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 A comparative study of the behavior of CFRP and GFRP laminates in a plate specimen using modified virtual crack closure technique (MVCCT)(Elsevier B.V., 2019) Javagal, S.; Raju, J.; Venkataramana, K.The applications of polymer composites in aircraft industry have exponentially increased in the recent years due to their high strength to weight ratio. Presence of delaminations in composites is inevitable which affects the structural stability due to reduction in structural stiffness and strength. The degradation of a structural component depends on the geometric characteristics of delamination, nature of loading and material characteristics. Damage tolerance study is thus essential to determine the extent of degradation of the structure due to the presence of delamination. The present paper brings about a comparision between the behaviour of a standard plate specimen made up of Carbon Fibre Reinforced Polymer (CFRP) and Glass Fibre Reinforced Polymer (GFRP) laminates with circular delaminations of varying diameters and subject to compressive load. A constant compressive load in terms of initial displacements was applied on a quasi-isotropic square plate specimen of dimensions 200 mm x 200 mm with a thickness of 2.88 mm of both CFRP and GFRP configurations. A circular delamination was introduced at the centre of the plate and its diameter and position along the thickness direction were varied and studied. Using ABAQUS codes of practice, Strain Energy Release Rate (SERR) was computed. The principles of Modified Virtual Crack Closure Technique (MVCCT) was used to compute SERR. Delamination propagates when the computed mixed mode energy release rate exceeds the critical value, GC. Depending on the external loading and material properties, Total strain energy release rate, GT (GT=GI+GII+GIII) was used to predict growth of delamination. The onset of delamination growth was determined by plotting the values of (GT/GC) across various delamination sizes along the thickness of the plate and reported. © 2019 The Authors. Published by Elsevier B.V.Item Studies on rotation capacity and torsional strength of normal, medium- and high-strength rc beams(Springer Science and Business Media Deutschland GmbH, 2021) Prakash, M.R.; Venkataramana, K.; Prabhakara, R.; Manjunatha, B.Understanding of the beam behaviour in torsion along with bending and shear is very important for the complex design of buildings and as well as recent developments in neo-concretes. An experimental investigation was carried out to determine the response of normal, medium- and high-strength concrete beams when subjected to torsion. In the present investigation under standard testing conditions, the torsional behaviour of total 27 beams which are grouped into nine categories like NSC, MSC and HSC beams with identical geometrical conditions like width, depth, effective span and varied area of steel in longitudinal and transverse directions has been investigated. The beam properties like rotation capacity, ultimate torsional strength and failure pattern of the beams are studied. The results obtained from the experimental investigations are validated with the help of similar work as cited in the literature survey. Also, the parametric analysis had carried out for different models, theories and codal equations as suggested by the different investigators. The obtained torsional strength experimental values of NSC beams are well agreement with the predicted torsional strength for most of the codes available in the literature. The experimental values of MSC and HSC beams are close agreement with EURO code II results. It was also observed that the rotation capacity of the beams depends on the grade of concrete, longitudinal steel and spacing of transverse reinforcement. © Springer Nature Singapore Pte Ltd 2021.Item Effect of diaphragm discontinuity on the seismic response of an rc building(Springer Science and Business Media Deutschland GmbH, 2021) Mable Vas, V.; Nagaraja, P.; Venkataramana, K.Although rigid floor diaphragm is a reasonable assumption for seismic analysis, certain building configurations may exhibit diaphragm flexibility. Detailed investigations have been carried out on modelling of flexible diaphragms compliant with various codes such as ASCE-07 and UBC 1997. Studies have shown that diaphragm flexibility amplifies both the deformation and the shear in the diaphragm. However, additional studies are essential to assess the magnitude of such amplification and to account for it in the design. The methodology is outlined by three major elements such as the choice of building models, the adopted method of analysis and the parameters studied. Buildings with large cut-outs and openings are observed to exhibit flexible