International journal of scientific and technical research in engineering (IJSTRE) Volume 1 Issue 4 ǁ July 2016.

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1 International journal of scientific and technical research in engineering (IJSTRE) Volume Issue ǁ July. Response Spectrum Method for the Analysis of a Vertically Irregular R.C. Building under Seismic Forces Considering Soil Structure Interaction- an Overviewwith Case Study Nawaraj Kapil, Karthik.N.M, Dr.Rajendra.S, Vijay.K, Likhitha.R P.G Student, Department of Civil Engineering, N.C.E.T, Bangalore, India. Assistant Professor, Department of Civil Engineering, C.M.R.I.T, Bangalore, India HOD(PG), Department of Civil Engineering, N.C.E.T,Bangalore, India Associate Professor, Department of Civil Engineering, N.C.E.T, Bangalore, India Assistant Professor, Department of Civil Engineering, N.C.E.T, Bangalore, India ABSTRACT:Irrégularités are not avoidable in construction of Buildings, However the behaviour of structures with thèseirrégularités must be studied. Thèseirrégularités are responsible for structural collapse of Buildings under the action of dynamicloads. In thispaper, attempt has been made to study the seismic behaviour of the vertically irregular structure with and withoutsoil structure Interaction. The structure modelled have been alreadyconstructed and modelling was carried out using E-Tabs Software and analysed by ResponseSpectumAnalysis. KEYWORDS-Displacement, Storey Shear, Storey Drifts, Overturning Moment, Base Shear and Soil Structure Interaction. I. INTRODUCTION In Earthquake Resistance Design, a structure depends upon the inelastic behavior in order to resist the ground motion. Based on the current scenario, many structural Buildings have irregular configuration both in plan and elevation which leads to damage of the structure element, when hit by an earthquake. In such cases, we need to examine the structure against such disaster caused by the seismic waves. Irregularities cannot be avoided but the behaviour of the irregular structure must be studied properly. The structural building considered in this case study has been already constructed in hilly terrain-sikkim, which falls under seismic zone IV. II. STRUCTURAL IRREGULARITIES AS PER I.S 89(P): As per I.S 89(part):, The breakdown of the structure starts at the point of weakness or faults and this faults spring up due to varying load path with respect to mass, stiffness, strength and geometry of the structure, these discontinuity are termed as Irregular Structures. It is sub categorized into two types:. HORIZONTAL IRREGULARITIES:.aTorsion Irregularity: Torsional irregularity to be considered to exist when the maximum storey drift, computed with design eccentricity, at one end of the structures transverse\ to an axis is more than. times the average of the storey drifts at the two ends of the structure.bre-entrant Corners: Plan configurations of a structure and its lateral force resisting system contain re-entrant corners, where both projections of the structure beyond there-entrant corner are greater than percent of its plan dimension in the given direction. Manuscript id Page 8

2 Response Spectrum Methodfor the Analysis ofa VerticallyIrregular R.C. Building under Seismic... cdiaphragm Discontinuity: Diaphragms with abrupt discontinuities or variations in stiffness, including those having cut-out or open areas greater than percent of the gross enclosed diaphragm area, or changes in effective diaphragm stiffness of more than percent from one storey to the next.. dout-of-plane Offsets: Discontinuities in a lateral force resistance path, such as out-of-plane offsets of vertical elements.. enon-parallel Systems: The vertical elements resisting the lateral force are not parallel to or symmetric about the major orthogonal axes or the lateral force resisting elements.. VERTICAL IRREGULARITIES:. astiffness Irregularity Soft Storey A soft storey is one in which the lateral stiffness is less than 7 percent of that in the storey above or less than 8 percent of the average lateral stiffness of the three storeys above.. bstiffness Irregularity Extreme Soft Store: A extreme soft storey is one in which the lateral stiffness is less than percent of that in the storey above or less than 7 percent of the average stiffness of the three storeys above. For example, buildings on STILTS will fall under this category.. cmass Irregularity: Mass irregularity shall be considered to exist where the seismic weight of any storey is more than percent of that of its adjacent storeys. The irregularity need not be considered in case of roofs.. dvertical Geometric Irregularity: Vertical geometric irregularity shall be considered to exist where the horizontal dimension of the lateral force resisting system in any storey is more than percent of that in its adjacent storey. ediscontinuity in Capacity Weak Storey: A weak storey is one in which the storey lateral strength is less than 8 percent of that in the storey above, The storey lateral strength is the total strength of all seismic force resisting elements sharing the storey shear in the considered direction. III. SOIL STRUCTURE INTERACTION Soil Structure Interaction can be defined as the coupling of the structure and the soil during an Earthquake. It is one of the most flourishing areas of research for structural engineer. SSI is influenced by two types of loading.i.e. Dynamic loading and static loading. Basically, engineers neglect SSI while designing ordinary structure as they evaluate the structure under the assumption of fixed based dynamic response. When the structure is hit by the seismic waves, these waves tend to generate vibrations or motion on the structure. In order to resist the motion, the structure needs to overcome its own inertia force which in result deals with SSI. There are two types of primary issues of soil structure interaction: Inertial Interaction. Kinematic Interaction. Manuscript id Page 9

