Faculty Publications
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Item A Study on the Seismic Behaviour of Embankments with Pile Supports and Basal Geogrid(Springer, 2020) Patel, R.M.; Jayalekshmi, B.R.; Shivashankar, R.For constructing the roads on soft grounds, basal geogrid-reinforced pile-supported embankments are a suitable solution over other conventional ground improvement techniques like preloading, embankment slope flattening, removing and replacing the soft soil, etc. Many studies are available on these basal geogrid-reinforced piled embankments to understand their behaviour under static loading conditions. But it is necessary to understand the behaviour of these geogrid-reinforced piled embankments under seismic excitations. Hence, finite element analysis of three-dimensional models of embankment having crest width of 20 m, height above ground of 6 m, with side slopes of 1V:1.5H consisting of pulverized fuel ash, overlying soft marine clay of 28 m thickness is carried out under seismic excitations corresponding to Zone III (IS:1893). Soft marine clay layer is improved by the addition of piles arranged in square grid pattern with 5.75% area replacement ratio. Geogrid with a tensile modulus of 4600 kN/m is used as the basal reinforcement. Initially, the embankment is analyzed without geogrid reinforcement and pile supports. Then, it is analyzed with (i) Basal geogrid (ii) With pile supports (iii) With basal geogrid and pile supports. The influence of various parameters of the embankment on maximum crest displacements, differential settlements at crest, toe horizontal displacements, stresses at pile head and foundation soil between piles and pile bending moment along the depth at peak acceleration are studied. Analysis of results shows that the embankment supported over piles with basal geogrid reinforcement will experience less crest settlements, differential settlements at crest and toe horizontal displacements due to earthquake load. © 2020, Springer Nature Singapore Pte Ltd.Item A Study on the Behavior of Piled Raft Foundation Under Seismic Loading(Springer Science and Business Media Deutschland GmbH, 2023) Reddy, D.M.M.; Krishna, S.V.; Jayalekshmi, B.R.High rise buildings require strong foundations which should bear heavy loads with less settlement. There has been an increase in the use of combined piled raft foundations because of the effectiveness in bearing heavy loads with comparatively very less settlements. This paper presents the variation in roof displacement, bending moment and shear force of a 10-storey building frame resting on a piled raft foundation having various pile stiffness under earthquake excitations corresponding to El Centro and Loma Prieta earthquakes. Column and beam dimensions of the frame are taken as 0.5 m × 0.5 m and 0.3 m × 0.45 m. The length of the pile is taken as 10 m and the diameter is taken for a range of 0.6 m to 1.2 m. Vertical loading condition is varied by considering different mass at each floor level. Not much variation in the roof displacement is found with a change in the pile stiffness. Variation in the response has been observed for different vertical loading and changes in the pile stiffness. The response of the structure for the two earthquake motions is entirely different. © 2023, The Author(s), under exclusive license to Springer Nature Switzerland AG.Item Seismic Response of Buildings Resting on Geosynthetics Reinforced Sand Bed(Springer Science and Business Media Deutschland GmbH, 2023) Sreya, M.V.; Jayalekshmi, B.R.; Venkataramana, K.An earthquake is a significant disaster that destroys structures all over the world. The structure must be designed to resist the impacts of the earthquake. The present study analyzes the efficacy of an Ultra-High Molecular Weight Polyethylene (UHMWPE) liner to lower the amount of seismic energy conveyed and the dynamic response of buildings. Finite element simulation of the transient response of an integrated soil isolation-building system in which buildings are resting on a raft in medium dense sand beds, with and without a soil-seismic isolation system, has been performed with the help of a recorded accelerogram of the El Centro (1940) earthquake. Two sets of space frame building models (two and three storey) of single bay reinforced concrete frames have been considered to estimate seismic response. UHMWPE thickness has been varied from 0.0064 m to 0.15 m to investigate its impact on peak acceleration at building roof levels. The analysis results indicate that earthquake vibration energy transmission to the superstructure is limited by the use of a UHMWPE liner, as a soil isolation medium and the thickness of the soil isolation liner significantly influences the building response during an earthquake ground motion. © 2023, The Author(s), under exclusive license to Springer Nature Switzerland AG.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.