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1.
In order to investigate the dynamic mechanical properties of amphibolite and sericite-quartz schist under confi ning pressure, two rocks are subjected to impact loadings with different strain rates and confi ning pressures by using split Hopkinson pressure bar equipment with a confi ning pressure device. Based on the experimental results, the stress-strain curves are analyzed and the effects of confi ning pressure and strain rates on the dynamic compressive strength, peak strain and failure mode are summarized. The results show that:(1) The characteristics of two rocks in the ascent stage of the stressstrain curve are basically the same, but in the descent stage, the rocks gradually show plastic deformation characteristics as the confi ning pressure increases.(2) The dynamic compressive strength and peak strain of two rocks increase as the strain rate increases and the confi ning pressure effects are obvious.(3) Due to the effect of confi ning pressure, the normal stress on the damage surface of the rock increases correspondingly, the bearing capacity of the crack friction exceeds the material cohesion and the slippage of the fractured rock is controlled, which all lead to the compression and shear failure mode of rock. The theoretical analysis and experimental methods to study the dynamic failure mode and other related characteristics of rock are useful in developing standards for engineering practice. 相似文献
2.
The cascading failure of multiple landslide dams can trigger a larger peak flood discharge than that caused by a single dam failure.Therefore,for an accurate numerical simulation,it is essential to elucidate the primary factors affecting the peak discharge of the flood caused by a cascading failure,which is the purpose of the current study.First,flume experiments were done on the cascading failure of two landslide dams under different upstream dam heights,downstream dam heights,and initial downstream reservoir water volumes.Then,the experimental results were reproduced using a numerical simulation model representing landslide dam erosion resulting from overtopping flow.Finally,the factors influencing the peak flood discharge caused by the cascading failure were analyzed using the numerical simulation model.Experimental results indicated that the inflow discharge into the downstream dam at the time when the downstream dam height began to rapidly erode was the main factor responsible for a cascading failure generating a larger peak flood discharge than that generated by a single dam failure.Furthermore,the results of a sensitivity analysis suggested that the upstream and downstream dam heights,initial water volume in the reservoir of the downstream dam,upstream and downstream dam crest lengths,and distance between two dams were among the most important factors in predicting the flood discharge caused by the cascading failure of multiple landslide dams. 相似文献
3.
The first part of the research reported here consists of an experimental campaign to study the scouring of a granular bed(glass beads, sand) induced by a dam break in an open channel. Two configurations are considered: with and without cylinders. In the second part of this study, the volume of fluid method coupled with the shear stress transport turbulent model and the lagrangian particle tracking method is used to simulate the local scour processes. The four-way coupling is realized by consider... 相似文献
4.
The growth in computer processing power has made it possible to use time-consuming analysis methods such as incremental dynamic analysis(IDA) with higher accuracy in less time.In an IDA study,a series of earthquake records are applied to a structure at successively increasing intensity levels,which causes the structure to shift from the elastic state into the inelastic state and finally into collapse.In this way,the limit-states and capacity of a structure can be determined.In the present research,the IDA of a concrete gravity dam considering a nonlinear concrete behavior,and sliding planes within the dam body and at the dam-foundation interface,is performed.The influence of the friction angle and lift joint slope on the response parameters are investigated and the various limit-states of the dam are recognized.It is observed that by introducing a lift joint,the tensile damage can be avoided for the dam structure.The lift joint sliding is essentially independent of the base joint friction angle and the upper ligament over the inclined lift joint slides into the upstream direction in strong earthquakes. 相似文献
5.
The propagation of stress waves in a large-diameter pipe pile for low strain dynamic testing cannot be explained properly by traditional 1D wave theories. A new computational model is established to obtain a wave equation that can describe the dynamic response of a large-diameter thin-walled pipe pile to a transient point load during a low strain integrity test. An analytical solution in the time domain is deduced using the separation of variables and variation of constant methods. The validity of this new solution is verifi ed by an existing analytical solution under free boundary conditions. The results of this time domain solution are also compared with the results of a frequency domain solution and fi eld test data. The comparisons indicate that the new solution agrees well with the results of previous solutions. Parametric studies using the new solution with reference to a case study are also carried out. The results show that the mode number affects the accuracy of the dynamic response. A mode number greater than 10 is required to enable the calculated dynamic responses to be independent of the mode number. The dynamic response is also greatly affected by soil properties. The larger the side resistance, the smaller the displacement response and the smaller the refl ected velocity wave crest. The displacement increases as the stress waves propagate along the pile when the pile shaft is free. The incident waves of displacement and velocity responses of the pile are not the same among different points in the circumferential direction on the pile top. However, the arrival time and peak value of the pile tip refl ected waves are almost the same among different points on the pile top. 相似文献
6.
