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International Research Journal of Engineering and Technology (IRJET)

e-ISSN: 2395-0056

Volume: 09 Issue: 06 | June 2022

p-ISSN: 2395-0072

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Effect of Soil Structure Interaction on Seismic Response of Multistorey Building Prof. Merin Mathews1, Aiswarya Jayakumar2, Sayoojya S Thannickal3, Akhil P4, Bensal Shaji5 1Professor, Dept. of Civil Engineering, M A College of Engineering, Kerala, India

2,3,4,5UG Students Dept of Civil Engineering, M A College of Engineering, Kerala, India

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Abstract - Seismic analysis of building is very much

lateral deflection compared to the corresponding rigidly supported structure.

important in the present scenario. Conventional structural design methods neglect the Soil structure Interaction (SSI) effects. Ignoring of SSI is reasonable for light structures in relatively hard soil. The effect of SSI, however becomes very dangerous for heavy structures resting on relatively soft soils such as clay silt. In order to study the effect, a G+9 storey structure resting on piled raft foundation is modelled in ANSYS 21. The effect of soil structure interaction on seismic response of building resting on three different types of soil- stiff clay, silty sand and hard rock is compared with the response of building with fixed base(without soil).Static and dynamic(response spectrum) analysis were performed to evaluate the total deformation and equivalent stress. On comparing the values of total deformation and equivalent stress of the building it is found that the structure with soil shows greater deformation and equivalent stress than structure without soil and silty sand shows the greatest

2. PROBLEM STATEMENT This paper analyses the effect of SSI on multi storey building under seismic loading. Aimed with the purpose, a G+9 building with piled raft foundation is analysed by Ansys 21 subjected to combination of gravity load and seismic load. Compare the same building using 3 types of soil with that of the building with fixed base.

3. OBJECTIVES [1] To study the effect of SSI on seismic response of multi storey building using ANSYS software [2] To compare the seismic response of multi storey building resting on different soil types with and without considering SSI using static analysis.

among them.

[3] To compare seismic response using dynamic analysis.

Key Words: Soil Sturcuture interaction, Piled Raft foundation, Total deformation, Equivalent stress.

4. MODELLING

1. INTRODUCTION

4.1 Geometry of the Building

In the seismic analysis of a structure resting on the ground, the response of the sub-soil affects the response of the structure and vice versa. Also, the structure displacements and the ground displacements are not independent of each other. This phenomenon is called soilstructure interaction (SSI). Thus the soil structure interaction can be defined as the process in which the response from the soil influences the motion of the structure and the motion of the given structure affects the response from the soil [1].

For this study, 10 storey building with piled raft foundation has been considered. A simple structure with base dimension 12m x 12m was modeled. Cross-section properties of superstructure elements have been kept same for all floors, column – 300 x600mm, beam – 300x50mm & floor slab – 150mm and cross-section properties of foundation elements raft – 850mm, pile diameter – 750 mm & pile depth – 15m, all dimensions are as per design requirements. The soil plan area, was fixed such that, horizontal dimension should be at least five times the horizontal dimension of building and depth of soil should be at least three times depth of foundation, Therefore, soil volume modeled is 60x60x45m.

The present work emphasizes the importance of soil structure interaction in the analysis. The construction of high-rise building, medium height buildings are usually using the pile and raft foundations to support the structure under the soft grounds and reclaimed land. The study of soil structure Interaction is one of the beneficial effects on the seismic response of the building. It decreases the frequency of the building , and also it increases the flexibility of the building, story drift and

Impact Factor value: 7.529

4.2 Finite Element Modelling The building models are modelled as three dimensional structural solids with element types assigned automatically by FEA software, ANSYS 21. Mesh convergence study was done for building and used

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International Research Journal of Engineering and Technology (IRJET)

e-ISSN: 2395-0056

Volume: 09 Issue: 06 | June 2022

p-ISSN: 2395-0072

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6. RESULTS AND DISCUSSIONS

3000mm element size and for soil a coarser mesh was used. No separation type contact was used between structure and soil elements and bonded contact type between structural elements. [2].

6.1. Static Analysis A.) Total Deformation

4.3 Boundary Conditions and Loading Soil is modelled as rectangular solid around the foundation due to scope limit. Since soil is extended in infinity in actual case, we modelled it as finite sized solid and applied boundary conditions. Pressure applied is 1000Pa. For static analysis, cyclic loading was applied and for dynamic analysis El centro data was given. Table -1: Material Properties of Concrete and Soil Properties Material Young ‘s Modulus , E(Pa) Poisson ‘s ratio , DENSITY, Kg/m3)

Structure Concrete 2.9 x 1010 0.15 2500

Soil Soft Soil 2.5 x 107 0.25 1900 Fig : fixed base

5. Methodology G+9 RC frame structure supported by a piled raft foundations of two high rise buildings are designed by considering the with and without soil structure interaction subjected to a seismic forces. Static (Cylic loading) and dynamic (Response Spectrum) analysis were conducted using ANSYS 21. Seismic analysis was carried out by using El centro earthquake data.

Fig : Stiff clay

Figure: Seismic Cyclic loading Table 2: El centro earthquake data Frequency(Hz) 0.1998 1.1428 2.3991 3.081 4.2166 5.2402 6.3584 7.0369 8.1511

Displacement(m) 0.02297 0.02368 0.02999 0.0341 0.03285 0.04617 0.03904 0.04171 0.05372

Impact Factor value: 7.529

Fig: Hard rock

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International Research Journal of Engineering and Technology (IRJET)

e-ISSN: 2395-0056

Volume: 09 Issue: 06 | June 2022

p-ISSN: 2395-0072

www.irjet.net

Fig : Silty sand Fig : Silty sand

Total deformation occurred to the building under consideration is greater for flexible base than fixed base model and is greatest for building with stiff clay. 6.2 Dynamic Analysis A.) Total deformation

Fig: Hard rock

7.CONCLUSIONS 1. Total deformation vary considerably for different soil types and are decreasing from soft soil to hard rock.

Fig : fixed base

2. Deformations under seismic loads are larger for building considering SSI effects than with fixed base 3. Total deformations under dynamic analysis are far greater than those under static analysis. Thus, dynamic analysis is preferred for buildings in earthquake prone areas. 4. Thus soil structure interactions need to be considered for seismic analysis of multistorey building.

8. REFERENCES [1] Anjali B , Raji M, Seismic Analysis and Soil Structure Interaction of Multistoried Building with Different Types of Footing ISSN: 2278-0181,Vol. 4 Issue 09, September2015.

Fig : Stiff clay

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Volume: 09 Issue: 06 | June 2022

p-ISSN: 2395-0072

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[2] Xilin Lu, Peizhen Li, Bo Chen, and Yueqing Chen (2005), Computer simulation of the dynamic layered soil–pile– structure interaction system1, CananaGeotechnical Journal Vol. 42. [3] Lewis Edgers, Masoud Sanayei & Joseph L. Alonge (2005), Modeling the Effects of Soil-Structure Interaction on a Tall Building Bearing on a MatFoundation, Design Considerations, and Civil Engineering Practice Fall/Winter [4] Julio A. García (2008), Soil Structure Interaction in the Analysis and Seismic Design Of Reinforced Concrete Frame Buildings, The 14th World Conference on Earthquake Engineering, 12-17.

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