3 Response Spectrum Methodfor the Analysis ofa VerticallyIrregular R.C. Building under Seismic.. When soil undergoes deformation and stress, they induce base shear and moments in the vibrating structure. Such cases lead to dynamic response of the structure by creating dynamic interacting system between soil and the structure. This type of interaction is known as Inertial Interaction. When seismic waves enter the soil, a discontinuity in medium of wave propagation is encountered at the interface of foundation and soil. This leads to reflection, scattering deflection, refraction of seismic waves at soil foundation interface along with change in nature of ground motion. Slippage occurs across the soil foundation interface which is affected by wave propagation in elastic medium. This phenomenon due to the wave propagation consideration is known as Kinematic Interaction. IV. STRUCTURAL DETAILING The structural building considered has been already constructed in Sikkim, India. It is vertically irregular in nature and comprises of B- and G+. The total area comprises of 8.m x.9 m. The soil condition of the structure is dense gravel soil with soil bearing capacity of 8 kn/m. The grade of concrete used is M and grade of steel is Fe. The loads considered are: Dead load of kn/m, Live Loads of kn/m, kn/m and kn/m respectively. The frame Loads provided were of kn/m as exterior wall load and.8 kn/m as partition wall load. The structure was modeled and response spectrum analysis was carried out using E-tabs software. The same structure was analyzed considering soil structure interaction for X and Y direction respectively. The material properties of a structure are shown in Table, frame properties of beam are shown in Table, frame properties of slab are shown in Table and frame properties of column are shown in Table. The frame loads are shown in Table and the shell loads are shown in Table. Table : Material properties of a structure considered SL.NO MATERIAL PROPERTIES VALUES UNIT Characteristic compressive strength of concrete Characteristic strength of reinforcement M kn/m Fe kn/m Table : Frame Properties of beam SL. NO PROPERTIES DIMENSION UNITS Beam(B) X mm Beam(B) x mm Table : Frame Properties of slab SL. NO PROPERTIES DIMENSION UNITS Slab(S) 7 mm Manuscript id Page

4 Response Spectrum Methodfor the Analysis ofa VerticallyIrregular R.C. Building under Seismic.. Table : Frame Properties of column SL. NO PROPERTIES DIMENSION UNITS Column (C) X mm Column (C) X mm Column (C) X mm Column (C) X mm Column (C) X` mm Table : Frame loads SL. NO FRAME LOAD VALUES UNITS Exterior wall load. kn/m Partition wall load.8 kn/m Table : Shell loads SL. NO SHELL LOAD VALUES UNITS Dead Load kn/m Live load kn/m Live load kn/m Live load kn/m Floor Finish kn/m V. RESULTS After analysis of the structure, seismic weight was obtained and base shear was calculated. The base shear calculated manually was compared to that obtained from E-Tabs. The seismic weight and base shear of the structure are shown in Table 7 and Table 8 respectively. The parameters considered such as Displacement and Story Shear was calculated and compared considering with and without soil structure interaction for both X and Y direction respectively. Table 7: Seismic Weight SL. NO Seismic weight VALUES UNITS Dead Load 8.8 kn Live Load.8 kn Floor Load 7. kn Wall Load kn Manuscript id Page

5 stories stories Response Spectrum Methodfor the Analysis ofa VerticallyIrregular R.C. Building under Seismic.. Table 8: Base Shear SL NO BASE SHEAR VALUES UNITS X direction(v BX) 9.9 kn Y direction(v BY) 9. kn DISPLACEMENT Graph. Maximum Storeys Displacement for X direction DISPLACEMENT - Graph. Maximum Storey Displacements for Y Direction Manuscript id Page

