An Investigation into the Effect of Irregularity on Modal Energy Dissipation and Hysteresis in Intermediate Isolated Structures

One of the main concerns of structure and earthquake engineers has been the reduction of damages caused by earthquake. Engineers and builders have a perception of construction technology, and it is that structures must be built as resistant as possible. Although this assumption is correct, we must also pay attention to designing the structural elements with appropriate dimensions, as it is very effective in lightening the buildings and hence the proper behavior of structure during an earthquake. Recently, seismic isolation technology has been used for some structures in Iran, and designers in developed countries use it for designing structures, as it is the safest, most resistant and least expensive structural system against earthquakes. One of the advantages of seismic isolators is elimination or reduction of structural and non-structural damages, by consuming seismic energy and reducing the architectural problems involved in the design of structure (irregularity in plan and height). In this study, four-, eight- and twelve-floor isolated structures (intermediate structures) with asymmetry in plan and with ۲۵% and ۵۰% unidirectional and bidirectional eccentricity (irregular in plan) and with asymmetry in height with ۱۰% and ۳۵% stiffness reduction (irregular in height), under the effect of ۷ earthquake records, have been studied and evaluated in the SAP ۲۰۰۰. In the present study, the values of .۸, ۱.۰ and ۱.۷ have been considered for the ratio of torsional frequency to lateral frequency of superstructure and isolation system. This study seeks to investigate the trend of modal energy dissipation and hysteresis energy of the samples under study. The results showed that modal energy and hysteresis energy dissipation decreased as eccentricity was enhanced, and it is noteworthy that the effect of eb on the ratio of the aforementioned energies was significantly less than that of es. Also, it was found that eccentricity in two directions has almost no effect on the ductility of structure. Thus, no significant change has been produced in the ratios of modal energy and hysteresis energy dissipation. This can be justified by the fact that the structures with eccentricity in two directions is trying to behave like plan-symmetric structures.

کلیدواژه ها:

modal energy ، hysteresis energy ، irregular structures ، seismic isolator ، eccentricity of superstructure ، eccentricity of isolator