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1.
This paper presents in-situ seismic performance tests of a bridge before its demolition due to accumulated scouring problem. The tests were conducted on three single columns and one caisson-type foundation. The three single columns were 1.8 m in diameter,reinforced by 30-D32 longitudinal reinforcements and laterally hooped by D16 reinforcements with spacing of 20 cm. The column height is 9.54 m,10.59 m and 10.37 m for Column P2,P3,and P4,respectively. Column P2 had no exposed foundation and was subjected to pseudo-dynamic tests with peak ground acceleration of 0.32 g first,followed by one cyclic loading test. Column P3 was the benchmark specimen with exposed length of 1.2 m on its foundation. The exposed length for Column P4 was excavated to 4 m,approximately 1/3 of the foundation length,to study the effect of the scouring problem to the column performance. Both Column P3 and Column P4 were subjected to cyclic loading tests. Based on the test results,due to the large dimension of the caisson foundation and the well graded gravel soil type that provided large lateral resistance,the seismic performance among the three columns had only minor differences. Lateral push tests were also conducted on the caisson foundation at Column P5. The caisson was 12 m long and had circular cross-sections whose diameters were 5 m in the upper portion and 4 m in the lower portion. An analytical model to simulate the test results was developed in the OpenSees platform. The analytical model comprised nonlinear flexural elements as well as nonlinear soil springs. The analytical results closely followed the experimental test results. A parametric study to predict the behavior of the bridge column with different ground motions and different levels of scouring on the foundation are also discussed.  相似文献   

2.
Lava flows of the Mangawhero Formation (ca. 15–60 ka) on Ruapehu volcano erupted during the last glaciation. In a distal flow lobe at Tukino, on the east side of the mountain, small secondary columns (10–20 cm thick) have formed on the sides of large, rectangular, primary (0.5–3 m thick) cooling columns. Thick (10 m+) zones of such small columns form a lateral and basal outer rind of the lobe. As they do not mark glassy zones of quenching, these secondary columns are interpreted as being formed by a second cooling event at temperatures below the boundary between the low creep and elastic regimes (∼ 600 °C) by rapid influx of copious amounts of water. Temperature drops deduced from extensional strains of the two sets of columns were used to gauge the viability of such a two-stage process. Absence of reliable data on andesite contraction coefficients was overcome by using a sliding scale to assess a large range of values. The estimates indicate that two-stage chilling is feasible. After flowing across relatively ice-poor terrain, the lava flow must have interacted with a valley glacier that provided water for further chilling the already formed primary columns and formation of the outer rind small columns. Given this evidence for lava/ice interaction, it is likely that prominent, thick flows elsewhere in the Mangawhero Formation may have been constrained to their ridge-top locations by ice conditions similar to those described by Lescinsky and Sisson [Lescinsky, D.T., Sisson, T.W., 1998. Ridge-forming, ice-bounded lava flows at Mount Rainier, Washington. Geology, 26, 351–354].  相似文献   

3.
Igneous rocks are fractured during cooling from magma to form cooling joints, which are typically columnar joints in volcanic rocks, while orthogonal joints are considered typical for plutonic rocks. We performed a 3D study of joint systems in a granitic batholith of the Okueyama granite in western Japan, which has its roof and its internal structures from the roof to 1000 m downward exposed. We used an unmanned aerial vehicle (UAV) to observe the joints in outcrops from various angles. Based on our study, we propose a schematic model for joint systems in a granitic pluton. A granitic pluton has zones of rock columns below the roof and next to the wall. The rock column zone below the roof is as thick as 300 m, and its higher portions form steep cliffs, probably because of increased resistance to weathering. The axes of the rock columns are nearly vertical below the roof and gently plunge next to the walls, with high intersection angles with the wall. The distribution of columnar joints near only the roof and walls suggests that the granite cooled more rapidly near the roof and walls than in the core of the pluton. When the granite was jointed by parallel joints during cooling, the rock slabs between the parallel joints near the roof and the walls are subdivided into columns with polygonal cross-sections. This suggests that the granite was fractured by parallel joints at a temperature immediately below the solidus, after which the rock slabs were subdivided into rock columns during further cooling.  相似文献   

