BEHAVIOR OF BUILDING FRAMES ON SOILS OF VARYING PLASTICITY INDEX

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1 International Journal of Civil Engineering and Technology (IJCIET) Volume 8, Issue 1, January 2017, pp Article ID: IJCIET_08_01_072 Available online at ISSN Print: and ISSN Online: IAEME Publication Scopus Indexed BEHAVIOR OF BUILDING FRAMES ON SOILS OF VARYING PLASTICITY INDEX Sai Kumar V B Y PG student Department of Civil Engineering, K L University, Vaddeswaram, AP, INDIA Hanumantharao Ch Professor Department of Civil Engineering, K L University, Vaddeswaram, AP, INDIA. ABSTRACT Objective: To find the seismic behavior of building frames on soils of varying plasticity index. Method: To achieve this goal soils of various plasticity indices are selected and building frames are selected according to the Indian standard codes. The building frames are modelled and analyzed using STAAD.pro software with two different boundary conditions (I) fixed base condition (without soil structure interaction (ssi)) (ii) flexible base model considering ssi using springs. Nonlinear dynamic analyses are run from earthquake ground motion data in EduShake software for the two boundary conditions discussed. Findings: The output on the basis of lateral displacements, base shears and the interstorey drifts to the stated boundary conditions are attained and discussed. Applications: used in the dynamic analysis of building frames. Key words: Soil Structure Interaction, Plasticity Index, Edushake, Staadpro, Seismic Behaviour. Cite this Article: Sai Kumar V B Y and Hanumantharao Ch, Behavior of Building Frames On Soils of Varying Plasticity Index. International Journal of Civil Engineering and Technology, 8(1), 2017, pp INTRODUCTION Dynamic properties of soils Shear modulus, damping are most important factors of amplification phenomenon during Earthquakes. The shear modulus, damping ratio curves are been generated based on nonlinearity soil from hysteresis loops. Two vital qualities of the state of hysteresis loop are the broadness and slant. The slant of the loop relies on upon the firmness of the soil, which can be described at any point during the loading process by the tangent shear modulus. Obviously, tangent shear modulus varies throughout a cycle of loading, but its average value over the entire loop can be estimated by secant shear modulus editor@iaeme.com

2 Sai Kumar V B Y and Hanumantharao Ch G as follows: G= τ /γ Where, WD is dissipated energy in one hysteresis loop, WS is the maximum strain energy, where the area of the hysteresis loop is denoted as A. Where, γc, τc are the shear strain and shear stress amplitudes at a defined point. Thus, G defines the slope of hysteresis loop 1. The breadth of the hysteresis loop is related to the area, which can be defined by the damping ratio ξ as follows: ξ = WD/4πWS Forms of the relationship expressing shear modulus and damping ratio as a function of shear strain, called backbone curves, play a crucial role for determining the results of soil-structure interaction analysis 2. Much information on this aspect of dynamic soil property determination has been presented since the early 1970 s by several researchers In cohesive soils, the backbone curves depend on Plasticity Index (PI). The distinction between the plastic and liquid cut off points is known as the Plasticity Index, Plasticity is an important characteristic in the case of fine soils Large number of studies dealing with relationship between damping ratio and shear modulus ratio (G/Gmax) with cyclic shear strain (backbone curves) in cohesive soils have been carried out 3. The backbone curves advised for use in seismic siteresponse evaluation and microzonation. They conducted a study on number of cyclic loading tests and concluded that the soil PI is main factor controlling the backbone curves for a variety of cohesive soils. In the paper, seismic behaviour of building frames on soils of varying plasticity index ranges i.e (0, 10-20, and 40-80) are investigated on the basis of base shear and storey drift and maximum lateral displacements 4,5. 2. METHODOLOGY 2.1. Earthquake Ground Motion In order to analyse the seismic response for building frames on soils of varying plasticity indices an earthquake record El-Centro 1940 earthquake is used which is shown in Figure1. and it is analysed for the soil data of various plasticity indices ranges (0, 10-20, and 40-80)in Edushake Software Package generates response spectrum method of time period vs spectral acceleration graphs which is used for our study. The Shear Wave velocity of soils is calculated by using the Empirical relations between Standard Penetration Number and Shear Wave Velocity 6 which is as follows Vs=82.46 N 0.4 Figure 1 Utilized earthquake acceleration record of El Centro earthquake (1940) in this study editor@iaeme.com

