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1.
Newmark永久位移是评价边坡在地震时稳定性的一个重要指标,近年来广泛应用于地震边坡危险性评价中。传统Newmark永久位移法在计算临界加速度时假定其为常数,未考虑滑动面上抗剪强度参数的变化,过低估计了边坡的永久位移。为了解决这一问题,本文从岩土结构理论获得思路,详细分析滑块底面抗剪强度参数在地震中的变化过程,以边坡震动过程中黏聚力逐步丧失为基本思路,在黏聚力符合一定概率分布的基础上,提出了一种利用蒙特卡罗法模拟其动态减小过程从而实现临界加速度动态变化的计算方法。经过算例计算,黏聚力和临界加速度体现了地震过程中边坡滑块黏聚力和临界加速度的动态变化,位移大小符合地震边坡实际位移的常规数值。本文提出的蒙特卡罗法实现动态黏聚力和动态临界加速度的计算过程与地震时程相对应,不仅在一定程度上解决了抗剪强度参数的动态变化问题,还解决了传统Newmark位移计算中永久位移比实际位移偏小的问题。 相似文献
2.
在区域边坡地震危险性评价中主要采用永久位移预测模型进行地震边坡永久位移计算。永久位移预测模型以Newmark滑块理论为基础,通过大量实测地震时程记录统计拟合得出。针对Newmark理论中滑动面抗剪强度参数保持不变和已有位移预测模型的计算位移小于实测位移的问题,利用动态临界加速度理论,分别构建含有峰值加速度和阿里亚斯强度的两种位移预测模型。对该模型计算出的永久位移合理性进行讨论,发现永久位移计算结果符合滑坡实测位移的数量级。采用本文模型计算的永久位移更加接近地震滑坡位移实际大小,可以解决一直存在的预测位移小于实测位移的问题。在更进一步讨论发展的基础上,本文模型可满足更多的理论应用和工程实际,为区域边坡地震危险性评价提供思路。 相似文献
3.
基于动态临界加速度计算地震边坡永久位移的方法应用了边坡分布的不均匀性，不均匀分布程度影响着永久位移计算结果。研究Newmark滑块底部或潜在滑动面上抗剪强度参数的分布特征，有利于了解地震过程中临界加速度的分布和变化过程，为地震边坡永久位移计算参数选取提供依据。通过计算发现：边坡土体标准差的线性关系比较微弱，在缺乏实验数据时，仅可参考使用；黏聚力随机数个数达到200时所计算的永久位移数值不再有波动；黏聚力无论设置为正态分布还是对数正态分布均不影响永久位移计算结果；黏聚力标准差的数值大小对永久位移的大小和离散性影响很大。在地震边坡计算时，尽量将其设置为符合正态分布；尽量根据实测数据设定黏聚力标准差，若缺乏实测资料，可参考两者的线性关系并结合经验进行标准差设定。 相似文献
4.
The paper focuses on seismic sliding displacement calculations of gravity wall bridge abutments when subjected to passive condition during earthquakes. Pseudo-dynamic approach has been used for the calculation of the passive seismic earth pressure. A novel element of the present investigation is the computation of seismic passive earth pressure coefficients by considering the composite curved rupture surface behind the abutment wall in the framework of limit equilibrium method. Sliding failure along the wall base is considered in the new pseudo-dynamic method. The critical seismic acceleration coefficient for sliding and sliding component of the displacement, resulting from horizontal and vertical sinusoidal ground accelerations, are computed by using Newmark's sliding block method. The effect of sliding on the response of earth structures is evaluated and comparisons are made between sliding displacements calculated using planar and composite failure mechanisms. Results of the comparative study showed that the assumption of planar failure mechanism for rough soil–wall interfaces significantly overestimates the critical seismic accelerations for sliding and underestimates the sliding displacements. 相似文献
5.
Soil shear wave velocity has been recognized as a governing parameter in the assessment of the seismic response of slopes. The spatial variability of soil shear wave velocity can influence the seismic response of sliding mass and seismic displacements. However, most analyses of sliding mass response have been carried out by deterministic models. This paper stochastically investigates the effect of random heterogeneity of shear wave velocity of soil on the dynamic response of sliding mass using the correlation matrix decomposition method and Monte Carlo simulation(MCS). The software FLAC 7.0 along with a Matlab code has been utilized for this purpose. The influence of statistical parameters on the seismic response of sliding mass and seismic displacements in earth slopes with different inclinations and stiffnesses subject to various earthquake shakings was investigated. The results indicated that, in general, the random heterogeneity of soil shear modulus can have a notable impact on the sliding mass response and that neglecting this phenomenon could lead to underestimation of sliding deformations. 相似文献
6.
