SEISMIC BEHAVIOUR OF FLAT SLAB BUILDING WITH SHEAR WALL ACCORDING TO I.S

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1 International Journal of Civil Engineering and Technology (IJCIET) Volume 9, Issue 5, May 2018, pp , Article ID: IJCIET_09_05_105 Available online at ISSN Print: and ISSN Online: IAEME Publication Scopus Indexed SEISMIC BEHAVIOUR OF FLAT SLAB BUILDING WITH SHEAR WALL ACCORDING TO I.S Bhavesh Rajesh Sahni M.Tech (Structural Engineering), Shri Ramdeobaba college of Engineering and Managment, Nagpur Dr. Prashant D. Hiwase Assistant Professor, Dept. of Civil Engineering, Shri Ramdeobaba college of Engineering and Management, Nagpur Prasad P.Dahale Assistant Professor, Dept. of Civil Engineering, Shri Ramdeobaba college of Engineering and Management, Nagpur ABSTRACT High rise structure is the need of the current developing scenario and this has led to advancement in the field of civil and structural engineering. This trend to High rise building will continue to overcome the everlasting demand of space in metro and developing cities. Rapid construction with quality work is required for this current scenario. Flat slab gives the advantage over conventional slab with reduced floor to floor height which gives flexibility in construction and reduction in construction time. As I.S does not allow flat slab in higher seismic zone we have studied various parameters in this paper such as deflection, story drift, overturning moment resistance and base reactions and compared three models first being conventional slab, second being pure flat slab and third being flat slab with shear wall. Since flat is vulnerable to lateral loading in higher seismic zones, the main objective of this paper to prove that flat slab with the application of shear wall show same results as that of conventional slab. The analysis is done by using Etabs software and results being compared in all seismic zones. Keywords: Flat Slab, Shear Wall, Conventional Slab, Deflection, Overturning moment. Cite this Article: Bhavesh Rajesh Sahni, Dr. Prashant D. Hiwase and Prasad P. Dahale, Seismic Behaviour of Flat Slab Building with Shear Wall According to I.S International Journal of Civil Engineering and Technology, 9(5), 2018, pp

2 Seismic Behaviour of Flat Slab Building with Shear Wall According to I.S INTRODUCTION With the rapid development and modernization of the world, the redundancy in the land in urban areas has led in the development in the vertical direction in the form of high rise towers. Preferably we go for framed structure when it comes to high rise buildings or structures. Frame structure is governed by application of both lateral loads and vertical loads. So a structure designed only for vertical load may not be able to resist lateral loads.lateral loads are assumed to be of deciding forces as they are likely to increase with an increase in the number of storeys. When a structure is subjected to both earthquake forces and wind loads then there are chances of large overturning moments to be generated at the base of the structures. So in higher seismic zones major cause of failure of structures has been that the structure is been not designed for seismic loads. So in order to safely design the structure in earthquake prone zones the reinforcement percentage is increased and thus making the structure heavy and uneconomical. This is why there is a huge need to study seismic loads in detail and at the same time the structural components affect by the effect of lateral loads. The effect of lateral forces is relatively higher in the top storey s rather than lower storey s and due to this effect only the building or structure starts behaving as a cantilever and the effect of these lateral loads make the structure to sway. Due to these reasons only the study of seismic forces becomes so vital. While considering about pure conventional structure i.e. beams, column and slabs the probability of shear failure increases as this structure is weak in shear and makes the column to bend under the seismic loads and this bending causes the whole structure to deflect absurdly. In order to restrain this deflection either we can alter the sizes of the load carrying elements beyond the requirement and make the structure uneconomical and over reinforced or we could apply property modifier and make the structure rigid which in turns makes the structure stable and eventually reduces the deflection. A frame structure may be constructed without using beams and the load of the slab is directly transferred to the column. This type of slab is referred to as flat slabs. When flat slab used in a reinforced concrete building it possess high merit over our conventional beam slab structure in terms of architectural flexibility, use of space, easier formwork and shorter construction time. The mode of construction of flat slabs is much painless, and is methodological in the sense that it results in lesser floor to floor height and thus increases in number of floors. Flat slab though possessing these advantages at the same time have a disadvantage that is its poor performance under seismic loading in higher seismic zones. This is due to the reason that this flat slab structure is more flexible than our conventional structure and thus more exposed to seismic or lateral loads. In higher seismic zones low ductility makes the structure very less efficient in terms of structural stability. The failure of the structure is mainly because of punching shear which is generated because of shear force and unbalanced moment between column and slab. A flat slab should not fail in shear and for that drop in flat slab is provided since the value of the moments is a lot higher at the column slab junction and thickness of slab required at the junction is more thus the necessity of drop. So to overcome the poor performance of flat slab in higher seismic zones we need to provide lateral load resisting systems. Moment resistant frames, Braced frame, in filled frame, Shear walls, Outrigger and Belt Truss system bracings, and Core system. Our study focuses on system of flat slab with shear wall and no other lateral load resisting systems. Many people have researched on the performance of flat slab on different criteria s Need of Research As I.S discourages the use of flat slab in higher zones due its poor performance in higher seismic zones but when used with shear wall its performance improves. Flat slab with shear wall should be used in higher seismic zones because of the advantages flat slab provides editor@iaeme.com

