Conference Papers
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Item Experimental investigation on dynamic characteristics of structures founded on a dispersive soil(2008) Jayalekshmi, B.R.; Lohith, K.; Shivashankar, R.; Venkataramana, K.The objective of this paper is to evaluate the Soil-Structure-Interaction (SSI) effects on the seismic response of structures founded on Shedi soil of Dakshina Kannada. Shedi soil, which is a dispersive type of soil is highly vulnerable to dynamic loading in the saturated condition. Experimental investigations have been carried out on 1:10 scaled single bay three dimensional multistorey building models made of aluminium with its foundation resting on locally available Shedi soil (classifying as sandy silt) and sand in the saturated and dry conditions. The combined system of Soil-Foundation-Structure models is subjected to dynamic loading. The response of the model is measured at each floor level. This structural response is compared with that of a fixed base model to isolate the effect of soil structure interaction. The variations in natural frequency with various parameters such as different types of soil, degree of saturation of soil, number of storeys and the stiffening effect of walls are evaluated. The experimental results are presented and the modifications in dynamic characteristics due to the incorporation of soil flexibility are studied. Free vibration analysis of the three dimensional finite element model of the soil foundation structure system is carried out and the results are compared with the experimentally obtained values.Item Shake table tests to investigate the effi cacy of geomembranes for soil isolation in a space frame with isolated footing(2011) Jayalekshmi, B.R.; Shivashankar, R.; Venkataramana, K.; Ramesh Babu, R.; Reddy, G.R.; Parulekar, Y.M.; Patil, S.J.; Gundlapalli, P.Generally a base isolator shifts the natural period of the building away from that of the predominant period of the most probable earthquakes and provides additional damping to absorb the energy. The present study focuses on the effi cacy of soil, geofi bre reinforced soil and a layer of smooth geosynthetic membrane placed in soil in reducing the seismic response of a structure. Shake table tests are carried out in a tri-axial shaker system on a 1/3rd scaled model of a single storey, single bay RC space frame. A steel tank fi xed to the shake table is used as a container for soil and reinforced soil. The structure with different base conditions is subjected to sine sweep tests and the motion corresponding to the response spectrum of Zone III as per IS 1893(Part1):2002. Analysis of results shows that smooth geomembrane in sand can be effectively used to reduce the seismic response of the structure.Item Effect of soil-structure interaction on along-wind response of tall RC chimneys(2011) Jayalekshmi, B.R.; Menon, D.; Meher Prasad, A.A parametric study has been carried out on tall reinforced concrete industrial chimneys to evaluate the effect of soil-structure interaction on the along-wind response of the structure. Three dimensional fi nite element model of the integrated chimney-raft-soil system under self-weight and wind load has been analysed to estimate the contact pressure distribution and variation of stress resultants in the annular raft. The bending moments in the raft foundation obtained from the soil-structure interaction analysis are compared with those computed assuming the chimney to be fi xed on a rigid foundation. The analysis of results on the effect of fl exibility of supporting soil reveals a considerable reduction in the bending moments in the annular raft foundation.Item Evaluation of the effect of soil-structure interaction on the raft of tall reinforced concrete chimneys under across wind load(Research Publishing Services editorial@rpsonline.com.sg, 2013) Jisha, S.V.; Jayalekshmi, B.R.; Shivashankar, R.A three dimensional soil-structure interaction (SSI) analysis of tall reinforced concrete chimneys with piled annular raft and un-piled annular raft subjected to across wind load is carried out in the present study. Effects of SSI were evaluated using four different soil types and three different ratios of external diameter to thickness of the annular raft. The across wind load was computed according to IS:4998 (Part 1)-1992. The integrated chimney-foundation-soil system was analysed by finite element software ANSYS based on direct method of SSI assuming linear elastic behaviour. FE analyses were carried out for two cases of SSI; (I) chimney with un-piled raft and (II) chimney with piled raft. The responses in raft were evaluated for both the cases and compared to that from conventional method of analysis. It is found that due to the addition of piles, there is considerable reduction in the responses in the raft when compared to that in the un-piled raft especially for loose sand and medium sand. © © 2013 APCWE-VIII. All rights reserved. Published by Research Publishing, Singapore.Item Dynamic soil-structure interaction analysis of 300m tall industrial reinforced concrete chimneys on piled raft foundations(Earthquake Engineering Research Institute, 2014) Jisha, S.V.; Jayalekshmi, B.R.; Shivashankar, R.Soil-structure interaction (SSI) analysis of 300m tall slender industrial reinforced concrete chimneys with piled raft foundation subjected to Elcentro (1940) ground motion is carried out in the present study. The transient analysis of three dimensional chimney-piled raft-soil system was conducted based on direct method of SSI using finite element method. Linear elastic material behaviour was assumed for the chimney, piled raft and soil. Parametric studies were conducted by considering different thickness of raft of piled raft foundation and different soil types to understand the significance of SSI. The time history analysis of the integrated chimney-foundation-soil was carried out with ground motion corresponding to the Imperial Valley earthquake at Elcentro (1940) with a magnitude of 7.0 and peak ground acceleration of 0.319g. The time history of acceleration was applied in the global X direction of the entire soil-structure model. The responses in terms of tangential and radial bending moments in raft, settlement of raft and tip deflection of chimney were investigated. The bending moments in raft of piled raft foundation obtained from SSI analysis were compared with that obtained from conventional analysis. It is found that the response in chimney and raft is considerably high for chimney-piled raft system resting on loose sand and it depends on the characteristics of ground motion also.Item Analysis of foundation of tall RC chimney with 3D finite element method(American Society of Civil Engineers (ASCE) onlinejls@asce.org, 2014) Jisha, S.V.; Jayalekshmi, B.R.; Shivashankar, R.3D finite element (FE) analyses were carried out for 100-m and 400-m-high RC chimneys having piled annular raft and annular raft foundations considering the flexibility of soil subjected to across-wind load. Stiffness of supporting soil and foundation were varied to evaluate the significance of SSI. The integrated chimney-foundation-soil system was analysed by finite element software ANSYS based on direct method of SSI assuming linear elastic material behaviour. FE analyses were carried out for two cases of SSI, namely: (1) chimney with annular raft foundation, and (2) chimney with piled annular raft foundation. The responses in raft, such as bending moments and settlements, were evaluated for both cases and compared to those obtained from the conventional method of analysis of annular raft foundation. It is found that the responses in raft depend on the stiffness of the underlying soil and the stiffness of foundation. © ASCE 2014.Item Response of tall chimneys with piled raft and annular raft foundation under wind loads considering SSI(Taylor and Francis - Balkema pub.nl@tandf.co.uk, 2015) Jayalekshmi, B.R.; Jisha, S.V.; Shivashankar, R.The effect of Soil-Structure Interaction (SSI) was studied for tall industrial Reinforced Concrete (RC) chimneys with annular raft and piled raft under along-wind load. Effects of SSI were evaluated using three different soil types and three different thickness of the annular raft.The along-wind loadwas computed according to IS:4998 (Part 1)-1992.The integrated chimney-foundation- soil systemwas analysed by finite element software ANSYS based on direct method of SSI assuming linear elastic behaviour. FE analysis was carried out for two cases of SSI; (I) chimney with annular raft and (II) chimney with piled raft. The responses in chimney and raft were evaluated for both the cases and compared to that from conventional method. It is found that due to the addition of piles, the radial bending moment and settlement of raft are significantly reduced by more than 40%, especially for very tall chimney resting on loose sand. © 2015 Taylor & Francis Group, London.Item Seismic analysis of piled raft foundations of tall chimneys considering the effect of SSI(Taylor and Francis - Balkema pub.nl@tandf.co.uk, 2015) Jayalekshmi, B.R.; Jisha, S.V.; Shivashankar, R.A direct method of Soil-Structure Interaction (SSI) analysis of 300m and 400m tall slender Reinforced Concrete (RC) chimneys with piled raft foundation subjected to Elcentro (1940) ground motion is carried out in the present study. The parametric studies have been conducted by taking different geometrical properties of raft of piled raft foundation and different material properties of soil stratum to understand the significance of SSI. Different responses in chimney, raft and pile are evaluated. The bending moments in raft and base moment of chimney with and without considering the SSI effect are compared. The maximum radial moment in raft of the chimney-foundation system resting on loose sand is more than that obtained from the conventional analysis whereas a reduction in tangential moment is seen when the piled raft foundation with rigid raft interacts with loose sand. © 2015 Taylor & Francis Group, London.Item Soil Structure Interaction Studies with Use of Geosynthetics in Soils Beneath Footings(Springer Science and Business Media B.V., 2018) Shivashankar, R.; Rebello, N.E.; Sastry, V.R.; Jayalekshmi, B.R.The present study consists of two parts. In the first part, the effect of using a geomembrane (slip) layer in soil beneath footings under seismic excitations from shake table tests is being investigated. A triaxial shaker system is used to carry out the tests on a one-third scaled model of single storey, single bay RC space frame. The structure with different base conditions are subjected to sine sweep tests and simulated seismic excitation corresponding to the design spectrum for Zone III as per the Indian standard code (IS 1893 (Part 1): 2002). It is observed that the natural frequency of the structure decreases with increase in the flexibility of supporting soil In the second part, effects of using geosynthetic reinforced soil beneath footings of multistoried structures with tunneling operations beneath are being looked into. Numerical investigations on shallow depth tunnels like metro tunnels in granular soils, response due to tunneling itself (single and twin tunnels) and also their impact on the buildings above are carried out, using 3DEC software. Tunneling for metro causes innumerable changes in the form of distortion taking place in strata surrounding the tunnel, and also affect the member forces of framed structures on the surface. Height of superstructure and building eccentricities from the tunnel centre line are also varied. Results reveal that the presence of geosynthetic reinforcement in soil considerably reduces the displacements under footings. © 2018, Springer International Publishing AG.Item Non-linear Soil-Structure Interaction Analysis of Multi-storey Shear Wall Buildings with Site Specific Ground Response(Springer Science and Business Media B.V., 2018) Jayalekshmi, B.R.; Chinmayi, H.K.Influence of local geology and soil conditions play a major role in varying the intensity of ground shaking. In the present study, by utilizing the geotechnical data of a specific site, amplification of earthquake motion is found out by ground response analysis. Seismic structural response variation in multistory shear wall buildings with different shear wall locations is determined from nonlinear soil-structure interaction (SSI) analysis using the ground motion with the highest peak ground acceleration obtained from the site. Geotechnical data from twenty bore holes at the site with depth varying between 7–15 m below ground level are considered. This specific site is very near to the Arabian Sea coast with a lot of variation in the geotechnical profile. Symmetric plan multi-storey reinforced concrete shear wall buildings of aspect ratio (h/d) ranging from 1 to 4 resting on raft foundation with shear walls placed symmetrically along the exterior frames, core and all four corners of the exterior frames are considered. Further, the structural responses obtained from SSI analysis and conventional method of assuming rigidity at the base of a structure is compared. Results show the significance of positioning of shear wall in symmetric buildings which attracts the least earthquake forces, with the consideration of nonlinear behavior of the underlying soil medium. © 2018, Springer International Publishing AG.