Structural Behavior of Two Major Concrete Dams in Sri Lanka Under Earthquake Loads

Abstract

Dams are built for a variety of purposes including hydropower generation, irrigation, water supply, and flood mitigation. Concrete and earth dams are common types of dams in Sri Lanka. Concrete dams can be categorized as Gravity dams and Arch dams. Gravity dams are most common in Sri Lanka. Dams can also pose safety hazards. Failure of a dam can cause serious damages to both people and property downstream. One of the major threats to dams is earthquakes. They can have significant impacts on the stresses within the dams. In extreme cases this can cause even failures of dams. These possibilities can be investigated using finite element analysis. In this study Rantambe and Moragahakanda concrete gravity dams were selected for 2-D finite element analysis under the action of suitable earthquakes. For each case linear time history analysis was performed using SAP2000 software. The stresses were examined for potential failures. Important considerations in this process were selection of dams, selection of suitable earthquake records, and identification of an appropriate failure criterion. The selection of earthquake records was based on proximity and geological conditions. Koyna earthquake was used to develop suitable earthquake loadings. Peak ground acceleration was varied from 0.05g to 0.15g. Westergaard method was used to assign hydrodynamic loads. Coulomb-Mohr criterion was employed to investigate potential failures in concrete. Stresses in dam models during the earthquakes was scrutinized for potential failures. Significant stress increases were observed in some areas of the dams. These critical areas and corresponding values of earthquake parameters were identified. It was concluded that the dams were unlikely to suffer material failures under earthquake loads even with a peak ground acceleration of 0.1g (which is the value recommended for use for critical structures in the areas concerned). KEYWORDS: Concrete gravity dams, Finite element model, Coulomb-Mohr criterion, Time history analysis, Westergaard method