Faculty Publications
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Item Numerical Modeling of Damage Behavior in Unidirectional Carbon/Carbon Composites(Springer, 2025) Vishnu, O.S.; Pavan, G.S.Carbon/carbon (C/C) composites are frequently employed in aerospace industries because of their outstanding mechanical properties at high temperatures. This study proposes a progressive damage development model for unidirectional C/C composites. C/C composite consists of carbon fibers and pyrolytic carbon matrix. A Representative Volume Element (RVE) incorporating the microstructural features is generated based on the Scanning Electron Microscopy (SEM) images of the C/C composite samples. The composite constituents, namely carbon fiber and pyrolytic carbon matrix, are modeled explicitly inside the RVE, and failure criteria are provided for the individual constituents. The damage model used in this study comprises damage initiation and evolution criteria. The carbon fibers are inserted inside the RVE using the Random Sequential Adsorption algorithm (RSA). The carbon fiber is modeled as a transversely isotropic material, and the damage initiation is based on the maximum stress criteria. The carbon matrix is considered as an isotropic material, and damage initiation inside the carbon matrix is based on modified von Mises stress criteria. The damage evolution criteria, which depend on the fracture energy of the material, are used to predict the post-peak behavior of the components following the onset of damage. The non-linear damage behavior of unidirectional C/C composite is studied under axial tensile loading conditions. © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2025.Item Replacement of River Sand with Coal Bottom Ash as Fine Aggregate in Cement Mortar(Springer Science and Business Media Deutschland GmbH, 2022) Wasnik, S.; Pavan, G.S.; Padhi, S.River sand is used as fine aggregate in concrete and cement mortar. The rapid expansion in construction activity witnessed in the country over the last decade has led to an incessant demand for river sand. Hence river sand is being excessively mined at the riverbeds and is leading to fast depletion of the precious natural resource. This presses the need for exploration of alternative materials which can be adopted as fine aggregate by construction industry to build concrete and masonry buildings. One possible candidate is coal bottom ash. Coal-based thermal power plants produce tonnes of coal bottom ash along with fly ash during power generation. Coal bottom ash is coarse particles settled at the bottom of cooling towers. The coarse nature of coal bottom ash particles can be harnessed and explored. The present study focuses on utilization of coal bottom ash as fine aggregate in cement mortars. River sand is fully and partially replaced by coal bottom ash. Five different proportions of river sand being replaced with coal bottom ash are adopted, namely 0, 25, 50, 75 and 100%. Performance of replacement of river sand with coal bottom ash is assessed in terms of particle size distribution (PSD) curves, workability and mechanical properties. Sieve analysis and mortar flow table test are conducted to assess the PSD curves and workability. Compression tests are conducted on cement mortar cubes (with different proportion of coal bottom ash) to determine compressive strength. Further, compression test is conducted on cement mortar cylinders in a displacement-controlled universal testing machine (UTM) to obtain the stress–strain curve and modulus of elasticity. The study found that river sand replaced with up to 50% coal bottom ash exhibited satisfactory performance as fine aggregate in cement mortar. © 2022, The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd.Item Strength and Durability Properties of Alkali-Activated Fly Ash Earth Bricks(Springer Science and Business Media Deutschland GmbH, 2022) Vasavi, G.S.; Mourougane, R.; Pavan, G.S.This study explores the strength and durability characteristics of alkali-activated fly ash earth bricks. Two kinds of bricks were produced, one set of bricks with the use of manufactured sand or M-sand and another set without M-sand. Alkali activator which is a combination of laboratory-grade sodium silicate and 10 M sodium hydroxide in 1:1 mass ratio is used in the study. Soil classified as clayey sand with a clay content of 14% is selected for the project. The fly ash/soil ratio and alkali activator/fly ash ratios of 0.4 and 0.6, respectively, are employed in the current study. Activator was added to the soil and M-sand and fly ash mixture and mixed thoroughly. The moist mixture was then added into the brick-making machine and compacted into bricks of size 114 mm × 102 mm × 230 mm. The bricks were subjected to ambient curing until the day of testing. Wet and dry compressive strength tests, complete saturation, flexure test, and split tensile test were conducted on the bricks. It was found that the dry compressive strength of the bricks is in the range of 8 to 10 MPa, wet compressive strength is around 70% of dry compressive strength, water absorption is around 8–12%, and split tensile strength is in the range of 0.47–0.55 MPa and with flexural strength of 0.85–1.01 MPa. © 2022, The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd.Item Modelling Interfacial Behaviour of Cement Stabilized Rammed Earth Using Cohesive Contact Approach(Springer Science and Business Media Deutschland GmbH, 2023) Pavan Kumar Reddy, T.; Pavan, G.S.A monolithic construction