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1.
Ground motion records obtained in recent major strong earthquakes have provided evidence that ground motions recorded near the near-fault regions differ in many cases from those observed further away from the seismic source. As the forward directivity and fling effect characteristics of the near-fault ground motions, they have the potential to cause more considerable damage to structures during an earthquake. Therefore, understanding the influence of near-fault ground motions on the performance of structures is critical to mitigate damage and perform effective response. This paper presents results of a study aimed at evaluating the effects of near-fault and far-fault ground motions on seismic performance of concrete gravity dams including dam-reservoir-foundation interaction. Koyna gravity dam is selected as a numerical application. Four different near-fault ground motion records with an apparent velocity pulse are used in the analyses. The earthquake ground motions recorded at the same site from other events that the epicenter far away from the site are employed as the far-fault ground motions. The seismic performance evaluation method based on the demand-capacity ratio, the cumulative overstress duration and the spatial extent of overstressed regions is presented. The concrete damaged plasticity model including the strain hardening or softening behavior is employed in nonlinear analyses. Nonlinear seismic damage analyses of the selected concrete dam subjected to both near-fault and far-fault ground motions are performed. The results obtained from the analyses show the effects of near-fault ground motions on seismic performance of concrete gravity dams and demonstrate the importance of considering the near-fault ground excitations. 相似文献
2.
Finite element method (FEM) is effectively used for evaluating roller-compacted concrete (RCC) dams, especially in high seismicity zones. The aim of this study is to investigate the effect of various reservoir lengths on the seismic response of a selected RCC dam under strong ground motion effects. Six different reservoir lengths, the lengths varies from h/2 to 10h (h, the height of dam), are used within finite element models. The hydrodynamic pressure of the reservoir water is modelled with the 2D fluid finite elements based on the Lagrangian approach. The horizontal and vertical components of the 1989 Mw 6.9 Loma Prieta earthquake are utilized in numerical analyses. The non-linear time-history analyses of those six models are investigated by using Drucker-Prager material model. According to the numerical analysis, it is obvious that the seismic behavior of the RCC dams is considerably dependent on the reservoir length. By increasing the length, we have obtained higher displacement values, which exist until the reservoir length reaches the 3h; at increased lengths, the values remain stable. This result proposes that 3h reservoir length is adequate to assess the seismic response of RCC dams. The principal tensile stresses are relatively lower in non-linear analysis compared to linear analyses. However, the principal compression stresses are close to each other in linear and non-linear analyses. The results imply that the non-linear response is influential on the total seismic response of a dam, which cannot be neglected in numerical analysis. 相似文献
3.
Dams constructed on the seismically active regions have a high-risk potential for downstream life and property. Strong ground
motion can result in instability of the dam and strength loss of foundation. Active faults within the foundation of dam have
the potential to cause damaging displacement of the structures. Appropriate design measures should be considered to obtain
rational solution to the problem of catastrophic release of water from the reservoir, and especially to resist earthquake
loads. Safety concerns for dams under the earthquake loads involve the seismic hazard evaluation of dam site for the overall
stability of structure. Various types of analyses can be used, ranging from a simplified analysis to more complex procedures
based on ground motion parameters and response spectra. This paper briefly evaluates seismic hazard analyses for dam structures,
and introduces the analyses for thirty-six dams with height ranging from 15 to 195 m in Kızılırmak basin, Turkey. The seismic
hazard analyses have indicated that peak ground acceleration varies within a wide range (0.09–0.45 g) for the dam sites of
the basin. 相似文献
4.
Natural Hazards - This study presents a numerical investigation on the seismic behaviour of aged concrete gravity dams under near source and far source ground motions. Two-dimensional formulation... 相似文献
5.
Comparison of near-fault and far-fault ground motion effects on geometrically nonlinear earthquake behavior of suspension bridges 总被引：2，自引：1，他引：1
Süleyman Adanur Ahmet Can Altuni?ik Alemdar Bayraktar Mehmet Akk?se 《Natural Hazards》2012,64(1):593-614
This paper presents a comparison of near-fault and far-fault ground motion effects on geometrically nonlinear earthquake behavior of suspension bridges. Bo?azi?i (The First Bosporus) and Fatih Sultan Mehmet (Second Bosporus) suspension bridges built in Istanbul, Turkey, are selected as numerical examples. Both bridges have almost the same span. While Bo?azi?i Suspension Bridge has inclined hangers, Fatih Sultan Mehmet Suspension Bridge has vertical hangers. Geometric nonlinearity including P-delta effects from self-weight of the bridges is taken into account in the determination of the dynamic behavior of the suspension bridges for near-fault and far-fault ground motions. Near-fault and far-fault strong ground motion records, which have approximately identical peak ground accelerations, of 1999 Chi-Chi, 1999 Kocaeli, and 1979 Imperial Valley earthquakes are selected for the analyses. Displacements and internal forces of the bridges are determined using the finite element method including geometric nonlinearity. The displacements and internal forces obtained from the dynamic analyses of suspension bridges subjected to each fault effect are compared with each other. It is clearly seen that near-fault ground motions are more effective than far-fault ground motion on the displacements and internal forces such as bending moment, shear force and axial forces of the suspension bridges. 相似文献
6.
综合采用时程分析法、整体变形分析法（等效节点力法和软化模量法）、极限平衡法等方法,以小打鹅尾矿库为例,分析了该高堆尾矿坝的永久变形和动力稳定性。分析了干滩面长度、尾矿堆积坝高度、设计地震加速度等影响因素对尾矿坝的安全系数和永久变形的影响,以及地震作用下尾矿坝安全系数的时程变化规律。结果表明：尾矿坝的地震永久变形与一般土石坝的存在差异,其水平方向的永久变形大于竖直方向的永久变形,且永久变形与坝高不一定呈单调递增关系;地震中尾矿坝的最小安全系数与各影响因素大体呈线性关系,而坝顶处的震陷与各影响因素之间呈非线性关系;地震过程中尾矿坝瞬时安全系数具有波动降低的特点,为此,完善了地震作用下尾矿坝最小平均安全系数的计算方法。该研究表明小打鹅尾矿库坝体的抗震性能能够满足相应抗震设防要求。 相似文献
7.
对国家强震动台网中心紫坪铺面板堆石坝区域台站实测主震记录以及大坝台网实测余震记录进行分析,研究主震与强余震地震动的基本特征。分别选取茂县地办、郫县走石山、成都中和这3组基岩台站实测主震地震动,紫坪铺台站2008年11月6日实测余震地震动以及按水工抗震规范人工生成地震动作为数值计算的地震动输入,对紫坪铺大坝进行三维动力有限元分析,并与实测结果进行对比。研究表明,郫县走石山与成都中和2个远场台站位于断层下盘,其实测地震动的加速度反应谱长周期（0.65 s以后）分量过于丰富,不宜作为断裂带附近紫坪铺大坝的地震动输入;紫坪铺大坝台站实测的余震地震动1 Hz附近（大坝基频）的频率成分相对较少,且持续时间较短,以至于难以激发大坝响应;对比坝顶实测地震动加速度反应谱和数值计算反应谱,建议汶川地震中紫坪铺大坝动力计算时可采用茂县地办台站实测地震动或按抗震设计规范反应谱人工生成地震动。 相似文献
8.
Farshid Vahedifard Christopher L. Meehan 《Geotechnical and Geological Engineering》2011,29(6):1023-1034
Predictive displacement-based methods provide a useful index of the seismic performance of earth dams and embankments and
can be used in preliminary assessments of these structures. In practice, simplified Newmark-type sliding block methods are
commonly used for this purpose. Using a database of 122 previously published case histories of permanent deformations of earth
dams and embankments, the performance of six simplified sliding block models was examined. The results show that all six simplified
methods underpredict seismic displacement for many of the embankment and earth dam cases that were examined, sometimes by
a significant amount. An empirical correlation was developed by performing linear multiple regression analysis utilizing multiple
slope and ground motion input parameters. This approach is believed to more properly reflect strong ground motion characteristics
than the use of a single ground motion parameter such as the peak ground acceleration, the approach that has been previously
employed in other correlations of this type. After exploring numerous functional forms, the final resulting seismic displacement
correlation that was proposed was determined to be a function of the critical acceleration, the critical acceleration ratio,
the slope height, the peak ground acceleration, the peak ground velocity, the spectral acceleration, and the predominant period
of earthquake shaking. The proposed empirical equation yields better correlation with the case history database than does
other existing empirical correlations or simplified sliding block models. 相似文献
9.
