PhD Theses (Civil Engineering)

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Understanding the In-stream Eco-morphodynamics of Large Braided River Systems
(2023) Nandi, Ketan Kumar
This thesis focuses on the spatiotemporal variability of sand bar dynamics in the large braided Brahmaputra River from 2000 to 2019 and its impact on the disorderness in the braided belt. A modified normalized difference water index (MNDWI) was used to detect the sand bar area, and an entropy-based intensity disorder index (1D1) was proposed to measure the disordemess of the braided reach. The study found that IDI varied from less than 0.5 to more than 0.9 for the study reach and displayed a declining trend in the first decade followed by an increasing trend in the next decade, indicating large-scale heterogeneity in the process-form interactions in the Brahmaputra. The relationship between IOI, stream power derivatives, and bar area classes was analyzed to understand the geomorphic adjustments. Additionally, the study aimed to understand the spatiotemporal heterogeneity in the vegetation-flow regime of the Brahmaputra using the Google Earth Engine (GEE) platform and advanced geospatial techniques. The results showed a significant increase in moderate and dense vegetation cover in the last decade and its role in the stability of the reach. A stability Trajectory Indicator (STI) was developed to identify the stability state of the braided reach using vegetation as a filter. Finally, experimental studies are conducted on a flume-scale midchannel bar model with different vegetation cover arrangements to demonstrate the process-form-vegetation interaction. The experiments used natural plant forms arranged in a staggered manner in a submerged condition, and the flow-turbulence behavior was observed using a three-imensional Acoustic Doppler Velocimeter (ADV). Results revealed that vegetation structure influences both velocity reduction and momentum transfer at different canopy zones, as well as the shear layer thickness . These findings may aid in a better understanding of channel dynamics near the mid-channel bar and support proper river health management.
Laboratory Study and Constitutive Model Development on Collapse and Torsional Shear Behaviour of Kaolin Under Hydro-Mechanical Loadings
(2023) Srivastava, Ankti
The present study investigated the compression, yielding, and collapse response of two different partially saturated compacted kaolin soils using suction-controlled compression tests conducted. The measured yielding data were validated against the well-known Barcelona Basic model (BBM). A significant discrepancy was found between the model and the measured data. A novel comprehensive model was proposed in this work by considering the wetting-induced changes to the clay fabric associations in compacted soils. The proposed method was capable of predicting three crucial mechanical characteristics, viz., loading-collapse yield, compression, and collape behaviour from the basic compression data at air-dry compaction state. Apart from the collapse characteristics of the clays, the shear strength response is also important for clays under extensive shear deformation in the slope stability analysis. The effect of inundation pressure consolidation pressure, pH of the aqueous solutions, and di-electric on the shear response of kaolin was experimentally investigated. A theoretical framework was developed by including micro-mechanism of clay fabric evolution during the shear and explicit expressions for electrochemical forces. The proposed framework provided useful expressions for predicting the shear strength behaviour of kaolin clays under large deformations, which were validated with experimental data from the present study and literature studies. This work further investigated the volume change response of treated compacted kaolin with sodium-based alkaline solution and sodium silicate as an activator at different concentrations due to inundation. The treated kaolin samples were cured for eight days to allow geopolymerization to take place. The collapse potential of treated kaolin reduced significantly at optimal concentrations of alkali activator solution. Finally, a most effective, simple method was proposed based on laboratory procedure to apply in field to minimize collapse deformations.
Demolition and Filtered Legacy Waste as a Resource in the Manufacturing of Fired Bricks and its Optimization
(2023) Duntsula, Mandefrot Dubale
Brick is the most widely used and oldest type of building material in the history of the construction industry. It is considered the mother of all building and construction materials due to its physical, chemical, environmentally friendly, aesthetic, and mineralogical properties. Brick production is around 1,500 billion tonnes per year on a global scale, and Asia accounts for 87% of all fired bricks manufactured in worldwide. India is the second biggest producer of bricks in the world, accounting for around 13% of total output. Brick manufacturing uses up a significant amount of one of the world's most valuable natural resources: fertile agricultural soil. The manufacture of bricks requires 3 kg of soil for each brick, totaling 720 billion kilograms of fertile soil each and every year. Waste management and resource utilisation in the construction and building materials industries is currently receiving a lot of attention.