formed by compacting processed soil in progressive layers in a formwork is called a rammed earth wall. A lot of applications of using rammed earth walls for both load bearing and non-load bearing can be seen across the world and carbon content is low in this building material. The construction of rammed earth structures involves layered compaction, thus forming an interface between two layers. Modelling of interface plays an important role in the strength and durability of these structures. The interface is modelled using a cohesive contact approach and the response of the rammed earth triplet is obtained. The slope of load vs displacement curve of the rammed earth triplet is 81% accurate with the experimental slope and the peak load of the triplet is 82% accurate with the experimental peak load. Thus, the comparison of load versus displacement obtained from the finite element method with experimental data of load versus displacement yields almost similar results. © 2023, The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd.Item Isogeometric Analysis of Composite Sandwich Plates Using Equilibrium-Based Stress Recovery Procedure(Springer Science and Business Media Deutschland GmbH, 2023) Chethan, J.; Pavan, G.S.Composite sandwich plates consist of a core and face sheets on the top and bottom.Accurate determination of three-dimensional stress states in sandwich plates by numerical approach requires the adoption of 3D finite element (FE) modeling or FE modeling based on layer-wise theories.Though both these numerical approaches give accurate results, they are computationally expensive.This study introduces an equilibrium-based stress recovery approach for determining three-dimensional stress state in composite sandwich plates subjected to transverse loading.This numerical approach is a two-part process, with the initial step based on the concept adopted by layer-wise theories, and the second step is a post-processing procedure.For approximating the unknown field variables, this computational approach employs non-uniform rational B-splines (NURBS).NURBS functions offer the flexibility of a higher degree of inter-element continuity.The study has adopted numerical examples based on the bending of sandwich plates under a sinusoidal load and an evenly distributed load with different edge conditions.Results obtained were compared with the 3D FE method and layer-wise theories and were found to be accurate.In comparison to the 3D FE method and the layer-wise approach, the study reveals that the proposed strategy can provide correct findings with a substantially lesser number of degrees of freedom. © 2023, The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd.Item Deconvolution of Earthquake Ground Motions for Dynamic Analysis of Masonry Gravity Dams(Springer Science and Business Media Deutschland GmbH, 2024) Singhal, U.; Pavan, G.S.The present study aims at deconvolution of earthquake ground motions pertaining to dynamic analysis of masonry gravity dams. Deconvolution is a process that can be used to remove the effects of these distortions and obtain the actual ground motion. Dynamic analysis of masonry gravity dams incorporating soil-structure interaction requires the application of earthquake motion to the base of the foundation. Soil strata up to a depth of three times the height of the dam is generally included in the dam analysis. Deconvolution procedure is performed in this study for different types of earthquake ground motions and different types of soil strata present beneath the dam. In order to perform deconvolution, frequency domain approach is considered. In this frequency domain approach, the recorded ground motion data is first transformed into the frequency domain using a Fast Fourier Transform (FFT). The response at dam-foundation interface is also transformed into the frequency domain, and the two spectra are divided point-by-point. This procedure is repeated until reasonable accuracy is achieved. The deconvolved signal is then transformed back into the time domain using the inverse Fourier transform. This study provides an overview of the deconvolution of seismic ground motion using a frequency domain approach and highlights its importance in seismic research and engineering applications. Also, the importance of performing deconvolution of ground motions is assessed with respect to different types of soil strata lying underneath the dam. © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2024.Item Strength and Durability Properties of Early Cement-Soil Mortar(Springer Science and Business Media Deutschland GmbH, 2024) Teja, K.S.; Pavan, G.S.Looking back at history can inspire new construction technologies and methodologies. Our ancestors used earth as a primary building material, and from prehistoric times, they adopted clever yet simple construction techniques. Mud, which is widely available locally, is a valuable material due to its flexibility in processing and energy efficiency. Mud has been used for construction in India and elsewhere for a long time, and even today, mud wall construction is common in rural parts of India. Although mud is prone to degradation from rain and wind, it is a reliable material with advantages such as affordability, abundance, and good fire resistance. For low-rise and low-cost buildings, mud remains a dependable material. Researchers have discovered methods to enhance mud's quality and durability through stabilization processes to overcome the disadvantages of pure mud