3 Bhavesh Rajesh Sahni, Dr. Prashant D. Hiwase and Prasad P. Dahale in comparison to conventional beam slab such as faster construction, flexibility for the occupier, saving in building height, flexibility in room layout and thus saving cost. The use of flat slab with shear wall is very extensive in the Mediterranean basin and the use of flat slab is also very common in the Arab countries. In this paper we have studied flat slab models with and without shear wall and compared them with conventional beam slab frame in different seismic zones, comparison being on parameters such as deflection, storey drift, overturning moment and base reactions with permissible limits according to I.S METHODOLOGY Three models were basically analyzed in this study and the relative study of flat slab with and without shear wall was made and then compared with the conventional beam slab structure in different zones and then different parameters are studied and checked their permissible values as per I.S Software used for the analysis purpose is E-tabs. The methodology is to achieve same value of deflection in flat slab with shear wall as the value of deflection attained in conventional frame and what percentage of shear wall is increased. So basically a comparison on the Wall Plan Density of the structure is also done in this study. Structure 1: Structure is modeled as a frame structure i.e. conventional beam slab structure (Shown in Fig.1).The model having beams of sizes 300x600 & 230x600 and columns of sizes 600x600 & 300x600 with slab thickness of 200mm. Figure 1 Plan of Conventional Beam Slab Structure Structure 2: Structure is modeled as structure with flat slab and drop (Shown in Fig.2). The thickness of the flat slab is taken as 250 mm and the drop is of size 2000x2000 mm.the model having beam of sizes 300x600 and columns of sizes 600x600. Figure 2 Plan of Flat Slab Structure with Drop Structure 3: Structure is modeled as structure with flat slab and shear wall (Shown in Fig.3). The thickness of the flat slab is taken as 250 mm and the thickness of the shear wall is taken as 300mm.The model having beam of sizes 300x600 and columns of sizes 600x editor@iaeme.com

4 Seismic Behaviour of Flat Slab Building with Shear Wall According to I.S Figure 3 Plan of Flat Slab with Shear Wall Structure The ultimate goal was to attain the value of deflection of flat slab with shear wall model i.e. Model 3 equal to the value of deflection in conventional model i.e. Model 1 by alternating the Wall plan Density and keeping the economy in mind too and studying the optimum position of shear wall for least value of deflection. The values of the loads assigned and material properties have been predefined in E-tabs. Following properties and loads have been assigned in the models. Grade of Concrete: M-30 Grade of Steel: fe-500 AAC blocks loads used instead of brick masonry Table 1 Details of data used in modeling Sr.no. Details Value 1 Dead Load: Floor Finish-1.0 kn/m²; Services-0.5 kn/m²; Partition Wall- 3.0 kn/m kn/m² 2 Live Load 3.0 kn/m 2 3 Type Of Soil Type II 4 Importance Factor 1 5 Response Reduction Factor 5 6 Zone II,III,IV&V 3. RESULTS AND DISCUSSION This paper investigates the behavior of a structure under different circumstances of variating slab type and the applications of these slabs with and without the deployment of shear wall. As explored prior that flat slabs performs poorly in higher seismic zones but their performance improves significantly when used with shear wall and therefore its usage should be encouraged in higher seismic zones. So here we have tried to achieve same value of deflection in the structure with flat slab and shear wall as that in our conventional frame structure and also making a comparison with the values given by the structure of pure flat slab. Conventional Frame Structure (mm) Table 2 Deflection in Zone II Flat Slab Structure (mm) Flat Slab with Shear X Y Here table 2 shows the value of deflection in Zone II in relation to figure 1,2and 3.From the above table we can conclude that flat slab with shear wall gives value of deflection same editor@iaeme.com