The impact of rainfall event movement on soil crust development was investigated via laboratory experiments and physics-based hydrological-response simulation.Runoff and soil water content data were analyzed in order to study different crustal development periods under a variety of precipitation conditions.The results showed that the formation of crust significantly changed soil saturated hydraulic conductivity(K_s) and runoff,while a steady state,which could be broken by an extended period of raindrop impact,was found to exist for both the crust and,subsequently,runoff characteristics.The decrease in K_S was as high as 86%for downstream-moving events,and 72%for upstream-moving events,illustrating that the direction of rainfall movement has a more significant impact on crust formation than rainfall intensity and duration.As downstream-moving rainfall events may have a greater effect than those moving upstream,the development of a depositional crust before raindrop impact may play an important role in determining the final K_S value. 相似文献
7.
Vehicle load is among the main factors affecting the deformation of subgrade soil.In this research study,the concept of impact type traffic load is introduced to investigate the effects of vehicle load based on the dynamic stress and displacement time histories acquired from seasonal frozen subgrade soils.Using freezing-thawing and dynamic triaxial tests and considering the amplitude and loading sequence of impact type traffic load,the residual deformation characteristics of subgrade soil under impact type traffic loads and freezing-thawing cycles is studied.It was found that under impact type traffic load,the residual deformation of soils increased sharply as the amplitude of impact type traffic load increased.It was also found that the increase in the amplitude of impact type traffic load led to the increase of residual deformation in a scale of power and exponential function.The amplitudes of impact type traffic load affect the development stress-strain path of the residual strain.After the soil experienced the proper amount of pre-vibration of the light load,residual deformation decreased by 15%.After freezing-thawing,the residual strain of soil increased as the amplitude of the impact type traffic loads increased.Also,when the amplification effect of freezing-thawing on the residual strain was basically stable,the residual deformation increased by about 10%.The peak impact type traffic load had a large effect on soil deformation after the freezing-thawing process,leading to the observation that of the earlier the peaks,the stronger the effect of freezing-thawing.After the soil was subjected to preloading with a small load,the influence of the freezing-thawing cycles gradually stabilized.The results may be useful in preventing and controlling the risk of subgrade soil failure when construction takes place spring thaw periods. 相似文献
8.
Mai Tong Thomas Liebner 《地震工程与工程振动(英文版)》2007,6(1):11-20
In a viscous damping device under cyclic loading, after the piston reaches a peak stroke, the reserve movement that follows may sometimes experience a short period of delayed or significantly reduced device force output. A similar delay or reduced device force output may also occur at the damper’s initial stroke as it moves away from its neutral position. This phenomenon is referred to as the effect of “deadzone”. The deadzone can cause a loss of energy dissipation capacity and less efficient vibration control. It is prominent in small amplitude vibrations. Although there are many potential causes of deadzone such as environmental factors, construction, material aging, and manufacture quality, in this paper, its general effect in linear and nonlinear viscous damping devices is analyzed. Based on classical dynamics and damping theory, a simple model is developed to capture the effect of deadzone in terms of the loss of energy dissipation capacity. The model provides several methods to estimate the loss of energy dissipation within the deadzone in linear and sublinear viscous fluid dampers. An empirical equation of loss of energy dissipation capacity versus deadzone size is formulated, and the equivalent reduction of effective damping in SDOF systems has been obtained. A laboratory experimental evaluation is carried out to verify the effect of deadzone and its numerical approximation. Based on the analysis, a modification is suggested to the corresponding formulas in FEMA 356 for calculation of equivalent damping if a deadzone is to be considered. 相似文献
9.
The anti-slide support structure is widely used in the anti-seismic reinforcement of bridge foundations, but related experimental research was processing slowly. Based on the prototype of the Jiuzhaigou bridge at the Chengdu-Lanzhou Railway, a 3-D simulation model was established on the basis of the shaking table model test, and the rationality of the dynamic analysis model was verified by indicators such as the bending moment of the bridge piles, peak soil pressure, and PGA amplification factors. The results show that the inertia force of the bridge pier has an important influence on the deformation of the pile foundation. The bending moment and shearing force are larger in lateral bridge piles, and the maximum value is near the pile top. The PGA amplification factor is stronger in the back of the rear anti-slide piles and so is it in front of the bridge pier, and the soil is prone to slip and damage. The bedrock is rigid and the dynamic response is maintained at a low level. The anti-slide piles in the rear row play a major role in the anti-seismic reinforcement design, and the anti-slide piles in the front row can be used as an auxiliary support structure. 相似文献
10.
