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桥梁结构在地震和冰荷载作用下的响应 总被引：2，自引：1，他引：1
柳春光 《地震工程与工程振动》2005,25(5):141-146
本文采用杆系有限元方法,研究了桥墩结构在地震和冰荷载作用下的响应问题。根据桥梁的结构特点,建立其力学模型,考虑柱墩受支座的约束作用,推导了桥墩结构的动力平衡方程,分别研究桥墩结构在地震和冰荷载作用下以及在其共同作用下的响应问题,比较了考虑柱墩受支座的约束作用与不考虑柱墩受支座的约束作用2种情况下桥墩结构的响应问题,为研究桥墩结构在多荷载作用下的响应问题提供理论依据。 相似文献
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Most rivers in Taiwan are intermittent rivers with relatively steep slopes and carry rapid sediment‐laden flows during typhoon or monsoon seasons. A series of field experiments was conducted to collect suspended load data at the Tzu‐Chiang Bridge hydrological station of the lower Cho‐Shui River, which is a major river with the highest sediment yield in Taiwan. The river reach was aggrading with a high aspect ratio during the 1980s. Because of sand mining and extreme floods, it was incised and has had a relatively narrow main channel in recent years. The experimental results indicated that typical sediment transport equations can correctly predict the bed material load for low or medium sediment transport rates (e.g. less than about 1000 tons/day‐m). However, these equations far underestimate the bed material load for high sediment transport rates. The effects of cross‐sectional geometry change (i.e. river incision) and earthquakes on the sediment load were investigated in this study. An empirical sediment transport equation with consideration of the aspect ratio was also derived using the field data collected before and after river incision. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
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Sediment transport in ice-covered channels 总被引：1，自引：0，他引：1
The existence of ice cover has important effects on sediment transport and channel morphology for rivers in areas with an annual occurrence of an ice season. The interaction of sediment transport and s... 相似文献
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Mountain streams with their tributary torrents build the upper part of the fluvial network. They are important regarding the transfer of sediment from headwaters to lower basins. Channels are typically steep with wide grain size distributions, ranging from fine sand up to large boulders, and a stabilized bed surface. Mountain streams often are supply-limited with respect to mobile bed load, which needs to be addressed when bed load transport equations are applied to such streams. To better understand supply limitation, laboratory experiments highlighting the effect of bed load supply on incipient motion and bed load transport rate are discussed. Experimental tests were done in which fine bed load was supplied to a previously armored channel bed, with flow conditions ranging from one-third to twice the critical dis-charge for the bed surface. At flows not exceeding the critical discharge, the time series of the bed load transport rate at the downstream model boundary featured consistent patterns which are attributed to distinct phases: (i) a temporal lag, (ii) an equilibrium state, and (iii) a post-supply phase. Bed load transport occurred even at flows distinctly below that for incipient motion of the bed surface. But, with the mass of total bed load outflow approaching the supply amount, the mass did not exclusively consist of supplied grains. The coarser the supplied bed load, the more sediment was mobilized from the bed surface. At higher flows, processes differed. Total bed load outflow exceeded the supply amount and the break-up of the armor layer caused a refining of the bed surface. 相似文献
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Chjeng-Lun SHIEH Chih-Ming TSENG and Shaohua Marko HSUProfessor Department of Hydraulics Ocean Engineering Director Disaster Prevention Research Center National Cheng-Kung University Tainan Taiwan China. Ph.D. Candidate Department of H 《国际泥沙研究》2001,16(1)
l INTRODUCTlONIn this study, formation of alluvial deltas was treated as a river-dominated type of topograPhy process,caused simply by sediment deposition from a channel into a wide basin. The influences of waves, tides,and density differences related to coastal effects were excluded. There have been numerous experimentalstUdies on river delta problems. For examPle, Shieh et al. (1988, 1997) used coarse sediment asexperimental material and revealed the development and the geometric simil… 相似文献
