Analysis Of Outrigger System For Frame Structures Subjected To Lateral Load

Abstract

Outrigger structural systems are widely used in tall buildings to improve lateral stiffness and control excessive drift generated by earthquake and wind actions. This article converts the thesis study into a journal-style manuscript and presents a comparative seismic assessment of a 32-storey reinforced concrete high-rise building modeled in ETABS. Ten analytical models were evaluated using the Equivalent Static Method and Response Spectrum Method for Seismic Zone V. The study focused on key response parameters including top-storey displacement, storey drift, base shear, fundamental natural time period, and overturning response. The results show that the inclusion of core walls, outriggers, and X-braced outrigger arrangements improves the lateral performance of the structure. Compared with the bare/reference frame, the thesis reports 21.71% reduction in top-storey displacement with a core wall, 29.73% reduction with outriggers, and 41.29% reduction when outriggers and X-bracing are combined. The corresponding maximum drift reductions were 21.65%, 25.77%, and 45.87%, respectively. The combined outrigger and X-bracing system increases base shear and overturning resistance while substantially reducing lateral deformation. The study confirms that properly configured outrigger systems are effective for enhancing seismic performance of high-rise RC buildings.