Sharif Digital Repository

At the present study, application of endurance time analysis (ETA) method in seismic evaluation of arch dams is investigated. ETA is a time-history based dynamic pushover procedure, which utilizes a set of predesigned intensifying acceleration functions to estimate the responses of the structural systems in various seismic excitation levels. Dez dam was chosen as the case study and all contraction and peripheral joints were modeled based on as-built drawings. The reservoir was modeled as a compressible medium and the foundation was assumed to be massless. Results show that ETA method is able to estimate dynamic responses of the dam with acceptable accuracy in comparison with time history... 

At present study, Endurance Time (ET) method that is a new dynamic pushover procedure is introduced and its application in predicting concrete arch dam behavior in linear domain is investigated. In this method structure is subjected to gradually intensifying acceleration functions. DEZ arch dam was selected as case study. FE model of dam-reservoir-foundation was excited in three levels of MCL, MDL, DBL using six records scaled based on design spectrum of the site and results were compared with those obtained from ET analyses. It was found that results obtained from ET method at equivalent target time are in good agreement with extreme results obtained from exciting the system using natural... 

Concrete arch dam is a complex geometric structure and designing such a structure requires experience and high knowledge. One of the important parameters in designing concrete arch dams is the tensile stress in arch concrete material. The static analysis results of high arch dam structure depend on structure analysis model, intensively. Stage construction is needed to be focused in modeling high arch dams. In this study, the necessity of considering stage construction in static analysis of dam structure is focused. Modeling stage construction uses Birth and Death technique of elements. Therefore, six stage construction models are provided including applying dam wall weight outright, two... 

Modal identification is a type of system identification, which studies on the modal parameters of systems by using modal test. In the case of using operational or ambient modal analysis, there is no need to measure excitation, and the system output data are adequate for identification purposes. These modal parameters of system are of great importance from the engineering point of view particularly in the area of system identification, damage detection, and condition monitoring. In a fully-automated identification approach, the modal parameters are extracted without intervention of a specialized user. In this study, a Fully Automated Operational Modal Identification algorithm is developed to... 

A three-dimensional finite element analysis was carried out to determine the annual variation of temperature and thermal stresses of a concrete arch dam. Appropriate heat transfer boundary conditions in the dam body were used for air and reservoir temperature as well as solar radiation variations. Karaj arch dam in Iran was used as a case study. The rate of convergence of the numerical solution is examined. Results of the finite element analysis show that probable cracks occur in a very narrow region of the downstream face. Thermal loads have the most significant effects for causing downstream cracks in comparison with self-weigh and hydrostatic loads. The cracked areas of downstream face... 

A novel and robust approach is proposed to find the optimum shape of concrete arch dams located on any unsymmetrical shape of a valley. The approach is capable of finding the optimum shape for any given valley type in suitable time, based on abutment stability analysis, against thrust forces from an arch dam. The behavior and stability of a concrete arch dam is strongly dependent on the bedrock on which the dam rests. The stability of the abutment is considered a constraint in the proposed approach. In addition, a new objective function is introduced to decrease the final volume of the arch dam. Furthermore, a computer program was developed, which takes the effect of the dam foundation... 

Seismic performance and safety of a jointed arch dam, as an arch-shaped mass concrete structure, are investigated through the nonlinear incremental dynamic analysis. In this way, 12 proper ground motions are selected, each of them is scaled to 12 successively increasing intensity levels and applied to the dam. Three and seven contraction joints are inserted within the dam body, and stage construction is taken into account. Several main assumptions including dam–reservoir–foundation dynamic interaction, absorbing boundary conditions at the far-ends of the reservoir and foundation, and material and joint nonlinearities are considered. The failure modes of the dam are determined according to... 

One of the methods in limiting tensile stresses in arch dams and removing stress concentrations at the dam-foundation interface is setting the dam body on a concrete saddle called a Pulvino. In the present study, the effects of Pulvino and peripheral joints on the static behavior and seismic performance of arch dams are investigated. Dez Dam with a height of 203 m was selected as a case study and all contraction joints of the dam body were modeled using the discrete crack approach based on as-built drawings. Also, the surrounding rock was modeled as a mass-less medium tied to Pulvino. The dam-reservoirfoundation system was analyzed under static loads accounting for stage construction... 

In the present paper, effects of non-uniform excitation due to spatially variation of seismic waves under the reservoir bottom on linear and nonlinear responses of arch dams are studied. Foundation is assumed to be massed and infinite elements are utilized to model semi-infinite medium via the far-end boundary of the foundation FE model. A continuum crack propagation model based on the smeared crack approach in 3D space is introduced. Reservoir's water is assumed compressible and the coupled system is solved using the staggered method. As a case study, Amir-Kabir double curvature arch dam in Iran is selected to investigate seismic behavior of the system. Two cases are analyzed in which wave... 

