An investigation on optimal outrigger locations for hybrid outrigger system under wind and earthquake excitation

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 (ISD_max), roof displacement (disp_roof), roof acceleration (acc_roof) 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 ISD_max, acc_roof and disp_roof under each load. The study concludes with a flowchart giving the preliminary recommendations for choosing the optimal position of hybrid outrigger system.