behaviour. These models are analysed dynamically using a site-specific response spectrum developed from probabilistic seismic hazard analysis (PSHA) for Mangalore region (a coastal city in Karnataka, Southern India). The analysis is carried out using a G+10 RC building. The effect of percentage of openings in the diaphragm is studied using structural parameters such as storey drift, base shear and storey displacement with the help of ETABS 2015 software, and the optimum shape for these openings in a building plan is finalized. Further, time history analysis is performed over the models, and the results obtained through response spectrum and time history analysis are compared. The study highlights the importance of diaphragm flexibility in determining the seismic response of a building. This flexibility causes significant increase in the building period, which results in reduction in the earthquake-induced base shear. Since the seismic input used for the study was developed for the moderate seismic zone, the outcomes of this investigation are believed to have vast applications. © Springer Nature Singapore Pte Ltd 2021.Item Effectiveness of base isolation using single friction pendulum in plan irregular structures(Springer Science and Business Media Deutschland GmbH, 2021) Sharika, R.; Venkataramana, K.Base isolation is found to be a very efficient earthquake-resistant construction method. When base isolation is introduced, the transfer of large amount of inertia forces is prevented by the moving action of an isolator during an earthquake. The application of base isolator in regular buildings is done from long before, but the usage and effectiveness of base isolation in irregular buildings are a topic which needs more research. In this study, single friction pendulum isolator is used to isolate the buildings and the effectiveness of isolators is discussed in regular as well as plan irregular buildings. Modal analysis and time history analysis using Chi-Chi earthquake accelerogram data is done. Time period obtained from modal analysis and the results of time history analysis, such as base shear, storey acceleration and storey drift of regular, as well as plan irregular buildings are compared. The time period is found to increase significantly and base shear, acceleration and storey drift are decreased significantly with the application of single friction pendulum isolator. Also, the effectiveness of isolator got reduced with the introduction of irregularity in the structure. © Springer Nature Singapore Pte Ltd 2021.Item Seismic Pounding Between Adjacent RC Buildings with Asymmetric Alignment(Springer Science and Business Media Deutschland GmbH, 2021) Ambili, P.; Krishnachandran, V.N.; Venkataramana, K.During earthquakes, adjacent structures may collide with each other due to different dynamic characteristics. When buildings vibrate out-of-phase and the separation gap provided between buildings is not sufficient to accommodate their relative motions, collisions can cause severe damage or even complete collapse of structures, and is known as seismic pounding. In metropolitan cities, due to increased population and land values, buildings have been constructed with inadequate separation distance between them. The seismic oscillations induced in a structure in a block of buildings will be partly restrained in lateral displacements and hence torsional movements are introduced (asymmetric pounding). Two different types of impacts may occur during pounding including floor-to-floor and floor-to-column (inter-storey) collisions. In this paper, the effects of asymmetric (contact asymmetry) pounding on the seismic response of adjacent buildings with symmetric plan and unequal building heights are studied. Time history analysis of adjacent buildings with different pounding cases involving 1, 2 and 3 column pounding is carried out using the software ETABS and the corresponding torsional response is evaluated. The influence of separation gap and floor heights between the adjacent structures on the torsion effect is investigated and the results are compared with no pounding case. © 2021, Springer Nature Switzerland AG.Item Study of Dynamic Characteristics of Circular Liquid Storage Tanks Using Acoustic Principles(Springer Science and Business Media Deutschland GmbH, 2021) Nimisha, P.; Jayalekshmi, B.R.; Venkataramana, K.Liquid storage tanks are lifeline structures, which should be designed with utmost care. Any damage to a tank, which is used to store hazardous liquid is catastrophic. The estimation of fundamental natural frequencies of liquid storage tanks situated in seismic regions is important for a seismic design. The present study deals with the estimation of natural frequencies of circular steel liquid storage tanks with reference