The wind-induced responses of a large-scale membrane structure, Expo Boulevard, are evaluated in this study. To obtain the wind pressure distribution on the roof surface, a wind tunnel test is performed. A brief analysis of wind pressure on the membrane roof is conducted first and then an analysis of the wind-induced responses of the structure is carried out using a numerical integral method in the time domain. In the process of calculation, the geometrical nonlinearity is taken into account. Results indicate that mean, RSM and peak values of the structure responses increase nonlinearly while the approaching flow velocity increases. Strong nonlinear characteristics are observed in the displacement responses, whereas the responses of nodal stress and cable axial force show minimal nonlinear properties when the membrane structure is subjected to wind loads. Different values of the damping ratio only have a minimal impact on the RSM response of the structure because the background component is a dominant part of the total dynamic response and the resonant component is too small. As the damping ratio increases from 0.02 to 0.05, the RMS responses of vertical displacement, nodal stress and cable axial force decrease by 8.1%, 6.7% and 17.9%, respectively. Since the mean component plays a significant role in the wind-induced response, the values of the gust response factor are not high for Expo Boulevard. 相似文献
11.
以显示动力学和接触碰撞理论为基础,应用ANSYS/LS-DYNA程序,对常规的泥石流重力拦挡坝和带支撑的新型拦挡坝进行了单个球体撞击下的多参数数值模拟计算及对比分析。结果表明：无论有无支撑,混凝土坝身的破坏模式均为由撞击区域应力骤增导致的局部混凝土压碎,但支撑使坝身迎击面应力分布均匀,提高了材料利用率;支撑能够显著减小混凝土坝顶动位移,最大减幅在30%以上,甚至可达近65%,坝身刚度得到大幅度提高;当撞击高度一定时,支撑间距越小,混凝土坝顶动位移越小;若设置了支撑,则可适当减小混凝土坝身厚度,其减小比例以1/3为宜;撞击力主要由混凝土坝身承担,其刚度显著大于支撑总刚度;撞击高度越高或者支撑间距越小,则混凝土坝底支反力所占比重相对越低,支撑的加强作用也就越显著。 相似文献
12.
在高应力状态下坝料的流变较为明显。为研究坝料流变对混凝土面板坝应力变形的影响,采用长科院九参数幂级数流变模型及其试验参数,对某高混凝土面板堆石坝进行应力、变形分析。结果表明,坝料流变使坝体变形明显增加,坝体应力有所减小。考虑坝料的流变特性后的面板法向位移(挠度)明显增加,面板坝轴向和顺坡向应力极值增加。对于分期浇筑面板和分期蓄水的高混凝土面板堆石坝,选用合适的流变本构模型正确地模拟堆石体的流变特性,可以为大坝填筑进度及面板分期浇筑时间的确定提供参考,并有助于正确地预测大坝的应力变形。 相似文献
13.
A new analytical development of the seismic hydrodynamic pressure inside pre-existing cracks on the upstream face of concrete dams is presented. The finite control volume approach is utilized to derive an expression for the seismic hydrodynamic pressure using the continuity principle and the linear momentum theorem for the fluid inside the crack. The derived pressure expression is a function of the relative crack-opening acceleration and velocity. The acceleration and velocity terms are then recast in the form of added mass and damping matrices which can then be included at the nodes inside the discrete crack of a finite element model. This procedure linearizes the solution of the problem. A dam, 55 m high and having an initial crack opening of 2 mm at the base or near the crest and subjected to two different accelerograms, is analysed. For high-frequency ground motion, the seismic hydrodynamic pressure inside the crack, at the base of the dam, appears to be 50 per cent higher than the corresponding hydrostatic pressure. 相似文献
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15.