5 Bhavesh Rajesh Sahni, Dr. Prashant D. Hiwase and Prasad P. Dahale as conventional frame structure in x direction but more value in y direction whereas structure with pure flat slab gives value quite higher than these two structures. So we can say deduce that we need to add shear wall in direction parallel to y-direction as deflection values are already less than that of conventional slab in x direction. In order to control the value of deflection we add or increase the percentage of shear wall in the direction parallel to Y direction. So below figure 4 shows our structure 4 of flat slab with shear wall with an increase in percentage of shear wall. Structure 4: Structure is modeled as structure with flat slab and shear wall (Shown in Fig.3). The thickness of the flat slab is taken as 250 mm and the thickness of the shear wall is taken as 300mm.The model having beam of sizes 300x600 and columns of sizes 600x600 Figure 4 Plan of Flat Slab with Shear Wall Structure after addition of shear wall in Y-direction Let s investigate the comparison with the model with an increase in the Plan Wall Density. Table 3 Deflection in Zone II Conventional Frame Flat Slab Structure Flat Slab with Shear Structure (mm) (mm) X Y Figure 5 Chart of Zone Vs Deflection in Y (Structure1, 2and3) From Table 3 we can observe that the value of deflection is less than that of the value of deflection in conventional frame structure. Let s see the results in higher seismic zones. Table 4 Deflection in Zone III Conventional Frame Flat Slab Structure Flat Slab with Shear Structure (mm) (mm) X Y editor@iaeme.com

6 Seismic Behaviour of Flat Slab Building with Shear Wall According to I.S Table 5 Deflection in Zone IV Conventional Frame Flat Slab Structure Flat Slab with Shear Structure (mm) (mm) X Y Table 6 Deflection in Zone V Conventional Frame Flat Slab Structure Flat Slab with Shear Structure (mm) (mm) X Y Figure 6 Chart of Zone Vs Deflection in Y (Structure1, 2and4) Looking at Figure 5 and Figure 6 we can come to the fact that addition of shear wall in direction parallel to y axis we can control deflection. As we can see in Figure 6 that value of deflection in Conventional Slab is same as that in flat slab with shear wall. Wall Plan Density in Figure 3 =1.5% Wall Plan Density in Figure 4 = 1.87% According to I.S (C.N ) minimum percentage of shear wall should be 2%. Now comparing the value of overturning moment in different models. Table 6a Table 6b editor@iaeme.com

7 Bhavesh Rajesh Sahni, Dr. Prashant D. Hiwase and Prasad P. Dahale Table 6c Table 6d Table 6a,6b,6c and 6d showing overturning moment capacity of different models in Zone II,Zone III,Zone IV and Zone V respectively for Structure 1,2and 4 in Y. Figure 7 Chart of Building Height Vs Overturning Moment Capacity in Y (Structure1, 2and4) From figure 7 we can see that with the addition of shear wall the overturning moment capapcity of the buildingis more than that of conventional structure. Lets examine the value of storey drift in the models. Table 7a Table 7b editor@iaeme.com

