Papyrus Press Advance Researches in Civil Engineering 2645-7229 6 2 2024 06 01 Strength Reduction Factor of Soil-Structure Systems in Comparison to Fixed-Base Structures 27 38 224606 10.30469/arce.2024.224606 EN Morvarid Hajian PhD. candidate, School of civil Engineering, University of Tehran Reza Attarnejad Professor, School of civil Engineering, University of Tehran Journal Article 2025 07 09 In this research, a proposed correlation was suggested to predict the strength reduction factor of soil-structure systems when compared to structures with rigid bases. In recent years, several studies have focused on how structural dynamic parameters evolve, taking into account the flexibility of the substrate. The strength reduction factor is a crucial parameter in seismic design, and it is calculated as the ratio of elastic strength demand to inelastic strength demand to ensure that the displacement ductility demand does not exceed a specific target ductility ratio. This study utilized various non-linear and two-dimensional time-history analyses on shear building models with 3, 5, 10, and 15 stories, fixed-base periods ranging from 0.1 to 3 seconds, and target ductility ratios of 2, 4, and 6, placed on the soil. 22 far-field seismic accelerometers were utilized to expose the structures. To account for soil-structure interaction, class D and E soils were utilized. Observing the results showed that the strength reduction factor of structures was decreased by soil-structure interaction. The softer the soil, the greater the soil-structure interaction effects, thus the smaller the strength reduction factor. In the three-story building, the change from type D soil to type E soil resulted in a 7% decrease in the strength reduction factor. However, this difference was not significant in the ten-story building when comparing the two types of soil. Using the results obtained, a correlation was established to determine the structural strength reduction factor based on the strength reduction factor of the rigid base case. https://www.arce.ir/article_224606_247317795ddabb54e6a24b29ae10f204.pdf