Browsing by Author "Shivashankar, R."

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3D soil–structure interaction analyses of annular raft foundation of tall RC chimneys under wind load
(Springer, 2014) Jisha, S.V.; Jayalekshmi, B.R.; Shivashankar, R.
Three dimensional soil–structure interaction (SSI) analyses of tall reinforced concrete chimneys with annular raft foundation subjected to wind loads are presented in this paper. Different ranges of height and slenderness ratios of the chimneys and different ratios of external diameter to thickness of the annular raft were selected for the parametric study. To understand the significance of SSI, four types of soils were considered based on the stiffness. The chimneys were assumed to be located in terrain category two and subjected to a maximum wind speed of 50 m/s as per IS:875 (Part 3)-1987. The alongwind and across-wind loads were computed according to IS:4998 (Part 1)-1992. The linear elastic behavior was assumed for the integrated chimney-foundation-soil system and it was analysed using finite element software ANSYS based on direct method of SSI. The radial and tangential moments and settlement of annular raft foundation were evaluated through SSI analysis and compared with that obtained from conventional method of analysis as per IS:11089-1984, assuming foundation system is rigid. From the analysis, it is concluded that the SSI analysis results in higher radial moments and lesser tangential moments as compared to conventional method. All these variations depend on the geometric properties of chimney and annular raft foundations. © Indian Geotechnical Society 2013.
A Critical Review of Construction, Analysis and Behaviour of Stone Columns
(Kluwer Academic Publishers, 2013) Dheerendra Babu, M.R.; Nayak, S.; Shivashankar, R.
Stone columns have been used as an effective technique for improving the engineering behaviour of soft clayey grounds and loose silt deposits. The soil improvement via stone columns are achieved from accelerating the consolidation of weak soil due to shortened drainage path, increasing the load carrying capacity and/or settlement reduction due to inclusion of stronger granular material. This paper discusses the techniques, methods of construction of stone columns, mechanisms of stone column behaviour under load and associated design philosophies along with some practical findings from recent research programs. © 2012 Springer Science+Business Media B.V.
A Numerical Study on Interference Effects of Closely Spaced Strip Footings on Cohesionless Soils
(Springer Science and Business Media Deutschland GmbH, 2021) Anaswara, S.; Shivashankar, R.
Foundations of buildings often need to be placed at close spacings to meet the various structural or functional requirements. In such cases, the combined action of adjacent footings is different from that of a single foundation. The combined effect causes interference of the stress zones. Numerical analysis is carried out on two closely spaced strip footings on sands, by varying the affecting parameters, to study the interference effects. Interference effects are analysed in terms of bearing pressure, settlement and tilt of foundations. In this study, the interference effects of closely spaced strip footings on the surface of cohesionless soils are being investigated. Parametric studies are done for two foundations by varying the clear spacing between the foundations. The results are presented in terms of interference factors. New structures near to the old construction may alter the settlement, pressure and rotational characteristics of the old footing and could lead to its distress. Above all, the load-carrying capacity of the new foundation will be very different from what it would have carried if it were independentâ€”without the interference of the other footing. First footing representing an already existing footing is loaded with half of the estimated failure load of single independentÂ strip footing and second adjacent footing loaded up to failure. The effect of interference of the old foundation is observed to be particularly significant in terms of the settlement and tilt. Â© 2021, Springer Nature Singapore Pte Ltd.
A Numerical Study on the Shear Strength of Pervious Concrete Column in Weak Ground
(Southeast Asian Geotechnical Society, 2022) Rashma, R.S.V.; Jayalekshmi, B.R.; Shivashankar, R.