Studies of Long High-level Railway Bridges in High Seismic Zone
(2023) Sengupta, Sumantra
Studies of long, high-level railway bridges in seismically active areas are presented in the thesis. For the current study, three different topics have been selected: 1) The response reduction factor (R) of large diameter hollow circular pier section, 2) Asynchronous motion and its impact on tall pier railway bridge response, and 3) The impact of tuned mass damper (TMD) on vehicle-induced vertical response of long span railway bridges. R is significantly affected by the pier's slenderness effect. Therefore, non-slender piers with slenderness ratios less than 50 should use the recommended values. The code recommended single values for similar structural elements are found to be on the higher side in some cases, leading to uneconomic design, and on the lower side in some other cases, leading to unsafe design when compared to the recommended R values for the hollow circular pier under the current study.
Progressive Collapse Analysis And Probabilistic Models For Analysis And Design Of Multi-Storey Buildings Subject To Blast Loading
(2023) Seethayya, Barri Chinna
Concrete and steel rigid frame structures are the most utilised civil engineering structures in building constructions. The rigid frame buildings can experience to blast loads (lateral loads) during their lifetime. This research presents a finite element simulations of charge shapes and their spherical equivalents, the validation of the Multi-Material Arbitrary Lagrangian Eulerian (MM-ALE) approach and the analysis of an RC frame subject to internal blast loading. This research develops a novel quadratic blast profiles and response spectra for both quadratic and exponential profiles, and presents the numerical validation of blast profile. This research also develops the multi-storey rigid frame structures' critical load factors analysis, probabilistic models of critical load factors, and the peak loads of multi-storey buildings, and presents their validation. This research also presents the dynamic analysis of multi-storey buildings subject to blast loading, eigen modal analysis, generalised equation of motion, development of modified shape function, and validation of the modified shape function. This research illustrates the framework for designing multi-storey buildings subject to blast loading and the member design approach, equivalent SDOF design method, and multi-storey building design procedure. This research also presents the methodology and framework to quantify the required resistance of multi-storey buildings to mitigate progressive collapse. This research also develops the probabilistic models for collapse resistance factors for the series of top and bottom column removal in the multi-storey buildings. Finally, this research presents a simple, accurate and probabilistic framework for the analysis and design of multi-storey building subject to blast loading. The MATLAB code is used to develop the quadratic blast profiles. The SAP2000 and LS-DYNA softwares are used to carry out the simulations of RC frame subject to blast loading. The OriginPro is used to develop probabilistic models of progressive collapse resistance and peak load factors. The limitations of building shape function, peak loads of multi-storey buildings, the charge shape and progressive collapse methods are addressed to enhance the blast resistant design techniques. This study is limited to the rigid frame multi-storey buildings subject to blast loading only.
Flow Characteristics in Multi-Layered Vegetated Channels
(2024) Barman, Jyotimoy
Riparian vegetation plays a crucial role in determining the flow behavior in the channel. The effect of flow on the slope and main channel varies based on the size, type, and density of floodplain vegetation in a compound channel. Though vegetation distribution in different water bodies is non-uniform, most studies mainly concentrate on uniformly distributed vegetation with fixed vegetation height. Laboratory studies were conducted to address this issue as it was not explored properly. Experiments were performed by taking partially vegetated rectangular channels and compound channels. Rectangular channels were considered to compare flow between homogeneous height/single-layered partially vegetated channels and heterogeneous height/multi-layered partially vegetated channels. Compound channels of three bank angles, namely 310, 450and 900 were considered with vegetated floodplains.