to codal provisions and numerical analysis by using acoustic principles with the aid of FEM software. The study has been carried out for circular tank of diameter 6 m and height 8 m with different liquid depths, viz. 1/3rd, 2/3rd and full tank conditions and stiffness conditions, incorporating the sloshing effect. The natural frequencies obtained by finite element analysis of tanks are compared with those values obtained as per various International codes, viz., IS 1893(part2):2014, API 650 and Eurocode 8. The results show that the convective mode frequencies are matching well whereas, there is slight variation in impulsive mode frequency values obtained as per IS 1893. © 2021, Springer Nature Singapore Pte Ltd.Item Nonlinear Soil Amplification Models for a Moderately Active Seismic Zone in India(Springer Science and Business Media Deutschland GmbH, 2021) Shreyasvi, C.; Venkataramana, K.The dynamic stiffness and damping of the soil material, depth of the soil profile, impedance between the soil and the underlying bedrock and soil nonlinearity are the factors influencing the local site response. The important parameter in assessing the site response is the “amplification factor,†which is usually correlated to Shear Wave velocity in the top 30 m (Vs(30)). Though using VS(30) as an index for amplification is simple and robust, it is not recommended for site-specific applications. In the present study, two distinct soil types i.e. “Sand†and “Clay†with the same value of VS(30) demonstrated variable amplification characteristics. Hence, distinct site amplification models were derived for the two soil types considering the intensity of the input bedrock motion as the primary independent variable. The borehole data from nearly 50 locations in North Kerala, an intraplate region in the Southern part of India was collected. The ground response was simulated in 1-dimension considering equivalent linear behavior of soils on the SHAKE 2000 platform. The ground motions used in the simulation were scaled to the target spectrum obtained from the regional seismic hazard assessment. The average spectral amplification observed is 5 for “Clay†and 3.5 for “Sand†in the study region. The soil profiles categorized as “sand†exhibits nonlinear behavior. “Clay†deposits reveal sustained amplification at longer periods and hence, can significantly influence ground response during longer duration ground shaking. The empirical amplification equations developed from the study can be used to modify the generic ground motion prediction models to region-specific applications. © 2021, The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd.Item Seismic Response of Buildings Resting on Raft Foundation with EPS Geofoam Buffer(Springer Science and Business Media Deutschland GmbH, 2021) Sreya, M.V.; Jayalekshmi, B.R.; Venkataramana, K.Seismic isolation is a technique that has been used around the world to protect building structures, non-structural components and content from the damaging effects of earthquake ground shaking. The present study deals with analysing the efficiency of Epoxy Polystyrene (EPS) geofoam buffer as a soil isolation medium to reduce the seismic energy transferred, thereby reducing the dynamic response of building under earthquake loads. The behaviour of an integrated soil isolation-building system has been investigated analytically, by using recorded accelerogram of El Centro earthquake. Finite element simulation of transient response has been carried out on three-dimensional field-scale models of one-storey, two-storey, three-storey and four-storey buildings resting on raft foundation in sand beds of different stiffnesses, with and without soil isolation mechanism. Four sets of three-dimensional buildings of single bay moment resisting concrete frames with 4 m bay length in either directions and 3 m storey height have been considered for the estimation of seismic response. EPS geofoam buffer of thicknesses 0.05, 0.10, 0.15 and 0.20 m and stiffnesses 22, 16, 10 and 5 MPa are placed at a depth of 0.15 m below the raft foundation of dimension 5 m × 5 m × 0.5 m. Different soil stiffnesses are considered to study its effects on the seismic response of building. Size of the soil stratum considered is 55 m × 55 m with a depth of 20 m. Absorbent boundaries have been used to eliminate the problem of reflection of the waves back into the soil from lateral boundaries. The interface between the underneath soil and EPS geofoam is formulated with a coefficient of friction 0.3. The results under field-scale conditions indicate that soil isolation provided by the EPS geofoam buffer substantially reduces the earthquake energy transmission to the superstructure during a strong earthquake. © 2021, The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd.