Faculty Publications
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Item Study on the strength parameters of high volume fly ash concrete and geopolymer concrete(2011) Shetty, A.; Anand, V.R.; Hegde, P.Concrete has been the most preferred construction material. It is being increasingly used day by day all over the world due to its versatility, mould ability and high compressive strength. But the large-scale production of cement is causing environmental problems on one hand and the unrestricted depletion of natural resources on the other. So the issue of sustainable development in concrete construction is addressed in this paper through development of concrete mixes by replacing certain percentage of cement with fly ash. Trials on concrete mixes with replacement of 40%, 50%, 60% and 70% of cement with fly ash are carried out and the results depict that at the replacement level of 40% cement by fly ash, the required strength is achieved. It is also observed that the rate of early strength gain is retarded as the percentage replacement of cement increases. But in case of Geopolymer concrete (100% replacement of cement by fly ash) under a curing temperature around 600C and above, the strength gain rate is very high in initial stages. It is observed that design strength is achieved within 28 hours of oven curing. © 2011 CAFET-INNOVA TECHNICAL SOCIETY. All rights reserved.Item 3D soil–structure interaction analyses of annular raft foundation of tall RC chimneys under wind load(Springer, 2014) Jisha, S.V.; Jayalekshmi, B.R.; Shivashankar, R.Three dimensional soil–structure interaction (SSI) analyses of tall reinforced concrete chimneys with annular raft foundation subjected to wind loads are presented in this paper. Different ranges of height and slenderness ratios of the chimneys and different ratios of external diameter to thickness of the annular raft were selected for the parametric study. To understand the significance of SSI, four types of soils were considered based on the stiffness. The chimneys were assumed to be located in terrain category two and subjected to a maximum wind speed of 50 m/s as per IS:875 (Part 3)-1987. The alongwind and across-wind loads were computed according to IS:4998 (Part 1)-1992. The linear elastic behavior was assumed for the integrated chimney-foundation-soil system and it was analysed using finite element software ANSYS based on direct method of SSI. The radial and tangential moments and settlement of annular raft foundation were evaluated through SSI analysis and compared with that obtained from conventional method of analysis as per IS:11089-1984, assuming foundation system is rigid. From the analysis, it is concluded that the SSI analysis results in higher radial moments and lesser tangential moments as compared to conventional method. All these variations depend on the geometric properties of chimney and annular raft foundations. © Indian Geotechnical Society 2013.Item Core recovery: a damage diagnosis tool for thermally deteriorated concrete(Emerald Group Holdings Ltd., 2019) Kulkarni, K.S.; Yaragal, S.C.; S.k, B.N.Purpose: This paper aims to study and assess residual strengths of concrete specimen exposed to elevated temperatures by core recovery tests. Design/methodology/approach: The appraisal of concrete structures is typically carried out by means of partially destructive tests such as tests on concrete cores taken from the structure and non-destructive testing. Findings: This paper presents results associated with determination of residual compressive strengths of plain and reinforced concrete elements exposed to elevated temperatures by core recovery test. Physical observations and results of compressive strengths of cores extracted from plain cement concrete, as well as from reinforced concrete beam elements exposed to elevated temperatures, have been presented. Originality/value: The empirical relations have been proposed between standard cube and core extracted for compressive strength of concretes exposed to elevated temperatures are useful for damage diagnosis. © 2019, Emerald Publishing Limited.Item Bond strength characteristics of fly-ash admixed selfcompacting alkali activated concrete mixes(Associated Cement Companies Ltd. priti.saldanha@acclimited.com, 2020) Manjunath, R.; Narasimhan, M.C.; Suryanarayana, L.R.Bonding in any type of concrete plays a crucial role in the performance of reinforced concrete structures, which are profoundly determined by many factors such as concrete compressive strength, diameter, type and size of the bar along with length of embedment and confinement of concrete. Herein, an attempt has been made to develop fly-ash admixed self-compacting alkali activated slag concrete mixes cured under laboratory ambient conditions and to evaluate the bond strength characteristics using direct pull out test along with their bond stress-slip behaviour at the age of 28 and 56 days. These self-compacting alkali activated slag concrete mixes were developed using Fly-ash and GGBFS as the major principal binder. Naturally available river sand was used as the fine aggregate; 12.5 mm down size crushed granite chips (Jelly) constituted the coarse aggregate fractions in all these mixes. The alkaline solutions basically consisted of mixtures of sodium hydroxide flakes dissolved in the calculated quantity of water and mixed with the liquid sodium silicate solution. The experiments were planned based on Taguchi’s design of experiments methodology. A total of fifteen mixes were developed and evaluated for their flow ability characteristics as per the requirements of EFNARC guidelines along with compressive strength values at the age of 7, 14, 28 and 56 days. In an initial, calibration phase, bond strength characteristics of a set of nine mixes were utilized for performance evaluation purposes. Strength prediction equations were then derived on the basis of such