Numerical and experimental studies to determine the subgrade soil resilient modulus using the RLCBR test
(2023) Kaushik, Supratim
Subgrade characterization in terms of resilient modulus is an important aspect of mechanistic pavement design methods. The resilient modulus is analogous to the Elastic modulus; however, repeated loads are applied instead of monotonic load and is expressed as the ratio of deviatoric stress to the resilient strain. The most commonly used laboratory method to determine resilient modulus is the Repeated Load Triaxial Test (RLTT). However, the test is complex, requires expensive test setup, skilled personnel and is time-consuming. Therefore, an alternate simple and cost-effective method for subgrade resilient modulus characterization using the simple CBR apparatus has been explored in this study. This study aims to characterize the subgrade resilient modulus using the Repeated Load CBR (RLCBR) test and compare it with the field modulus. It combines numerical modelling of the CBR test, with laboratory studies using the Repeated load CBR (RLCBR) test to propose methodologies and predictive models to characterize the subgrade resilient modulus using the RLCBR test. A 3D Finite Element Model of the CBR test was formulated in the commercial package LS-DYNA® to understand the mechanics of the test. The objective was to obtain mathematical relationships between the octahedral shear stress and the bulk stress with the plunger stress, which can be measured experimentally. Results showed that a linear relationship between the bulk stress and octahedral shear stress with the plunger stress can be assumed under elastic conditions. A total of twelve soils were tested in the laboratory in the present study. RLCBR tests were conducted on all twelve soils in deformation-controlled mode and five soils (out of twelve) in load-controlled mode. The deformation-controlled RLCBR tests were used to standardize the test and propose a predictive model which estimates the subgrade resilient modulus at stress levels typical of a subgrade soil element.Results showed that the proposed RLCBR model agreed with the modulus calculated at the recommended stress levels using the MEPDG model. Further, statistical analysis of the proposed model showed that the model could capture the effects of moisture on the resilient modulus. In contrast, the load-controlled test results were used for stress-based non-linear elastic characterization of subgrade soils. The results showed that the proposed methodology predicted the MEPDG model coefficients with an R2> 0.8 for all the cases. Further, the model coefficients were validated with those obtained from empirical correlations and showed promising agreement. The proposed methodology can be cost-effective in characterizing resilient moduli for MEPDG Level 1 applications. The laboratory resilient modulus was compared with the field resilient modulus determined using the Light Weight Deflectometer and the Dynamic Cone Penetrometer (DCP) tests. The laboratory-resilient modulus was much higher than the field modulus obtained using the DCP and the LWD due to variations in field and laboratory moisture-density conditions. However, it was also observed that as the moisture and density conditions were nearer to the laboratory conditions, the RLCBR and field modulus approached each other. The comparison assessment of the field and RLCBR test results suggest that a reference modulus from the laboratory RLCBR test can be used to evaluate the construction quality in the field in terms of modulus in addition to traditional density checking. Hence the resilient modulus prediction model developed using RLCBR, a quick and simple test, could provide more inputs to design and quality control characteristics in the field for constructing subgrade soils.
Groundwater Dynamics in Hardrock-dominated Headwaters Regions of Paschimi Nayar River, Mid-Himalaya through Assessment of Stream Flow, Spring flow and borehole data
(2023) Tarafdar, Soukhin
Small basin research has contributed significantly to the process based understanding of internal functioning of the catchments. In this study, two microwatersheds of area < 10km2 and a small hydrological response unit (HRU) (< 0.4km2) nested within one of experimental microwatershed are being investigated through hydrological instrumentation in terms of rain gauges, water level recorders at the outlet for continuous stream gauging as well groundwater level measurements in shallow and deep fractured bedrock aquifers in the smallest HRU to better understand the hydrological functioning in the headwater regions of Paschimi Nayar Basins. The precipitation variability of ISM during 2009 to 2018 period showed inter-annual variability with drought, intermittent multiple deficient rainfall periods and normal monsoon rainfall years. Analysis of long-term records of spring flow through flow duration curve indicates a significant reduction in lowflows as well as high flow periods. Recession curve analysis using single non-linear and two exponential linear reservoir models for the recession period indicate an overall non-linearity in storage-discharge relationship. A parallel offset was observed between years in yearly-prolonged post-monsoon recession curve in -dQ/dt verses Q plot indicating the control of antecedent storage over rate of outflow. Shallow piezometer (< 4 m) and deep borewell (< 80 m) monitored over two monsoon period indicate a rapid response to any rainfall amount exceeding 5mm. The episodic recharge and water level fluctuation method indicate a monsoonal recharge of 4% to 24% for a low specific yield value (1 to 5%). The study also highlight that effectiveness of recharge is controlled by the rainfall intensity.
