Keywords ETABS 2013, Earthquake, Waffle Slab, Flat Slab, Seismic Analysis, Storey Drift, Maximum Displacement. 1.1 Objective

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1 COMPARATIVE STUDY OF SEISMIC PERFORMANCE AND ECONOMICAL ASPECT OF WAFFLE SLAB AND FLAT SLAB Ms.S. Kalaiyarasi 1 1 ( Civil Engineering Department, Anna University, Coimbatore, India, kalaisaro@gmail,com) Abstract In multi-storeyed buildings flat slab and waffle slab are generally engaged when column spacing is more. Flat slabs and waffle slabs are used in buildings in requirement of more working space like commercial buildings, workshops, assembly buildings, etc. The main disadvantage of structures with flat slab and waffle slab are there lack of withstanding seismic loads. Special features like shear walls are used to help the building to resist the lateral loads caused due to high winds and seismic loads. In this paper, an attempt has been made to investigate the seismic effect on multi storey building of G+9 & G+14 floors with waffle slab and flat slab using the software ETABS The seismic evolution is performed by response spectrum analysis as per IS 1893 (2002). It is observed that waffle slabs are advisable for structure with a height less than 40m, whereas for structures of height above 40m it is advisable to go with flat slab. Keywords ETABS 2013, Earthquake, Waffle Slab, Flat Slab, Seismic Analysis, Storey Drift, Maximum Displacement 1.INTRODUCTION In general normal frame construction utilizes columns, beams and slabs. However it may be possible to undertake construction without providing beams, in such a case the frame system would consist of slab and column without beams. These types of slabs are called flat slabs. The slab directly rests on the column and load from the slab is directly transferred to the columns and then to the foundation. Flat slabs have been widely used in building construction due to their advantages in reducing storey height and construction period (compared with RC frames with beams and columns), leading to a reduction of construction costs ribs are typically designed as T-beams, often spanning in the long direction. A solid drop panel is required at the columns and load bearing walls for shear and moment resistance. 1.1 Objective Fig. 2 Waffle Slab Fig. 1 Flat Slab Ribbed floors consisting of equally spaced ribs are usually supported directly by columns. They are either one-way spanning systems known as ribbed slab or a two-way ribbed system known as a waffle slab. A rib thickness of greater than 125 mm is usually required to accommodate tensile and shear reinforcement. Ribbed slabs are suitable for medium to heavy loads, can span reasonable distances are very stiff and particularly suitable where the soffit is exposed. Slab depths typically vary from 75 to 125 mm and rib widths from 125 to 200 mm. Rib spacing of 600 to 1500 mm can be used. The overall depth of the floor typically varies from 300 to 600 mm with overall spans of up to 15 m if reinforced, longer if posttensioned. The use of ribs to the soffit of the slab reduces the quantity of concrete and reinforcement and also the weight of the floor. The saving of materials will be offset by the complication in formwork and placing of reinforcement. For ribs at 1200-mm centres (to suit standard forms) the economical reinforced concrete floor span L is approximately D x 15 for a single span and D x 22 for a multi-span, where D is the overall floor depth. The one-way Where developing in construction industry when constructing large slab areas necessity to reduce the cost as well with fulfilment of economic section. For this reason in this project we are comparing the waffle, flat and conventional system. To Study the seismic performance of the waffle slab system, Flat slab system To compare the cost of the waffle, Flat slab system. To the study the behaviour of both structure for the parameters like shear, storey displacement Drift ratio, axial forces by applying response spectrum analysis for buildings. 2. REVIEW OF LITERATURE Analysis And Design of Flat Slab and Grid Slab and their Cost Comparison by Amit A. Sathawane, R.S. Deotale/ International Journal of Engineering Research and Applications (IJERA) ISSN: Vol. 3, Issue 3, May-Jun 2013, pp The aim of the project is to determine the most economical slab between flat slab with drop, Flat slab without drop and grid slab. The proposed construction site is Nexus point apposite to Vidhan Bhavan and beside NMC office, Nagpur. The total length of slab is m and width is m. total area of slab is sqm. It is designed by using M35 Grade concrete and Fe415 steel. Analysis of Volume:03 Issue:

2 the flat slab and grid slab has been done both manually by IS and by using software also. Flat slab and Grid slab has been analyzed by STAAD PRO. Rates have been taken according to N.M.C. C.S.R. It is observed that the Drops are important criteria in increasing the shear strength of the slab and the Flat slab with drop is more economical than flat slab without drop and grid slab. Comparative Study of Seismic Performance of Multistoried RCC s With Flat Slab and Grid Slab by Salman I Khan1 and Ashok R Mundhada of International Journal of Structural and Civil Engineering Research (ISSN ) Vol.4 No.1, February This paper presents a review of the seismic performance of multi-storied buildings for different floor heights and having different floor systems like Flat slabs, Grid slabs and conventional solid slab-beam systems. It seems that the seismic performance of buildings having grid slab and flat slab is comparable but the differences exist. For e.g. the base shear of a multi-storey structure with flat slab is less as compared to Grid slab, whereas the axial force in the intermediate columns are more in case of flat slabs than grid slabs. s having the flat slab system are weaker in shear as compared to those with conventional or even grid slab systems. The storey drift in building with flat slab construction was significantly more as compared to conventional RCC building. As a result, additional moments were developed. Therefore, the columns of such buildings should be designed by considering additional moments caused by the drift. Base shear of flat slab building would be less than the base shear in grid slab building. To draw definitive conclusions, more research is required. Dynamic Analysis of Multi-storey RCC Frame with Flat Slab and Grid Slab by Ravi Kumar Makode, Saleem Akhtar, Geeta Batham Int. Journal of Engineering Research and Applications ISSN : , Vol. 4, Issue 2( Version 1), February 2014, pp The flat slab buildings in which slab is directly rested on columns, have been adopted in many buildings constructed recently due to the advantage of reduced floor to floor heights to meet the economical and architectural demands. Base shear of flat slab building is less than the base shear in grid slab building in both X and Y-directions. Axial force in end columns of flat slab building is less as compared to grid slab building. Axial force in intermediate columns of flat slab building is more as compared to grid slab building. Maximum shear force is occurs in column of story-3. For zone-ii and soil type-ii building drift in flat slab building and grid slab building is within limit in both X and Y-directions. drift in grid slab building is less as compared to flat slab building in each story in both X and Y-directions. Punching Shear in Waffle Slab Seismic Design by E. Arellano- Méndez & O.M. González-Cuevas Universidad Autónoma Metropolitana, México D.F Five full-sized post tensioned flat slab-column connections subjected to axial load and flexural moment were tested to study their mode of failure, strength and ductility. The variables that were tested are: 1) provision of stirrups or stud shear reinforcement; 2) spacing between stirrups or shear studs; and 3) relationship between the applied axial load, Vu, and the punching shear strength of the slab with axial load and without shear reinforcement, VcR. In this research, waffle slabs were used, being more used in Mexico than solid slabs for economic reasons. Both types of shear reinforcement used were suitable to resist the applied load at low levels of inter story drift ratio. When levels of inter story drift ratio larger to those allowed in ductile structures regulations were applied, problems arose in the connections with stud shear reinforcement (SSR), because SSR does not properly confine the longitudinal reinforcement bars in the ribs. Buckling of the bars occurred when the cover concrete was lost. Since current design regulations require designing for low inter story drift ratio (ψ=0.006), it may be said that with both types of reinforcement it is possible to reach similar deformations with the same safety. Shear stud reinforcement has an advantage in the co-location rate, but with the inconvenience that they may not confine properly the compression steel. The use of post tensioned waffle slabs without a solid zone around the column is not recommended. Although this testing evidence seems to show that the system can reach deformation levels larger than those specified in the Normas tecnicas complementarias para el diseño y construcción de estructuras de concreto (NTC-Conceto, 2004), more studies are required before such recommendation can be made. Finite Element Analysis and Parametric Study