Rigid sliding block analysis is a common analytical procedure used to predict the potential for earthquake-induced landslides
for natural slopes. Currently, predictive models provide the expected level of displacement as a function of the characteristics
of the slope (e.g., geometry, strength, yield acceleration) and the characteristics of earthquake shaking (e.g., peak ground
acceleration, peak ground velocity). These predictive models are used for developing seismic landslide hazard maps which identify
zones with risk of earthquake-induced landslides. Alternatively, these models can be combined with Shakemaps to generate “near-real-time”
Slidemaps which could be used, among others, as a tool in disaster management. Shakemaps (a publicly available free service
of the United States Geological Survey, USGS) provide near-real-time ground motion conditions during the time of an earthquake
event. The ground motion parameters provided by a Shakemap are very useful for the development of Slidemaps. By providing
ground motion parameters from an actual earthquake event, Shakemaps also serve as a tool to decouple the uncertainty of the
ground motion in sliding displacements prediction. Campania region in Italy is studied for assessing the applicability of
using Shakemaps for regional landslide-risk assessment. This region is selected based on the availability of soil shear strength
parameters and the proximity to the 1980 Irpina (M
w
= 6.9) Earthquake. 相似文献
7.
Flow and deformation failure of sandy slopes 总被引：2，自引：0，他引：2
The effects of earthquake induced pore pressure on seismic and post seismic stability conditions of cohesionless slopes are investigated with reference to the infinite slope scheme. In cohesionless slopes the shear strength reduction caused by pore pressure build-up may lead the slope to a deformation failure or to a flow failure if liquefaction conditions are approached. Two critical values of the seismic induced pore pressure ratio are introduced to evaluate the effect of shear strength reduction on the slope failure mechanism. The results are given in the form of stability charts and a procedure for the evaluation of the seismic stability condition is described. The procedure gives useful information about the failure mechanism that slopes may exhibit and the displacement analysis which should be carried out. 相似文献
8.
This paper presents a comprehensive study on the rigid block sliding displacement of slopes subjected to ground motions with large velocity pulses. A comparison of the performance of various existing empirical displacement models is provided through analyses of the displacement residuals of slopes subject to pulse-like motions. Except for the PGA- and PGV-based Saygili and Rathje model (2008, referred to as SR08), positive medians of residuals are observed for selected models, indicating an under-estimation. There is a negative constant shift in the total residuals for the SR08 model, which can be easily fixed by changing the constant term in the predictive equation. The residuals from the SR08 model also have the smallest standard deviation compared to the other models. A modified SR08 model is developed for predicting rigid block sliding displacements for pulse-like motions. The modified predictive model is used in probabilistic seismic displacement analyses of slopes in a hypothetical near-fault region. 相似文献
9.
A co-seismic viscoplastic sliding model, composed of two consequential behaviour phases, was realised in order to assess the co-seismic and post-seismic stability of natural slopes. The model takes into consideration the development and distribution of available strengths in pre-seismic conditions, as well as the viscoplastic behaviours manifested during monotonic and impulsive fast shearing tests on different clayey soils. In relation to the strength increase produced by the shear displacement rate, phase I is present during sliding on pre-existing failure surfaces at the residual state and/or in weak bands at the fully softened state. In this latter case, this is limited to small displacements. Conversely, phase II is characterised by strength decrease and occurs if and when the inertial dynamic load mobilises the “impulsive critical shear strength”, which is greater than the shear strength available in the pre-seismic static field. This implies the development of a first failure or a new failure surface with high shear displacements along these surfaces. The simplified dynamic analysis for infinite slopes, integrated by the behaviour model introduced in this paper, highlights a less conservative nature in comparison to that of the classic Newmark approach with one single exception. This occurs on attainment of the “static break point” where the co-seismic displacements obtained are comparable or even greater than those attainable from the classic Newmark approach. Furthermore, in relation to the co-seismic development of shear strength, it is possible to estimate in the short term as well as in the long term the post-seismic instability after the main shock. 相似文献
10.
Deterministic sliding block methods for estimating seismic displacements of earth structures 总被引：5，自引：0，他引：5
A review and quantitative comparison of existing deterministic sliding block methods for predicting permanent displacements of earth structures subjected to seismic loading is presented. The reviewed sliding block methods are divided into two main groups based on the characteristic earthquake parameters referenced in each method. One group uses the maximum horizontal ground acceleration and velocity, and the other uses the maximum horizontal ground acceleration and the predominant period of the acceleration spectrum. Displacement functions published by previous authors are reformulated to give common non-dimensionalized displacement functions of the critical acceleration ratio which are then used to compare the different methods for the estimate of permanent seismic displacement of soil structures. The results show that despite the fact that the different methods were formulated using a wide range of earthquake records and different characteristic seismic parameters, permanent displacement values predicted using these methods fall within a reasonably narrow band. Selected acceleration data from three recent earthquakes that occurred in California are used to evaluate and compare the accuracy of the reviewed displacement methods for practical applications. 相似文献
11.