3 Behavior of Building Frames On Soils of Varying Plasticity Index 2.2 STRUCTURAL MODELS To study the seismic behaviour of building frames Structural sections of single bay two storeys three dimensional with storey height of 3mt is adopted which is as shown in Figure 2.The building frame is analysed in the Software Package of Staadpro 7,8 using the response spectrum method time period vs spectral acceleration graphs of various soils of different plasticity indices obtained from Edushake Software. Nonlinear dynamic analyses were carried out for structural model in both (i) fixed base conditions (ii) flexible condition considering SSI by using springs with stiffness constant 9. Ks=kn=10[k+4/3]δ Where K=Bulk modulus of soil G= Shear modulus of soil Z min = the smallest width of an adjoining zone in the normal direction Young s Modulus of E = 6000kN/mt kn/mt 2 Figure 2. Three Dimensional Building Frame 3. RESULTS AND DISCUSSIONS The dynamic analyses results of structural model on the basis of base shears Table1, maximum lateral deflections Table2, average inter storey drifts are shown in Table 3, for fixed and flexible base models on the soil, having different plasticity, it was concluded that the base shear values gradually decreased as the plasticity index of the soil decreases in comparison with plasticity index 0 and the base shear values decreased for fixed as compared with plasticity index 0 and increased for other plasticity index cases. It is observed that the maximum lateral storey displacement increases as the storey increases in all the cases and for PI=o it has significant impact as compared with the fixed condition case. For remaining plasticity index cases i.e other than PI=0 maximum storey displacement has lesser influence has compared to that of the fixed condition. It was noted that the plasticity index with 0and has considerable effects on the storey drift of the building as compared to that of fixed case.and has so little impact when compared the fixed base condition with other plasticity index ranges. From the above results it was concluded that the building frames on soils of PI =0 are more severe to seismic behaviour as compared editor@iaeme.com

4 Sai Kumar V B Y and Hanumantharao Ch to the other cases.where as for other cases of PI the seismic vulnerability is low as compared to the fixed case. Table 1. Base Shear (Vb) kn values for the structure Storey height PI: 0 PI:10-20 PI:20-40 PI:40-80 Fixed Table 2. Maximum Lateral Storey Displacement (cm) values for each Storey Storey height PI: 0 PI:10-20 PI:20-40 PI:40-80 Fixed Table 3 Storey Drift (cm) values for each Storey Storey Height PI: 0 PI:10-20 PI:20-40 PI:40-80 Fixed CONCLUSIONS In this paper, the seismic behaviour of building frames have been investigated for the wide range of Plasticity Indices of soils varying between 0 to 100%. To achieve this goal, a numerical ssi model is developed in staadpro. EDUSHAKE Software Package generates response spectrum method of time period vs spectral acceleration graphs which is used for our study Nonlinear performance of the soil has been developed using backbone curves of (G/G max) and damping ratio vs shear strain. It can be noticed from obtained results that ssi has noticeable influence on seismic behaviour of building frames on soils of varying Plasticity Indices of Indian soils. Therefore, the conventional design procedure - structure interaction may not be provide the structural performance of building frames on soil deposits. The effects of soil plasticity should be carefully taken into consideration. REFERENCES [1] Kramer S L. Geotechnical Earthquake Engineering. 3 rd Pearson Education Publication, Indian branch, New Delhi, India [2] Behzad Fatahi, Hamid R S. Effects of Soil Plasticity on Seismic Performance of Mid-Rise Building Frames Resting on SoftSoils. Advances in Structural Engineering May; 17 (10), [3] Đnanc B O, Mustafa T, Ahmet T. An experimental study for determining the shear modulus of toyoura sand. Proceedings of Second European Conference on Earthquake Engineering and Seismology, Istanbul, [4] Payman A, Mahdy K, Khairul A K, Azlan A, Ali D B, Nima L. The Influence of Plasticity Index on the Dynamic Soil Behavior. 2013; [5] Vucetic, M. and Dobry, R.Effects of soil plasticity on cyclic response, Journal of Geotechnical Engineering, ASCE. 1991; 117(1), editor@iaeme.com

5 Behavior of Building Frames On Soils of Varying Plasticity Index [6] Hanumantharao C, Ramana GV. Dynamic Soil Properties for Microzonation of Delhi, India. Journal of Earth System Science. 2008; [7] Patil S S, Ghadge S A, Konapure C G, Ghadge C A. Seismic Analysis of High-Rise Building by Response Spectrum Method, International Journal of Computational Engineering Research. 2008; 3(3), [8] S. J. Abbey, S. Ngambi and E. Coakley, Effect of Cement and by-product Material Inclusion on Plasticity of Deep Mixing Improved Soils. International Journal of Civil Engineering and Technology, 7(5), 2016, pp [9] U. D. Gulhane, S. B. Mishra, P. K. Mishra, Enhancement of Surface Roughness of 316l Stainless Steel and Ti-6al-4v Using Low Plasticity Burnishing: Doe Approach. International Journal of Civil Engineering and Technology, 3(1), 2012, pp [10] Dr. K.v.krishna reddy, Correlation between California Bearing Ratio and Shear Strength on Artificially Prepared Soils with Varying Plasticity Index. International Journal of Civil Engineering and Technology, 4(6), 2013, pp [11] Bharath R R, Sai Gopi N, Taneja A S, Kalyana R J S. Comparative Study on the Lateral Load Resistance of Multi-Storied Structure with Bracing Systems Indian Journal of Science and Technology December; 8(36), 1-9. [12] Rayhani M H, Naggar E L. Numerical modelling of seismic Response of rigid foundation on soft soil. International Journal of Geomechanics. 2008; 8 (6), editor@iaeme.com