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1.
There are several alternatives to evaluate seismic damage‐cracking behavior of concrete arch dams, among which damage theory is the most popular. A more recent option introduced for this purpose is plastic–damage (PD) approach. In this study, a special finite element program coded in 3‐D space is developed on the basis of a well‐established PD model successfully applied to gravity dams in 2‐D plane stress state. The model originally proposed by Lee and Fenves in 1998 relies on isotropic damaged elasticity in combination with isotropic tensile and compressive plasticity to capture inelastic behaviors of concrete in cyclic or dynamic loadings. The present implementation is based on the rate‐dependent version of the model, including large crack opening/closing possibilities. Moreover, with utilizing the Hilber–Hughes–Taylor time integration scheme, an incremental–iterative solution strategy is detailed for the coupled dam–reservoir equations while the damage–dependent damping stress is included. The program is initially validated, and then, it is employed for the main analyses of the Koyna gravity dam in a 3‐D modeling as well as a typical concrete arch dam. The former is a major verification for the further examination on the arch dam. The application of the PD model to an arch dam is more challenging because the governing stress condition is multiaxial, causing shear damage to become more important than uniaxial states dominated in gravity dams. In fact, the softening and strength loss in compression for the damaged regions under multiaxial cyclic loadings affect its seismic safety. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
2.
Earthquake safety assessment of concrete arch and gravity dams 总被引：9，自引：1，他引：8
Based on research studies currently being carried out at Dalian University of Technology, some important aspects for the earthquake safety assessment of concrete dams are reviewed and discussed. First, the rate-dependent behavior of concrete subjected to earthquake loading is examined, emphasizing the properties of concrete under cyclic and biaxial loading conditions. Second, a modified four-parameter Hsieh-Ting-Chen viscoplastic consistency model is developed to simulate the rate-dependent behavior of concrete. The earthquake response of a 278m high arch dam is analyzed, and the results show that the strain-rate effects become noticeable in the inelastic range. Third, a more accurate non-smooth Newton algorithm for the solution of three-dimensional frictional contact problems is developed to study the joint opening effects of arch dams during strong earthquakes. Such effects on two nearly 300m high arch dams have been studied. It was found that the canyon shape has great influence on the magnitude and distribution of the joint opening along the dam axis. Fourth, the scaled boundary finite element method presented by Song and Wolf is employed to study the dam-reservoir-foundation interaction effects of concrete dams. Particular emphases were placed on the variation of foundation stiffness and the anisotropic behavior of the foundation material on the dynamic response of concrete dams. Finally, nonlinear modeling of concrete to study the damage evolution of concrete dams during strong earthquakes is discussed. An elastic-damage mechanics approach for damage prediction of concrete gravity dams is described as an example. These findings are helpful in understanding the dynamic behavior of concrete dams and promoting the improvement of seismic safety assessment methods. 相似文献
3.
Lateral response of dams in semi-elliptical rigid canyons 总被引：2，自引：0，他引：2
An analytical closed-form solution is developed for the lateral response of earth and rockfill dams built in semi-elliptical canyons. The dam is idealized as a linearly hysteretic elastic body deforming only in shear, whereas the canyon is assumed to be rigid. The solution for the dam response is given in terms of prolate spheroidal radial and angular functions of the first kind and zero order. Results are presented for natural frequencies, modal displacement shapes, participation factors, and response to transient and steady-state harmonic base excitation for various dam length-to-height ratios. Comparisons are made of the effects of the length-to-height ratio and the canyon shape on the response of dams built in semi-elliptical and rectangular canyons. A subsequent study (Dakoulas, P. & Hsu, C.H., Response of earth dams in semi-elliptical flexible canyons to oblique SH waves, Report, Rice University, Houston, Texas, 1993) extends this model to a semi-elliptical canyon consisting of flexible elastic rock, subjected to obliquely incident harmonic SH waves. 相似文献
4.
Inspired from the simplified single degree of freedom modeling approach used in the preliminary design of concrete gravity dams, a pseudo‐dynamic testing method was devised for the seismic testing of a concrete gravity dam section. The test specimen was a 1/75 scaled section of the 120‐m‐high monolith of the Melen Dam, one of the highest concrete gravity dams to be built in Turkey. The single degree of freedom idealization of the dam section was validated in the first stage of the study using numerical simulations including the dam–reservoir interaction. Afterwards, pseudo‐dynamic testing was conducted on the specimen using three ground motions corresponding to different hazard levels. Lateral displacement and base shear demands were measured. The crack propagation at the base of the dam was monitored with the measurement of the crack widths and the base sliding displacements. After the pseudo‐dynamic loading, a static pushover test was conducted to determine the reserve capacity of the test specimen. Despite major cracking at the base of the monolith, neither significant sliding nor a stability problem that might jeopardize the stability of the dam was observed. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
5.