results, whose predictive capacity was then evaluated and ascertained in the prediction phase with actual results of experiments on a set of three new mixes. Test results indicated higher flow ability characteristics for all the mixes satisfying the requirements as per the EFNARC guidelines. Higher compressive strengths values in the range of 46 – 85 MPa were obtained at the age of 56 days. Further acceptable bond strength values were obtained varying in the range of 8.0 – 14.5 MPa as compared to control OPC based reference concrete mix. © 2020, Associated Cement Companies Ltd.. All rights reserved.Item Time-dependent safety performance of reinforced concrete structures(Emerald Group Holdings Ltd., 2020) Worabo Woju, U.W.; Balu, A.S.Purpose: Performance of the structure depends on design, construction, environment, utilization and reliability aspects. Other factors can be controlled by adopting proper design and construction techniques, but the environmental factors are difficult to control. Hence, mostly in practice, the environmental factors are not considered in the analysis and design appropriately; however, their impact on the performance of the structures is significant along with the design life. It is in this light that this paper aims to perform the time-dependent performance analysis of reinforced concrete structures majorly considering environmental factors. Design/methodology/approach: To achieve the intended objective, a simply supported reinforced concrete beam was designed and detailed as per the Euro Code (EC2). The time-dependent design parameters, corrosion parameters, creep and shrinkage were identified through thorough literature review. The common empirical equations were modified to consider the identified parameters, and finally, the time-dependent performance of reinforced concrete beam was performed. Findings: Findings indicate that attention has to be paid to appropriate consideration of the environmental effect on reinforced concrete structures. In that, the time-dependent performance of reinforced concrete beam significantly decreases with time due to corrosion of reinforcement steel, creep and shrinkage. Originality/value: However, the Euro code, Ethiopian code and Indian code threat the exposure condition of reinforced concrete by providing corresponding concrete cover that retards the corrosion initiation time but does not eliminate environmental effects. The results of this study clearly indicate that the capacity of reinforced concrete structure degrades with time due to corrosion and creep, whereas the action on the structure due to shrinkage increases. Therefore, appropriate remedial measures have to be taken to control the defects of structures due to the environmental factors to overcome the early failure of the structure. © 2020, Emerald Publishing Limited.Item Fuzzy uncertainty and its applications in reinforced concrete structures(Emerald Group Holdings Ltd., 2020) Worabo Woju, U.W.; Balu, A.S.Purpose: The aim of this paper is mainly to handle the fuzzy uncertainties present in structures appropriately. In general, uncertainties of variables are classified as aleatory and epistemic. The different sources of uncertainties in reinforced concrete structures include the randomness, mathematical models, physical models, environmental factors and gross errors. The effects of imprecise data in reinforced concrete structures are studied here by using fuzzy concepts. The aim of this paper is mainly to handle the uncertainties of variables with unclear boundaries. Design/methodology/approach: To achieve the intended objective, the reinforced concrete beam subjected to flexure and shear was designed as per Euro Code (EC2). Then, different design parameters such as corrosion parameters, material properties and empirical expressions of time-dependent material properties were identified through a thorough literature review. Findings: The fuzziness of variables was identified, and their membership functions were generated by using the heuristic method and drawn by MATLAB R2018a software. In addition to the identification of fuzziness of variables, the study further extended to design optimization of reinforced concrete structure by using fuzzy relation and fuzzy composition. Originality/value: In the design codes of the concrete structure, the concrete grades such as C16/20, C20/25, C25/30, C30/37 and so on are provided and being adopted for design in which the intermediate grades are not considered, but using fuzzy concepts the intermediate grades of concrete can be recognized by their respective degree of membership. In the design of reinforced concrete structure using fuzzy relation and composition methods, the optimum design is considered when the degree of membership tends to unity. In addition to design optimization, the level of structural performance evaluation can also be carried out by using fuzzy concepts. © 2020, Emerald Publishing Limited.Item Influence of sample preparation techniques on microstructure and nano-mechanical properties of steel-concrete interface(Elsevier Ltd, 2020) Goudar, S.K.; Das, B.B.; Arya, S.B.; Shivaprasad, K.N.Interface between steel and concrete is characterized as highly porous and weakest region which influences both mechanical properties and durability of a reinforced concrete structure. The properties of the steel-concrete interface (SCI), especially the porous zone thickness are prime factors in predicting the time for corrosion initiation to corrosion cracking in service life prediction models. Measurement of porous zone thickness of reinforced concrete samples is sensitive to the sample preparation technique for microscopic observations. It is observed that there are hardly any research articles are available in the literature regarding the sample preparation technique of reinforced concrete sample for SCI analysis. In the present study, a detailed and