The purpose of this paper is to determine the optimal shape of double curvature concrete arch dams by using the sensitivity of design objective to design variables. Design sensitivities quantify the relationship between the design variables such as thickness of crown cantilever, left and right abutment thickness, crown cantilever upstream profile, radius of curvature of water and air faces on one hand and the objective function such as the volume of the concrete arch dam on the other hand. For this aim, first a methodology was developed to provide interface between a finite element method and an optimization algorithm for shape optimization of double curvature concrete arch dams. The... 

In this study, multi-criteria shape optimization of an asymmetrical doublecurvature arch dam is presented. Simultaneous cost minimization of dam construction and maximum allowable tensile stress are investigated for an economical and safe design approach in the current study. Pareto front method was used to balance both the economy and safety of the design simultaneously, which can be difficult for both analysts and decision-makers. A non-dominated solution based on the important parameters of dam analysis and design is presented. To help decision-makers in their decision, two different methods are proposed. These methods for the case of an arch dam are Lombardi coefficient and equilibrium... 

Abutments of concrete arch dams are usually crossed by several joints, which may create some rock wedges. Abutment stability analysis and controlling the probable wedge movements is one of the main concerns in the design procedure of arch dams that should be investigated. For decades, the quasi-static method, due to its simple approach, has been used by most of dam designers. In this study, the dynamic method is presented and the obtained time history of sliding safety factors is compared with the quasi-static results. For this purpose, all three components of Kobe (1979) and Imperial Valley (1940) earthquakes are applied to the wedge, simultaneously, and the magnitude and direction of wedge... 

Recorded ground accelerations at various locations of Karun III Dam during November 20, 2007, were recorded by an array of accelerometers located on the dam. In terms of amplitude and phase, these accelerations show non-uniformities in different elevations. In this paper, the effect of these non-uniform ground motions on the seismic response of the dam taking dam-reservoir-foundation interaction into account is investigated. The EACD-3D-2008 finite element program and ABAQUS Software are used for carrying out the seismic analyses. For this purpose, time histories of the earthquake accelerations are interpolated at nodal points located on the dam foundation interface. The analysis has been... 

Damage assessment of concrete arch dams is carried out through nonlinear Incremental Dynamic Analysis (IDA) of a typical arch dam. In this study the Morrow Point arch dam is subjected to a set of 12 three-component earthquakes each scaled to 12 increasing intensity levels. The dam-foundation interaction effects have been investigated by varying foundation's modulus of elasticity to be equal and half of dam concrete's modulus of elasticity. Damage propagation through the dam body is investigated and various IDA curves are created. The performance and various limit-states of the dam structure are examined based on the obtained results. Simple damage indices are proposed through comparison of... 

In the present paper, the seismic response of an arch dam subjected to spatial variation of ground motions along the interface with its foundations is investigated. Recorded ground accelerations at the dam foundation interface of an arch dam were used for the purpose of this investigation. Topographic amplification between various points of the interface was studied by obtaining ratios of the response spectral displacement and spectral pseudo acceleration. Time shift and amplification between stations show the nonuniform nature of ground motions for large structures like dams. Recorded ground accelerations were interpolated for different nodes of the finite element model. The seismic... 

This paper describes a methodology to develop the interface between a finite element software and optimization algorithm for optimization of concrete high arch dams. The objective function is the volume of the dam. The numbers of design variables are 31 including the thickness and upstream profile of crown cantilever, thickness of the left and right abutments, radius of curvature of water and air faces left and right by use of polynomial curve fitting and cubic spline function. The constraint conditions are the geometric shape, stress, and the stability against sliding. Initially, a program is developed in MATLAB in order to generate the coordinates of nodes; then, finite element software... 

In the present paper, spatially variation input effects on seismic responses of arch dams have been studied. Recorded ground accelerations at the dam foundation interface of Pacoima dam during January 13, 2001 were used for the purpose of this investigation. A numerical finite element model was developed for dynamic analysis of the dam reservoir system. The modified version of NSAD-DRI finite element program was used for the analysis and the ground acceleration time histories were interpolated at all dam foundation interface nodal points. Total and pseudo static displacements as well as developed stresses due to uniform and non uniform excitations are obtained. The results reveal that... 

Investigation of the dynamic characteristics of an existing structure system based on field tests is of practical significance, since it can be employed in the field of examining construction quality, validating or improving analytical finite element structural models, or conducting damage assessment. The main purpose of this study is to investigate the dynamic characteristics of dams using the seismic response data. Whereas, in the process of frequency domain identification of dam properties, frequency response function (FRF) plays the most important role, evaluating the corresponding parameters with better accuracy has always been desirable. Therefore, a comparison was made between some... 

A finite element model for seismic analysis of concrete arch dams is proposed. Material inelasticity as well as joints nonlinearity is considered. A damage-plastic formulation governs nonlinear behavior of concrete. Degeneration occurring during nonlinear behavior of concrete induces anisotropy into its microstructure. This anisotropy becomes more complex in seismic simulations, in which the state of stress expeditiously changes with time. Thus, anisotropic formulation is preferred over classical isotropic models. Utilizing rate-dependent anisotropic damage-plastic model, irreversible deformations, stiffness degeneration, induced anisotropy, closing/reopening of cracks, and viscous response...