AbstractThe two numerical procedures previously presented by the authors to model crack closure during seismic fracture of concrete gravity dams are employed herein to study the 1967 performance of the Koyna dam. First, a brief description of the general procedure is given, followed by the detailed formulation of the force method for simulation of crack closure. The latter was introduced to prevent the hypothetical overlap phenomenon which was originally assumed in the modelling of crack closure by the impulse method. Also presented are the results obtained for a model of the Koyna dam tested on a shaking table to study the cracking process under simplified loading conditions. Satisfactory agreement between the test and numerical results is shown. Finally, the cracking process of the Koyna dam prototype subjected to the 1967 earthquake is evaluated numerically by employing the aforementioned techniques. From the results, it is concluded that both procedures for simulating the impact effect of crack closing predict complete penetration of the crack through the upper part of the dam, which is consistent with the observed prototype behaviour.