6 stories STORIES STORIES Response Spectrum Methodfor the Analysis ofa VerticallyIrregular R.C. Building under Seismic DRIFTS Graph. Storey Drifts for X Direction DRIFTS Graph. Storey Drifts for Y Direction STOREY SHEAR Graph. Storey Shear for X Direction Manuscript id Page

7 STORIES STORIES stories Response Spectrum Methodfor the Analysis ofa VerticallyIrregular R.C. Building under Seismic STOREY SHEAR Graph. Storey shear for Y Direction OVERTURNING MOMENT Graph.7 Overturning Moment for X Direction OVERTURNING MOMENT Graph. 8 Overturning Moment for Y Direction Manuscript id Page

8 Response Spectrum Methodfor the Analysis ofa VerticallyIrregular R.C. Building under Seismic.. VI. CONCLUSION From the above study, the parameters considered were compared and the following conclusion were drawn:. From Graph ; the structure undergoes. % more displacement when SSI is taken into consideration comparative to without soil structure interaction in x direction.. From Graph ; the structure undergoes.9 % more displacement when SSI is taken into consideration comparative to without soil structure interaction in y direction.. From graph ; the comparative drift at respective stories for RS in X Direction with and without SSI, here the drift at ground level is.7 larger with SSI than without SSI. So.% more drift is observed when the SSI is taken in to account comparative to without SSI. Maximum drift is observed in ground level as the stiffness and fixity conditions changes between the stories.. From Graph ; the comparative drift at respective stories for RS in Y Direction with and without SSI, here the drift at ground level is.9 larger with SSI than without SSI.So. % more drift is observed when the SSI is taken in to account comparative to without SSI. Maximum drift is observed in ground level as the stiffness and fixity conditions changes between the stories.. From graph ; 9. % more story shear was observed when soil structure interaction was taken into consideration comparative to without soil structure interaction in x direction.. From graph ; 7. % more story shear was observed when soil structure interaction was taken into consideration comparative to without soil structure interaction in y direction. 7. From Graph 7, the comparative Overturning Moment at respective stories for RS in X Direction with and without SSI, here the Overturning Moment at basement is 8. kn-m larger with SSI than without SSI. So 7. % more Overturning Moment is observed when the SSI is taken in to account comparative to without SSI. 8. From Graph 8, the comparative Overturning Moment at respective stories for RS in Y Direction with and without SSI, here the Overturning Moment at basement is.7 kn-m larger with SSI than without SSI.So. % more Overturning Moment is observed when the SSI is taken in to account comparative to without SSI.Due to vertical irregularities and large lateral spacing between the foundations in Y direction, the overturning moment is more in basement than in basement in Y axis. REFERENCES Following are the various technical papers, text books, code books, guidelines, internet references etc. referred in the present analytical study: [.] S.Monish, S.Karuna, on Effect of vertical Irregularity in R.C. Framed building in severe seismic zone. International Journal of Emerging Technology and Advanced Engineering(IJETAE).(ISSN - 9,ISO 9:8 certified Journal, volume, issue,june ). [.] E.Pavan Kumar, A.Naresh, M.Nagajyoti, M.Rajasekhar, on Earthquake Analysis of multi storied residential building- a case study. International Journal Of Engineering Research and Application(IJERA)(ISSN: 8-9,volume, Issue (version ),November ). [.] Sri. M. Pawan Kumar, SateeshKonni, on Effect of Vertical Irregularities of RC Framed Structures by using Non- Linear Static Analysis. International Journal of Engineering Research (IJER)(ISSN: 9-89, volume, issue number, November ). [.] Karthik. K.M, Vidyashree.D, on Effect of Steel Bracing on Vertically Irregular Rc building frames under seismic loads. International Journal of Research in Engineering and Technology (IJRET)(ISSN:9-, volume, June ). [.] ShreyaThusoo, Karan Modi, Rajesh Kumar, Hitesh Madahar, on Response of building with soil structure interaction with varying soil types. International Journal of Civil, Environmental, Structural, Construction and Architectural Engineering. Volume 9, November. [.] PankajAgarwal, Manish Shrikhande, Earthquake Resistant Design of Structures. Pinlished by Prentice Hall of India Prentice Hall, 7. [7.] Indian Standard code I.S. 89 (part):. [8.] Earthquake Tips, IIT Kanpur. Manuscript id Page