construction. In this study, durability aspects of cement-sand-soil mortar are explored. Soil with varying ranges of clay content is considered. Different amounts of cement content are added to obtain different proportions of cement-sand-soil mortar. Durability aspects of mortar that are explored by conducting tests like workability, compressive strength, sulfate-resistance test, acid resistance test, drying shrinkage test, and water absorption test are determined for cement-soil mortar and compared with cement mortar. © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2024.Item Pseudo-Dynamic Analysis of Gravity Masonry Dams(Springer Science and Business Media Deutschland GmbH, 2024) Shalini, S.; Kumar, M.A.; Pavan, G.S.According to USGS estimates, approximately 5 million earthquakes occur annually, of which 1 million are felt. In the north-eastern and north-western regions of India, where the Indo-Australian plate is subducted beneath the Eurasian plate, seismic activity is extremely high. In addition to the immediate damage, an earthquake can cause minor vulnerabilities that lead to future crises. Safety of important infrastructure like dams, bridges, tunnels, elevated structures, and nuclear power plants under earthquake ground motion is critical. In the past 50 years, seismic analysis of dams has attracted considerable research interest. In this study, a pseudo-dynamic analysis of non-overflowing section of a masonry gravity dam is conducted. Invoking plane-strain condition, a 2D model of the dam is developed in Abaqus software. The dam is modeled using four node rectangular elements. The loads at various levels along the dam's height are computed for the fundamental, higher, and static modes. The effects of hydrodynamic forces acting on the dam are also incorporated. The loads are applied separately, and stress analysis is performed. Stress values are combined using the SRSS method, these stresses are compared to the material's strength properties, and the risk factor is evaluated. A comparison of the stresses obtained from FEM model and stresses obtained by considering beam idealization is also presented in this work. © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2024.Item Detection and Visualization of Corroded Surfaces Using Machine Learning(Springer Science and Business Media Deutschland GmbH, 2024) Shrivathsa, B.J.; Dhanya, R.; Meghana Nayak, D.; Pavan, G.S.The use of artificial intelligence in asset management greatly assists the industry and structural health monitoring systems. Using machine learning techniques for asset inspections can increase safety, reduce access costs, provide objective classification, and improve digital asset management systems. The detection and visualization of corrosion from digital images present significant advantages like automation, access to remote locations, mitigation of risk of inspectors, cost savings, and detecting speed. This paper used deep learning convolutional neural networks to build simple corrosion detection models and used an extreme gradient boosting algorithm to visualize the corroded surfaces. A large dataset of 1900 images with corrosion and without corrosion was collected using web scraping techniques and labeled accordingly. Training a deep learning model requires massive and high-resolution image datasets and intensive image labeling to approach high-level accuracy. The results and findings will improve the development of deep learning models for detecting and visualizing specific features on corroded surfaces. © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2024.Item Determination of Effective Properties of Masonry Using FEA-Based Homogenization Approach(Springer Science and Business Media Deutschland GmbH, 2024) Honnalli, S.; Pavan, G.S.Masonry is a widely used construction method. Masonry is typically heterogeneous in nature, consisting of bricks and mortar joints with varying mechanical properties. Thus, masonry will behave like a composite material with orthotropic material characteristics. However, the material heterogeneity of masonry will be ignored in the analysis of masonry structures, assuming it is a homogeneous, isotropic element, which is not true and leads to incorrect assessment. Thus, it is necessary to predict the orthotropic properties of masonry for the accurate assessment of masonry structures. On the other hand, predicting such orthotropic characteristics of masonry becomes a complex task, due to the presence of material heterogeneity. Therefore, researchers adopted numerical homogenization methods to assess the orthotropic properties of masonry. In this study, the FEA-based homogenization method is proposed to predict the orthotropic properties of masonry. Toward this direction, a small periodic part called the repetitive unit cell (RUC) of the English bond masonry prism available in the literature study is considered and modeled in ABAQUS software for the homogenization process. The constituents of RUC are modeled as a continuum element with linear and isotropic behavior. A series of linear stress analyses of RUC has been conducted using six-far field unit strains. The effective orthotropic properties of masonry can be predicted using the stress–strain relationship obtained from the linear stress analysis of masonry RUC. Finally, the results obtained from the numerical homogenization process are validated with the experimental results available in the literature study. © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2024.