In this study, the response of pervious concrete column-treated ground under shear loading is examined by employing a series of numerical analyses. The shear behaviour of pervious concrete column-treated ground is compared with stone column-treated ground and weak ground. Two types of analyses were carried out to assess shear strength of the composite ground. Conventional direct shear test model and large shear test models were evaluated using ABAQUS software. The pervious concrete column-treated ground is observed to have greater shear strength than the mere stone column-treated ground. The lateral deflection pattern of the pervious concrete column is also noticed to be very much lesser than conventional stone columns under static shear loading. The overall shear performance of the pervious concrete column-treated ground is found to be improved than the typical stone column-treated ground. © 2022, Southeast Asian Geotechnical Society. All rights reserved.
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.
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).
Analysis of foundation of tall RC chimney with 3D finite element method
(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.
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. Â© ASCE 2014.
Bearing capacity of interfered adjacent strip footings on granular bed overlying soft clay: An analytical approach
(Salehan Institute of Higher Education, 2021) Shivashankar, R.; Anaswara, S.
In the present paper, the interference effects on bearing capacity of two and three closely spaced strip footings resting on granular bed overlying clay are being studied. A simple analytical model is proposed to predict the load-carrying capacity and the interference factor of an interfered footing, when adjacent strip footings are optimally placed on the surface of a Granular Bed (GB) overlying clay and both the footings are simultaneously loaded. A punching shear failure mechanism is envisaged in the analytical model. The load-carrying capacity of the footing is taken as the sum of total shearing resistances along the two vertical planes through the edges of the strip footing in the upper granular layer and the load-carrying capacity of the soft clay beneath the GB. Insights gained from finite element simulations are used to develop the new modified punching shear model for interfering footing. Bearing capacity can be easily calculated by using the proposed punching shear model for interfering footing. The analytical model is validated with numerical analyses and previous experimental results and found to be in reasonably good agreement. The influence of different parameters such as granular bed thickness, width of footing, number of footings are carried out in this study. © 2021 by the authors. Licensee C.E.J, Tehran, Iran.
Behaviour of Adjacent Strip Footings on Unreinforced/Reinforced Granular Bed Overlying Clay with/without Void
(National Institute of Technology Karnataka, Surathkal, 2021) S, Anaswara.; Shivashankar, R.
In many situations, due to rapid urbanisation, such as lack of construction sites, structural and architectural restrictions, buildings are placed close to each other. In such cases, the stress isobars or the failure zones of closely spaced foundations may interfere with each other leading to the phenomenon called ‘Interference’. It has an impact on the stresses in the subsoil due to overlapping of stresses, bearing capacities, settlements and tilts of footings due to the superstructure loads. Recognising the effects of interference and designing the footings accordingly ensures the safety and good performance of the structures. The first part of this doctoral research work studies the interference effects of two/three-strip footings placed adjacent to each other on unreinforced/reinforced granular soils, including some experimental studies. Effects on stresses in foundation soil; bearing capacities, settlements and tilts of footings are being investigated. Parameters varied in this study are (i) Number of footings (In the case of two footings loaded simultaneously, both experimental and numerical studies are conducted. In the case of two footings loaded sequentially and three footings, numerical studies are done) (ii) Loading conditions (iii) Clear spacing between the footings and (iv) Number of reinforcement layers in foundation soil. With two footings, two loading conditions are considered. In the first loading condition, both the footings are loaded simultaneously up to failure. In the second loading condition, one of the footings representing an already existing foundation is loaded with half of the estimated failure load of single strip footing and adjacent footing loaded up to failure. It is observed that in the case of simultaneous loading, there is a certain critical spacing (S=2B) at which the footing/s carry the maximum load. At S/B=2, the interference effect improves the bearing capacity of the 50mm and 100mm footings by 37% and 74%, respectively. The effect of providing the reinforcements in layers in the foundation soil, beneath the footings, is seen in the increased bearing capacities, reduced settlements, and reduced tilts of the footings. Tilts are also found to be influenced by the loading conditions. On unreinforced soil, increasing the distance from 1B to 4B between