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Item Effect of soil-foundation-structure interaction on fundamental frequency of rc chimneys(2013) Jayalekshmi, B.R.; Menon, D.The construction of tall reinforced concrete chimneys has been increasing, worldwide, in recent times due to industrialization. These tall and slender structures are usually wind-sensitive, requiring a dynamic analysis, to account for a proper assessment of responses under along-wind and across-wind directions and also under seismic loading. The modelling is usually carried out assuming the base (usually raft foundation supported on soil) as fixed. However, in reality, the base is compliant, due to compressibility of the soil, and this can significantly alter the dynamic characteristics of the chimney. This paper presents a comprehensive assessment of modification in the fundamental natural frequency of tapered RC chimneys in the height range of 100m to 400m due to the effect of soil-foundation-structure interaction (SFSI) through a parametric study. The parameters considered for the investigation are the height to mean base diameter ratio of the chimney, rigidity of raft foundation and the flexibility of soil. The flexibility of the supporting soil is represented by a series of Winkler springs, attached to the bottom of the raft foundation, corresponding to soft, medium and hard soils. The results of modal analysis of the three dimensional finite element model of the integrated soil-raft foundation-chimney system are compared with that of a chimney with fixed base.Item Dynamic soil-structure interaction studies on 275m tall industrial chimney with openings(Techno Press technop2@chollian.net, 2014) Jayalekshmi, B.R.; Thomas, A.; Shivashankar, R.In this paper, a three dimensional soil-structure interaction (SSI) is numerically simulated using finite element method in order to analyse the foundation moments in annular raft of tall slender chimney structures incorporating the effect of openings in the structure and the effect of soil flexibility, when the structure-soil system is subjected to El Centro (1940) ground motion in time domain. The transient dynamic analysis is carried out using LS-DYNA software. The linear ground response analysis program ProShake has been adopted for obtaining the ground level excitation for different soil conditions, given the rock level excitation. The radial and tangential bending moments of annular raft foundation obtained from this SSI analysis have been compared with those obtained from conventional method according to the Indian standard code of practice, IS 11089:1984. It is observed that tangential and radial moments increase with the increase in flexibility of soil. The analysis results show that the natural frequency of chimney decreases with increase in supporting soil flexibility. Structural responses increase when the openings in the structure are also considered. The purpose of this paper is to propose the need for an accurate evaluation of the soil-structure interaction forces which govern the structural response. © 2014 Techno-Press, Ltd.Item Seismic behavior of rc framed shear wall buildings as per is 1893 and IBC provisions(Techno-Press, 2015) Jayalekshmi, B.R.; Chinmayi, H.K.Usually the analyses of structures are carried out by assuming the base of structures to be fixed. However, the soil beneath foundation alters the earthquake loading and varies the response of structure. Hence, it is not realistic to analyze structures by considering it to be fixed. The importance of soil-structure interaction was realized from the past failures of massive structures by neglecting the effect of soil in seismic analysis. The analysis of massive structures requires soil flexibility to be considered to avoid failure and ensure safety. Present study, considers the seismic behavior of multi-storey reinforced concrete narrow and wide buildings of various heights with and without shear wall supported on raft foundation incorporating the effect of soil flexibility. Analysis of the three dimensional models of six different shear wall positions founded on four different soils has been carried out using finite element software LS DYNA. The study investigates the differences in spectral acceleration coefficient (Sa/g), base shear and storey shear obtained following the seismic provisions of Indian standard code IS: 1893 (2002) (IS) and International building code IBC: 2012 (IBC). The base shear values obtained as per IBC provisions are higher than IS values. © 2015 Techno-Press, Ltd.Item Numerical study of basal reinforced embankments supported on floating/end bearing piles considering pile-soil interaction(Elsevier Ltd, 2015) Bhasi, A.; Rajagopal, K.Construction sites consisting of soft soils may require ground improvement to prevent excessive settlements or bearing capacity type failures and shear movements, which results in construction delays and premature failures. Among the various ground improvement techniques, the Geosynthetic Reinforced Piled Embankment Systems (GRPES) provide a practical and efficient solution due to the low cost and short construction times. Most of the piled embankments are constructed on end bearing piles. At large depths of foundation soil, floating piles are more economical and technically feasible than the end bearing piles. The design of floating piles involves complex soil-structure interaction and there are no clear uniform guidelines available for the design of embankments supported on floating piles. This paper presents the results of numerical investigation into the performance of geosynthetic reinforced embankments supported on end bearing as well as floating piles considering the pile-soil and geosynthetic-soil interaction. 