EFFECT OF CONFIGURATION OF R.C.C. BUILDING SUBJECTED TO SEISMIC LOADING

Abstract

Multistoried buildings with open (soft) ground floor are inherently vulnerable to collapse due to earthquake load, their construction is still widespread in the developing nations due to social and functional need for provide car parking space at ground level. Engineering community warned against such buildings from time to time. In the present thesis, an analysis has been performed to study the lateral forces and base shear of a multistoried (G+3) building for five different cases. 1st case is when no infill wall is provided, 2nd case is when stiffness of each floor is same, 3rd case is when considering the stiffness of infill from top to bottom, 4th case is when the ground floor is used for parking and the above stories are provided with infill walls and the last 5th case is when Infill wall is provided at alternate floor levels. The structural action of masonry infill panels of has been taken into account by modeling them as diagonal struts. Building is subjected to earthquake load in accordance with equivalent static force method as well as response spectrum method as per IS 1893(Part 1) : 2002.To perform analysis by equivalent static force method as well as by response spectrum method computer programs are written in matlab. Equivalent static force method produces same magnitude of earthquake force regardless of the infill present in the model. However, when the same buildings are subjected to response spectrum method, significant increase in lateral forces as well as total base shear has been observed in presence of infill. It has been found that when infill wall is incorporated in lumped mass model, it shows different mode shapes indicating that dynamic behavior of buildings changes when infill is incorporated in the model. More than two fold increase in base shear has been observed when infill is present on upper floors with ground floor open when compared to the base shear given by equivalent static force method. Study of the sway characteristics also reveals significantly high demand for ductility for columns at ground floor level. There is substantial change in the lateral forces when any type of unsymmetrical like soft or weak storey, Infill wall etc. is incorporated in the building. Most severe case is observed when the Ground floor is devoid of infill walls.