<b>Parametric Study Of Multisoried R.C.C. Flat Slab Structure Under Seismic Effect Having Different Plan Aspect Ratio And Slenderness Ratio</b> Flat slab building structures possesses major advantages over traditional slab beam column structures because of the free design of space, shorter construction time, architectural –functional and economical aspects. Because of the absence of deep beams and shear walls, flat slab structural system is significantly more flexible for lateral loads then traditional RC frame system and that make the system more vulnerable under seismic events. The critical moment in design of these systems is the slab column connection, i.e., the shear force in the slab at the connection, which should retain its bearing capacity even at maximal displacements. The behavior of flat slab building during earthquake depends critically on ‘Building Configuration’. This fact has resulted in to ensure safety against earthquake forces of tall structures hence, there is need to determine seismic responses of such building for designing earthquake resistant structures. Response Spectrum analysis is one of the important techniques for structural seismic analysis. In the present work dynamic analysis of 15 models of multi storied RCC Flat slab structure is carried out by response spectrum analysis.The BIS guideline in IS 1893 2002 {Clause 7.1} says “Regular and Irregular Configuration to perform well in an earthquake, a building should possess four main attributes, namely simple and regular configuration, and adequate lateral strength, stiffness and ductility. Buildings having simple regular geometry and uniformly distributed mass and stiffness in plan as well as in elevation, suffer much less damage than buildings with irregular configurations”. Similarly in IS 4326 1993 {Clause 4.4.1} it is mentioned that “The building should have a simple rectangular plan and be symmetrical both with respect to mass and rigidity so that the center of mass and rigidity of the building coincide with each other.” But the limiting “plan aspect ratio” and “Slenderness ratio” for the regular structure is not prescribed.This study is concerned with the behavior of structure having same plan area but different plan aspect ratio L B and slenderness ratio H B under seismic condition. The structures are simulated in ETABS 13 software and analyzed using Response Spectrum method. Aspect Ratio, Slenderness Ratio, Response Spectrum Analysis, Drift , Displacement, Storey shear, SMRF R.C.C. flat slab structure Issue-4 Volume-1 Renuka Ramteke