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
6.
Numerical models of continental and submarine erosion: application to the northern Ligurian Margin (Southern Alps,France/Italy) 
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下载免费PDF全文 We present a new numerical surface process model allowing us to take into account submarine erosion processes due either to submarine landslides or to hyperpycnal currents. A first set of models show that the frequency of hyperpycnal flows influences the development of submarine canyons at the mouth of continental rivers. Further experiments show that an increase in submarine slope leads to faster regressive canyon erosion and a more dentritic canyon network, whereas increasing the height of the unstable sediment pile located on the shelf break leads to wider and less dendritic canyons. The models are then applied to the western segment of the north Ligurian margin (northwestern Mediterranean), which displays numerous submarine canyons with various sizes and morphologies. From west to east, canyon longitudinal profiles as well as margin‐perpendicular profiles progressively change from moderately steep, concave‐up shapes to steeper linear to convex‐up shapes suggesting increasing eastward margin uplift. Moreover, the foot of the margin is affected by a marked slope increase with evidences of mass transport due to landslides. Numerical models which reproduce well the North Ligurian margin morphologic features indicate that the western part of the margin is submitted to rather low (i.e. 0.4 mm yr?1) uplift and intense submarine erosion due to frequent hyperpycnal currents, whereas the eastern part bears more rapid (i.e. 0.7 mm yr?1) uplift and has little or no hyperpycnal currents. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
7.
This paper presents a step-by-step procedure using the three-dimensional boundary element approach to study the behavior of semi-circular canyons under seismic shear waves. The boundary element code TDASC allows utilization for various canyon geometries, evaluation of concurrent seismic waves and calculation of the ground motions on canyons due to an excitation at any arbitrary point of the incident field. Considering the widening ratio of the canyon(including prismatic, semi-prismatic and non-prismatic canyons), wave characteristics(wavelength, dimensionless period, direction) and maximum amplification pattern, the solution was applied to carry out a series of parametric studies. It was shown that canyon form can significantly affect the displacement amplification, especially at the points located on its edges. By increasing the wave dimensionless frequency(η 1), the amplification pattern becomes more complex. On the basis of the results from a variety of considered cases, a new expression has been presented for the limiting wavelength beyond which the widening of the canyon will not have a major effect on the displacement amplification. To verify the reliability of the proposed approach, the obtained results, expressed in terms of displacement amplitude, were compared with those from the available published literature and a reasonably good agreement was observed. 相似文献
8.
Uncertainties in structural engineering are often arising from the modeling assumptions and errors, or from variability in input loadings. A practical approach for dealing with them is to perform sensitivity and uncertainty analysis in the framework of stochastic and probabilistic methods. These analyses can be statically and dynamically performed through nonlinear static pushover and IDA techniques, respectively. Of the existing structures, concrete gravity dams are infrastructures which may encounter many uncertainties. In this research, probabilistic analysis of the seismic performance of gravity dams is presented. The main characteristics of the nonlinear tensile behavior of mass concrete, along with the intensity of earthquake excitations are considered as random variables in the probabilistic analysis. Using the tallest non‐overflow monolith of the Pine Flat gravity dam as a case study, its response under static and dynamic situations is reliably examined utilizing different combinations of parameters in the material and the seismic loading. The sensitivity analysis reveals the relative importance of each parameter independently. It will be shown that the undamaged modulus of elasticity and tensile strength of mass concrete have more significant roles on the seismic resistance of the dam than the ultimate inelastic tensile strain. In order to propagate the parametric uncertainty to the actual seismic performance of the dam, probabilistic simulation methods such as Monte Carlo simulation with Latin hypercube sampling, and approximate moment estimation techniques will be used. The final results illustrate the possibility of using a mean‐parameter dam model to estimate the mean seismic performance of the dam. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
9.
Panos Dakoulas 《Soil Dynamics and Earthquake Engineering》2012,34(1):11-24
The seismic behavior of tall concrete face rockfill dams in narrow canyons is investigated, based on numerical simulation of the staged construction, creep settlements, reservoir impoundment and seismic shaking of the dam. The study takes into account the flexibility of the canyon rock, the hydrodynamic effects and potential dynamic rockfill settlements. The static analysis uses a hyperbolic model for the rockfill, whereas the dynamic analysis uses a nonlinear hysteretic model, which accounts for the initial dynamic stiffness and produces hysteresis loops in agreement with the experimental data regarding the shear modulus and damping ratio. A damage plasticity model is used for the reinforced concrete, whereas frictional contact behavior is considered at the base and vertical walls of the concrete slab panels. An existing 150-m-high dam is used to investigate some key issues on the seismic behavior of such dams subjected to upstream−downstream and vertical excitation. Emphasis is placed on the evaluation of the tensile stresses within the slab panels, the compressive stresses at the slab-to-slab vertical interfaces and the opening of the joints. Moreover, the effect of potential dynamic settlements on both the slab stresses and joint openings is investigated. Recommendations for increasing the dam safety and reducing the water leakage through the dam body are given. 相似文献
10.
