CURRENT METHODOLOGY AT THE BUREAU OF RECLAMATION FOR THE NONLINEAR ANALYSES OF ARCH DAMS USING EXPLICIT FINITE ELEMENT TECHNIQUES

The Bureau of Reclamation is using explicit finite element techniques to perform static and seismic non-linear structural analysis of concrete dams. The analyses presented are for a 500-foot-high thick arch dam in a wide canyon and a 260-foot-high thin arch dam in a narrow canyon. The thick arch dam has 160,000 nodes, 26 contraction joints and a potentially moveable foundation block. The reservoir upstream from the older arch dam and the water between the dams is modeled with fluid finite elements. The fluid elements provide hydrostatic and hydrodynamic interactions for this complex condition. Contact surfaces capable of sliding and opening represent the contraction joints, unbonded lift lines, foundation discontinuities, and interfaces between the dam, foundation, and reservoir. Non-reflecting boundaries are at the foundation and reservoir extents. Deconvolved ground motions are applied at depth in the foundation, propagate up through the foundation and provide spatially varying motions around the canyon. Material properties were obtained from laboratory tests and further calibrated using natural frequencies. Photogrammetry techniques were used for accurate surface topography and foundation bedding plane orientations. The finite element model of the thin arch dam has over 400,000 nodes. There is an older 210-foot-high arch dam just 7 feet upstream that is included in the model. Seasonal thermal loads are applied to the thin arch dam. The program TRUEGRID was used to create the model geometry and LSDYNA was used for the structural analyses.