Seismic response analysis of a zoned earth dam including vertical input motion

Many existing earth dams were designed before the establishment of a seismic code or in a period when the seismicity of the dam sites was approximately assessed. Accordingly, the evaluation of their seismic performance is a crucial issue and, for both new and existing dams, the design or retrofitting procedures should aim to the improvement of their seismic resilience. In this framework the dynamic analyses devoted to the prediction of the dam seismic performance are usually carried out accounting only for the horizontal component of the expected ground motion. However, the vertical seismic motion can play an important role since it could affect the earthquake induced plastic mechanisms and the magnitude and distribution of the corresponding permanent strains. In this vein, the paper presents the results of a large set of 2D finite-elements dynamic analysis carried out with reference to a zoned earth dam located in a high seismic area of Southern Italy, using an isotropic hardening elasto-plastic hysteretic model. The analyses point out the influence of the amplitude and energy content of the vertical component of the input motion on the dam performance. Specifically, the numerical results are presented and discussed focusing on the on the magnitude of the crest settlements, considered a good proxy of the seismic-induced level of damage, and on their relationship with the seismic parameters describing the energy and frequency content of the vertical component of the input motion.