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SSRG International Journal of Civil Engineering (SSRG-IJCE) – EFES April 2015 Alternative Approach to Soft Storey in Seismic Analysis of R.C.C Building Structures AbhishekArora#1 # PG Scholar, Department of Civil Engineering, SDDIET, (Kurukshetra University), Haryana, India Abstract-With urbanization and increasing unbalance of required area to availability, it is important to provide open ground storey in both type of buildings that is commercial and residential. These open storey’s without brick infill reduce the stiffnessof theload carrying memberand progressive increase in load exhibit higher stresses in the load carrying member and these members i.e. columns fail as the plastic hinges are not for medon predefined positions. Therefore, the collapse of this soft storey during earthquake has caused structural engineer store think the design of a soft storey. The present analytical study finds out some provisions to soft storey which can reduce the damage during earthquake. The modeling of the whole building is carried out using the computer program ETABS. In this study deals with provision to soft storey in seismic analysis of RCC building has been given in two ways, firstly by providing stiff column which increases the stiffness of the load carrying member or byprovidingadjacent infillwall panelin buildingframe which increase the load carrying strength. Keywords- stiffness, shear wall, displacement , natural time period storey shear, drift , I. INTRODUCTION Reinforcedconcreteframebuildings are becoming progressively common in India. Many RCC buildings constructed in having a feature open the ground level storey for the purpose of parking, i.e. partition walls are not provided in between the columns inthe ground storey The two distinct characteristic of the building having stilt parking are as follows Difference in flexibility, i.e. the relative horizontal displacement in the ground storey is much larger than upper story having both columns as well aswall. Thisflexiblegroundstoreyis also called softstorey. Ground storey having only columns are weaker than upper storey having both column and walls i.e. the lower storey can bear the horizontal earthquake force less efficiently than the upper storey. II. APPROCH TOSOFTSTOREY A . By Providing Stiff Column at Open Ground Storey Stiffness of column is directly proportional to its load carrying ISSN: 2348 – 8352 capacity i.e. higher the stiffness, higher is the load carrying capacity. Stiffness can be increased by increasing the size of these loads carrying member as they are able to bear the excessive load during earthquake. B. By Providing Brick Infill with Column at Open storey Masonry in fill has several advantages like good sound and heat insulation properties, high lateral strength and stiffness. This increases strength and stiffness of RC frame and hence to decrease lateral drift, energy dissipation capacity due to cracking of infill and friction between in fill and frame III. ANALYTICAL WORK A four - storeybuilding with R C momentresistingframe has been chosenforthis study. Typesofcasesusedforanalysisofstructure are as follows MODEL NO .1 Building modelwithsoftstorey:buildingmodelwithnomasonrywallinfirst groundstorey andfullinfillmasonry wallinall above stories with column size 300 mm x 600 mm MODEL NO .2 Building modelwith column and masonry wall in the ground storey and one full in fill masonry wall in all above stories. A. StructuralData Story Data Name Story4 Height Elevation mm mm 2950 12150 Master Story No None Splice Story No Similar To Story3 2950 9200 No None No Story2 2950 6250 No None No Story1 3300 3300 No None No 0 0 No None No Base Gravity loading Story Story4 Story3 Story2 Story1 S.W P.C P.C P.C P.C www.internationaljournalssrg.org LIVE 1.5 2 2 2 SIDL 2 1.5 1.5 1.5 Page 40 SSRG International Journal of Civil Engineering (SSRG-IJCE) – EFES April 2015 P.C- PROGRAM CALCULATED SIDL- SUPER IMPOSED DEAD LOAD Lateralloading(as perIS: 1893(Part-I)-2002) Lateral loading consists of earthquake loading. Earthquake loading has been calculated by the program and it has been applied to the mass center of the building. Since the building under consideration was in Zone–III. Load Cases Name Type Dead Live SIDL EQx EQy FF SPEC X SPEC Y Linear Static Linear Static Linear Static Linear Static Linear Static Linear Static Response Spectrum Response Spectrum Fig 2 ETABS Models Factors and Coefficients {as per IS:1983 (P-1)-2002} Seismic zone factor Response reduction factor Importance factor Site type Z R I TYPE 0.16 4 1 II B. Model Analysis Model No. 1 – building with only columns at open storey Fig3Stiffness Plot for Model with Only Columnat first floor Fig 4Drift plot for model with only columns at first floor Fig 1 Building Plan TABLE 1 ISSN: 2348 – 8352 www.internationaljournalssrg.org Page 41 SSRG International Journal of Civil Engineering (SSRG-IJCE) – EFES