Takashi Furumura Shunsuke Takemura Shinako Noguchi Teito Takemoto Takuto Maeda Kazuhisa Iwai Simanchal Padhy 《Landslides》2011,8(3):333-338
The dense recordings of the K-NET and KiK-net nationwide strong motion network of 1,189 accelerometers show clearly the radiation
and propagation properties of the strong ground motions associated with the 2011 off-the-Pacific Coast-of-Tohoku, Japan (Mw = 9.0)
earthquake. The snapshots of seismic wave propagation reveal strong ground motions from this earthquake that originate from
three large slips; the first two slips occurred over the plate interface of off-Miyagi at the southwest and the east of the
hypocenter, and the third one just beneath the northern end of Ibaraki over the plate interface or in the crust. Such multiple
shocks of this event caused large accelerations (maximum 1–2 G) and prolonged ground shaking lasting several minutes with
dominant high-frequency (T < 1 s) signals over the entire area of northern Japan. On the other hand, ground motions of relatively longer–period band
(T = 1–2 s), which caused significant damage to wooden-frame houses, were about 1/2–1/3 of those observed near the source area
of the destructive 1995 Kobe, Japan (M = 7.3) earthquake. Also, the long-period (T = 6–8 s) ground motion in the Kanto (Tokyo) sedimentary basin was at an almost comparable level of those observed during
the recent Mw = 7 inland earthquakes, but not as large as that from the former M = 8 earthquakes. Therefore, the impact of
the strong ground motion from the present M = 9 earthquake was not as large as expected from the previously M = 7–8 earthquakes
and caused strong motion damage only to short-scale construction and according to instruments inside the buildings, both have
a shorter (T < 1 s) natural period. 相似文献
10.
High and Aswan Dams Authority (HADA) proposed a plan aiming at constructing a rockfill dam in the Kalabsha area, about 60 km south of Aswan High Dam. The aim of this dam is to restrain the overflow of water to the Kalabsha Valley for keeping one billion cubic meters from being lost due to seepage and evaporation. The safety of dams during earthquakes is extremely important because failure of such a structure may have disastrous consequences on life and property. Therefore, different factors were considered as part of a site assessment. Five seismic source zones, close enough to the site to give rise to potentially damaging earthquake ground motions, were identified. Seven active faults that have the potential for producing significant earthquakes and that pass through or near the dam site were also identified. The earthquake loading represented by ground motions at the site was evaluated. Probabilistic seismic hazard procedures were used for assessing the earthquake loading at six individual sites using Area-and Line-Source Models (ASM & LSM). The ASM is based on current observed seismicity, whereas the LSM is based on geological slip rates. The output represents the expected acceleration amplitude with 90 percent probability of not being exceeded in exposure times of 20, 50, and 100 years. The results from the two models appear to be different, the expected ground motions from ASM were twice as high as expected from LSM. This difference is due to the load of the Aswan reservoir (Nasser Lake) triggering earthquakes on those parts of the faults that lie under the lake at Kalabsha area. The hazard at the selected sites is given by the hazard curve that is represented by the relationship between the peak ground acceleration and its annual exceedance probability. By comparing the curves for the six individual sites for the same source model, it can be concluded that the potential ground acceleration level for all the sites is almost the same. Considering the mean results from the two models, the annual exceedance probability of the expected ground acceleration from ASM is approximately ten times higher than the annual exceedance probability from LSM.Since ASM is based on current seismicity, it is more appropriate forrepresenting the actual hazard for the dam site. 相似文献
11.