stepwise sample preparation technique is proposed where there is minimal damage found to be observed to SCI. The major focus is on the speed of cutting tool that is being used for obtaining a relatively small size of sample from the bulk reinforced concrete member. The properties such as porous zone thickness and nano mechanical properties around the SCI were determined through scanning electron microscopy and nano-indentation, respectively. A significant variation in porous zone thickness around SCI was observed and measured value of average porous zone thickness is found to be approximately 1.8 times higher from high-speed cutting to low-speed. A similar kind of observation was noticed for nano mechanical properties. In addition to speed of cutting, there found to be other factors such as pressing force for specimen, duration of polishing and heating temperature has significant influence on interfacial properties. © 2020 Elsevier LtdItem Flexural behavior of reinforced high performance self-compacting alkali activated slag concrete beams(Associated Cement Companies Ltd., 2020) Manjunath, R.; Prashanth, M.H.; Narasimhan, M.C.; Bala Bharathi, U.K.The present manuscript discusses the results of a series of tests conducted to study, in detail, the performance of reinforced, alkali activated slag concrete beams in terms of their flexural behavior. The present authors have developed and evaluated the performance of a new class of high-performance, self-compacting, alkali-activated slag concrete (HPAASC) mixes, using three industrial by-products, all from the iron and steel industry. While these HPAASC mixes have higher compressive strengths (around 70-90 MPa), reasonable splitting and flexural strengths along with moduli of elasticity, here, in this investigation, reinforced concrete beams made of these mixes are evaluated for their flexural performances in order to promote their applicability in large-scale infrastructural applications. Twelve under-reinforced concrete beams, were cast and were tested. Their flexural behaviors were experimentally evaluated in terms of loads at first crack, ultimate loads, strain-distributions, their load-deflection characteristics along with ductility values. Results of the present study indicate that, all the reinforced beams made of HPAASC mixes exhibit comparable flexural performances, as compared to that of beams cast with a reference OPC-based concrete mix, making a strong case for the possible application of these HPAASC mixes as structural elements in large-scale infrastructure projects. © 2020, Associated Cement Companies Ltd.. All rights reserved.Item Stiffness maximization of concrete structures using topology optimization in static and dynamic problems(Structural Engineering Research Centre, 2021) Resmy, V.R.; C, C.This study highlights the generation of truss-like patterns for Strut and Tie Modeling (STM) using bidirectional evolutionary topology optimization in concrete structures. STM is an effective approach for the design of Discontinuity regions (D-regions) where standard Bernoulli’s hypothesis cannot be applied. As the conventional methods of STM generally follow a trial and error procedure, the final solution may not be unique. Topology optimization is classified under structural optimization to find the effective layout of structure based on the load path method. It is a scientific method that relies on structural mechanics; the inaccuracies related to STM can be avoided with the aid of topology optimization. In static problems, minimizing compliance leads to reasonably more stiff structures. In free vibration problems, the maximization of eigen frequency can be taken as an objective to get the maximum stiff structure. Solid Isotropic Material with Penalization (SIMP) material model assumes a constant and isotropic material properties in each discretized rectangular element. Evolutionary optimization derives the optimum structural layout by removing the ineffective elements and adding the effective elements in subsequent iterations. Method of Moving Asymptotes (MMA) developed by Svanberg (1997) is a kind of convex approximation has also been implemented in static problems. © 2021, Structural Engineering Research Centre. All rights reserved.Item Influence of Fiber Content on Acoustic Emission Characteristics Related to Steel Fiber-Reinforced Concrete Subjected to Unconfined Uniaxial Compression(American Society of Civil Engineers (ASCE), 2021) Vidya Sagar, R.; Ghosh, S.; Kalloli, P.J.; Singh, M.This article reports the experimental study of the influence of the fiber volume content in steel fiber-reinforced concrete (SFRC) on the acoustic emission (AE) characteristics. Plain concrete and SFRC specimens with various steel fiber contents were tested under unconfined uniaxial compression in the laboratory. Both AE testing and ultrasonic pulse velocity (UPV) methods were used to study the fracture process in the specimens. During the fracture process, the generated AE and axial compressive strain were recorded. The differences in AE characteristics of plain concrete and SFRC specimens were discussed. An absence of a considerable amount of AE for a certain period was observed (silent period of AE) near the peak load for SFRC specimens. The AE-based b-value suddenly decreased near the peak load during the fracture process in plain concrete. However, in the case of SFRC specimens, a sudden decrease near the peak load was not observed, and the b-value decreased gradually until failure, at which point it attained its minimum value. More AE related to shear cracking was observed in the case of SFRC specimens. This was due to interlocking between steel fibers, cement matrix, and coarse aggregates. AE testing is useful for studying the material characterization of SFRC, and is beneficial for assessing damage in structures constructed with SFRC. © 2021 American Society of Civil Engineers.