Influence of Outrigger system in RC Structures for Different Seismic Zones

Construction of tall structures having residential and commercial purposes has improved in conjunction with the growth of construction technique. In general, earthquake (EQ) ground motion is unpredictable and the problem considered with tall buildings, especially under heavy earthquakes, it should be extensively studied. Construction of tall buildings has laid more challenges for engineers to meet the requirements with respect to the demand growth. In the recent trend of tall buildings, horizontal loads due to seismic or wind action are resisted by arrangement of coupled shear walls. When the structure increases in height, the structural stiffness becomes more significant and introduction of outrigger beams between the exterior columns and shear walls is more commonly used to give lateral stiffness to the structure. The outrigger system is the most commonly used structural lateral load resisting system as to mitigate the excessive drift due to lateral load in an effective manner. The analysis has been carried out to study the effect and performance of outrigger system in a 35 story building. The outrigger system is provided at different levels along the height of the building by varying the relative stiffness. Loads are considered as per Indian Standards IS: 875(Part1)-1987 and IS: 1893(Part-1): 2002. The analysis is done with Equivalent static method for different seismic zones. The modeling and analysis were performed using finite element software ETABS 9.7.4. It is found that, with the increase in relative stiffness of the outrigger system, there is a decrease in lateral displacement and inter-story drift. Further there is increase in base shear of the structure with higher relative stiffness in all seismic zones. 

Influence of Outrigger system in RC Structures for Different Seismic Zones
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