4.
In this paper, we estimated the effective size of ice crystals in cirrus clouds using fall velocity derived from LiDAR (light detection and ranging) measurements at Chung-Li (24.58°N, 121.1°E), Taiwan. Nine shapes of the ice crystals, viz. hexagonal plates, hexagonal columns, rimed long columns, crystals with sector-like branches, broad-branched crystals, stellar crystal with broad arms, side planes, bullet rosettes and assemblages of planar poly-crystals of specific dimensions have been analyzed. The results show that the lidar derived most probable mean effective size of ice crystals is 340±180 μm with a dominant size range of 200–300 μm. The lidar derived mean effective size of cirrus crystals are parameterized in terms of cloud mid-height temperature as well as optical depth. The discussed method will be useful to study the most probable effective size distribution of ice crystals in cirrus cloud.  相似文献   

5.
The paper discusses the mechanism of deep magma activity beneath island are volcanoes and similar structures on the basis of data from geophysical investigations in Kamchatka; the analyses of forces that cause the ascent of magma; and related phenomena that are due to hydrostatic forces. It is shown that the ascent of magma through the astnenosphere occurs most likely in magma columns with a diameter of approximately 700–2,000 m and with a velocity of about 0.8–3 m/year. A regular line of such columns spaced in Kamchatka at a distance of about 30 km gives rise to a chain of separate Etrge volcanoes or volcanic centers. Ultrabasic magmas are most likely accumulated near the M discontinuity, whereas the apparent place of andesitic magma accumulation is in the earth’s crust near the boundary between the basement and sediments.  相似文献   

6.
Infiltration of water into two frozen engineered soils of different gradation was studied in laboratory soil columns 1.2 m long and 0.1 m in diameter. Prior to testing, the soil moisture was adjusted to two levels, described by the gravimetric water content of 5% or 10%, and soils were compacted to about 80–90% of the maximum dry density and refrigerated to temperatures ranging from ?8 to ?2 °C. Water with temperatures 8–9 °C was thereafter fed on the top of columns at a constant head, and the times of water breakthrough in the column and reaching a steady percolation rate, as well as the percolation rate, were recorded. The soil water content was a critical factor affecting the thawing process; during freezing, soil moisture was converted into ice, which blocked pores, and its melting required high amounts of energy supplied by infiltrating water. Hence, the thawing of soils with higher initial water content was much slower than in lower moisture soils, and water breakthrough and the attainment of steady percolation required much longer times in higher moisture soils. Heat transfer between infiltrating water, soil ice, and frozen soil particles was well described by the energy budget equations, which constitute a parsimonious model of the observed processes. The finer grained soil and more compacted soil columns exhibited reduced porosity and required longer times for soil thawing. Practical implications of study results for design of bioretention facilities (BFs) in cold climate include the use of coarse engineered soils and fitting bioretention facilities with a drain facilitating soil drainage before the onset of freezing weather. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

7.
利用微动勘察方法探测煤矿陷落柱   总被引：27，自引：7，他引：20       下载免费PDF全文
陷落柱是危害煤矿安全生产的主要因素之一,如何有效探测陷落柱是实现煤矿安全、高效生产的当务之急.本文首次将微动勘察方法应用于煤矿采区勘探,结果表明,该方法对陷落柱异常区反映敏感.在山西潞安漳村煤矿2002工作面测区已知陷落柱上,无论是单点反演获得的S波速度结构,还是微动视S波速度剖面,均能清晰显示陷落柱.微动剖面确定的陷落柱位置与巷道揭露位置一致,边界误差在10 m左右.微动勘察方法是探测陷落柱的一种行之有效的物探方法,由于其分辨率高、无需人工源、野外施工方法灵活便捷、不受施工场地限制等特点,对探测村庄覆盖区之下的煤层构造、圈定陷落柱等,具有得天独厚的技术优势和应用前景.  相似文献   