of Grid Floor Slab by Muhammed Yoosaf.K.T, Ramadass S, Jayasree Ramanujan American Journal of Engineering Research (AJER) e- ISSN : ;p-ISSN : Volume-3 pp This paper deals with the influence of various parameters on the economical spacing of the transverse beams in grid floor. The parameters considered in this study are span to depth ratio, spacing of transverse beams, thickness of web and thickness of flange. The magnitude of span to depth ratio considered is 16 to 60. The spacing of transverse beams is varied from 0.5m to 2.0 m. Thickness of slab and the ribs are made constant and are equal to 0.1m and 0.15m respectively. The bending moment, the shear force and the mid span deflection developed in grid floor beams have been predicted by conventional and numerical methods and the results are compared. The parametric study is carried out using the model proposed by ANSYS 12.0 software. The results of the study give an insight to the range for the magnitude of the various parameters to be considered for the optimum performance of grid floors. Based on the present study, the following conclusions are arrived at. The spacing of grid beams influences the mid span deflection and the bending moments developed in the grid beams The span to depth ratio of grid floor slab system influences the mid span deflection and the bending moments developed in the grid floor beams It is expected that the monogram developed in this study is useful for arriving at economical spacing of grid beams for the design of grid floor slabs. Study on Economical Aspect of R.C.C Beam Slab Construction and Grid Slab by Uzma A. Shaikh, Prof. Mohd. Shahezad, International Journal of Engineering Sciences & Research Technology (ISSN: ) Scientific Journal Impact Factor: (ISRA), Impact Factor: [Shaikh, 3(8): August, 2014] The aim of this work is to design R.C.C Beam Slab, One-Way Continuous Slab as well as Grid Slab for spans 15m X 27m and then compare the results. This work includes the design and estimate for Conventional Beam Slab and Grid Slab of same span of 15m X 27 m by M20, M25 and M30 grade of concrete. For smaller spans, associated with normal building works, conventional beam slabs are found more cost effective, in this project comparison of conventional beam slab and grid slab is made on the basis of major material requirements of the slab. Based on the study and design conducted for a plan of 15 m x 27 m it could be concluded that RCC One way ribbed slab is more preferable than other two types of slab that is RCC one way continuous slab and grid slab. From cost point two way grid slab is more costlier than other two types, there is a slight difference in between cost of One way continuous slab and one way ribbed slab of 700 mm depth but in Volume:03 Issue:

3 case of one way continuous slab the clear head is less as depth of beam is 900 mm where as in one way ribbed slab we are getting more clear head. Besides, two way grid slab of 700 mm depth provide greater headroom and give column free space and good architectural view. From economical point view RCC one way continuous slab is 5.21% costlier than one way ribbed slab of 700 mm depth. Similarly two way grid slab of 900 mm depth is % costlier and two way grid slabs of 700 mm depth is 32 % costlier than one way ribbed slab. Seismic Evaluation of Old RC Waffle Flat-Plate Systems by X. Cahís, A. Benavent-Climent and A. Catalan, The 14 th World Conference on Earthquake Engineering October 12-17, 2008, Beijing, China. In moderate-seismicity southern European countries it is very common to use reinforced concrete waffle flat-plate structures for sustaining both vertical and lateral earthquake loads. In the case of Spain, many of these structures were designed during the seventies, eighties and nineties according to earlier seismic codes which required relatively small lateral strength and did not contain any provision for attaining ductility. Past earthquakes have raised serious concerns about the safety of these structures in the case of a severe earthquake. In this paper, a numerical investigation is carried out to evaluate the seismic demands on old RC waffle plate systems located in southern Spain, in a moderate-to-high seismicity region. A prototype building, designed according to Spanish codes from the 1970 s to 1990 s and current construction practices, was analysed with SAP2000 by using a non-linear static method. The frame model was equipped with user defined hinges based on testing. The low gravity shear ratio and the consideration of punching reinforcement (a usual Spanish practice even when it was not deemed necessary from calculation) lead to a strong column/weak slab behaviour. Experimentally based moment-rotation hinge models, for interior and exterior waffle slab-column connections, are herein defined for use in effective beam frame analysis. The test specimens were provided with punching reinforcement, a usual practice in southern Spain during the decades of the 1970 s, 80 s and 90 s for waffle flat-plate frames. Torsion cracking in the exterior column spandrel beams and adherence failure of bottom reinforcement in the interior connections can be considered as the main degrading factors. The effective slab-width and strength models proposed by ACI present good correlation with experimental results in the interior connections. In the case of the exterior connection, meanwhile, a trapezoidal effective cross section was considered, c1+3h and c1+c2 being the upper and bottom dimensions, respectively. A strength model for exterior connections accounting for the flexure of the effective slab-width as well as the torsion capacity of the edge spandrel beams is calibrated based on experimental data. The hinge models obtained and presented here appear to accurately reproduce the experimental load-deformation curves derived from tests, thus proving useful for RC waffle flat-plate building assessment. A pushover curve taking into account hinge nonlinearities and P-Delta effects has been obtained for a waffle flatplate equivalent frame; the performance point in the Service, Design and Maximum Earthquakes using the Capacity Spectrum Method have been calculated. Strong column-weak slab behaviour was appreciated until reaching collapse, slightly beyond the Maximum Earthquake performance point. Before collapse, which occurred at 2.3% of maximum displacement, the inter story drift was almost uniformly distributed throughout the height of the frame. Structural behavior analysis of Two-Ways (Waffle) Composite Slabs by M. Khalaf, A. El-Shihy, H. Shehab, S. Mustafa, International Journal of Engineering and Innovative Technology (IJEIT) Volume 2, Issue 12, June 2013 (ISSN: ) ISO 9001:2008 Certified The main aim of this research is to analyze the structural behaviour of the new suggested composite slab type under different conditions using the well known structural analysis program SAP2000. Indeed, this analysis requires a very careful choice of the used modelling technique to accurately simulate the waffle composite slabs. Therefore firstly, a modelling techniques evaluation of waffle composite slabs was achieved numerically using the finite element technique and compared to the previously available experimental results of one-way composite slab types to achieve the best modelling among three models named real shape, equivalent and grillage models assuming full interaction between steel sheeting and overlaying concrete. Many influencing parameters such as the waffle rectangularity, boundary conditions, depth and corrugation cell aspect ratio and corrugation type (trapezoidal and re entrant) which were expected to affect the structural behaviour of the two-ways waffle composite slabs were investigated under uniformly distributed loads. The motivating force to achieve this research is trying to avoid some undesired structural features and executive conditions of the well-known traditional composite slabs reinforced with one-way corrugated steel sheets. 3. METHODOLOGY Fig. 3 Flow Chart 4. MODELLING In this paper, the structures with waffle slab and flat slab for various heights are modelled using the software ETABS To obtain the results for the effect of seismic force on flat slab and waffle slab framed structures different load combinations, as per IS: 1893 (2002) are considered for the analysis. The parameters studied here are storey drift and maximum displacement. Volume:03 Issue:

4 4.1 Plan View for the Given Structure Number of Column in Y 5 Direction Height of Basement 4.5m Height of Each Floor 3.5m Total Height of the building 57m Table 3 Description of Model 4.4 Description of Waffle Slab Adopted in : Slab Thickness Size of Rib beam 200mm 200mm X 375mm Table 4 Description of Waffle Slab 4.5 Description of Flat Slab Adopted in : Slab Thickness 200mm Table 5 Description of Flat Slab 4.2 Description of Load: Fig. 4 Waffle Slab Different loads are considered for the calculations: LOADS REFERENCES Finishing Load As per IS: 875 (Part 1) 1987 Live Load As per IS: 875 (Part 2) 1987 Earthquake load As per IS: 1893(2002) Table 1 Description of Loads Different Parameters are considered for the calculations: Response Reduction Factor 5 Importance Factor 1.5 Damping Ration 0.05 Table 2 Parameters 4.3 Description of Geometry Adopted in : Description of framed structure Adopted for modelling: Type of Structure Ordinary moment resisting frame Type of building Office / Business Total number of building 1 Total Area of the 21328Sqm (31.70m X 42.05m X 16) No of Floors G RESULT AND DISCUSSION (SEISMIC ANALYSIS) Seismic analysis is done on waffle slab and flat slab. After seismic analysis changes in parameters such as maximum displacement and storey drift of the structure are noticed. 5.1 (G+15) Maximum Displacement in X Direction Number of Column in X Direction 4 Table 6: Max Displacement in X-Direction (Mm) For (G+15) Storey Volume:03 Issue:

5 Fig 6: Max Displacement in Y-Direction (Mm) For (G+15) Storey Fig 5: Max Displacement in X-Direction (Mm) For (G+15) Storey 5.2 (G+15) Maximum Displacement in Y Direction (G+15) Storey Drift in X Direction: Table 8: Storey Drift in X-Direction (Mm) for (G+15) Storey Table 7: Max Displacement in Y-Direction (Mm) For (G+15) Storey Fig 7: Storey Drift in X-Direction (Mm) for (G+15) Storey Volume:03 Issue:

6 5.4 (G+15) Storey Drift in Y Direction: Table 9: Storey Drift in Y-Direction (Mm) for (G+15) Storey 6. RESULT AND DISCUSSION (ECONOMIC ANALYSIS) 6.1 Quantity of Slab Work: DESCRIPTION UNIT WAFFLE SLAB FLAT SLAB Concrete Quantity Cum Steel Quantity MT Weld mesh Quantity Shuttering Quantity Sqm Nil Sqm Table 10: Quantity for (G+15) Storey 6.2 Amount of Slab Work: DESCRIPTION UNIT /RATE WAFFLE SLAB (Rs) FLAT SLAB (Rs) Concrete Rs/ Cum 19,920,211 19,650,600 Steel Rs/ MT 16,686,244 21,947,172 Weld mesh Rs/ Sqm 194,615 Nil Shuttering Rs/ Sqm 13,767,880 67,18,244 Total 50,568,952 48,316,017 Rate per Sqm Table 11: Total Amount for (G+15) Storey Fig 8: Storey Drift in Y-Direction (Mm) for (G+15) Storey RATE PER SQM WAFFLE SLAB FLAT SLAB RATE PER SQM Fig 9: Total Amount for (G+15) Storey Volume:03 Issue:

7 7. CONCLUSIONS Based on the results obtained it can be said that the maximum displacement value of flat slab is about 16% higher compared to waffle slab in both X and Y direction for up to G+9 Storey & Maximum displacement value of Waffle slab is 89% higher compared to flat slab in X and Y direction increases upto 86%. Whereas as for up to G+9 storey, storey drift value of flat slab varies from 11% to 14% both in X and Y direction from waffle slab. From G+14 storey, storey drift value of waffle slab is 45% to 47% higher compared to flat slab both in X and Y direction. From the above obtained result it can be observed that for structure with a height less than 40m it is advisable to use waffle slab other than flat slab, whereas for structures of height above 40m it is advisable to use flat slab. Concrete required for the flat slab is slightly less than the concrete required for Waffle slab. Steel required for the flat slab is more than the Waffle slab. Shuttering cost for the waffle slab is more than the flat slab and this is one of the dis advantage for the waffle slab. Flat slab is more economical than the waffle slab. Volume 2, Issue 12, June 2013 (ISSN: ) ISO 9001:2008 Certified [14] X. Cahís, A. Benavent-Climent and A. Catalan, The 14th World Conference on Earthquake Engineering October 12-17, 2008, Beijing, China. 8. REFERENCES [1] STAAD Pro 2003 User s Manual. Research India Ltd., Bently Systems, E2-4, Block GP, Sector-V, Salt Lake, Kolkata [2] N.Krishnaraju, Design of reinforced concrete structures, CBS Publications & Distributors. [3] P.C.Vargese, Limit State Design of Reinforced Concrete second edition. [4] P.C.Vargese Advanced Reinforced Concrete Design. [5] IS 456:2000 Plain and Reinforced Concrete code of practice. [6] IS 1893:2000 Criteria for Earthquake Resistant design of structures. [7] IS13920:1993 Ductile Detailing of Reinforced concrete structures to seismic forces-code practice. [8] S.R.Damodarasamy, S.Kavitha, Basics of structural dynamics and Aseismic design [9] Amit A. Sathawane, R.S. Deotale (2013) Analysis and Design of Flat Slab and Grid Slab and their Cost Comparison [10] Salman I Khan1 and Ashok R Mundhada (2015) Comparative study of seismic performance of multi storied RCC buildings with Flat Slab and Grid Slab Ravi Kumar Makode, Saleem Akhtar, Geeta Batham Int. Journal of Engineering Research and Applications Muhammed Yoosaf.K.T, Ramadass S, Jayasree Ramanujan American Journal of Engineering Research (AJER) e-issn : p-issn : Volume-3 pp [11] Uzma A. Shaikh, Prof. Mohd. Shahezad, International Journal of Engineering Sciences & Research Technology (ISSN: ) Scientific Journal Impact Factor: (ISRA), Impact Factor: [Shaikh, 3(8): August, 2014] [12] Alaa C. Galeb, Zainab F. Atiyah, International Journal Of Civil And Structural Engineering Volume 1, No 4, 2011 (ISSN ) [13] M. Khalaf, A. El-Shihy, H. Shehab, S. Mustafa, International Journal of Engineering and Innovative Technology (IJEIT) Volume:03 Issue: