Active seismic control by considering nonlinear behavior of structure and soil, using fuzzy theory

The science of seismic control of the structures always seeks to reduce and control the destructive effects of the forces which are produced during an earthquake event. However, the yield of the soil under intensified seismic loads can cause some irreversible effects on the structural elements and the structure may withstand the increased moments and the forces for which it is not formerly designed. This unfavorable phenomenon significantly affect the seismic response and performance of the structures, and will ultimately leads to disappearance of all functional goals that are sought to create in the structural design stage by the designer of the structure. In this research, by a relatively accurate three dimensional finite element modeling, from a high-rise concrete structure equipped with the active mass damper, and by examining the lesser-known aspects of the problem such as uplift of the foundation and the effects of nonlinear interaction of soil and structure, an attempt has been made to conduct a relatively comprehensive study on the questions of seismic control of structures equipped with active mass dampers due to the nonlinear effects of the underneath soil behavior. For this purpose, time history dynamic analysis was performed on the structural model under the effect of 22 horizontal records of distant basin earthquakes in x and y directions followed by the Appendix A of FEMA P695. The Ibarra model (a reviewed and modified model based on the Clough model) is used for modeling of the hysteresis behavior of concrete materials. The underneath soil is modelled by three springs approach presented in ATC 40 and FEMA 440 with equivalent stiffness based on soil modulus of elasticity and Poisson’s ratio of three categories (the main C category and upper and lower C and E categories ). To achieve the goal of optimization and evaluation of the active mass damper parameters (consist of tuning ratio, mass ratio and damping ratio), the mass damper spectra method with investigation of changes in structural responses has been used. The Fuzzy theory has been used to calculate the control force of an active mass damper. The results indicate that with respect to entrance of the structure to non-linear zone and its interaction with non-linear behavior of the soil, the efficiency of the active mass damper in uplift control of the foundation decreases, but a good efficiency is observed in the lateral displacement and inter story drift control. By evaluation of the three dimensional analysis results of a nonlinear soil structure system equipped with the active mass damper, the researchers observed that for the set of the recorded earthquake and based on the specifications considered for fuzzy algorithm, the active mass damper has a satisfactory effect in the control of displacements and drifts of the structure, in the amount of almost 15 percent. It was also identified that the active mass damper has a negligible effect on the foundation uplift in the structures which constructed on the hard soil. But when the soil becomes softer, a 3 percent mean decrease is observed in the uplift displacements in foundation.