Research Article Volume 6 Issue No. 6

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1 DOI / ISSN IJESC ` Research Article Volume 6 Issue No. 6 Seismic Analysis of RC Building with Underground Stories Considering Soil Structure Interaction Navya N 1, Karuna S 2 PG Student 1, Assistant Professor 2 Department of Civil Engineering The Oxford College of Engineering, Bangalore, Karnataka, India Abstract: Out of Several Countries in the world that is subjected to repeated natural calamities, India is also one of them. While mentioning the natural calamities, one of the calamities that leads to the loss of human life is the earthquake. Earthquake does not give any clue prior to its influence on human life and natural resources. Inspite of the improved technologies it has become difficult to manage with the influence of earthquake. One of the best way to save the loss of human life is that to design the structure in such a way so that it is capable if resisting the earthquake forces to a maximum extent. Hence in present study, an attempt has been made to study the effect of soil structure interaction on an RC framed building with underground stories under seismic loading. Structure is analyzed using response spectrum method. Modeling and analysis is carried out using SAP2000. Results are considered for structure resting on three types of soil namely soft, medium and hard. Raft foundation type is adopted for all models. Keywords: Soil Structure Interaction, Underground Stories, Raft foundation I. INTRODUCTION Seismic waves are generated due to the release of energy in the Earth s crust, which is in turn due to the disturbance caused on the earth s surface. It is well known fact that the building is resting on the soil and the building undergoes displacement during the earthquake. But usually buildings are modeled and analyzed without considering soil structure interaction. When earthquake waves reach the structure, it is subjected to motion. This motion produced due to the earthquake waves depends on vibration characteristics of structure and also on the plan of the structure. If the structure overwhelms its own Inertia force then it is possible for structure to respond to the motion. As a result of this, soil and structure interacts. It is known that at foundation level earthquake motions are observed and character of earthquake motion is based on the level of response of the structure. These factors mainly depend on stiffness and mass of both structure and the soil. From this it can be inferred that, the foundation property plays a major role in the structure s response during earthquake. But when considering the influence of earthquake on the building it is important to consider the interaction effects of the soil and the structure as both the structure and the soil show their influence on each other. In the present thesis underground stories is also considered, since it has become an important wing in the modern urban construction. Due to the reason that underground stories does not fluctuate during the earthquake, basement floors are being ignored throughout the seismic analysis of building which includes underground stories. Hence in the present study, it is shown how the seismic response of those structures that include underground stories is affected. II OBJECTIVE OF STUDY The main objective of the thesis is to find the seismic response of the building with underground stories which includes the soil structure interaction. For the sake of analysis and modelling, SAP2000 software is used. The structure is modeled with different types of soil. III STUDY METHODOLOGY Using the suitable soil conditions, and by giving the suitable input details of the building, building is modeled and analyzed. For the purpose of the analysis, response spectrum method is adopted. The software used for the study is the SAP2000. The different models considered are fixed base model, Winkler and FEM model. In FEM model, soil is assumed as linear elastic continuum, with its depth equal to 1.5 times the base of the building. Typical 3D model of all types are presented from fig 2, fig 3, fig 4. Table Ι. Geometric and material properties Component Description Data Number of storeys 15 Number of bays in X 2 Model details Materials Seismic parameters Foundation Type Number of bays in Y Storey Height 3m Bay width in X Bay width in Y Size of beam 0.3m*0.3m Size of column 0.45m*0.45m Thickness of slab 0.125m Grade of steel Fe-415 Grade of concrete M30 Seismic zone ΙΙ Importance factor 1 Response reduction factor 3 Raft Footing Size:24m*24m Depth:1m International Journal of Engineering Science and Computing, June

2 Model Description: Fig 1. Plan of the building Loads At various Floor levels, Dead Load=3.75kN/m² Live Load and Floor Finish=3kN/m² At Roof level, Dead Load=3.75kN/m² Live Load and Floor Finish=1.5kN/m² Dead Load are considered as per IS 875 Part Ι Live Load are considered as per IS 875 Part ΙΙ Fig 4. FEM model IV PARAMETRIC STUDY Different paramters considered for results are Shear force, Bending moment, Displacement, Inter-Storey drift, Base shear, Time period. They are discussed as follows 1. Shear force Fig 2. Fixed base model Fig 5. Storey Level vs Shear Force graph for different models for soft soil Fig 3. Winkler model Fig 6.Storey Level vs Shear Force graph for different models for Medium soil International Journal of Engineering Science and Computing, June

3 Fig 7. Storey Level vs Shear Force graph for different models for hard soil From the Fig 5 to Fig 7, it is observed that, as the storey level increases the value of the shear force decreases. Shear force is found to be more in the lower stories i.e. underground stories. It is also seen that shear force is maximum for the fixed base model and lowest for the FEM model. When compared with different types of soil it is found that, shear force value obtained for the soft soil is more than the value obtained for the hard soil. 2. Bending moment Fig 10. Storey Level vs Moment graph for different models for hard soil From fig 8 to fig 10 it is observed that the as the storey level increases, the value of bending moment decreases. i.e. bending moment is found to be maximum in the lower stories and minimum at the upper stories. When compared to the three types of models used FEM model shows the least value of the bending moment than the other models. When compared to the three types of soils used, it is observed that the soft soil shows the maximum value of bending moment than the hard soil. 3. Displacement Fig 8. Storey Level vs Moment graph for different models for Soft soil Fig 11. Comparison of Displacements of Different Models vs Storey Level for Soft soil Fig 9. Storey Level vs Moment graph for different models for Medium soil Fig 12. Comparison of Displacements of Different Models vs Storey Level for Medium soil International Journal of Engineering Science and Computing, June