In this paper a general methodology for the analysis of large concrete dams subjected to seismic excitation is outlined. It is valid both for gravity dams (2D representation) and arch dams (3D representation). The method allows for non-linear material behaviour of the dam, ‘transparent fictitious boundaries’ for dealing properly with in-coming and out-going seismic waves, and an efficient procedure to deal with dam-soil-fluid interaction. The mechanical behaviour of concrete is modelled using an isotropic damage model which allows for tension and compression damage, and exhibits stiffness recovery upon load reversals. Emphasis is placed in the treatment of fluid-structure interaction, regarding both formulation and efficiency aspects. A gravity dam and an arch dam are analysed subjected to artificially generated earthquakes of different intensities, and the results are used to study the degree of (un)safety of the dams. 相似文献
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A new method is presented to study the scattering and diffraction of plane SH-waves by periodically distributed canyons in a layered half-space. This method uses the indirect boundary element method combined with Green’s functions of uniformly distributed loads acting on periodically distributed inclined lines. The periodicity feature of the canyons is exploited to limit the discretization effort to a single canyon, which avoids errors induced by the truncation of the infinite boundary, and the computational complexity and the demand on memory can be significantly reduced. Furthermore, the total wave fields are decomposed into the free field and scattered field in the process of calculation, which means that the method has definite physical meaning. The implementation of the method is described in detail and its accuracy is verified. Parametric studies are performed in the frequency domain by taking periodically distributed canyons of semi-circular and semi-elliptic cross-sections as examples. Numerical results show that the dynamic responses of periodically distributed canyons can be quite different from those for a single canyon and significant dynamic interactions exist between the canyons. 相似文献
13.
A finite element model of incremental displacement constraint equations (IDCE), based on an existing node‐to‐surface concept, is implemented to deal with dynamic contact surfaces in the seismic behaviour analysis of cracked concrete gravity dams. After verification for sliding, rocking and impact, the IDCE model is applied to study the seismic responses of concrete gravity dams with different profiles and crack locations for a variety of parameters, such as coefficient of friction, water level and type of earthquake, as well as impact damping based on the concept of coefficient of restitution. It is revealed that cracked concrete gravity dams can experience not only sliding and rocking modes, but also the drifting mode in some cases of crack either at the base or at a height. Downstream sliding is normally accompanied by rocking, especially for the cases of crack at a height. Due to rocking and drifting, a cracked dam may still acquire a certain amount of residual sliding even if the effective coefficient of friction is relatively high. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
14.
A general procedure for analysis of the response of concrete gravity dams, including the dynamic effects of impounded water and flexible foundation rock, to the transverse (horizontal) and vertical components of earthquake ground motion is presented. The problem is reduced to one in two dimensions, considering the transverse vibration of a monolith of the dam. The system is analysed under the assumption of linear behaviour for the concrete, foundation rock and water. The complete system is considered as composed of three substructures—the dam, represented as a finite element system, the fluid domain, as a continuum of infinite length in the upstream direction, and the foundation rock region as a viscoelastic half-plane. The structural displacements of the dam are expressed as a linear combination of Ritz vectors, chosen as normal modes of an associated undamped dam-rock system. The effectiveness of this analytical formulation lies in its being able to produce excellent results by considering only a few Ritz vectors. The generalized displacements due to earthquake motion are computed by synthesizing their complex frequency responses using Fast Fourier Transform procedures. The stress responses are calculated from the displacements. An example analysis is presented to illustrate results obtained from this analytical procedure. Computation times for several analyses are presented to illustrate the effectiveness of the procedure. 相似文献
15.
A new concept to determine state of the damage in concrete gravity dams is introduced. The Pine Flat concrete gravity dam has been selected for the purpose of the analysis and its structural capacity, assuming no sliding plane and rigid foundation, has been estimated using the two well‐known methods: nonlinear static pushover (SPO) and incremental dynamic analysis (IDA). With the use of these two methods, performance and various limit states of the dam have been determined, and three damage indexes have been proposed on the basis of the comparison of seismic demands and the dam's capacity. It is concluded that the SPO and IDA can be effectively used to develop indexes for seismic performance evaluation and damage assessment of concrete gravity dams. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
16.