《Engineering Geology》2007,89(1-2):155-170
Reservoirs constructed near urban areas pose a high-risk potential for downstream life and property. Turkey is one of the most seismically active regions in the world and has at least 1200 large dams with different types. Major earthquakes with the potential of threatening life and property occur frequently here. The Euphrates basin studied in this article is located in a seismically very active part of Turkey. The northern part of the basin is structurally cut by numerous faults. Many large dams are located on or close to these faults. In this paper we summarize the methods used for the analysis of seismic hazards and total risk, discuss the seismic hazards of thirty-two large dams constructed on the Euphrates basin on the basis of the seismic activity of the dam site and their total risk as based on physical properties and the position in the basin. The seismic hazard analyses have indicated that peak ground acceleration changes within a wide range (0.011 g and 0.564 g) for the dam sites of the basin. A seismic hazard map showing the equivalent PGA (peak ground acceleration) values was developed so as to use for the preliminary analysis of dam structures, which will be designed in the basin. The total risk analyses depending on the seismic hazard rating of dam site and risk rating of the structure have concluded that fifteen large dams have high-risk class in the basin. These dams must be analyzed with high priority and redesigned to increase the safety of the embankments and their appurtenant structures, if necessary. 相似文献
12.
通过动力有限元时程法分析了金沙江阿海混凝土重力坝在设计地震动(0.344g)作用下的动态响应,计算模型考虑了动水压力作用、大坝-岩基相互作用,用黏弹性吸波边界模拟了地震动能量向无限远域逸散的地基“辐射阻尼”效应。通过将坝体惯性力时程极大值与振型分解反应谱法的惯性力极值对比,从而验证了复杂动力数值模拟结果的正确性,为后续分析打下了基础。采用沿滑面的应力积分法得到了大坝沿建基面的瞬态抗滑安全系数时程。计算结果表明：阿海重力坝在设计地震动(0.344g)作用下的安全系数时程的极小值为1.146,大坝整体稳定性良好,可不采取提高整体抗滑 相似文献
13.
This paper presents a numerical investigation of the seismic response of earth dams by employing results from 110 nonlinear two-dimensional (2D) dynamic analyses of four different cross-sections with heights ranging from 20 to 120 m. The analyses were of a parametric nature, considering the effects of seismic excitation characteristics (intensity and frequency content), foundation soil stiffness, and the existence of typical stabilising berms and/or an impounded reservoir. The results of these studies indicated that the predominant period of a dam’s vibration was strongly affected by its height and the input motion characteristics. The results also indicated that the peak acceleration at the dam’s crest was governed by its height, the input motion characteristics, and the stiffness of the foundation soil, but not by the other parameters. These same analyses yielded results on pseudo-static seismic coefficients for a total of 1084 potential sliding masses within the analysed cross-sections, demonstrating that the seismic coefficients decreased as the sliding mass became deeper and bulkier, increased if the mass was located upstream rather than downstream, and were strongly affected by the seismic excitation characteristics and stiffness of the foundation soil. Moreover, these results allowed for a thorough evaluation of existing methodologies for seismic coefficient estimation, quantifying their accuracy and depicting their limitations. This evaluation process also illustrated the fact that there is currently no methodology accounting for all significant problem parameters. 相似文献
14.
Economic importance of major ports is well known, and if ports are located in seismically active regions, then site-specific
seismic hazard studies are essential to mitigate the seismic risk of the ports. Seismic design of port sites and related structures
can be accomplished in three steps that include assessment of regional seismicity, geotechnical hazards, and soil structure
interaction analysis. In the present study, site-specific probabilistic seismic hazard analysis is performed to identify the
seismic hazard associated with four typical port sites of Gujarat state (bounded by 20°–25.5°N and 68°–75°E) of India viz.
