ANALYSIS OF HIGH-RISE RCC STRUCTURE FOR INVESTIGATING OPTIMUM POSITION OF RCC OUTRIGGERS FOR DIFFERENT EARTHQUAKE ZONES AND TYPE OF SOILS

Abstract

— Rapid growth of infrastructure to accommodate modern civilization is demanding tall structures in cities. As buildings become taller the problem of their lateral stability and sway needs to be tackled by engineering judgment. Outrigger systems have been successfully applied in reducing the lateral displacement of tall buildings under wind and earthquake forces. Numerous studies have been carried out for determining optimum positions of outriggers in high rise structures; however, effect of earthquake zones and soil types on optimum position of outriggers has not been adequately studied. In the present paper, an analysis of a 70 storied RCC highrise structure provided with and without virtual outrigger system is carried out for determining optimum position of RCC outriggers. The structure has been analyzed to study its behavior under wind and earthquake forces, considering its location in different seismic zones (II, III. IV and V) and also in different types of soils (soft, medium and hard) using “ETAB” software. The virtual outriggers (RCC belt) were provided at seven different levels along the height structure (H/4, 3H/8, H/2, 5H/8, 3H/4, 7H/8 and H) with top level outrigger as fixed and others were varied for their locations. Thus, the structure has been analyzed considering it has been provided with two outriggers at a time, one at the top of structure (H) and the other at a specific level along the heights. Results of the analysis shows lower values for storey displacement, drift and base shear when the structure is considered with one outrigger at top (H) and other at 1/4th height (H/4) for all seismic zones (II, III, IV and V) and all soil conditions (soft, medium and hard). Thus, it is concluded that optimum position of outrigger lies at 1/4th height (H/4) along the height of structure and it goes well in agreement with the values found in literature.