8.
在已完成的包括16个构件的等位移循环加载钢筋混凝土柱的系列试验中，通过在其中3根柱的塑性铰区沿混凝土受力方向安设位移计，较准确测定了混凝土测试标距内的平均应变在一个加载循环内的变化规律及其随周数增长的变化规律；发现了单周最大压应变随周数的增长而持续增大，单周最大名义拉应变随周数增长而持续减小的重要现象；并与柱顶水平力-水平位移滞回规律实测结果相对应，结合截面受力特征对所得单周和多周应变变化规律的成因作了分析。  相似文献   

9.
Batch and continuous flow adsorption experiments are carried out and the design of a full‐scale facility for removing dissolved natural organic matter (DNOM) from Catalan Lakewater is demonstrated. The adsorption efficiency is proportional to the temperature and the amount of adsorbent unlike pH increase. The highest DNOM removal rate is obtained at 35 °C, pH 4, and an adsorbent amount of 0.8 g L?1. Optimum contact time for batch studies is 60 min at equilibrium. Correlation constants (r) of Langmuir and Freundlich isotherms are 0.8905 and 0.9739, respectively. Based on the Freundlich isotherm, the highest adsorption capacity (qmax) obtained is 2.44 and 6.01 mg DNOM/g granulated activated carbon (GAC) for raw and enriched water, respectively. Consequently, the effects of adsorbent amount, bed depth, empty bed contact time, and organic loading on removal performance are investigated in the rapid small‐scale column test (RSSCT) columns. The targeted effluent concentration of 1 mg DNOM/L can easily be achieved in the columns. At the design capacity of the facility, 15 adsorption columns with dimensions of 7 m height, 4.33 m diameter, and 22 days of operation cycle are required to remove DNOM from raw water.  相似文献   

10.
通过分别开展包裹碎石桩加固、碎石桩加固以及未加固的饱和砂土液化振动台试验,对比分析不同加固类型下的抗液化性能,重点剖析包裹碎石桩加固的砂土液化机理。试验表明:振动加载过程中,包裹碎石桩始终保持桩体的完整性与良好的排水性能且其加固模型地基的总沉降量相较于未加固模型地基减少了50%,相较于碎石桩加固模型地基减少了31.8%。包裹碎石桩加固模型排出水量较未加固模型地基提高了33.3%,较碎石桩加固模型地基提高了16.6%;包裹碎石桩加固模型地基的超静孔压值下降显著且地基下层砂土出现未液化的现象;并进一步发现包裹碎石桩的排水加固作用沿土层竖向深度呈递增趋势。因此,可以发现包裹碎石桩加固砂土液化的抗震性能优于碎石桩。  相似文献   

11.
为讨论近断层地震动下摇摆-自复位(Rocking Self-Centering, RSC)桥墩连续梁的地震反应及其抗震优缺点。基于OpenSees有限元分析平台讨论了RSC桥墩三维建模方法,通过对6个试验构件的模拟,比较模拟与试验桥墩滞回曲线、预应力筋最大应力等指标,验证了模型准确性。建立设置RSC桥墩和普通钢筋混凝土(Reinforced Concrete, RC)桥墩的上部结构相同的两座连续梁桥,输入3组含有强速度脉冲的近断层地震波进行非线性动力时程分析,对比其抗震性能。结果表明：在0.4 g近断层地震动下,RSC桥墩与普通RC桥墩相比,RSC桥墩的最大位移角为普通RC桥墩的78.1%～97.6%,墩底曲率延性系数仅为普通RC桥墩的24.0%～34.0%,减小了桥墩的最大变形,也减轻了桥墩地震损伤,不利的一点是使用RSC桥墩会导致支座位移增大。RSC桥墩震后的残余位移较小,且预应力筋处于弹性受力阶段,为实现震后桥梁功能的快速恢复提供了条件。  相似文献   

