Seismic Analysis of Pine Flat Concrete Dam

Abstract

Seismic safety of Pine Flat gravity dam is reevaluated by conducting a dam-reservoir-foundation interaction analysis. Contrary to conventional procedures, a foundation with mass is assumed and to avoid unrealistic detrimental effects of wave reflection at truncated boundaries of model, resort is made to non-reflecting boundary conditions. Plane strain 2D model with different element types are prepared. Solid elements are used to model dam and foundation. Compressible fluid elements is utilized in reservoir. Solid and fluid elements are tied (coupled) together on wet interfaces. To simulate elastic wave propagation in a uniform half-space and non-reflecting conditions at boundaries of truncated FE model, infinite elements along with appropriate free-field boundary conditions are incorporated. Efficiency of adopted numerical model is verified by imposing the foundation block to high and low frequency shear traction impulses applied at the base and calculating resulting velocity responses. Loading consists of self-weight, hydrostatic pressure, harmonic nodal force and base excitations due to earthquake records. Since, the FE model is a foundation with mass, thus the deconvolved acceleration records or the equivalent shear traction records are imposed at the base of foundation. Linear and nonlinear material properties are assumed for concrete. Nonlinearity is consistent with concrete damage plasticity model. In compression, uniaxial stress-strain relation as proposed by Saenz and in tension, stress-crack opening displacement relation as suggested by Hordijk are adopted. Analysis works consist of eigenvalue solution, displacement, acceleration and hydrodynamic pressure time histories for a few selected points. In addition, extent of damage suffered in dam when exposed to earthquake records of Taft and Endurance Time Acceleration Function is estimated.