Faculty Publications
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Item Experimental and finite element analysis of power transformer(Structural Engineering Research Centre, 2014) Nandam, N.; Ramesh Babu, R.R.; Venkataramana, K.Post earthquake studies have clearly shown that the seismic performance of substation is very weak and results in damage causing huge direct and indirect loss to the power utilities. Considerable time is spent to repair, retrofit or replace the damaged substation equipment and to restore power supply. Many substation equipments failed when installed in the substation due to moderate earthquake forces though these equipment were experimentally qualified. Power transformer is one of such critical equipment of substation. Vibrations due to earthquake amplified by the transformer tank causes failure in the porcelain bushings mounted on the top of the transformer tank. An attempt has been made in this study to identify resonance frequencies and corresponding damping ratios of a typical transformer by both experimental and numerical methods. In addition, ground acceleration amplification is also calculated from shake table experiments and response analysis of finite element model.Item Probabilistic Seismic Hazard Assessment of Mangalore and Its Adjoining Regions, A Part of Indian Peninsular: An Intraplate Region(Birkhauser Verlag AG, 2019) Shreyasvi, C.; Venkataramana, K.; Chopra, S.; Rout, M.M.The Southwestern part of India investigated in the present study mainly comprises of states such as Goa, north Kerala and a major portion of Karnataka. A comprehensive regional seismic catalog has been compiled spanning over 190 years apart from a few prehistoric events from the early 16th century. The classical Cornel–McGuire approach has been incorporated in the estimation of seismic hazard. The seismic sources are modeled as area sources and the entire study region is divided into four seismogenic source zones. The uncertainties involved in the formulation of the seismic source model and ground motion prediction model has been discussed in detail. Further, the procedure for selecting appropriate GMPEs involves the evaluation of multidimensional (M, R, T) ground motion trends and performance against observed macroseismic data. The epistemic uncertainty in the estimation of seismicity parameters and ground motion prediction equations (GMPEs) has been addressed using logic tree computation. The results of the hazard analysis demonstrate that the existing seismic code underestimates the seismic potential of seismic zone II (BIS 1893) areas. The de-aggregation of the predicted seismic hazard revealed earthquakes of magnitude range (Mw) 4–6 occurring within a distance of 35kms to be most influential for any given site of interest. Sensitivity analysis has been performed for crucial input parameters in the formulation of seismic source and ground motion models. Site amplification study has been carried out using topographic slope as a proxy to shear velocity in the top 30 m (Vs30). A maximum of 60% to 80% amplification has been observed in the study area. The seismic hazard maps in terms of PGA have been plotted for the seismic hazard estimated at the bedrock level as well as the surface level for 2% and 10% probability of exceedance in 50 years. The hazard estimation specifically for the southern part of the west coast is the first of its kind. The investigation suspects mining-induced seismicity in Bellary and Raichur districts though there is no mention of this in the prior literature. © 2019, Springer Nature Switzerland AG.Item Local site effect incorporation in probabilistic seismic hazard analysis – A case study from southern peninsular India, an intraplate region(Elsevier Ltd, 2019) Shreyasvi, C.; Venkataramana, K.; Chopra, S.The inclusion of local site effects into seismic hazard analysis is an important issue and has been attempted previously in both deterministic and probabilistic manner. The present study is an attempt to combine the local site response with the standard probabilistic seismic hazard analysis. The site response was computed by performing an equivalent linear analysis in the frequency domain. The input soil profiles for the analysis were taken from the borehole data of the North Kerala region (one of the Southerly states in India). The uncertainty in estimating the shear velocity profile (VS) has been addressed by applying multiple VS–N correlations. The variability in the choice of input motions has been reduced by selecting multiple ground motions representing distinct hazard levels (return period of 50–2000 years). The uniform hazard spectrum developed for the host reference site conditions has been adjusted to the target region and the input motions are scaled accordingly. The analyzed soil profiles were categorized into three distinct soil types namely ‘Sand’, ‘Clay’ and ‘All soil’ based on the predominant soil content. The empirical amplification equation as a function of input rock spectral acceleration (Sa r) was developed for each soil type. ‘Sand’ exhibits nonlinear behavior for Sa r > 0.1 g whereas ‘clay’ demonstrates sustained amplification at longer periods. The average spectral amplification observed is 3 for ‘All soil’, 5 for ‘clay’ and 3.5 for ‘sand’ in the study region. The regionally developed amplification function aids in transforming a Ground Motion Prediction Equation (GMPE) from generic to site-specific. The modified GMPE is integrated with the regional seismic source model to estimate site-specific probabilistic seismic hazard. The study produces site-specific spectrum and surface hazard maps which can be of direct use to planners and designers in creating a seismic resilient built environment. © 2019 Elsevier LtdItem Strong Motion Data Based Regional Ground Motion Prediction Equations for North East India Based on Non-Linear Regression Models(Taylor and Francis Ltd., 2022) Ramkrishnan, R.; Kolathayar, S.; Sitharam, T.G.Existing Ground Motion Prediction Equations (GMPE) in practice for North East India have been developed using limited or simulated datasets of recorded ground motions. The current study presents the development of a new GMPE based on a well-established model considering actual recorded ground motion data comprising of acceleration, magnitude, and hypocentral distances. A larger dataset with magnitudes ranging from 4.2 to 6.9 and up to 640 kms, with a total of 204 recordings is used in non-linear multiple-regression. The newly developed GMPE could predict ground acceleration realistically over larger ranges of distance and magnitudes, compared to existing GMPEs. © 2020 Taylor & Francis Group, LLC.Item Dynamic stability evaluation of nail stabilised vertical cuts in various site classes(Techno-Press, 2024) Amrita; Jayalekshmi, B.R.; Shivashankar, R.The soil nailing method entails the utilisation of nails to reinforce and stabilise a zone of soil mass. This is widely used for various applications due to its effective performance under various loading conditions. The seismic response of 6m high vertical soil-nailed cut in various site classes under dynamic excitations has been investigated in this study considering various lengths and inclinations of nails. The influence of frequency content of dynamic excitation on the response of structure has been assessed through finite element analysis using time history data of three different earthquakes. The seismic stability of the nailed cut in retaining soil in various sites under El Centro, Kobe and Trinidad earthquake ground motion is evaluated based on maximum acceleration response, maximum horizontal deformation, earth pressure distribution on the wall and maximum axial force mobilised in nails. The optimum nail inclination is identified as 15° and a minimum nail length ratio of 0.7 is essential for a stable vertical cut under dynamic excitations. © 2024 Techno-Press, Ltd.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.Item Integrating soil-nailed walls with RC building for seismic stability in space-constrained sites(Springer Science and Business Media Deutschland GmbH, 2024) Amrita; Jayalekshmi, B.R.; Shivashankar, R.In urban environments, space constraints necessitate innovative construction methods. Due to rising demand for infrastructures and scarcity of plane ground, structures are built on sloping or irregular ground. To make use of available land, vertical cuts or excavations are made in the natural soil stratum which can be effectively retained using the soil nailing technique. However, if the area adjacent to the nailed vertical cut is utilised for constructing a multi-storeyed building, the behaviour of the nailed structure may vary. This study examines the impact of the presence of multi-storeyed RC buildings on the response of soil-nailed structures in their proximity during earthquake ground motion. The seismic response of a soil-nailed structure is evaluated in the presence of various heights of medium-rise multi-storeyed buildings. Three-dimensional multi-storeyed buildings and soil-nailed structures are analysed with various arrangements and connectivities between them, taking into account different soil profiles at the site. Dynamic finite element analyses of integrated soil-nailed wall-building systems have been performed using time history data of ground motion. The findings suggest that the integration between the two structures enhances the seismic stability of both the structures under dynamic load as evident in the reduced deformation and acceleration of the structures. It restricts the lateral movement of the nailed wall and reduces its displacement by about 40%. This integration can be implemented in space-constrained sites for optimum utilisation of available space. © The Author(s) 2024.Item Deterministic Seismic Hazard Analysis of Sree Padmanabhaswamy Temple, Kerala State(Springer, 2025) Padmanabhan, M.P.H.; Siddhardha, R.; Kolathayar, S.; Hegde, R.; Beekanahalli Mokshanatha, B.M.Deterministic seismic hazard analysis (DSHA) is a technique employed to estimate potential hazards and ground shaking resulting from specific earthquake scenarios at a given location. In the present study, DSHA is conducted for the Sree Padmanabhaswamy Temple, situated in the southernmost district of Kerala, India. This seismic hazard study is crucial due to the temple’s proximity to seismic events such as the 1900 AD Coimbatore earthquake with a magnitude of 6.3 Mw and the 2000 Pala earthquake with a magnitude of 4.7 Mw. This study examines earthquake data within a 500 km radius surrounding the Sree Padmanabhaswamy Temple in Thiruvananthapuram District, Kerala, from 1819 to 2022 AD. The seismic zone of the temple site is III according to the Indian zonation map (IS 1893 (Part 1): 2016), relying on past earthquakes recorded throughout India. The collected earthquake data underwent a homogenization process to determine the moment magnitude (Mw), distinguishing foreshocks and aftershocks from the main shocks. A seismotectonic map was developed comprising of geological discontinuities and 316 earthquakes events with moment magnitudes between 3.0 and 6.3 Mw. The software tools employed for this work include MATLAB, QGIS and ZMAP. The Log-likelihood technique (LLH) was used to choose the ground motion prediction equations (GMPEs) for the location. The GMPEs were then given weights based on the computed values of the data support index (DSI). The study region was partitioned into a grid size of 0.05° × 0.05° (5 km × 5 km). Using MATLAB code, the peak ground acceleration (PGA) was estimated for the site and PGA was found in the center of each grid cell, taking into account all seismic sources within a 500 km radius. In addition, site-specific deterministic spectrum was also developed. The findings show that Sree Padmanabhaswamy Temple has low seismicity, which is defined by weak to moderate earthquakes that have sources close to the temple. © The Author(s), under exclusive licence to Indian Geotechnical Society 2024.