IJRET: International Journal of Research in Engineering and Technology eISSN: 2319-1163 | pISSN: 2321-7308 _______________________________________________________________________________________________ Volume: 05 Issue: 07 | Jul-2016, Available @ http://ijret.esatjournals.org 282 PERFORMANCE BASED EVALUATION OF FLAT SLAB STRUCTURES WITH SQUARE COLUMNS Balesh.B.Koni 1 , S.S.Dyavanal 2 1 Post Graduate Student, Department of Civil Engineering, BVBCET, Hubli, Karnataka, India 2 Professor, Department of Civil Engineering, BVBCET, Hubli, Karnataka, India Abstract Most of the reinforced concrete structures comprise of conventional beam-column frames. In the present era, the multi-story structures are given higher priority with lack of availability of land. However, there are limits for the height and weight of the structures. Thus, the construction industry is more concentrated on measures to reduce the weight and height of the storey, without compromising with usable space. The flat slab structures serve the purpose as they are the structures involving slabs directly resting on columns; hence, negating the need for beams, which would consume lot of space and also lead to heavy weight of the structure. Even though, flat slabs are found to be advantageous in functional as well as economic aspects; the key issue with flat slabs is their inability to withstand lateral loads efficiently. In the present study, the seismic behaviour of flat slab structures is studied. The 7 storey building models involving flat slab without drops, with drops and with edge beams are modelled considering both bare frame and brick infill frame structures with square columns. The buildings are located in medium soil cover with seismic zone III. The analysis is performed using ETABS 2013 V13.2. The non-linear behaviour of the building models is studied by pushover analysis, considering FEMA 440 parameters. The prime emphasis is made to consider user defined hinge properties to establish the actual hinging pattern of the members. The performance of the building models is studied by evaluating the parameters like hinge locations, ductility ratio, safety ratio and global stiffness. Keywords: Soft Storey, Infill, Flat Slabs, Pushover Analysis, Ductility, Stiffness, Performance Levels, Safety Ratio, User Defined Hinges --------------------------------------------------------------------***---------------------------------------------------------------------- 1. INTRODUCTION Earthquake has been the prominent disaster since early era. But, the tendency and intensity of earthquakes is increasing with the global warming, pollution and depletion of earth. Previously many of the structures were built considering gravity loads only. Initially many structures were built with the infill masonry walls. The infill walls add up to stiffness of the building to some extent. Presently, bare framed structures are coming up, which prove to be weaker in withstanding lateral loads. With the growing need for safety anddevelopment, requires multi-storey structures to be designed with seismic considerations. Another problem of multi-storey structuresis their heavy weight. With increasing weight of the building, the cost offoundation increases. There are also certain bye-laws of Municipal Corporation restricting the height of building to certain limit. The beams add up greatly to the weight of building and consume most of the space. Thus the story height increases, thereby affecting space requirements and foundation costs. Hence, the thought of beamless structures came into light. These are also called as flat slabs. The flat slab structures may be classified into slabs without drops, with drops, with edge beams and with column heads. The ease of construction, better aesthetical look, reduction in storey height and reduction in weight are some of the key features of flat slab structures. But, the flat slabs have proved to be weak in withstanding the seismic loads coming on it, due to their higher flexibility. The aim of this paper is to study the performance of various flat slab structures located in seismic zone III and medium soil cover. The pushover method of analysis with FEMA 440 parameters is considered for the analysis in ETABS 2013 V13.2. There are many studies carried out on seismic behaviour of pushover analysis. Dhananjay D. J. and Pranesh B. M.(2013) found that the displacement at performance point for flat slab is 48% higher compared to conventional slabs [16]. SahanaPonnamma T.D. et al. (2015) concluded that the percentage difference in the base shear and displacement of conventional slab and flat slab with outrigger at mid height were 6.9674% and 2.4% respectively [17].Gouramma G. and Jagadish K. G. (2015) observed that the base shear of flat slab at performance point was around 60% less than conventional slab and displacement was 35% more than conventional slab [18].Anuj B. andAditi P. (2016) concluded that the base shear of flat slabs was almost similar to that of grid slabs but displacements of flat slabs were more comparatively [19].Amit A. S. and Deotale R.S (2012) studied the cost comparison of flat slab models without drop, with drop and with edge beams and grid slabs. It was observed that the models with drops were efficient and economic [20]. Mehmet I. and Hayri B.O. (2006) found that user defined hinge properties are more effective in resembling the actual behaviour of plastic hinge formation [21].