April 2015 STOREY DRIFT AND STIFFNESS FOR PLAN HAVING ONLY COLUMNS TABLE 2 CHECK FOR SOFT STOREY (FOR PLAN HAVING ONLY COLUMNS) Model No. 2 – Building with both shear wall and column at open storey Fig 6 Plan with Shear Wall Fig 7 ETABSModel with Shear Walls TABLE 3 ISSN: 2348 – 8352 www.internationaljournalssrg.org Page 42 SSRG International Journal of Civil Engineering (SSRG-IJCE) – EFES April 2015 STOREY DRIFT AND STIFFNESS FOR PLAN HAVING COLUMNS&SHEAR WALL BOTH TABLE 4 CHECK FOR SOFT STOREY (FOR PLAN HAVING BOTH COLUMN AND SHEAR WALL BOTH) Fig 8 - Stiffness Plot for Model with Shear Wall at First Floor Fig 9 Drift Plot for Model with Shear Wall and columns at First Floor 1. IV. RESULTS ISSN: 2348 – 8352 In Model No. 1, which contains columns at the first storeyhas less stiffness as compared to the Model No. 2 having shear wall at the first wall. When shear wall is www.internationaljournalssrg.org Page 43 SSRG International Journal of Civil Engineering (SSRG-IJCE) – EFES April 2015 provided at the first floor the overall stiffness in both Xdirection and Y-direction is increased due to which the load carrying capability for this floor will be also increased, which will act more predominantly when earthquake occurs. 2. The comparison for story displacement can be done MODEL 1(for plan having only columns) Fig 10Sudden displacement can be easily seem in plan with column only when earthquake occurs MODEL 2(for plan having both column and shear wall both) Fig 11Even displacement can be easily seem in plan with shear wall and column when earthquake occurs 3. Comparison with lateral load acting ` MODEL 1(for plan having only columns) ISSN: 2348 – 8352 www.internationaljournalssrg.org Page 44 SSRG International Journal of Civil Engineering (SSRG-IJCE) – EFES April 2015 stiffer than open ground storey. Hence the upper storey move almost together as a single block and most of the horizontal displacement of the building occurs in the soft ground storey itself such building moves to and fro when earthquake occurs. Thus it is clear that building with only column in the ground storey has poor performance during earthquake as compared to building with both wall and column in the ground storey. REFERENCES [1] [2] [3] MODEL 2(for plan having both column and shear wall both) 4. Comparison of natural time period MODEL NO 1(for plan having only columns) [4] Direction Period Used (sec) W (N) Vb (kN) [5] X + Ecc. Y 0.332 30686613.31 1534330.67 [6] Y + Ecc. X 0.294 30686613.31 1534330.67 MODEL NO 2(for plan having both column and shear wall both) X + Ecc. Y Period Used W (sec) (N) 0.204 30565238.41 Vb (kN) 1528261.92 Y + Ecc. X 0.246 1528261.92 Direction 1. 2. 3. 30565238.41 [7] [8] [9] J. N. Arlekar, S. K. Jain and C.V.R. Murty, “Seismic Response of RC Frame Buildings with Soft First Storeys,” Dept. of Civil Engineering, IIT Kanpur, India. (CBRI) 1997. Sujatha A., Jiji Anna Varughese, Bindhu K.R, “The Influence of Masonry Infill in RC Multi-Storey Buildings,” (NCTT09) 6-7 Nov 2009. S. Haque, Khan M. A., “Seismic Vulnerability of Columns of RC Framed Buildings with Soft Ground Floor,” International Journal Of Mathematical Models And Methods In Applied Sciences, Issue3, Volume-2,2008. M.R. Amin, P. Hasan, B.K.M.A. Islam, “Effect of soft storey on multistoried reinforced concrete building frame,” Bangladesh, ISBN: 9789843343635, 4th Annual Paper Meet and 1stCivil Engineering Congress, December 22-24, 2011. C V R Murty, the Classroom section, a series of short articles, 'Earthquake Tips', related to earthquakes design & construction of buildings. IIT Kanpur and BMTPC, New Delhi. August 2004. A.K. Chopra, D.P. Clough, R.W. Clough, “Earthquake Resistance of Building with a „SOFT‟ First Storey”, Earthquake Engineering and Structural Dynamics, Vol.1, 347-355, 1973. Bento R., Azevedo J., “Behavior coefficient assessment for Soft Storey Structures”, 12WCEE,2000. P.Agrawal, M. Shrikhande Earthquake resistant design of structure (PHI Learning Pvt.Ltd. New Delhi, 2009). Mario Paz & William Leigh, Structural Dynamics (Springer Pvt. Ltd. New Delhi, 2007). IV. CONCLUSION WhenModel No. 1issubjectedtolateral load,each floorwill drift with respect to adjacent floors as each floor mass actsindependently. Thus the distribution of horizontal shear will be distributed across floors as building frame act in flexible manner. In presence of infill wall and column as in Model No. 2, mass of the upper floors to act together as a single mass, as relative drift between adjacent floors is restricted. Natural time period for the model having on column in the ground storey is more than the model having both column and shear wall in the ground storey. Thus this indicates that the model with only columns is not appropriate for analysis as compared to other model having both wall and column in the ground storey. The presence of wall sin upper storey makes the much ISSN: 2348 – 8352 www.internationaljournalssrg.org Page 45