PERFORMANCE BASED EVALUATION OF MULTISTOREY RC BUILDINGS WITH AND WITHOUT FLOATING COLUMNS BY USER DEFINED HINGES

Abstract

There is a growing tendency of providing floating column in many multi-storeyed buildings in urban India now a days, due to the lack of availability space for parking, assembly hall and reception lobbies. Building with floating columns is constructed to take advantage of urban bylaws. As per urban bylaws, a pre-specified space should be left open between all sides of the building and the plot boundary. These floating columns are highly undesirable features in building built in earthquake prone areas, because this has been verified in numerous experiences of strong shaking during the past earthquakes like Bhuj 2001. Therefore in the present study the effect of floating columns in multistory RC building is compared with regular building. For the study, four and seven storey symmetric 3D special moments resisting RC frame structure with and without floating columns are considered. The floating columns are provided at cantilever length 1.5 m along the periphery of the building starting from first floor level up to roof level. ETABS 2013 V13.2 is used for modelling and analysis. The buildings are considered as a fixed based located in seismic zone III on medium soil condition. Linear static such as equivalent static analysis and response spectrum analysis and non-linear static such as pushover analysis are carried out by considering FEMA 440 parameter. Flexural M and PM hinges for beam and column are considered with user defined hinges because user defined hinge represents actual behaviour of members in the structures. The pushover parameters like hinge status, ductility ratio, safety ratio and global stiffness are studied to compare the building with and without floating columns.