This paper describes the results of numerical analysis of a hydraulic structure subjected to seismic load. The paper is divided into two main parts. First, a numerical procedure for the description of mechanical effects of alkali-aggregate reaction in concrete structures is briefly outlined. Subsequently, a single unit of the Beauharnois power plant, situated in Quebec (Canada), is analysed in the context of seismic excitation. The numerical simulations are aimed at assessing the dynamic stability of this unit and investigating the evolution of damage associated with inception of macrocracks.Key words: alkali-aggregate reaction, plasticity, seismic analysis, hydraulic structures.