Kandla, Mundra, Hazira, and Dahej ports. The primary aim of the study is to develop consistent seismic ground motion for the
structures within the four port sites for different three levels of ground shaking, i.e., operating level earthquake (72 years
return period), contingency level earthquake (CLE) (475 year return period), and maximum considered earthquake (2,475 year
return period). The geotechnical characterization for each port site is carried out using available geotechnical data. Shear
wave velocities of the soil profile are estimated from SPT blow counts using various empirical formulae. Seismicity of the
Gujarat region is modeled through delineating the 40 fault sources based on the seismotectonic setting. The Gujarat state
is divided into three regions, i.e., Kachchh, Saurashtra, and Mainland Gujarat, and regional recurrence relations are assigned
in the form of Gutenberg-Richter parameters in order to calculate seismic hazard associated with each port site. The horizontal
component of ground acceleration for three levels of ground shaking is estimated by using different ground motion attenuation
relations (GMAR) including one country-specific GMAR for Peninsular India. Uncertainty in seismic hazard computations is handled
by using logic tree approach to develop uniform hazard spectra for 5% damping which are consistent with the specified three
levels of ground shaking. Using recorded acceleration time history of Bhuj 2001 earthquake as the input time motion, synthetic
time histories are generated to match the developed designed response spectra to study site-specific responses of port sites
during different levels of ground shaking. It is observed that the Mundra and Kandla port sites are most vulnerable sites
for seismic hazard as estimated CLE ground motion is in order of 0.79 and 0.48 g for Mundra and Kandla port sites, respectively.
Hazira and Dahej port sites have comparatively less hazard with estimated CLE ground motion of 0.17 and 0.11 g, respectively.
The ground amplification factor is observed at all sites which ranges from 1.3 to 2.0 for the frequency range of 1.0–2.7 Hz.
The obtained spectral accelerations for the three levels of ground motions and obtained transfer functions for each port sites
are compared with provisions made in Indian seismic code IS:1893-Part 1 (2002). The outcome of present study is recommended for further performance-based design to evaluate the seismic response of the
port structures with respect to various performance levels. 相似文献
15.
土工结构地震滑动位移统计分析 总被引：1，自引：0，他引：1
土工结构在地震荷载下的滑动位移是评估结构安全性能的重要参数。采用一种新型的地震波选择方法,在强震数据库中选择修改地震波,以有效地在结构动力分析中引入不同特征地震波的影响。通过一个简单的土工结构地震滑移模型,系统地分析了结构基本周期和滑动面屈服系数对地震滑移概率及相应滑移距离的影响,并提出了滑动体在不同地震场景和基本周期条件下的滑移概率和累积滑动位移的统计模型,对基于性能的土工结构抗震设计具有重要的参考意义。 相似文献
16.
In this paper, the gravity dam–water–foundation system including the physical and mechanical properties of the sediment at the reservoir bottom is modelled using a finite element and infinite element coupling model. The sediment at the reservoir bottom has been assumed to be a viscoelastic solid medium. The effects of thickness, elastic modulus, Poisson's ratio and material damping of the sediment on the response of the dam have been studied. The related numerical results from this study illustrated that the existence of the sediment at the bottom of the reservoir has significant effects on the response of concrete gravity dams since the soft layer of the sediment plays two main roles in the dam–water–foundation system, the energy dissipation of the system and the amplification of the incident wave on the water–sediment interface. It is the amplified acceleration on the water–sediment interface that results in different mechanisms of the effect of the sediment on the response of the dam. Therefore, apart from the incident wave, the thickness, the softness and the damping ratio of the sediment can also affect the response of the dam. 相似文献
17.
The assessment of local site effects on seismic ground motions is of great importance in earthquake engineering practice.
Several destructive earthquakes in the past have demonstrated that the amplification of ground motion and associated damage
to structures due to local site conditions is a significant consideration in earthquake hazard analysis. A recent paper published
in this journal highlights the hazard posed by earthquakes in the megacity of Kolkata in India due to its seismic and geological
settings. The seismic hazard assessment study speculates that the deep alluvial deposit in the city may increase the seismic
hazard probably due to the amplification of the seismic energies. This paper focuses on the seismic response studies of the
various soil strata (i.e. for local subsurface conditions) obtained from various construction sites in the city for predicted
earthquake. It is very well recognized that site response studies (a part of seismic microhazard zonation for urban areas)
are the first step towards performance-based foundation design or seismic risk analysis and mitigation strategy. One of the
problems for carrying out site-specific study in Kolkata is the lack of recorded strong motion data in the city. Hence, this
paper outlines a methodology to carry out site-specific study, where no strong motion data or seismic data are available.
