Modal, Dynamic and Seismic Analyses of the Pine Flat Concrete Gravity Dam

Abstract

This paper presents studies (models used, calculations and results) performed at Sixense Necs in the context of the 15th ICOLD International Benchmark Workshop on Numerical Analysis of Dams. This work has been proposed by United States Society on Dams (USSD) and concerns the Pine Flat Gravity Dam. The formulated case studies define several different dynamic analyses of the dam, rock foundation and reservoir system. The model consists of the 15.24 m-wide 16th dam monolith (the tallest the monolithic block) and a corresponding strip of the foundation. The tri-dimensional mesh is exclusively composed of linear hexahedron elements. Mechanical behavior of the dam and the foundation is described using 3D continuous medium elements. Displacement restrictions are implemented as dam and foundation boundary conditions, adapted for each involved face. We use the first suggested case to discuss two assumptions: first the reservoir water level modelling influence (added mass or acoustic elements) and secondly massless foundation hypothesis consequences on modal analyses. This work leads us to better describe and understand harmonic crest excitation results and highlight modal analyses dependency of single harmonic excitations. Seismic transient linear and nonlinear analyses are then computed, with seismic loading introduced as an inertial loading. Several results such as dam crest acceleration and dam heel hydrodynamic pressure are presented and compared in order to assess the importance of reservoir water levels and dam material properties. Nonlinear computations show higher crest amplifications, which indicate a loss of dam body stiffness. All numerical analyses are carried out with Code_Aster® software [1].