en Applications Applications پژوهشي Research <span lang="IT" style="font-size:11.5pt"><span style="line-height:107%"><span new="" roman="" style="font-family:" times=""><span style="letter-spacing:-.2pt"><span style="layout-grid-mode:line">Identification of damping properties for a mixed structure and its interaction with underlying soil is a challenge for structural designers. Current codes and available commercial software packages do not provide analytical solutions for such structural systems. Due to irregular damping ratios, dynamic response of each part of a mixed structure differs significantly. In addition, when the structure is subjected to seismic loads, the soil-structure interaction effects cannot be neglected. To manage these issues, this paper proposes an equivalent damping ratio for mixed structures by means of a semi-empirical error minimization method which considers soil-structure interaction. The results of numerical simulations indicate that the use of the equivalent damping ratios makes the results of dynamics analyses closer to the ones obtained by the actual damping ratios. Consequently, proposed method provides a much better approximation than the case in which the conservative overall ratio of 2% or 5% is used.</span></span></span></span></span> Mixed structure, equivalent damping ratio, soil-structure interaction, semi-empirical error minimization 97 110 http://ijoce.iust.ac.ir/browse.php?a_code=A-10-6463-19&slc_lang=en&sid=1 A. Kaveh alikaveh@iust.ac.ir 180031947532846002816 180031947532846002816 Yes School of Civil Engineering, Iran University of Science and Technology, Narmak, Tehran-16, Iran Sh. Rezazadeh Ardebili 180031947532846002817 180031947532846002817 No School of Civil Engineering, Iran University of Science and Technology, Narmak, Tehran-16, Iran