A Comparative Study Between Conventional Outrigger System and Hybrid Outrigger System considering Performance Index Criterion

Abstract

AbstractOutriggers are regarded as a structural component which can effectively lessen the reactions generated by lateral loads in tall buildings. Depending on the connectivity between the core and the peripheral columns, the outrigger system can be divided into virtual outrigger system and conventional outrigger system (COS). The hybrid outrigger system (HOS) has one conventional outrigger and one virtual outrigger at two distinct floor levels. This study gives a comparison of optimal position and performance between COS and HOS based on formulated performance index criterion (PIC) for building heights of 140, 210, 280 and 350 m by considering variations in stiffness of the outrigger belt wall and beam, the stiffness of the building's core, the height of the structure and the length of the outrigger arm under static wind and equivalent static earthquake load. The outrigger behaviour assessed using PIC takes into account the combined response of displacement at top, absolute maximum inter storey drift ratio and acceleration response at the roof. Based on PIC, performance of both COS and HOS at their evaluated optimal position are compared, and is found that HOS are less effective than COS. Therefore, to enhance the performance of HOS to be in par with COS, an optimization study is performed by increasing the axial stiffness of column, stiffness of outrigger, and stiffness of slab while maintaining the increase in total concrete volume of the structure a minimum. From the findings, PIC values of HOS (PICHOS) for 40 to 100 storeys exhibits an increase of 10 to 1.1, 20.2 to 2.2 and 12.5 to 1.9% for variation in core thickness, length of outrigger arm, and outrigger thickness, respectively, compared to PIC values of COS (PICCOS). For PICHOS to be comparable with PICCOS, increase in the total concrete volume of HOS reduces from 1.4–16.5 to 0.6–2.5% as the model's height increases from 40 to 100 storeys, respectively, suggesting that the HOS with marginal increase in total concrete volume can perform effectively for taller structures.