用引起的裂缝等等。在实际工程中要区别对待,根据实际情况解决问题。 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