为了研究混凝土重力坝在地震动荷载作用下的潜在失效模式，以金安桥碾压混凝土重力坝5号非溢流坝段为例，运用粘弹性边界法和流固耦合法建立了反映重力坝在地震动作用下动力响应特征的坝体-地基-库水抗震分析模型。基于增量动力分析（IDA）法:绘制了以相对位移转角为x轴（损伤指标，DM）和峰值地面加速度为y轴（强度指标，IM）的IDA曲线簇；分析了金安桥大坝在极端荷载作用下的潜在失效模式和其在不同峰值地面加速度下重力坝的损伤破坏过程。结果表明:金安桥大坝在地震动荷载作用下，可能发生功能失效的地方多出现在坝体折坡处、碾压分区交界处、坝踵与坝基交界处、廊道顶等应力集中处。因此，加强对这些区域的抗震防护有利于提高大坝整体的抗震水平。 相似文献
16.
《国际泥沙研究》2022,37(5):589-600
The dynamic impact force of debris flow on dams with a curved upstream face curved was investigated using laboratory experiments and a theoretical approach. Equations describing the impact force and maximum run-up height were derived. The experiments and theoretical considerations reveal that the impact force and maximum run-up height are mainly controlled by the Froude number (Fr) reduced by the cosine of the channel slope angle (cosα). Both the impact force and the maximum run-up height have a quadratic relation with the modified Froude number (Fr/(cosα)0.5). The experimental data and the results of the theoretical approach are in good agreement, indicating that the theoretical approach can be used in practical applications. It is concluded that the comparison between the curved-joint dam and the more conventional sharp-joint dam shows no differences in the maximum impact force and run-up height for the same modified Froude number. With the sharp-joint dam, the peak values of the impact force are reached more quickly than with the curved-joint dam. 相似文献
17.
Tensile stresses exceeding the tensile strength of concrete can develop in concrete dams subjected to earthquake ground motion. This study examines the earthquake response of gravity dams including tensile cracking of the concrete. The interaction between the dam and compressible water is included in the analysis using a numerical procedure for computing the non-linear dynamic response of fluid-structure systems. The crack band theory is used to model tensile cracking with modifications to allow for the large finite elements necessary for dam analysis. The earthquake response of a typical gravity dam monolith shows that concrete cracking is an important non-linear phenomenon. Cracking is concentrated near the base of the dam and near the discontinuities in the face slope. The extensive cracking, which develops due to ground motion typical of maximum credible earthquakes, may affect the stability of dams during and after strong earthquakes. 相似文献
18.
考虑流固耦合效应的辽宁葠窝水库溢流坝段抗震性能分析 总被引：1，自引：0，他引：1
针对辽宁葠窝水库混凝土重力坝抗震问题,采用耦合的拉格朗日-欧拉有限元分析技术,建立了可考虑库水-坝体-基岩动力耦合效应的典型溢流坝段抗震分析数值模型。模型中,采用等效一致粘弹性边界模拟基岩的人工截断边界;采用混凝土弥散裂缝本构模型模拟混凝土的动力特性。根据烈度与地震动之间的关系,确定了水库坝体抗震设计的输入加速度峰值。据此,分析了在不同季节水位变化条件下坝体地震反应的基本特性。研究表明：完好的辽宁葠窝水库混凝土重力坝溢流坝段能满足8度的抗震设防烈度要求。地震下溢流坝段峰值位移出现在胖坝和瘦坝的坝顶迎水面位置处,胖坝的动位移较瘦坝动位移大。胖坝在闸墩与溢流堰交接处出现了拉应力最大值。有库水条件下,瘦坝峰值拉应力出现在坝趾处,无库水条件下,瘦坝最大拉应力出现在溢流堰与闸墩交接处。 相似文献
19.
为限制隔震层位移，研发了同时提供刚度和阻尼力的新型弹塑性软碰撞防护装置，该装置主要由铅芯橡胶支座、剪力键及中空连接钢板组成。首先对铅芯橡胶支座进行了设计压应力12MPa下基本性能试验及压应力0 MPa下剪切试验；然后进行了弹塑性软碰撞防护装置的水平力学性能测试试验，测定装置的屈服后刚度、屈服力及支座顶端转角，探讨了剪力键外圆面罩橡胶套对试验结果的影响，对比分析了装置的水平力学性能指标与支座在0MPa下剪切试验结果的差异；最后，对弹塑性软碰撞防护装置进行了数值模拟，对比了数值模拟与试验的水平力-位移滞回曲线。结果表明:弹塑性软碰撞防护装置可提供刚度及阻尼力，在剪力键外圆面罩上橡胶套后对试验结果基本无影响；与0MPa下支座测试结果相比较，装置的屈服后刚度及屈服力有所降低；支座顶端转角随支座剪应变的增大而增大；数值模拟与试验的滞回曲线吻合良好，该装置具有良好的滞回耗能能力。 相似文献