12.
The scattering behaviour of bullet-rosette and bullet-shaped ice particles is investigated using model calculations (ray tracing method) with special emphasis on the asymmetry factor g. Because the variability of the geometrical features of these particles is very large, some representative shapes are used in the calculations. The model is based on geometrical optics, and particles are assumed to be oriented randomly; a wavelength of 0.56 m is considered; absorption is neglected. The scattering behaviour of bullet rosettes is compared to that of single branches out of the bullet rosette. It turns out that there are slight differences in the asymmetry factor values, depending on the lengths of the branches (g\approx0.02) and on the angles between the branches (g\approx0.01). Bullets show some special features in their phase functions due to the pyramid. The length of the particle influences the asymmetry factor (g\approx0.10), as does the shape of the pyramid (g\approx0.07). The influence of the pyramidal shape decreases with increasing particle length. Bullets were compared to hexagonally shaped columns. This was done for two columns, one as long as the columnar part of the bullet (length without pyramid), and one for a column as long as the bullet including the pyramid. Asymmetry factor values of bullets with a pyramidal angle of 28° deviate less than g\approx0.01 from the range given by the two values of the columns.  相似文献   

13.
对基于位移的方钢管混凝土柱抗震设计方法进行了研究：介绍了基于位移抗震设计方法的概念、原理和设计的一般过程；探讨了方钢管混凝土柱的等效刚度、等效阻尼等设计中的关键问题，并确定了参数的具体取值；最后对方钢管混凝土柱进行了具体的基于位移的抗震设计，并研究了主要参数的影响。结果表明：在通常范围内，第二阶段刚度系数对滞回阻尼比影响不大；随着轴压比的增加，钢管壁厚度增加，柱延性系数增加；随着截面尺寸增加，钢管壁厚度减小，屈服弯矩也减小。  相似文献   

14.
A new model for Plinian eruption columns is derived from first principles and investigated numerically. The dynamics particular to the momentum-driven basal gas-thrust region and the upper buoyancy-driven convective region are treated separately. The thermal interactions in the column are modelled by the steady-flow-energy equation. The main results of the present paper are that: (1) the basal gas-thrust region model predicts a very rapid initial expansion of the material on leaving the vent; (2) the gas-thrust region height decreases with initial temperature, inital gas content of the erupted material and initial velocity, but increases with vent radius; (3) the total column height increases with initial temperature, initial velocity and vent radius, but decreases with initial gas content; (4) column collapse occurs for initial velocities of the order of 100 m/s; the precise value increases as the initial gas content in the erupted material decreases; (5) for large vent radii or low initial gas content of the erupted material, the velocity in the column can increase with height once in the buoyancy-driven region instead of decaying to zero monotonically; (6) the interaction of the potential energy with the enthalpy is found to be the dominant thermal interaction in the upper part of the column. Previous models of eruption columns involve inconsistencies and simplifications; these are shown to lead to significant differences in the results in comparison to the present model.  相似文献   

15.
The dimensions and dynamics of volcanic eruption columns   总被引：5，自引：1，他引：5  
Eruption columns can be divided into three regimes of physical behaviour. The basal gas thrust region is characterized by large velocities and decelerations and is dominated by momentum. This region is typically a few hundred metres in height and passes upwards into a much higher convective region where buoyancy is dominant. The top of the convective region is defined by the level of neutral density (heightH B ) where the column has a bulk density equal to the surrounding atmosphere. Above this level the column continues to ascend to a heightH T due to its momentum. The column spreads horizontally and radially outwards between heightH T andH B to form an umbrella cloud. Numerical calculations are presented on the shape of eruption columns and on the relationships between the heightH B and the mass discharge rate of magma, magma temperature and atmospheric temperature gradients. Spreading rate of the column margins increases with height principally due to the decrease in the atmospheric pressure. The relationship between column height and mass discharge rate shows good agreement with observations. The temperature inversion above the tropopause is found to only have a small influence on column height and, eruptions with large discharge rates can inject material to substantially greater heights than the inversion level. Approximate calculations on the variation of convective velocities with height are consistent with field data and indicate that columns typically ascend at velocities from a few tens to over 200 m/s. In very large columns (greater than 30 km) the calculated convective velocities approach the speed of sound in air, suggesting that compressibility effects may become important in giant columns. Radial velocities in the umbrella region where the column is forced laterally into the atmosphere can be substantial and exceed 55 m/s in the case of the May 18th Mount St. Helens eruption. Calculations on motions in this region imply that it plays a major role in the transport of coarse pyroclastic fragments.  相似文献   