4 Fig 13. Comparison of Displacements of Different Models vs Storey Level for Hard soil From fig 11 to fig 13 it is observed that the displacement is maximum at the top storey and minimum at the bottom storey. When compared with the other models used in the study, it is found that FEM model displays maximum displacement than the Winkler and fixed base model. Also when compared to three types of soil used, building which rests on soft soil shows maximum displacement than the building which is resting on the hard soil. 4. Inter-storey Drift Fig 16. Comparison of Inter-Storey Drifts of different model vs Storey Level for Hard soil From fig 14 to fig 16 it is observed that the inter-storey drift is maximum from storey 7 to storey 9 and minimum at the bottom stories. It is a known fact that lesser the drift lesser the damage. When compared to the three models used, it is found that inter-storey drift is maximum for the fixed base model and minimum for the FEM model. When compared to the three types of soil used it is found that inter-storey drift is maximum for the building which rests on soft soil and minimum for the building that rests on hard soil. 5. Base Shear Fig 14. Comparison of Inter-Storey Drifts of different model vs Storey Level for soft soil Fig 17. Comparison of Base Shear results for different model for Soft soil Fig 15.Comparision of Inter-Storey Drifts of different model vs Storey Level for Medium soil Fig 18. Comparison of Base Shear results for different model for Medium soil International Journal of Engineering Science and Computing, June

5 model and also the building resting on soft soil shows the maximum time period. Fig 19. Comparison of Base Shear results for different model for hard soil From fig 17 to fig 19 it is found that magnitude of Base shear is maximum for the fixed base model and minimum for the FEM model. Also it is found that base shear is maximum in soft soil and minimum in hard soil. 6. Time Period V CONCLUSION The results of the analysis conclude the following. 1. It is observed that the shear force and the bending moment is maximum for the building resting on the soft soil and minimum for the building resting on the hard soil. 2. When the parameter displacement and inter-storey drift is considered, it is observed that the displacement and inter-storey drift is maximum for the soft soil and minimum for the hard soil. 3. Magnitude of base shear is found minimum for the FEM model and maximum for the building resting on soft soil. 4. It is observed that the time period is found to be maximum for the FEM model and maximum for the building which rests in soft soil V REFERENCES 1. Nithya Chandran J, Abhilash Rajan, Soni Syed, (2014), Seismic Analysis of Building with Underground Stories Considering Soil Structure Interaction, International Journal of Emerging Technology and Advanced Engineering,ISSN , Volume 4,Issue 11, November 2014 Fig 20. Mode vs Time Period graph for different models for soft soil 2. Vaibhav Singh, Kanchan Mala, (2016), Effect on Seismic Response of Building with Underground Storey Considering Soil Structure Interaction, International of Engineering Research and Technology(IJERT) ISSN: , Vol.5, Issue 06,June G.Saad, F.Saddik & S.Najjar, (2012), Impact of Soil Structure Interaction on the Seismic Design of Reinforced Concrete Buildings with Underground Stories, American University of Beirut,Lebanon Fig 21. Mode vs Time Period graph for different models for Medium soil 4. Shehata E. Abdel Raheem, Mohammed M.Ahmed and Tarek M.A.Alazrak,(2014), Soil-Structure Interaction Effects On Seismic Response of Multi-Story Buildings on Raft Foundation, Journal of Engineering Sciences Assiut University Faculty of Engineering Vol.42,No.4,July Shehata E. Abdel Raheem, Mohammed M.Ahmed and Tarek M.A.Alazrak, (2014), Evaluation of soilfoundation-structure interaction effects on seismic response demands of multi-story MRF buildings on raft foundations, Int J Adv Struct Eng, November 2014 Fig 22. Mode vs Time Period graph for different models for hard soil From fig 20 to fig 22 it is observed that the time period is maximum at the lower modes and is maximum for the FEM 6. Kraus & D.Dzakic, (2013), Soil-Structure interaction effects on seismic behaviour of reinforced concrete frames,josip Juraj Strossmayer University of Osijek,Faculty of Civil Engineering Osijek International Journal of Engineering Science and Computing, June

6 7. Pankaj Agarwal and Manish Shrikhande, (2010), Earthquake Resistant Design of Structures, PHI Learning Private Limited, May 2010, pp Dr.S.A.Halkude, Mr.M.G.Kalyanshetti, Mr.S.H.Kalyani, (2014), Soil Structure Interaction Effect on Seismic Response of R.C. Frames with Isolated Footing, International Journal of Engineering Research & Technology(IJERT),ISSN: ,Vol.3 Issue 1,January R.M.Jenifer Priyanka, N.Anand, Dr.S.Justin, (2012), Studies on Soil Structure Interaction of Multi Storeyed Buildings with Rigid and Flexible Foundation, International Journal of Emerging Technology and Advanced Engineering,ISSN ,Volume 2,Isssue 12,December IS 456:2000, Plain and Reinforced Concrete-Code of practice,bureau of Indian Standards, New Delhi. 11. IS (Part-1), Criteria for Earthquake resistant design of structures, General provisions and buildings, Bureau of Indian Standards, New Delhi ACKNOWLEDGEMENT I Would like to thank my guide and advisor, Mrs. Karuna S, Asst. Prof., Department of civil engineering at the oxford college of engineering, Bangalore for her guidance. And my special thanks to the Head of the Department, Management, Faculty and Friends of the oxford college of engineering, Bangalore, Karnataka for their support. International Journal of Engineering Science and Computing, June