地震引起的滑坡对生命、环境和经济造成了巨大的威胁。目前，对于地震作用下边坡稳定性的研究主要集中在单一滑动面破坏模式，对于具有多个潜在滑动面边坡的地震稳定性研究比较欠缺。基于此，利用有限差分软件FLAC对不同边坡进行地震稳定性数值模拟，对比分析不同强度地震动作用下均质土体、分层土体和含软弱夹层土体边坡的滑动面演化过程和永久变形分布特征。结果表明：对于均质边坡，地震引起的滑动面为单一的整体滑动面，地震动强度的增加仅导致沿滑动面的永久变形量增大；对于非均质边坡，在地震作用下还可能形成通过土层交界面的局部滑动变形，且地震作用下最先形成和发生变形的滑动面与静力条件下得到的最小安全系数对应的最危险滑动面一致；同时，地震引起的边坡浅层和深层变形破坏存在复杂的相互影响，当局部浅层滑动先发生时，地震动的进一步增大很容易诱发更深层的坡体滑动，而当深层滑动先发生时，由于塑性变形影响地震惯性力向上部坡体的传播，浅层坡体的进一步滑动变形相对较难被触发。 相似文献
12.
Cheung Pakchiu 《地震工程与工程振动(英文版)》2012,11(2):173-183
During past strong earthquakes, highway bridges have sustained severe damage or even collapse due to excessive displacements and/or very large lateral forces. For commonly used isolation bearings with a pure friction sliding surface, seismic forces may be reduced but displacements are often unconstrained. In this paper, an alternative seismic bearing system, called the cable-sliding friction bearing system, is developed by integrating seismic isolation devices with displacement restrainers consisting of cables attached to the upper and lower plates of the bearing. Restoring forces are provided to limit the displacements of the sliding component. Design parameters including the length and stiffness of the cables, friction coefficient, strength of the shear bolt in a fixed-type bearing, and movements under earthquake excitations are discussed. Laboratory testing of a prototype bearing subjected to vertical loads and quasi-static cyclic lateral loads, and corresponding numerical finite element simulation analysis, were carried out. It is shown that the numerical simulation shows good agreement with the experimental force-displacement hysteretic response, indicating the viability of the new bearing system. In addition, practical application of this bearing system to a multi-span bridge in China and its design advantages are discussed. 相似文献
13.
Miguel B. Brito Mitsuyoshi Akiyama Yoshitaka Ichikawa Hiroki Yamaguchi Riki Honda Naomitsu Ishigaki 《地震工程与结构动力学》2020,49(8):817-837
A novel low-cost friction sliding system for bidirectional excitation is developed to improve the seismic performance of reinforced concrete (RC) bridge piers. The sliding system is a spherical prototype developed by combining a central flat surface with an inclined spherical segment, characterized by stable oscillation and a large reduction in response accelerations on the flat surface. The inclined part provides a restoring force that limits the residual displacements of the system. Conventional steel and concrete are employed to construct a flat-inclined spherical surface atop an RC pier. The seismic forces are dissipated through the frictions generated during the sliding movements; hence, the seismic resilience of bridges can be ensured with a low-cost design solution. The proposed system is fabricated utilizing a mold created by a three-dimensional printer, which facilitates the use of conventional concrete to construct spherical shapes. The concrete surface is lubricated with a resin material to prevent abrasion from multiple input ground motions. To demonstrate the effectiveness of the system, bidirectional shaking table tests are conducted in the longitudinal and transverse directions of a scaled bridge model. The effect of the inclination angle and the flat surface size is investigated. The results demonstrate a large decrease in response acceleration when the system exhibits circular sliding displacement. Furthermore, the inclination angle that generates the smallest residual displacement is identified experimentally. 相似文献
14.
To study the effectiveness of sliding supports in isolating structures from damaging earthquake ground motions, a mathematical model of a single degree of freedom structure supported on a sliding foundation and subjected to the N-S component of the El Centro 1940 earthquake is considered. Spectra for absolute accelerations, relative displacements, relative-to-ground displacements, sliding displacements and residual sliding displacements are evaluated for three mass ratios, four coefficients of friction and a damping of 5 per cent critical. It is observed that, for structures with periods less than 1-8 s, for the coefficients of friction considered, the suprema of relative-to-ground displacements, sliding displacements and residual sliding displacements are only of the order of 1–25 times the peak ground displacement. To study the response sensitivities, the spectra for absolute acceleration and sliding displacement of the 1949 Olympia earthquake (S86E component) are also presented. It is concluded that sliding supports can be quite effective in isolating structures from support excitations. 相似文献
15.
