The investigation of Damage Pattern on Concrete Gravity Dams under Earthquake near and Far Field

To evaluate the safety of concrete gravity dams, especially in severe loading conditions such as the earthquake in MCL-scale has caused major concern and investigation of the non-linear behavior of these structures, taking into account the various interactions with water and foundation that needs further research. Nature and forcing records of far and near field of an earthquake are different on structures. In this thesis, first, has been investigated the different criteria for the classification of far and near field of an earthquakes and then two near-field records and two far-field records were selected for analysis. Two far-field records on the basis of the maximum horizontal acceleration of corresponding near-field records are scaled. Koyna dam has been chosen as a case study. And to obtain crack length by using static analysis, first assumed longitudinal cracks in the dam heel and is considered increases the crack length to the extent that tensile stress at the end of the crack is less than from permissible tensile stress in concrete. For elements of dam using ANSYS software from PLANE 183 eight-node elements and nonlinear dynamic analysis that is a tool to check the seismic safety of concrete gravity dams. In this thesis linear and nonlinear dynamic analysis have been done under five different earth quake with PGA and different frequency content and the dynamic interaction between the dam and the lake that has been modeled with added mass. After performing dynamic analysis on Koyna, cracked dam, before and after cracking have completely different results. In cracked case the value of shift is less than the un cracked case.
The main tensile stress at the end of the crack is more than n cracked case. According to what is shown on analysis, in addition to the PGA, earthquake frequency content is effective in the destructive power of earthquakes.