Abstract
Calculating the natural frequency of dams is an essential part of its seismic behavior analysis. Therefore, it is important to calculate the natural frequency. This paper aims simulation and analysis the finite element (FE) model of the Koyna concrete gravity as a case study. For the investigation of the suitable mesh size to achievement the grid independence, the element size considered as a variable parameter and calculated its optimized value by using the Response Surface Optimization (RSO) method. In the independent grid, the Error Contour utilized for controlling mesh quality, which indicates fast variations of the energy in the adjacent elements and can recognize parts of the model that has a high error in calculating responses. The modal response of the dam with a rigid and flexible foundation with and without mass were appraised. The results indicated that modal frequencies in the condition of with and without Pre-stress were different value in all cases. Moreover, the frequency of first four modes by increasing mass and decreasing the stiffness of foundation, frequencies in the case without initial condition (without Pre-stress) has a slightly increased and in the case with initial condition (Pre-stress) had considerable decrease.
Highlights
In the design of structures based on the response spectrum, the period of the first mode of the structure is used to define spectrum acceleration (Sa)
A parametric study of the effect of different conditions on the frequency behavior of the dam was investigated by using the finite element method (FEM)
Due to the effect of discretization and dimensions of the elements on the stiffness and softness of the model, the effect of the mesh size on frequencies was investigated to optimize the dimensions of mesh based on grid independence
Summary
In the design of structures based on the response spectrum, the period of the first mode of the structure (structural period) is used to define spectrum acceleration (Sa). The results showed that the accurate modeling of dam-reservoir-foundation and their interaction considerably affects the modal periods, mode shapes and modal hydrodynamic pressure distribution. Sevim et al [9] determined the dynamic characteristics of a prototype arch-reservoir-foundation dam system using the modal analysis method including local vibration tests in the arc dam model identifying its natural frequencies and modes of vibration. Aghajanzadeh and Ghaemian [13] investigated the seismic performance of a concrete gravity dam to evaluate the effect of the foundation on the nonlinear response using the FEM They used an elasto-plastic formulation to model the foundation. Silveira and Pedroso [18] evaluated the influence of the foundation and reservoir on the dynamic response of concrete gravity dams as a function of their parameters in terms of natural frequencies and mode of vibration. The main innovations of this paper are the Response Surface Optimization (RSO) method utilization to investigate the influence of grid dimension on responses and the Error Contour method utilization to verify the appropriate dimension for the minimum computational error on achieving the grid independence
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