Characterizing Dam Augmented Flow in Downstream of a Hydropower Project to Assist Management Strategies
(2023) Devi, Dipsikha
The recent increase in human activities, such as the construction of dams along rivers, has led to significant hydrological changes in downstream regions. A significant effect of dam construction is the disruption of natural flow patterns leading to erratic water levels, seasonal fluctuations, and sporadic sediment transport. This study introduces a modelling framework to analyze the downstream flow impact of hydropower dams. The framework comprises both a reservoir operation model and a hydrodynamic model. A comprehensive investigation was undertaken to assess the hydropower dams' influence across the entire water year. Moreover, a detailed examination was conducted to characterize the outflow hydrographs from Inter Basin Water Transfer (IBWT) and Non Inter Basin Water Transfer (NIBWT) hydropower dams. For NIBWT hydropower, Lower Subansiri Hydropower Project is considered for the analysis. Results showed that with the presence of the dam, the flashy characteristic of the outflow hydrograph increases. Thus, dam-induced flood is a combination of regional flood as well as flash flood. Based on the statement ranking of the dam-induced flood was provided among the global hazards considering the factors suggested by Bryant. To assess the flow contribution by the ungauged tributaries downstream of the dam, a streamflow generation module was developed using the Drainage Area Ratio (DAR) incorporated into the developed model and applied in the operational IBWT hydropower project.
Thermal and Strength Characteristics of Soil-Biochar-Biopolymer Composite Backfill
(2023) Patwa, Deepak
Thermal backfill is essential for underground crude oil pipelines, crude oil storage tanks, and geo-energy storage units. The major function of such backfills is to prohibit heat migration from the source as well as sub-structural stability. Often the thermal characteristics of locally available soils are not adequate for thermal backfill applications. Hence, it is required to modify the native soil by amending it with appropriate materials that possess suitable thermal characteristics and provide enhanced sub-structural stability. Biochar is a low thermal conductive, highly chemically stable, and eco-friendly material and has the potential to mitigate heat loss and may increase soil strength. However, the thermal characteristics of soil-biochar composite (SBC) in the compacted condition in view of applying it as thermal backfill material have largely been unaddressed in literature. Therefore, this study aims to explore the possibility of biochar-based soil composite as thermal backfill material. In the current study, two types of locally available soil and three types of biochar (hardwood biochar, water hyacinth biochar, and sugarcane bagasse biochar) are used to investigate the applicability of SBC as thermal backfills. The experimental results revealed that the SBC has lower thermal conductivity and volumetric heat capacity compared to bare soil under dry, wet, and near-saturation conditions. However, the UCS of soil also reduces with biochar amendment, which depends upon soil type and particle size fractions. To overcome this, a biopolymer-based stabilization technique is used to make it a high-strength sustainable biochar-biopolymer-based composite thermal backfill that is capable of providing efficient thermal insulation and strength. The findings of this study establish the synergistic attributes of biopolymer and biochar amendment for developing a high-strength and low thermal-conductive soil composite. A bench-scale study on the thermal insulation efficiency of SBC and soil-biochar-biopolymer composite (SBPC) in terms of heat transfer was conducted to facilitate field-scale applications. The SBC and SBPC exhibit lower temperatures than bare soil at all radial distances. The temperature difference between bare soil and SBC varies from 4 to 20 °C. A pyrolysis temperature of 400ºC is determined to be a suitable temperature regardless of the feedstock type because of the least energy consumption, considerable yield, required thermal characteristics, and carbon stability for the design period. The finding from the current study unravels the potential of biochar-based thermal backfill to restrict heat transfer from energy storage facilities.
Development of Speed Based Consistency Evaluation of Four-Lane Highway Geometry Using Naturalistic Driving Data
(2023) Nama, Suresh
India has experienced rapid growth in its infrastructure, including the expansion of two-lane to four-lane highways and the construction of new four-lane highways in mountainous terrains. However, the safety of these highways has not kept up with their development. In 2019 alone, there were over 1,80,000 fatalities due to accidents on Indian highways mainly over curves. To address this issue, a study was conducted on a 65km four-lane highway in mountainous terrain to understand driving behavior and improve safety. Data was collected from GPS equipped passenger cars driven by various drivers, revealing that the highway covered 285 horizontal curves with varying design speeds, curve lengths, vertical gradients, and superelevation. The data showed that most drivers were traveling above the design speed, and operating speeds varied across curve from point of curvature (PC) to point of tangent (PT), indicating the need for separate four-lane consistency criteria. To evaluate the safety of mountainous terrain four-lane horizontal curves, two safety criteria were developed: Speed Synchronization (SS) and Speed Harmony (SH), which consider the variation in speed across the curve. The SS criterion evaluates safety based on speed variation between successive locations within the curve, while the SH criterion evaluates safety due to variation in operating speed from the curve design speed. These criteria were used to develop a new speed-based geometric design for four-lane highways, which, along with vehicle dynamics, can be used to evaluate the safety of existing four-lane curves. Geometric parameters influencing drivers speed over four-lane horizontal curves were also identified, including tangent length, gradient, curve length, and deflection angle. A continuous percentile speed distribution model was developed to accurately predict any percentile speed across the four-lane highway alignment using ANN machine learning models. In addition to improving highway safety through design and warning systems, the study also developed a three-level over-speed warning system using operating speed (V85) and design speed (V95) to assist drivers in identifying upcoming hazards. The studies outcomes have several benefits, including the ability to predict percentile speed values using the developed speed models to evaluate highway safety and design, overcoming the limitation of uniform speed assumptions across curves, improving four-lane highway geometric design on mountainous terrains, and enhancing driver safety through the over-speed warning system.
