Dynamic Response Of Concrete Dams Research Articles

Uncertainty quantification of the effect of concrete heterogeneity on nonlinear seismic response of gravity dams including record-to-record variability

Although the effects of the concrete heterogeneity on the seismic response of concrete gravity dams have been explored based on random finite element method, the results of different studies vary greatly and there are few quantitative studies on the effects. In addition, the correlation between concrete modulus and strength is usually ignored, which is a departure from the reality. In this study, the effects of the concrete heterogeneity on the nonlinear seismic response of concrete gravity dams under different input ground motions are systematically studied based on random field theory. The dispersion and uncertainty of the seismic responses and the damage pattern are quantified. In addition, the effects of the correlation between concrete modulus and strength are also investigated and quantified based on the cross-correlated random fields simulation method. It is found that the effects of the concrete heterogeneity on the nonlinear dynamic response of concrete dams are strongly dependent on the input seismic motions, which provides an explanation for the conflicts in the previous studies. The results also show that the correlation between concrete modulus and strength has important effects on the dispersion of the seismic response and damage pattern of concrete gravity dams. Under certain ground motions, ignoring the correlation may underestimate the failure probability of the dams.

Structural Behavior of a Coupled Concrete Dam-Reservoir system under Effect of Earthquake loads Using Concrete Damaged Plasticity Model

In this study the effect of dam-reservoir interaction on the dynamic response of gravity dam by assuming the mass concrete is able to be cracked and crushed in tension and compression, respectively is considered. Where the effect of reservoir fluctuation on the dynamic response of concrete dam is investigated. In this study, to simulate the nonlinear behavior of concrete and specifying the position and direction of cracks which is occurred in gravity dam, the concrete damaged plasticity model is used. The results of this study indicate that, the maximum relative displacement in the downstream direction of a dam subjected to an earthquake is occurred when the height of water in the reservoir is at the middle of the dam. In addition, in the case of water level in the reservoir is at the base of dam, the maximum relative displacement of the dam is at the upstream.

Nonlinear dynamic response of concrete gravity dams considering the deconvolution process

In order to model any physical system, including concrete dams, one needs to apply simplifications to the real system to make the modeling feasible. To study the dynamic response of concrete dams, relevant assumptions are made regarding foundation modeling, input motion mechanism, dam-reservoir interaction, and material behavior. Some of these simplifications may lead to more conservative and uneconomical outcomes. In this paper, nonlinear time-domain dynamic analyses are conducted to evaluate the effect of the input motion mechanism on the concrete gravity dam response. An ideal model of a dam-reservoir-foundation system, considering the inertia of the foundation, appropriate boundary conditions and precise deconvolved base motions, is selected as the reference model. The process of deconvolution of seismic waves through the frequency- and time-domain approaches is discussed, and suggestions for the selection of an appropriate damping model for the rock foundation are presented. The results are compared to those of the standard model of a massless foundation system as recommended by the US Army Corps of Engineers. The numerical results indicate that, generally, the nonlinear response of the two dam models follow similar patterns, but with a larger amplitude for the massless system. It is noted that the consequence of neglecting the dynamic effect of the foundation can be significant. Additionally, the results demonstrate that the degree of overestimation varies dramatically for the various seismic excitations. The average overestimation of the massless system for the crest displacement, crest acceleration, and the contact opening and sliding are 57%, 45%, 152%, and 90%, respectively. It is further shown that the use of the deconvolved input excitation at the base of the finite foundation derived from the frequency-domain approach can yield discrepancies between the target and convolved surface ground motions, which can also have a considerable effect on the dam response.

A New Cavitation Simulation Method: Dam-Reservoir Systems

Based on one-fluid cavitation model, a novel finite element method for the simulation of acoustic cavitation is presented. The proposed approach is used to investigate cavitation effects on dynamic response of concrete dams. The resultant nonlinear equation of motion of fluid domain is discretized using a pressure-based finite element method and a standard displacement-based finite element formulation is used to discretize linear equation of structure motion. An iterative partitioned solution method is applied for the simultaneous integration of coupled equations.

Finite element simulation of acoustic cavitation in the reservoir and effects on dynamic response of concrete dams

A 3D finite element formulation for the dynamic analysis of concrete dams is presented. A mixed Eulerian–Lagrangian formulation is used to simulate fluid–structure system. During severe ground motion, the impounding fluid in the reservoir may separate from the dam and causes forming of micro bubbles. As a result, the compressibility of water is reduced. This nonlinear phenomenon of the reservoir is termed as cavitation. When the direction of ground motion is changed, the micro bubble's region of fluid collapses, and an impact will occur. In order to eliminate the spurious oscillations, which are caused by the impact, a small amount of artificial stiffness proportional damping is added in the fluid domain. To capture cavitation effects a bilinear equation of state is employed and incorporated with finite element formulation of fluid domain. An iterative partitioned method is used to simultaneous time integration of equations of motion of fluid and structure domains. The developed method is validated by testing it against problem for which, there is existing solution. Also the effects of cavitation on dynamic response of Koyna gravity dam and Morrow Point arch dam subjected to the first 6 second of the May 1940 El-Centro, California earthquake, is considered. In order that truly consider the effects of cavitation phenomenon, maximum acceleration was scaled to give an amplitude of 1 g. Obtained results show that impact force caused by cavitation has a small effect on the dynamic response of dam–reservoir systems.

Earthquake safety assessment of concrete arch and gravity dams

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.