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Annual erosional denudation (ED) and chemical denudation (CD) rates are determined on four forested watersheds located in the Idaho batholith, Idaho, U.S.A. Bedrock in the study area is a coarse-grained quartz monzonite. Annual sediment yields are computed from sediment collected in settling ponds at the watershed mouths and corrected for trapping efficiency. Solution loads for denudation components (Na, K, Ca, Mg, SiO2, A12O3 and FeO) are computed using equations relating concentration to flow and by integration of mean daily flow values. Eleven years of water chemistry data and 19 to 23 years of sediment yield data are used in the denudation estimates. Strong relationships exist between CD, ED and annual water yield, so probability distributions of annual water yield are used in Monte Carlo simulations to establish frequency distributions of annual CD and ED rates. Mean annual total denudation for the four watersheds (CD + ED) equals 235 kg ha ?1 yr?1 or 8-9 Bubnoffs. The 11 -year mean ED rates exceed CD rates for three of the four watersheds, although it is more probable in any given year that CD will exceed ED for three of the watersheds. ED is temporally more variable than CD for all watersheds. Simulations of denudation over 1000-year periods indicate that the frequency of occurrence of ED is skewed toward higher denudation values, and the modal ED rate is substantially lower than the mean value. CD rates are less skewed, with mean and mode in the same class. Ninety-seven per cent of CD is composed of Na, Ca and SiO2 fluxes. Episodic high ED rates are related to high peak flows from snowmelt runoff associated with winters of large snow accumulation. Perturbations such as fire or road construction would be expected to accelerate ED more than CD. 相似文献
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目前的AASHTO LRFD桥梁规范主要考虑重力荷载和卡车等活荷载的组合情况,而没有在概率基础上考虑地震等极端荷载的组合问题.包括LRFD在内的很多桥梁抗震规范都是主要考虑地震的作用,甚至设计时不考虑其他荷载的作用,LRFD设计指导手册中在考虑地震等极端荷载时,也只是提到在特殊情况和桥梁比较长的情况下再考虑卡车的作用,... 相似文献
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1 INTRODUCTION At present, most of the instruments used for sampling sediment loads at the canal intakes along the Yellow River in Shandong Province are horizontal samplers. These kinds of samplers cannot sample the suspended load 0.3 m from the riverbed. More recently use of bottle samplers has allowed sampling of the sediment load up to 0.1 m from the riverbed. However, bottle samplers are not able to measure suspended loads with high sediment concentrations and coarse sediment particl… 相似文献
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2012年以来,河北省易县地震台SS-Y型伸缩仪NE向观测曲线转折异常,调查发现,该台周边采石场荷载变化可能是导致数据变化的原因。因此,利用三维实体结构有限元模型,结合荷载变化与地应变异常时间进行对比分析,结果表明:计算得到的伸缩仪NE向年变幅理论值为2.62×10~(-7),而实际观测异常年变幅为4.08×10~(-7),实测应变值几乎是理论值的2倍,可见应变异常变化与采石造成的荷载变化有关。 相似文献
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Peter E. Ashmore 《地球表面变化过程与地形》1988,13(8):677-695
Bed load transport rate was measured in ten self-formed small-scale gravel braided streams developed in a laboratory flume at several different values of steady discharge and flume gradient. The streams are approximate Froude models of typical prototype braided streams but of no particular river. Slight viscous effects may be present in the models because particle Reynolds numbers are close to 70. Total bed load discharge was measured every fifteen minutes throughout each 60 hour run. In addition, 80 channel cross-sections were measured in each run to establish the average channel geometry. Total bed load transport rate correlates well with total discharge and total stream power, although at a given stream power bed load discharge is greater when braiding is less intense and the width/depth ratio is lower. Analysis using unit stream power and cross-section average bed shear stress reveals that the laboratory data conform to existing empirical bed load transport relationships. However, comparison with field data from gravel-bed rivers shows discrepancies that may be due to differences in bed material size gradation and bed sediment structure. At constant discharge, wide fluctuations in bed load discharge occur with some regularity. Periods range from 2 to 10 hours in the models, which is equivalent to several tens of hours in a prototype. The presence of these long-period fluctuations compounds the problems of field measurement of bed load in braided streams. 相似文献
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H. M. Pantin 《地球表面变化过程与地形》1982,7(5):503-505
The experiments of Southard and Mackintosh prove only that autosuspension did not occur under the tested conditions; these were based on the Bagnold (1963) criterion, which is unsound. An alternative criterion is re-emphasized, and a method for testing its validity suggested. Two separate derivations are given for the power required for sediment suspension. 相似文献