8 Seismic Behaviour of Flat Slab Building with Shear Wall According to I.S Table 7c Table 7d Table 7a,7b,7cand 7d showing storey drift of different models in Zone II,Zone III,Zone IV and Zone V respectively for Structure 1,2and 4 in Y. As it can be seen from Table 7a,7b,7c and 7d the value of storey drift in flat slab with shear wall is less or nearly equal to value conventional slab and also in the permissible limit. Figure 8 Figure 9 Figure 8 and 9 represents Chart of Zone Vs Story Drift in (Structure1, 2and 3) and (Structure 1,2and 4) respectively. Figure 8 and Figure 9 Shows us how the addition of shear wall in Y direction drastically improves the performance of structure in terms of story drift. According to I.S (C.N ) permissible value of story drift should be 0.12 in our structures. Now considering base reactions that is how much of base shear is taken by columns and how much is taken by shear wall. Table 8 Base Reactions in X and Y Base Reaction (%) Zone 2 Zone 3 Zone 4 Zone 5 Shear Wall in X Column in X Shear Wall in Y Column in Y As we can see in Table 8 the base reactions taken by shear wall is approximately 75% in X direction and nearly 100% in Y direction which satisfies our requirement of I.S (C.N.7.2.6) about Flat slab with Shear Wall system editor@iaeme.com

9 Bhavesh Rajesh Sahni, Dr. Prashant D. Hiwase and Prasad P. Dahale 4. CONCLUSION From this study we can conclude that flat slab structure is more flexible than conventional frame structure and because of that it does not perform well in higher seismic zones but with the application of shear wall flat slab structures showcase properties same or even better than conventional structure. Discussing about the parameters studied the value of deflection is same or even less in flat slab with shear wall than conventional slab which was the main objective of the study. Overturning moment capacity value being higher in flat slab with shear wall structure thus possessing higher resistance to lateral and wind loads. The value of storey drift is within permissible limits and also less in flat slab with shear wall structure than other structures. Base reactions taken by shear wall and column also possess nearly same value as given by I.S So with the results we got we can conclude that though flat slab being vulnerable to lateral loads could be provided in higher zones with shear wall as the flat slab structure when provided with shear wall manifest properties same as conventional structure with wall plan density less than what is suggested by I.S. code although it may vary from structure to structure. REFERENCES [1] IS , Criteria for Earthquake Resistant Design of Structures Part I, General provisions and buildings Sixth Revision).Bureau of Indian Standards, New Delhi. [2] Sumit Pahwa, Vivek Tiwari, Madhavi Prajapati, Comparative study of flat slab with traditional two way slab, International Journal of Latest Trends in Engineering and Technology. Vol. 04, pp , 2014 [3] Dr. Uttamasha Gupta, Shruti Ratnaparkhe, Padma Gome Seismic behavior of building having flat slab with drop, International Journal of Emerging Technology and Advanced Engineering, vol. 02 pp , 2012 [4] Subhajit Sen and Yogendra Singh, Seismic Performance of Flat Slab Buildings", Advances in Structural Engineering, Vol.No.2, (2015), PP [5] Ahmad J. Durrani S. T. Mau, Amr Ahmed AbouHashish and Yi Li Earthquake Response Of Flat-slab Buildings, Journal of Structural Engineering, Vol. 120, No. 3, March, 1994 Paper No [6] H.S. Kim, D.G. Lee, "Efficient Analysis of Flat Slab Structures Subjected To Lateral Loads", Engineering Structures 27 (2005), PP [7] P.N. Pagare1, P.R. Bhosale2, A.P. Birar3, V.D. Hayatnagarkar4, D.C. Sawant5, Parametric Study of Buildings with and without Shear Walls for Seismic Performance [8] Pradip S. Lande1, Aniket B. Raut, Seismic Behaviour of Flat Slab Systems [9] Wani Ahmad, Singh Amarpreet, Iqbal Sana, Lal Nawaf and Bhat Javed, Development of Economized Shaking Platforms for Seismic Testing of Scaled Models, International Journal of Advanced Research in Engineering and Technology (IJARET), Volume 3, Issue 2, July-December (2012), pp [10] K. Sunil Kumar, Dr. B. Nagalingeswara Raju, J. Arulmani and P. Amirthalingam, Design and Structural Analysis of Liquified Cryogenic Tank under Seismic and Operating Loading. International Journal of Mechanical Engineering and Technology, 7(6), 2016, pp