3-D Column models are employed to carry out the parametric studies on factors such as the development of arching, skin friction distribution along the pile length and axial force distribution. Full three-dimensional analyses are carried out to study the overall behavior of the GRPES system and the results obtained from the analyses were compared with those from British Standard BS8006-2010. The results indicated that the use of floating piles could considerably reduce the settlements and the embankment load transferred through the piles to the foundation soil is found to depend very much on the length of the piles. This aspect needs to be accounted for while calculating the arching factor in the empirical equations. © 2015 Elsevier Ltd.Item Dynamic soil-structure interaction analysis of RC framed building with various positions of shear walls(CAFET INNOVA Technical Society 1-2-18/103, Mohini Mansion, Gagan Mahal Road, Domalguda, Hyderabad 500029, 2016) Chinmayi, H.K.; Jayalekshmi, B.R.In the present study, a three-dimensional dynamic soil-structure interaction analysis of symmetric buildings in time domain is performed using IS spectrum ground motion record corresponding to zone III to evaluate the dynamic response of structure-foundation-soil system. Three types of shear wall buildings of aspect ratio 1, 1.5, 2, 3 and 4 categorized based on the shear wall locations were considered in conjunction with four types of soil of shear wave velocities ranging from 150m/s to 1200 m/s, symbolizing soil classes B, C, D and E of FEMA-356: 2000. Integrated structure-foundation-soil systems were analyzed using commercial finite element software LSDYNA, based on direct method of soil-structure interaction (SSI) assuming linear elastic behavior. The study shows considerable variation in dynamic characteristics and structural seismic response of the structure due to the incorporation of the effect of flexibility of soil and position of shear walls. Tall buildings with shear walls placed at the exterior corners experience the least base shear. © 2016 CAFET-INNOVA TECHNICAL SOCIETY. All rights reserved.Item Seismic analysis of shear wall buildings incorporating site specific ground response(Techno-Press, 2016) Jayalekshmi, B.R.; Chinmayi, H.K.During earthquake, the motion of ground is affected significantly by source characteristics, source-to-site path properties and local site conditions. Due to the influence of local soil conditions different places experience distinctive amplitude of surface ground motion. Ground response analysis of a specific site utilizing the borehole information at different locations is done in present study. The ground motion with the highest peak ground acceleration for this site obtained from the ground response analysis is used in finite element soil-structure interaction analysis of multi-storey shear wall buildings with various positions of shear walls. The variation in seismic response of buildings and advantageous position of shear wall are determined. The study reveals that providing shear wall at the core of buildings at the specific site is advantageous among all shear wall configurations considered. © © 2016 Techno-Press, Ltd.Item Analysis of Foundation of Tall R/C Chimney Incorporating Flexibility of Soil(Springer India sanjiv.goswami@springer.co.in, 2017) Jayalekshmi, B.R.; Jisha, S.V.; Shivashankar, R.Three dimensional Finite Element (FE) analysis was carried out for 100 and 400 m high R/C 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 Soil-Structure Interaction (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 the cases and compared to those obtained from the conventional method of analysis of annular raft foundation. It is found that the responses in raft vary considerably depending on the stiffness of the underlying soil and the stiffness of foundation. Piled raft foundations are better suited for tall chimneys to be constructed in loose or medium sand. © 2017, The Institution of Engineers (India).Item Pore Water Pressure Analysis in Coir Mat-Reinforced Soil Incorporating Soil-Structure Interaction(Springer Science and Business Media Deutschland GmbH, 2022) Sreya, M.V.; Jayalekshmi, B.R.; Venkataramana, K.The proposed study investigates the effectiveness of reinforcing the soft soil by a coir mat, a natural material, to act as a seismic soil-isolation medium. A 3D finite element simulation in PLAXIS 3D software has been carried out on models of five-storey buildings resting on raft foundations in soft soil with and without the soil-isolation mechanism. This study also deals with the coir composites, coir–polyethylene and coir–rubber were proposed to increase the durability of the coir mat. The isolated soil-structure system was exposed to four different earthquake motions, such as the ground motions corresponding to the elastic design spectrum for Zone III as per the Indian standard code (IS 1893 (Part 1): 2016), the