Faculty Publications
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Item Studies on Uniaxial compressive strength of laterite masonry prisms(2011) Unnikrishnan, S.; Narasimhan, M.C.; Venkataramana, K.Laterite is a well known conventional building material in Asian countries. In spite of its large popularity in construction, a systematic characterization of this material, as a building block, has not been seriously attempted so far. The strength and elastic properties of laterite masonry are influenced by the individual properties of the laterite blocks and the mortar. In the present study, characterization of the laterite block and the mortar and compressive strength of laterite masonry prisms have been investigated using detailed laboratory experiments and numerical analysis. The experimental results, related to the compressive strength and stress-strain characteristics of laterite and mortar and compressive strength of laterite masonry prisms are presented. Finite element analysis of laterite masonry prism has also been carried out. The studies have shown that the modulus of elasticity of laterite blocks tested is less than that of mortar used in making the laterite masonry. Further, the laterite masonry prisms have been observed to have failed by bond failure and subsequent splitting of laterite blocks. Also, increase in thickness of mortar joint gives rise to a decrease in laterite tensile stresses in mortar joint leading to higher prism strengths, if bond remains intact. © 2011 CAFET-INNOVA technical society. All right reserved.Item Free vibration studies of box type laterite masonry structures(2012) Unnikrishnan, S.; Narasimhan, M.C.; Venkataramana, K.Box-type laterite masonry structures are widely seen in south-west coastal areas of India. Not many studies are available in the literature on the dynamic response of such structures. Free vibration analysis of box-type laterite masonry structures has been attempted in this study, as a preliminary to a detailed dynamic analysis. Finite element analysis has been conducted to And the natural frequencies and corresponding mode shapes of box-type laterite masonry buildings. Results of detailed parametric studies conducted to find the effect of various parameters like modulus of elasticity of laterite masonry, provision of a lintel band or a roof slab, openings in long walls and aspect ratio on the natural frequencies and their mode shapes of box-type laterite masonry buildings are presented and discussed in this paper.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 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 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.