Seismic analysis of dam-foundation-reservoir system including the effects of foundation mass and radiation damping

One of the main concerns in using commercial software for finite element analyses of dam-foundation-reservoir systems is that the simplifying assumptions of the massless foundation are unreliable. In this study, an appropriate direct finite element method is introduced for simulating the mass, radiation damping and wave propagation effect in foundations of damfoundation-reservoir systems using commercial software ABAQUS. The free-field boundary condition is used for modeling the semi-infinite foundation and radiation damping, which is not a built-in boundary condition in most of the available commercial software for finite element analysis of structures such as ANSYS or ABAQUS and thus needs to be implemented differently. The different mechanism for modeling of the foundation, earthquake input and far-field boundary condition is described. Implementation of the free-field boundary condition in finite element software is verified by comparing it with analytical results. To investigation the feasibility of the proposed method in dam-foundation-reservoir system analysis, a series of analyses is accomplished in a variety of cases and the obtained results are compared with the substructure method by using the EAGD-84 program. Finally, the massed and massless foundation results are compared and it is concluded that the massless foundation approach leads to the overestimation of the displacements and stresses within the dam body.

Effect of seismic wave propagation in massed medium on rate-dependent anisotropic damage growth in concrete gravity dams

Seismic modeling of massive structures requires special caution,as wave propagation effects significantly affect the responses.This becomes more crucial when the path-dependent behavior of the material is considered.The coexistence of these conditions renders numerical earthquake analysis of concrete dams challenging.Herein,a finite element model for a comprehensive nonlinear seismic simulation of concrete gravity dams,including realistic soil-structure interactions,is introduced.A semi-infinite medium is formulated based on the domain reduction method in conjunction with standard viscous boundaries.Accurate representation of radiation damping in a half-space medium and wave propagation effects in a massed foundation are verified using an analytical solution of vertically propagating shear waves in a viscoelastic half-space domain.A rigorous nonlinear finite element model requires a precise description of the material response.Hence,a microplane-based anisotropic damage-plastic model of concrete is formulated to reproduce irreversible deformations and tensorial degeneration of concrete in a coupled and rate-dependent manner.Finally,the Koyna concrete gravity dam is analyzed based on different assumptions of foundation,concrete response,and reservoir conditions.Comparison between responses obtained based on conventional assumptions with the results of the presented comprehensive model indicates the significance of considering radiation damping and employing a rigorous constitutive material model,which is pursued for the presented model.