Faculty Publications
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Item Effect of containment reinforcement on the seismic response of box type laterite masonry structures-an analytical evaluation(2013) Unnikrishnan, S.; Narasimhan, M.C.; Venkataramana, K.Laterite blocks are used for construction of masonry walls since ages in the South-western coastal areas of India. The south-west coastal areas of India lie in zone III of seismic zonation map of Indian code IS 1893-2002. In spite of the fact that laterite is the most favored masonry material in these regions of India, the structural performance of laterite masonry has not been systematically investigated. Again there are no previous studies addressing, in detail, the seismic performance of laterite masonry buildings. Now that these areas are becoming more and more important from point of view of trade and commerce, there is a need for a detailed research on the seismic response of laterite masonry structures located in these areas. The present paper reports the results of such a study of the seismic response of box-type laterite masonry structures. Time history analysis of these structures under El-Centro acceleration has been performed using commercial finite element software ANSYS. Effect of 'containment reinforcement' on the seismic response of box type laterite masonry structures has been evaluated. © 2013 Techno-Press, Ltd.Item Seismic response analysis of reinforced concrete frames including soil flexibility(Techno-Press, 2013) Jayalekshmi, B.R.; Deepthi Poojary, V.G.; Venkataramana, K.; Shivashankar, R.The seismic response of RC space frame structures with isolated footing resting on a shallow soil stratum on rock is presented in this paper. Homogeneous soil stratum of different stiffness in the very soft to stiff range is considered. Soil, footing and super structure are considered to be the parts of an integral system. A finite element model of the integrated system is developed and subjected to scaled acceleration time histories recorded during two different real earthquakes. Dynamic analysis is performed using mode superposition method of transient analysis. A parametric study is conducted to investigate the effect of flexibility of soil in the dynamic behaviour of low-rise building frames. The time histories and Fourier spectra of roof displacement, base shear and structural response quantities of the space frame on compliant base are presented and compared with the fixed base condition. Results indicate that the incorporation of soil flexibility is required for the realistic estimate of structural seismic response especially for single storey structures resting on very soft soil. Copyright © 2013 Techno-Press, Ltd.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 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.