the footings results in a nearly 12% reduction in tilt in interfered footing. At S/B=2, introducing three reinforcing layers beneath simultaneously loaded interfering footings results in a 2.6 per cent tilt viii reduction. In the case of sequential loading of old and new footing, providing reinforcement beneath the new footing and loading it to maximum, causes a somewhat larger tilt (6.32% increment) of already existing strip footings. As the second part of this doctoral research work, numerical studies are undertaken on the behaviour of two adjacent strip footings on unreinforced (GB) and reinforced granular bed (RGB) overlying clay with/without voids. The influence of different parameters such as granular bed thickness, length of reinforcement/s, number of layers of reinforcement, presence of void/s beneath the footing/s in the weak soil etc., on the behaviour of footings are carried out. With two adjacent strip footings on GB overlying weak soil, the bearing resistance of each footing is more (14% for B=1m and 36% for B=2m) than a single independent strip footing on GB overlying weak soil. The voids could be formed in weak soil due to various reasons, and the presence of voids will affect the performance of footings. Such voids tend to reduce the load-carrying capacity of the footing/s and alter the failure pattern of foundation soil. In the case of a single void under two footings, the maximum reduction in the bearing capacity of new footing (53% reduction for B=1m, H/B=1) is reported when the void is formed directly below the new footing. When a void is formed anywhere beneath the footing/s in the weak soil, either directly beneath or nearby close to the centre line of the footing/s, failure surfaces developed from the nearest footings tend to move towards the void and are found to be narrower than the no void case. However, providing a reinforced granular bed (RGB) over weak soil can be used as an effective method to maintain the good performance of footings, even when voids could be formed in future. The interference effect in top granular soil combined with the reinforcement effect is seen to effectively nullify the void effect. This research work attempted to provide an analytical model to estimate the ultimate bearing capacity of two and three adjacent strip footings resting on granular bed overlying weak soil, with a fair and acceptable degree of accuracy. The accuracy of the proposed model has verified with finite element simulations and the percentage error is about 13%.
Behaviour of Prestressed Geosynthetic Reinforced Granular Beds Overlying Weak Soil
(2014) Shivashankar, R.; Jayamohan, J.
This paper presents an analytical model for predicting the improvement in bearing capacity of geosynthetic reinforced granular beds overlying weak soil due to prestressing the reinforcement. A punching shear failure mechanism is envisaged in the analytical model. Results obtained from a series of laboratory scale bearing capacity tests and finite element analyses are used to validate the model. The addition of prestress to the reinforcement results in significant improvement of the settlement response and the load-bearing capacity of the foundation. The parameters studied are strength of underlying weak soil, thickness of granular bed, magnitude of prestressing force, direction of prestressing forces, type of reinforcement and number of layers of reinforcement. The bearing capacity ratios (BCRs) values predicted by the analytical model are found to be in good agreement with the experimentally obtained BCR values. Finite element analysis are carried out using the FE program PLAXIS to study the effect of prestressing the reinforcement. Results obtained from finite element analysis are found to be in reasonably good agreement with the experimental results. © 2013 Indian Geotechnical Society.
Behaviour of prestressed reinforced foundation beds overlying weak soil
(2014) Shivashankar, R.; Jayamohan, J.
Geosynthetics in foundation beds demonstrate their beneficial effects only after considerable settlements, since the strains occurring during initial settlements are insufficient to mobilize significant tensile load in the geosynthetic. Prestressing the reinforcement is a promising technique to overcome this shortcoming. This paper presents results from a series of laboratory scale bearing capacity tests carried out on model square footings to investigate the improvement in bearing capacity of geosynthetic reinforced foundation bed overlying weak ground due to prestressing the reinforcement. Prestressing the reinforcement in foundation bed results in significant improvement of bearing capacity of weak soil. A numerical model is suggested to predict the improvement in bearing capacity of footings with all the three cases - i.e., Granular Bed (GB), Reinforced Granular Bed (RGB), or Prestressed RGB on weak soil - by assuming a punching shear mechanism. These predictions are compared with laboratory scale experimental results. The proposed model is found to give good prediction of bearing capacity improvement. Finite element analyses are carried out using the FE program PLAXIS to study the effect of prestressing the reinforcement. Results obtained from finite element analyses are found to be in reasonably good agreement with the experimental results. � ASCE 2014.
Behaviour of prestressed reinforced foundation beds overlying weak soil
(American Society of Civil Engineers (ASCE) onlinejls@asce.org, 2014) Shivashankar, R.; Jayamohan, J.
Geosynthetics in foundation beds demonstrate their beneficial effects only after considerable settlements, since the strains occurring during initial settlements are insufficient to mobilize significant tensile load in the geosynthetic. Prestressing the reinforcement is a promising technique to overcome this shortcoming. This paper presents results from a series of laboratory scale bearing capacity tests carried out on model square footings to investigate the improvement in bearing capacity of geosynthetic reinforced foundation bed overlying weak ground due to prestressing the reinforcement. Prestressing the reinforcement in foundation bed results in significant improvement of bearing capacity of weak soil. A numerical model is suggested to predict the improvement in bearing capacity of footings with all the three cases - i.e., Granular Bed (GB), Reinforced Granular Bed (RGB), or Prestressed RGB on weak soil - by assuming a punching shear mechanism. These predictions are compared with laboratory scale experimental results. The proposed model is found to give good prediction of bearing capacity improvement. Finite element analyses are carried out using the FE program PLAXIS to study the effect of prestressing the reinforcement. Results obtained from finite element analyses are found to be in reasonably good agreement with the experimental results. Â© ASCE 2014.
Behaviour of Prestressed Reinforced Granular Bed Overlying Soft Soil
(National Institute of Technology Karnataka, Surathkal, 2014) J, Jayamohan.; Shivashankar, R.
The use of geosynthetics to improve the bearing capacity and settlement performance of shallow foundations has proven to be a cost-effective foundation system. In marginal ground conditions, geosynthetics enhance the ability to use shallow foundations. This is done by either reinforcing cohesive soil directly or replacing the poor soils with stronger granular fill in combination with geosynthetic reinforcement. In low-lying areas with poor foundation soils, the geosynthetic reinforced granular bed can be placed over the weak soil. The resulting composite ground (reinforced granular bed) will improve the load carrying capacity of the footing and provide better pressure distribution on top of the underlying weak soils, hence reducing the associated settlements. It is now well established that geosynthetics demonstrate their beneficial effects only after considerable settlements, since the strains occurring during initial settlements are insufficient to mobilize significant tensile load in the geosynthetic. This is not a desirable feature for foundations of certain structures, since their permissible values of settlement are small. Thus there is a need for a technique which will allow the geosynthetic to increase the load bearing capacity of soil without the occurrence of large settlements. One technique yet to be comprehensively studied is the effect of prestressing the geosynthetic layer before implementing them as reinforcement in field applications. In this thesis, extensive investigations are made to study the effects of prestressing the geosynthetic reinforcement on the behaviour of reinforced granular bed overlying weak soil. The study involved laboratory scale plate load tests to observe the physical behaviour of prestressed geosynthetic-reinforced soil system. Non-linear FE analyses were carried out using the FE program PLAXIS, version 8, and the results were compared with those obtained from model tests. The parameters studied are effects of magnitude of prestress, direction of prestress, number of layers of prestressed reinforcement, type of geosynthetic reinforcement, size of reinforcement, thickness of granular bed, strength of underlying weak soil, presence of voids in granular bed and weak soil etc. In this thesis an analytical model is proposed to predict the improvement in bearing capacity due to prestressing the reinforcement in the granular bed. The results of the analytical model are validated by comparing it with those obtained from experimental and finite element studies.
Behaviour of tunnel and surrounding strata using 3Dec numerical modelling: Case study of an U/G metro rail project
(CAFET INNOVA Technical Society cafetinnova@gmail.com 1-2-18/103, Mohini Mansion, Gagan Mahal Road, Domalguda, Hyderabad 500029, 2012) Rebello, R.; Sastry, V.R.; Shivashankar, R.; Laksmi, S.
Tunnel serves various purposes including transportation. A case study of an underground metro rail project involving considerable length of the tunnel was taken up for this study. This paper presents the analysis carried out for a stretch of 350m long tunnel being constructed for an underground metro. Modeling was carried out at seven different cross sections of tunnel, using 3DEC software, incorporating the strata characteristics. Study was carried out for the stability of tunnel with and without support. Observations were made about the behaviour of tunnel under given conditions for Vertical Stress, Vertical Displacement, at points like crown of tunnel and at the surface. Minute displacement of 0.05mm was observed particularly at the chainage where the tunnel is completely passing strong rock at Chainage 9345m. Tunnel is passing through Moderately Weathered Rock at Chainage 9295m, and the analysis resulted in a displacement of 4mm without support which has reduced to 0.5mm after placing the lining. Higher displacements were observed at chainages where the tunnel is passing through Silty sand, Highly Weathered Rock and Sandy Silt. Displacement at the tunnel crown increased to 18.6mm where the tunnel is passing through Silty sand (Chainage 9495m). © 2012 CAFET-INNOVA TECHNICAL SOCIETY.
Dynamic response assessment of RC buildings featuring basement storeys integrated with soil-nailed structures
(Elsevier Ltd, 2025) Amrita; Jayalekshmi, B.R.; Shivashankar, R.
The rising demand for high-rise buildings and infrastructure has led to construction on hilly and sloping terrains, necessitating their stabilisation. The area adjacent to a vertical cut, stabilised through the soil nailing technique, presents opportunities for constructing multi-storey buildings. Incorporating basement levels in buildings is also a common practice to maximise the utility of space. This study evaluates the seismic performance of integrated soil-nailed wall-building systems, where the multi-storey building is connected to the soil-nailed structure through a shear wall, termed the Shear wall (SW) system. The effect of providing two basement levels on the seismic response of the integrated SW system is analysed in soft soil conditions, denoted as the SWB system (Shear wall system with basement floors). Finite element analysis of three-dimensional models of these integrated systems is conducted in PLAXIS software. The influence of the frequency content of dynamic excitations on the responses of these structures is assessed using time history data of three different earthquakes, considering various heights of the building. Results indicate that the SWB system provides substantial benefits, including a 35.17 % reduction in seismic building deformation, a 19.23 % reduction in soil-nailed wall acceleration, an 81.66 % reduction in axial nail force and a 54.77 % reduction in inter-storey drift. However, these improvements come with increased lateral earth pressure on the soil-nailed wall, necessitating careful design to ensure optimal seismic performance. These integrated configurations are recommended as suitable for optimum space utilisation in space-constrained urban sites while ensuring structural stability under seismic loading. © 2025 Elsevier Ltd
Dynamic Response of Soil Nailed Wall
(Springer Science and Business Media Deutschland GmbH, 2021) Amrita; Jayalekshmi, B.R.; Shivashankar, R.
Soil nailing is a technique used to stabilize steep cut slopes and to retain excavations. The method consists of inserting nail bars into the ground to stabilize the soil mass. The present study evaluates the dynamic response of a soil nailed wall supporting a vertical cut of height 6Â m. The finite element analysis has been carried out to study the stability and performance of the soil nailed wall using PLAXIS 2D software. The seismic resistance and failure mechanism of the wall are analyzed under the El Centro ground motion. The seismic response variation for different parameters such as angle of inclination of nail and length of nail is studied. The results are observed in terms of maximum lateral displacement, development of maximum tensile force in nails and failure mechanism of soil nailed wall under static and dynamic conditions. The results of the study indicate that the soil nailed structure is an effective method which imparts stability to the retaining system under dynamic conditions. Â© 2021, The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd.
Dynamic soil-structure interaction analysis of 300m tall industrial reinforced concrete chimneys on piled raft foundations
(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.
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.
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.