Novel Investigations on Potential of Balanites Aegyptiaca and Sesamum Indicum for Surfactant Preparation and Application in Foam Concret
(2023) Selija, Khwairakpam
Synthetic surfactants commonly used in foam concrete production is reported to exhibit serious environmental threat. Hence utilization of natural surfactants could present new sight in improving the environmental impact of foam concrete. However, studies on valorization and extraction of natural surfactants from different plant and animal sources for use in foam concrete is very scarce from Indian context. Considering the above facts, the current study aims to use natural surfactants valorized and extracted from two different biological sources, namely sesame seed (rich in protein) and hingot fruit (rich in saponin) as prospective supplementary alternative to conventional synthetic foaming agents in foam concrete production. Balanites aegyptiaca also known as hingot is found all over the world and studies on phytochemistry of various parts of plant indicate that fruit, seeds and bark part of plant has 22-27% of saponin. Adding to above, excellent plant's adaptability, high yield features and abundant availability are other added reasons for selection of this plant for this study as it can add economical as well as environmental benefits. Another plant source used for surfactant extraction in the present study is Sesamum indicum commonly known as sesame seed. Studies have proved that sesame seed has rich protein content of 20 to 25% and hence has excellent potential foamability. Despite the huge potential foamability of above surfactants (sesame and hingot), it is surprising to find that to date, its potential has not been assessed for use in foam concrete production. The first phase of present study comprises of the optimization of surfactant extraction and foam production processes through systematic experiment design based on response surface methodology (RSM). The possible response surface models have been developed for prediction of various foam and surfactant characteristics such as initial foam density (IFD), foam stability, foam bubble size and viscosity of surfactant solution. The validity of models is tested by ANOVA and verified experimentally. Analysis of influence of various input parameters on responses indicated that surfactant concentration has significant effect on all the responses studied. Further the parameters associated with heating process (heating temperature and duration) also have substantial influence on various foam and surfactant characteristics as it promotes the hydrolysis of protein and saponin. The obtained results established that increase in surfactant concentration, heating temperature and heating duration resulted in increase in viscosity of surfactant solution eventually leading to reduction in foam liquid fraction, foam drainage and bubble size. Hence good correlation is established between above mentioned foam and surfactant parameters. Furthermore, performance of surfactants in foam cement paste was assessed and ASTM requirements are found to be met confirming foam stability. The outcomes of the present study could help the industry to gain confidence in the usage of recommended natural surfactant for foam concrete production.
Experimental and Numerical Evaluation of Flow beneath Mini Disc Infiltrometer for Estimating Wetting Characteristics of Soils
(2023) Naik, Aparimita Priyadarshini
Precise determination of soil water infiltration and sub-surface water movement is essential for developing soil-water management practices. For modeling flow and transport in the sub-surface zone and unsaturated porous media, the knowledge of the wetting hydraulic properties, including, water retention characteristics curve (WRCC) and soil hydraulic conductivity functions (SHCF), are critical. This study evaluated the potential of mini disc infiltrometer (MDI) measurements for characterizing wetting soil hydraulic properties using both laboratory and field measurements and various soil textures. It analyzed the influence of tension head and initial soil conditions on estimated parameters from MDI measurements, evaluated time dependence on transient analysis from MDI, and compared MDI measurements with other established devices. In addition, with the help of independent measurements and inverse modelling, it demonstrated the utility of MDI for rapidly and effectively characterizing the WRCCs and SHCFs from laboratory measurements. This study demonstrated that MDI is a useful, non-intrusive, and non-invasive tool for characterizing soil hydraulic properties, with important implications for improving our understanding of infiltration at the soil surface and redistribution, and further movement of soil water in the vadose zone.
