a Bahmani - M.Sc., School of Civil Engineering, University of Tehran, Tehran, Iran
a Hosseini - Assistant Professor, School of Civil Engineering, University of Tehran, Tehran, Iran

Survey of short period structures on soft soils and on modelings represents that the response of structures in nonlinear static analysis is in conflict with the real response. As a matter of fact, transition period of soil is obtainable with nonlinear static procedure in soft soils, but this studyrepresents that this estimation in valid Codes is underestimation of about two times and that difference will reach to maximum in near-field earthquakes. Studies show if the R ratio (Ratio of elastic strength demand to calculated yield strength coefficient) is big or the structure is nearthe fault, the elastic and in-elastic displacement will be considerably different, especially the target displacement in time history analysis exceeds the amount of nonlinear static analysis, and it means the underestimation. Moreover, the soil structure interactions can alter the demand on structures. It can alter the spectral acceleration and lateral forces and consequentially it alters lateral displacements and P-Delta effect. Considering the present challenges in valid authorities it is obvious the analytical methods for estimation of C1 is not complete. In this study we model a great number of structures on soft soils in a variety of districts in Iran, evaluating the maximum displacement ratio with a new approach utilizing different accelerograms of Iran, and eventually a new graph will be presented to evaluate the C1 for short period structure on soft soils.

Time History analysis, Hysteretic Behavior, Short Period, Soft Soils