16.
Transfer of zoonotic bacterial pathogens through intact soil columns was monitored in an outdoor lysimeter over 36 d. Manure spiked with Salmonella enterica serovar Senftenberg was applied to either the soil surface or injected 0.08 m into the soil to compare leaching associated with the two manure application methods. The highest concentrations of S. enterica (up to 60,000 S. enterica CFU/mL) were detected on Day 1 in the first drainage samples, with measurable but declining concentrations persisting for 10 to 36 d depending on replicate columns. The total recovery of leached S. enterica in drainage samples ranged from 0.08% to 13.8%. When comparing the two application methods, there was no statistically significant difference in the leaching concentration of S. enterica at each sampling time during the study period. In addition, comparison of enumerations by selective plating and real-time polymerase chain reaction yielded similar concentrations of S. enterica, indicating that mainly viable and culturable cells were leached from the columns. When the experiment was terminated, the fluorescent dye Acid Yellow was applied to four selected columns and the distribution of dye and size of active (dye-stained) pores were measured with a digital camera and visualization software. The profiles showed that the area covered by active pores ranged from 0.1% to 3.6%. The relatively small fraction of active pores in the soil profile was consistent with the evidence of rapid transport of S. enterica and chloride in the columns.  相似文献   

17.
整理了国内外相关规范与相关研究中对RC柱抗震性态划分方法与指标限值,发现均是针对未震损未加固的RC柱.以相关试验得到的未预损未加固、未预损直接加固、预损后再加固的RC柱骨架曲线为对象,直接套用现有针对未震损未加固RC柱的性态划分方法与指标限值进行划分,得到对应各抗震性态分隔点处的位移角限值,发现3类RC柱在相同位移角下...  相似文献   

18.
为了研究钢筋混凝土框架柱在爆炸冲击波作用下的反应,本文使用有限元分析软件AUTO-DYN对一个典型的钢筋混凝土底层框架柱进行了爆炸分析.设定了1m、3m、5m三种比例距离,各比例距离分别设置10 kg、50 kg、100 kg三种量级的TNT炸药.分析得到了各爆炸工况下柱子的动力响应及损伤形态.研究表明:柱子在爆炸冲击波作用下的动力响应对于比例距离的改变十分敏感;当炸弹在地面爆炸时,柱子最终破坏的区域总是在柱底到柱高的三分之一处;随着比例距离的增大,柱子最终的破坏形态由剪切型转变为弯曲型.  相似文献   

19.
为了解地震作用下纤维编织网增强钢筋混凝土柱的抗震性能,采用钢筋、混凝土、纤维编织网浇筑纤维编织网增强钢筋混凝土柱,编织网主材为碳、玻璃纤维束;利用电液伺服加载系统为试件加载地震作用,监测相关数据,部分试件置入氯化钠溶液进行多次干湿循环。不同环境下的实验结果显示:纤维编织网层数越多,纤维编织网增强钢筋混凝土柱承载能力越强,抗震性能越好;配箍间距较大时,纤维编织网增强钢筋混凝土柱的抗震性能仅在地震作用的后期呈现较差状态;干湿循环次数越多,纤维编织网增强钢筋混凝土柱承载力越弱,抗震性能越差。对于氯盐环境而言,可增加纤维编织网增强钢筋混凝土柱的抗腐蚀措施改善抗震性能。适当增加纤维编织网的数量、降低配箍间距有利于提升纤维编织网增强钢筋混凝土柱的抗震性能。  相似文献   

20.
碳纤维布改善高强混凝土柱延性的试验研究   总被引：8，自引：2，他引：8  
本文进行了8根高强混凝土柱在低周反复荷载作用下的试验，研究了使用碳纤维布横向包裹的高强混凝土柱来提高其延性这种加固方法的有效性。本文研究了碳纤维布横向包裹高强混凝土柱的受力特性，分析了加荷角度，碳纤维布拉伸强度以及碳纤维布的包裹层数等因素对构件抗震加效果的影响，并对碳纤维布加固高强混凝土柱使其延性提高的机理进行了探讨，试验结果表明，横向缠裹碳纤维布可显著提高高强混凝土柱的延性。  相似文献   

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