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Coarse bed load was sampled in a gravel/cobble bed stream during two major floods in the snowmelt runoff season. The channel is characterized by high rates of bank erosion and, therefore, high rates of sediment supply and bed load flux. Peak discharge reached four times bank‐full, and bed load was sampled at flows 0·7–1·7 times bank‐full. A large aperture bed load sampler (1 m by 0·45 m) captured the largest particles in motion, and specifically targeted the coarse bed load size distribution by using a relatively large mesh (32 mm or D25 of streambed surface size distribution). Bed load flux was highly variable, with a peak value of 0·85 kg/s/m for the coarse fraction above 38 mm. Bed load size distribution and maximum particle size was related to flow strength. Entrainment was size selective for particles D70 and larger (88–155 mm), while particles in the range D30–D70 (35–88 mm) ceased to move at essentially the same flow. Bed load flux was size selective in that coarse fractions of the streambed surface were under‐represented in or absent from the bed load. Painted tracer particles revealed that the streambed surface in the riffles could remain stable even during high rates of bed load transport. These observations suggest that a large proportion of bed load sediments was sourced from outside the riffles. Repeat surveys confirmed major scour and fill in pools (up to 0·75 m), and bank erosion (>2 m), which together contributed large volumes of sediment to the bed load. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
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在强震状态下,建筑物的横拉承压受力较为复杂,另外由于建筑物形状及在地震中受力面积大小不同,在强震下造成碰撞大小影响不一导致其横拉承压力的随机复杂性十分突出。传统的建筑承压负荷检测方法中钢筋负荷受力测量能力不足,检测结果易出现误差。将建筑钢筋的机械性能设为理想弹塑性,利用建筑物横拉承压力钢筋负荷测量方法,对不同结构、不同工况的建筑钢筋载荷的变化规律进行测试分析,结合建筑局部承压特点和整体结构聚力方式,设计横拉承压力钢筋负荷检测方法,并进行仿真实验,结果表明该方法模型所得数据更加精准,有良好的适用性。 相似文献
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浆固碎石柱是一种新型的桩基技术,已成功应用于铁路、高速公路等工程中。但由于浆固区的存在,浆固碎石桩荷载传递机理的复杂性制约了其发展和工程应用。荷载传递分析法是桩荷载传递机理分析的重要方法之一。本文采用线性弹塑性和双折线传递函数,分别模拟桩侧土体的非线性和桩端土的硬化特性,同时考虑浆固区存在对桩荷载传递的影响,推导出一种浆固碎石桩单桩荷载传递分析方法。最后,通过对工程实例进行计算,验证了本文计算方法的实用性。结果表明,浆固碎石桩除具有一般刚性桩的桩体置换作用外,浆固区的存在对提高浆固碎石柱承载力、减小沉降量也有着重要作用。 相似文献
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土体动力特性主要与其受力状态、土体加载类型、试验控制方式以及荷载等参数有关。以往非饱和黄土累积变形试验研究通过单向动应力加载方式开展相关研究,并不能真实反映土体受力状态。现运用WF-12440型动三轴-空心圆柱扭剪试验系统,通过单向荷载和双向荷载两种不同的动应力加载方式,进行黄土的长期重复载荷试验,对比不同动应力加载方式对非饱和黄土累积变形发展特征的影响。试验结果发现：黄土在单向荷载或双向荷载作用下,其软化指数均随着循环次数的增加,呈非线性减小的趋势,在相同循环振次时,土体软化指数随着动应力幅值的增大而减小;黄土在不同加载方式作用下,软化指数减小速率在循环振次100次以内较快,后期随振次增加,土体软化速率逐渐趋于平稳;黄土在双向荷载作用下,当轴向动荷载较小时,径向荷载的施加,将加速黄土的软化程度,随着轴向动荷载的增大,径向荷载对黄土软化的影响逐渐减弱,其对于黄土变形的影响存在一临界轴向循环动应力。本研究的开展,可更准确地进行不同荷载耦合变化下,黄土场地震陷评估或路基土体变形计算,实现有效控制路基的整体稳定和工后沉降量,以期根据路基土参数预测后期沉降,极具重要的科研和工程意义。 相似文献
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Centrifuge modelling of raked piles 总被引：1，自引：1，他引：0
Sandra Escoffier Jean-Louis Chazelas Jacques Garnier 《Bulletin of Earthquake Engineering》2008,6(4):689-704
Inclined piles are prohibited by many codes in seismic areas. Nevertheless the battered effect has not yet been clarified
because very few data are available. The present work is a comparison, at reduced scale in the centrifuge, of the response
of two simplified pile groups: a 1 × 2 vertical piles and 1 × 2 pile group with one inclined pile. Two configurations are
considered: end-bearing and floating pile group, both with pile heads rigidly fixed with a massive cap. First, repeatability
tests under horizontal cyclic loading were performed on both floating pile groups. Secondly, repeated horizontal impact tests
were performed on both end-bearing pile groups. These impact tests, which highlight the influence of inclined piles on the
inertial response of a group, are a first step for the more complex analysis of the performance of such groups under seismic
loads where inertial and kinematic interactions are combined. The first part of this work revealed the influence of sand structure
around the inclined pile tip on the repeatability of the tests performed on floating pile groups. The second part highlighted
differences in the dynamic response between the two end-bearing pile groups through measurements of the pile cap acceleration,
the bending moment profile and the axial load in the piles. 相似文献
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本文研究了电力供应系统地震功能失效评估方法,尤其对电力供应系统功能潮流分析方法与负荷的控制问题作了深入的探讨.不仅分析了供电系统的潮流(包括电压和功率)变化对供电系统的影响问题,而且建立了电流控制模型,利用DSEA控制算法对供电系统进行负荷控制,并在此基础上进行了系统过负荷时的数值模拟研究;另外,通过一实例分析,对本文的研究方法进行了验证,从而为供电系统抗震分析、功能评估及灾害预防提供理论基础. 相似文献