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 Full scale experiment and finite element modeling of support structures of substation equipment for evaluation of ground motion amplification(2012) Nandam, S.; Ramesh Babu, R.; Venkataramana, K.Post earthquake performance of porcelain insulators installed for high voltage substation equipment, in general, revealed their vulnerability to failure, not due to any quality deficiency, but due to failure of their supporting structures. Most of the equipment in standalone state, withstood to tests of induced vibrations conforming to International standards. The same tested equipment, when erected in position over its supporting structure failed to sustain earthquake ground accelerations, as the supporting structure adversely contributed to amplification of the ground seismic motions while traversing to the top of the structure or the base of the insulator. This paper critically examines salutary effects of damping of vibrations on a typical instrument- transformer, using a rubber based elastic damper, with particular reference to the connected porcelain insulators, in partial containment of amplification of earthquake acceleration or in minimizing attendant distress on them. The analytical study carried out is based on experimental studies conducted on the equipment using shake table and then correlating the results obtained using finite element analysis, on the full scale model to draw meaningful conclusions. © 2012 CAFET-INNOVA TECHNICAL SOCIETY.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 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 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.Item Parametric Study on Frequency Characteristics of Cylindrical Liquid Tanks(Springer, 2022) Nimisha, P.; Jayalekshmi, B.R.; Venkataramana, K.The response of liquid-storage tanks under seismic loading is a key research area. The study of free vibration characteristics is a prerequisite for understanding the dynamic behaviour of liquid tanks under seismic loading. Hence, the present study focuses on the analysis of different parameters that may influence the frequency characteristics of cylindrical liquid tanks. For this, a database of 560 three-dimensional cylindrical liquid tank models was developed by carrying out modal analysis using ANSYS Mechanical APDL software. The database was analysed with the aid of artificial neural networks and nonlinear regression analysis. Average deviations of 30% and 32% were observed for the impulsive frequency values estimated based on IS1893 (Part2):2014 and Eurocode-8, respectively, compared to the finite element results. Hence, modification coefficients were suggested with aspect ratio as the demarcating parameter and obtained a Pearson correlation coefficient of rXY > 0.9, between the predicted values of frequency and actual values. The predicted formulae reduced the deviations observed between the frequency estimated based on the codal expressions and those obtained from finite element analysis to 13% and 15%, corresponding to IS1893 (Part2):2014 and Eurocode-8, respectively. © 2022, The Institution of Engineers (India).