Hydrologic and Structural Safety Evaluation of Aged Concrete Gravity Dam Using Finite Element Method

History shows that several dams were failed and discharged the stored water which causes incalculable damage on life and property. Several researches disclosed that the methods used to design and re-evaluate concrete gravity dams after the 1970s have shown significant advancement. This starts when contemporary structural analysis methods such as a finite element method were incorporated into computer programs. Structural safety evaluation criterion, design standards and guidelines were also updated. Hence, periodical structural safety evaluation of older dams using state of art techniques is an important activity of the dam experts to ensure a safe operation of dams. This study was focused on hydrological and structural safety evaluation of Koka dam by using HEC-HMS and Abaqus models, based on USACE load combination. The Hydrologic Modeling System, HEC-HMS model was calibrated and used to determine the reservoir elevation reached when the peak outflow resulted from the Probable Maximum Flood (PMF) passes over the spillway. Result of the HEC-HMS model shows that the elevation reached by peak outflow was 1.4m lower than the dam crest which indicates no overtopping of the dam due to PMF. The peak reservoir elevation reached when the peak outflow from PMF passes over spillway was used to apply hydrostatic load on the dam. The dam was analyzed by static general method in Abaqus model. The results of Abaqus model indicate that the maximum principal stress in the dam body was under tensile sense near the heel during PMF with the peak magnitude of 0.602MPa. The corresponding minimum principal stress was under compressive sense throughout the base with the peak magnitude of -0.431MPa. All the results were below the compressive and tensile strength, hence, the dam concrete does not fail under PMF due to material overstressing. The aging of concrete, do not change the stress, but displacement. The results of displacement clearly show a significant increment. This result tells that the aging of concrete reduces the stiffness of the dam and increases its flexibility.