This paper proposes a new algorithm for modeling the nonlinear seismic behavior of fractured concrete gravity dams considering dam–reservoir interaction effects. In this algorithm, the cracked concrete gravity dam is modeled by distinct element (DE) method, which has been widely used for the analysis of blocky media. Dynamic response of the reservoir is obtained using boundary element (BE) method. Formulation and various computational aspects of the proposed staggered hybrid approach are thoroughly discussed. To the authors' knowledge, this is the first study of a hybrid DE–BE approach for seismic analysis of cracked gravity dam–reservoir systems. The validity of the algorithm is discussed by developing a two-dimensional computer code and comparing results obtained from the proposed hybrid DE–BE approach with those reported in the literature. For this purpose, a few problems of seismic excitations in frequency- and time-domains, are presented using the proposed approach. Present results agree well with the results from other numerical methods. Furthermore, the cracked Koyna Dam is analyzed, including dam–reservoir interaction effects with focus on the nonlinear behavior due to its top profile crack. Results of the present study are compared to available results in the literature in which the dam–reservoir interaction were simplified by added masses. It is shown that the nonlinear analysis that includes dam–reservoir interaction gives downstream sliding and rocking response patterns that are somehow different from that of the case when the dam–reservoir interaction is approximated employing added masses. 相似文献
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18.
《Soil Dynamics and Earthquake Engineering》2012,32(12):1678-1689
Study on the failure process of high concrete dams subjected to strong earthquakes is crucial to reasonable evaluation of their seismic safety. Numerical simulation in this aspect involves dynamic failure analysis of big bulk concrete dam subjected to cyclic loading. The Rock Failure Process Analysis (RFPA) proposed by C.A. Tang, with successful applications to failure modeling of rock and concrete specimens mainly subjected to static loading, is extended for this purpose. For using the proposed model, no knowledge on the cracking route needs to be known beforehand, and no remeshing is required. Simulation of the whole process of elastic deformation, initiation and propagation of microcracks, severe damage and ultimate failure of concrete dams in earthquakes with a unified model is enabled. The model is verified through a shaking table test of an arch dam. Finally a practical gravity dam is employed as a numerical example. Considering the uncertainty in ground motion input and concrete material, typical failure process and failure modes of gravity dam are presented. Several small cracks may occur due to tension particularly at dam neck, dam faces and dam heel, and a few of them evolve into dominant ones. Relatively smaller earthquake may cause damage to the dam neck while a bigger one may bring on cracks at lower parts of the dams. Cracking at the dam bottom may incline to a direction almost perpendicular to the downstream face after propagating horizontally for a certain distance when the shaking is strong enough. 相似文献
19.
In this study, the earthquake damage response of the concrete gravity dams is investigated with considering the effects of dam–reservoir interaction. A continuum damage model which is a second-order tensor and includes the strain softening behavior is selected for the concrete material. The mesh-dependent hardening technique is adopted such that the fracture energy dissipated is not affected by the finite element mesh size. The dynamic equilibrium equations of motion are solved by using the improved form of the HHT-α time integration algorithm. Two dimensional seismic analysis of Koyna gravity dam is performed by using the 1967 Koyna earthquake records. The effects of damage on the earthquake response of concrete gravity dams are discussed. Comparison of the Westergaard and Lagrangian dam–reservoir interaction solutions is made. The effects of viscous damping ratio on the damage response of the dam are also studied. 相似文献
20.
Ryan T. Bailey Eric D. Morway Richard G. Niswonger Timothy K. Gates 《Ground water》2013,51(5):752-761
A numerical model was developed that is capable of simulating multispecies reactive solute transport in variably saturated porous media. This model consists of a modified version of the reactive transport model RT3D (Reactive Transport in 3 Dimensions) that is linked to the Unsaturated‐Zone Flow (UZF1) package and MODFLOW. Referred to as UZF‐RT3D, the model is tested against published analytical benchmarks as well as other published contaminant transport models, including HYDRUS‐1D, VS2DT, and SUTRA, and the coupled flow and transport modeling system of CATHY and TRAN3D. Comparisons in one‐dimensional, two‐dimensional, and three‐dimensional variably saturated systems are explored. While several test cases are included to verify the correct implementation of variably saturated transport in UZF‐RT3D, other cases are included to demonstrate the usefulness of the code in terms of model run‐time and handling the reaction kinetics of multiple interacting species in variably saturated subsurface systems. As UZF1 relies on a kinematic‐wave approximation for unsaturated flow that neglects the diffusive terms in Richards equation, UZF‐RT3D can be used for large‐scale aquifer systems for which the UZF1 formulation is reasonable, that is, capillary‐pressure gradients can be neglected and soil parameters can be treated as homogeneous. Decreased model run‐time and the ability to include site‐specific chemical species and chemical reactions make UZF‐RT3D an attractive model for efficient simulation of multispecies reactive transport in variably saturated large‐scale subsurface systems. 相似文献