The methodology uses wavelet-based spectrum compatibility approach to generate synthetic earthquake motions and equivalent
linear method for seismic site response analysis. The Mega City of Kolkata has been considered to explain the methodology.
Seismic hazard zonation map by the Bureau of Indian Standards classifies the City of Kolkata as moderate seismic zone (Zone
III) with a zone factor 0.16. On the other hand, GSHAP(Global Seismic Hazard Assessment Program) map which is based on 10%
probability of exceedance in 50 years specifies a maximum peak ground acceleration (PGA) of 1.6 m/s2 (0.163 g) for this region. In the present study, the seismic response has been carried out based on GSHAP. The results of
the analysis indicate the amplification of ground motion in the range of 4.46–4.82 with the fundamental period ranging from
0.81 to 1.17 s. Furthermore, the maximum spectral accelerations vary in the range of 0.78–0.95 g. 相似文献
18.
In the present study an analytical procedure based on finite element technique is proposed to investigate the influence of vertical load on deflection and bending moment of a laterally loaded pile embedded in liquefiable soil, subjected to permanent ground displacement. The degradation of subgrade modulus due to soil liquefaction and effect of nonlinearity are also considered. A free headed vertical concrete elastic nonyielding pile with a floating tip subjected to vertical compressive loading, lateral load, and permanent ground displacement due to earthquake motions, in liquefiable soil underlain by nonliquefiable stratum, is considered. The input seismic motions, having varying range of ground motion parameters, considered here include 1989 Loma Gilroy, 1995 Kobe, 2001 Bhuj, and 2011 Sikkim motions. It is calculated that maximum bending moment occurred at the interface of liquefiable and nonliquefiable soil layers and when thickness of liquefiable soil layer is around 60% of total pile length. Maximum bending moment of 1210 kNm and pile head deflection of 110 cm is observed because of 1995 Kobe motion, while 2001 Bhuj and 2011 Sikkim motions amplify the pile head deflection by 14.2 and 14.4 times and bending moment approximately by 4 times, when compared to nonliquefiable soil. Further, the presence of inertial load at the pile head increases bending moment and deflection by approximately 52% when subjected to 1995 Kobe motion. Thus, it is necessary to have a proper assessment of both kinematic and inertial interactions due to free field seismic motions and vertical loads for evaluating pile response in liquefiable soil. 相似文献
19.
This paper presents the numerical and experimental investigation of a dam foundation. The site consists of granite and especially
weathered granite. Numerical and analytical analyses have been conducted to evaluate suitability of the granite for a dam
foundation. Mohr–Coulomb failure criterion has been used to calculate the compressive strength of the rock mass. Finite element
implementation of Mohr–Coulomb criterion has been used for deformation and settlement analysis. Packer testing and in-situ
estimation of rock mass deformability using the Goodman jack have been performed. The results of the evaluations show that
very small normal and differential settlements can be expected in structural regions due to dam construction, and the compacted
concrete dam can safely be constructed on either the competent granite or the weathered granite. However, the dam foundation
on the weathered granite has high conductivity potential problems for the reservoir. 相似文献
20.
M. A. Hariri-Ardebili P. Boodagh 《Georisk: Assessment and Management of Risk for Engineered Systems and Geohazards》2019,13(1):34-52
This paper presents a methodology to evaluate the seismic reliability of geostructures in an optimal way. Taguchi design of experiments are adopted to find the most efficient and cost-effective combination of material properties in the uncertainty domain. Twelve uniform and mixed design models are tested. A polynomial-based response surface meta-model is built for each one and the accuracy of perdition is examined using 10,000 Monte Carlo simulations. A two-dimensional gravity dam is used as a vehicle for probabilistic transient analyses. The ground motion record-to-record variability is added as well using over one hundred earthquake records selected based on probabilistic seismic hazard analysis. Dynamic sensitivity of epistemic random variables are evaluated for the first time. Finally, an efficient and practical procedure is proposed in order to determine the reliability index of the geostructures. This approach, in fact, can be generalised for any type of engineering structures dealing with multi-hazard problems. 相似文献