scaled Northridge earthquake (1994), El Centro earthquake (1940) and Chi-Chi earthquake (1999). A pore water pressure analysis of soil bed has been carried out to study the efficacy of these materials to reduce the excess pore water pressure generated in soil under earthquake loading. The other parameters, such as shear strain mobilized shear strength, effective stress in soil, and roof acceleration, in the building were analyzed. Isolation efficiencies of reinforcement materials to reduce the excess pore water pressure generated in soil under different earthquake motions obtained are 75–82%, 71–80% and 67–72% with coir, coir–polyethylene and coir–rubber, respectively. The resulting shear strain in soil reinforced by isolation mats is lower than that in unreinforced soil because the isolation mats strengthen the soil. Compared to the unreinforced soil, the mobilized shear strength and effective stress in the soil are increased when it is reinforced with coir and coir composites. The roof acceleration and bottom acceleration in the building got reduced by the isolation mechanism. © 2022, The Author(s), under exclusive licence to Springer Nature Switzerland AG.Item Effect of Coir Reinforced Soil on the Seismic Response of RC Framed Buildings(Springer, 2022) Sreya, M.V.; Jayalekshmi, B.R.; Venkataramana, K.This study examines the effectiveness of reinforcing the soil with coir mat, a natural material, to act as a seismic soil-isolation medium. A 3D finite element simulation has been carried out on models of five-storey buildings resting on raft foundations in soft and stiff soil with and without the soil-isolation mechanism. The optimum values of the parameters such as the depth of embedment, width, and thickness of the coir mat have been analyzed. The isolated soil-structure system was exposed to two different earthquake motions, such as El Centro (1940) and simulated seismic excitation corresponds to the elastic design spectrum for Zone III as per the Indian Standard code (IS 1893 (Part 1): 2016). The optimum value for the depth of embedment, width, and thickness of the coir mat was identified as B/18, B/0.45 and B/36. The proposed study also deals with the coir (C) mat composited with other isolation materials such as polyethylene (PE) foam, rubber (RU) mat and geomembrane (G) to form C-PE, C-RU and C-G mats. These composites were proposed to increase the durability of the coir mat. The reinforcement of the C-PE mat shows a maximum of about 30% reduction in roof acceleration and 68% reduction in contact pressure. A pore water pressure analysis of soil bed also has been carried out to study the efficacy of these materials to reduce the excess pore water pressure generated in soil under earthquake loading. For that, a simple soft soil is modelled in Cyclic 1D software with and without the soil-isolation mechanism. The soil bed was exposed to El Centro (1940) and Northridge (1994) input motions. C-PE mat significantly reduces the excess pore water pressure by almost 93% and 88% in soil under El Centro and Northridge input motions, respectively. © 2022, Indian Geotechnical Society.Item Site specific fragility modification factor for mid-rise RC buildings based on plastic energy dissipation(Techno-Press, 2024) Mathews, M.; Jayalekshmi, B.R.; Venkataramana, K.The performance of reinforced concrete buildings subjected to earthquake excitations depends on the structural behaviour of the superstructure as well as the type of foundation and the properties of soil on which the structure is founded. The consideration of the effects due to the interaction between the structure and soil-foundation alters the seismic response of reinforced concrete buildings subjected to earthquake motion. Evaluation of the structural response of buildings for quantitative assessment of the seismic fragility has been a demanding problem for the engineers. Present research deals with development of fragility curve for building specific vulnerability assessment based on different damage parameters considering the effect of soil-structure interaction. Incremental Dynamic Analysis of fixed base and flexible base RC building models founded on different soil conditions was conducted using finite element software. Three sets of fragility curves were developed with maximum roof displacement, inter storey drift and plastic energy dissipated as engineering demand parameters. The results indicated an increase in the likelihood of exceeding various damage limits by 10-40% for flexible base condition with soft soil profiles. Fragility curve based on energy dissipated showed a higher probability of exceedance for collapse prevention damage limit whereas for lower damage states, conventional methods showed higher probability of exceedance. With plastic energy dissipated as engineering demand parameter, it is possible to track down the intensity of earthquake at which the plastic deformation starts, thereby providing an accurate vulnerability assessment of the structure. Fragility modification factors that enable the transformation of existing fragility curves to account for Soil-Structure Interaction effects based on different damage measures are proposed for different soil conditions to facilitate a congenial vulnerability assessment for buildings with flexible base conditions. © 2024 Techno-Press, Ltd.