Jeen-Shang Lin 《地震工程与结构动力学》1990,19(6):911-923
A method for constructing seismic slope failure probability matrices is presented. The core of the method is a probabilistic sliding block model which allows for systematic incorporation of the uncertainties associated with both the ground excitation and the strength of the slope materials. The extent of damage to a slope is defined in terms of the magnitude of the earthquake-induced permanent displacement. The intensity of the ground shaking is characterized by a peak ground acceleration as well as an earthquake magnitude, and the possible scatter in the ground motion details is included through the use of an equivalent stationary motion model. After the effects of essential contributing factors are discussed, regional seismic slope failure probability matrices are presented for general applications. 相似文献
16.
Decoupled seismic analysis of an earth dam 总被引：2，自引：0，他引：2
The seismic stability of an earth dam is evaluated via the decoupled displacement analysis using the accelerograms obtained by ground response analysis to compute the earthquake-induced displacements. The response analysis of the dam is carried out under both 1D and 2D conditions, incorporating the non-linear soil behaviour through the equivalent linear method. Ten artificial and five real accelerograms were used as input motions and four different depths were assumed for the bedrock.1D and 2D response analyses were in a fair agreement with the exception of the top third of the dam where only a 2D modelling of the problem could ensure that the acceleration field is properly described. The acceleration amplification ratio obtained in the 2D analyses was equal to about 2 in all the cases considered, consistently with data from real case histories.The maximum permanent displacements computed by the sliding block analysis were small, being less than 10% of the service freeboard; a satisfactory performance of the dam can then be envisaged for any of the seismic scenarios considered in the analyses. 相似文献
17.
本文通过弹性和弹塑性时程分析,研究了水平地震作用下梁铰型屈服RC框架模型结构的楼层屈服剪力系数、基本自振周期、楼层数3个因素对弹塑性位移增大系数的影响,通过非线性回归分析给出了弹塑性层间位移增大系数经验公式;通过分析滞回耗能沿楼层高度的分布,初步确定了梁铰型屈服RC框架结构的薄弱楼层位置;基于结构损伤分析,讨论了抗震规范中RC框架结构弹塑性层间位移角限值的水准。 相似文献
18.
After the occurrence of various destructive earthquakes in Japan, extensive efforts have been made to improve the seismic performance of bridges. Although improvements to the ductile capacities of reinforced concrete (RC) bridge piers have been developed over the past few decades, seismic resilience has not been adequately ensured. Simple ductile structures are not robust and exhibit a certain level of damage under extremely strong earthquakes, leading to large residual displacements and higher repair costs, which incur in societies with less-effective disaster response and recovery measures. To ensure the seismic resilience of bridges, it is necessary to continue developing the seismic design methodology of RC bridges by exploring new concepts while avoiding the use of expensive materials. Therefore, to maximize the postevent operability, a novel RC bridge pier with a low-cost sliding pendulum system is proposed. The seismic force is reduced as the upper component moves along a concave sliding surface atop the lower component of the RC bridge pier. No replaceable seismic devices are included to lengthen the natural period; only conventional concrete and steel are used to achieve low-cost design solutions. The seismic performance was evaluated through unidirectional shaking table tests. The experimental results demonstrated a reduction in the shear force transmitted to the substructure, and the residual displacement decreased by establishing an adequate radius of the sliding surface. Finally, a nonlinear dynamic analysis was performed to estimate the seismic response of the proposed RC bridge pier. 相似文献
19.
The essence of performance-based design of gravity earth-retaining structures lies in the estimation of the residual (i.e. permanent) displacements after a seismic event. The accomplishment of this task however can be very complicated due to two interacting phenomena: the coupled sliding and tilting rigid body motion of the wall on an inelastic base and the formation of failure surfaces in the soil backfill. In this study a large number of fully non-linear, time-history analyses of gravity retaining walls (GRW) were performed using advanced numerical modelling. Different types of soil parameters and varying wall geometry within a practical range were investigated. The influence of different ground motion parameters was discussed and the results were compared with some of the most common limit equilibrium Newmark׳s sliding block procedures, including the recommendations by Eurocode 8, Part 5 [20]. Lastly, some recommendations for fast preliminary assessment of the seismic permanent displacements of GRW were provided. 相似文献