Base isolation techniques have emerged as the most effective seismic damage mitigation strategies. Several types of aseismic devices for base isolation have been invented, studied, and used. Out of several isolation systems, sliding isolation systems are popular due to their operational simplicity and ease of manufacturing. This article discusses the historical development of passive sliding isolation systems, such as pure friction systems, friction pendulum systems, and isolators with other sliding surface geometries. Moreover, multiple surface isolation systems and their behavior as well as the effectiveness of using complementary devices with standalone passive isolation devices are examined. Furthermore, the article explored the various modeling techniques adopted for base-isolated single and multi-degree freedom building structures. Special attention has been given to the techniques available for modeling the complex phenomena of sliding and non-sliding phases of sliding bearings. The discussion is further extended to the development in the contemporary areas of seismic isolation, such as active and hybrid isolation systems. Although a significant amount of research is carried out in the area of active and hybrid isolation systems, the passive sliding isolation system still has not lost its appeal due to its ease of adaptability to the structures.
Outriggers are considered as an effective system to alleviate the responses caused due to the lateral loads on high rise buildings. The concept of hybrid outrigger system which has a conventional and a virtual outrigger at different levels has been proposed. This study analyzes the static and dynamic behaviour of hybrid outrigger system based on stiffness of core, stiffness of outrigger beam and belt wall, length of the outrigger arm, and height of the building as varying parameters, and investigated on optimal positions of hybrid outrigger system under wind and earthquake loads. The dynamic behaviour was evaluated using nonlinear time history analysis, and the static wind and earthquake response using Indian Standard codes. Analytical models of 40, 60 and 80 storeys having building heights of 140 m, 210 m and 280 m, respectively were considered for the parametric study. The optimal positions for hybrid outrigger system were obtained based on the response from absolute maximum inter storey drift ratio (ISDmax), roof displacement (disproof), roof acceleration (accroof) and base bending moment. A performance index criterion was introduced which was utilized to obtain the optimal position of the hybrid outrigger system considering the combined effect of ISDmax, accroof and disproof under each load. The study concludes with a flowchart giving the preliminary recommendations for choosing the optimal position of hybrid outrigger system.
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