Data-Driven and Machine Learning Frameworks for Condition Assessment of Plate Structure using Elastic Waves
(2024) Kalimullah, Nur Mahammad Mussa
The evolving domain of structural health monitoring (SHM) is crucial for ensuring the integrity and extending the service life of engineering structures. This thesis presents a suite of data-driven and machine learning frameworks developed to enhance the condition assessment of plate structures, particularly focusing on the complexities of piezoelectric materials and anisotropic composites. In a comprehensive exploration of data-driven and machine learning frameworks for assessing the condition of plate structures, this dissertation presents a series of interconnected studies, each contributing to the advanced insights and application in SHM, particularly focusing on piezoelectric materials and anisotropic composites.
Studies on Enhancement of Stability, Rheology, and Mechanical Performance of 3D Printable Foam Concrete
(2024) Uday, Boddepalli
Multifunctional properties are a requirement due to the increasing need for the thermal resistance, acoustic insulation, fire resistance, and etc. for the modern construction. Nevertheless, the material must be both mechanically sound and porous in order to fulfil these requirements. One such concrete that satisfies the demands of modern building is foam concrete (FC). FC is a cellular concrete produced using binder, fine aggregate or filler, foam and water as ingredients. Proper control in dosage of foam can result in wide range of densities ranging from 300 to 1800 kg/m3. FC is a unique, non-structural and low-cost light weight concrete with special properties such as low density, high acoustic insulation, low thermal conductivity, high energy absorption capacity, good fire resistance, and good freeze and thaw resistance. The aforementioned properties of FC are mainly dependent on the microstructure of FC which is influenced by the foam production parameters (air pressure, type of foam generator), foam stability (drainage, density, size, shape, and etc.) and surfactant characteristics (type of surfactant, viscosity, surface tension, and etc.). FC has an extensive spectrum of demands to satisfy an array of applications.
Optimal Crop Planning in A Canal Command Area with Due Emphasis on Nutrient Balance and Climate Change
(2023) Debnath, Mridusmita
Rainfed agriculture plays a vital role in providing food and livelihoods globally. However, its production is adversely affected due to uncertainty in rainfall patterns which is increasing under the impact of climate change. Supplemental irrigation helps minimization of risk thus stabilizes the crop yield. Given that rice is a primarily grown crop in rainfed conditions and is the staple food of half the global population, it is under the pressure of increasing production due to the burgeoning population globally. Therefore, proper farming management such as balanced fertilization practices, irrigation etc are required. On the other hand, monocropping of cereal is a growing phenomenon among the farmers, due to known yield, reduced investment, prior knowledge of the activity calendar, insufficient irrigation and lower market risk resulting in a rice-fallow cultivation system. However, the introduction of pulses, oilseeds and vegetable crops during the fallow season is the key to providing better nutrition and improving household food security. Thus, irrigation water management is required for maximizing yield of these crops during the fallow season.
Studies on Restrained Steel Beams and its Material Characterization Under Heating and Cooling Fire
(2023) Mushahary, Suman Kumar
This thesis presents results from material level experimental tests on E350 steel and 10.9 grade level bolts as well as numerical studies on steel beams having an I shaped cross-section. The experimental program comprised of subjecting specimens to monotonic heating as well as heating followed by cooling scenarios to simulate natural conditions as expected during fire exposure. Post—fire properties were evaluated as part of the experimental studies as well. The results from the experimental program were used to derive temperature dependent mechanical properties of E350 steel during heating, cooling, and residual conditions of fire exposure. These results were then combined with studies published in literature to propose reduction factors in mechanical properties of E350 steel. Similarly, results from experiments conducted on tensile and shear capacity of 10.9 grade bolts during heating, cooling and residual phases are presented. A three-dimensional numerical model of a steel I beam was developed using general purpose software Abaqus. The numerical studies were focused on predicting evolution of axial (catenary) forces that develop in the steel beam for varying support conditions (restraint levels) and load levels. The mechanical properties derived for the heating and cooling phases through experimentation were applied in this numerical model. Furthermore, the axial (catenary) forces that develop during heating and cooling phases of fire exposure were predicted with the help of the numerical model. A parametric study was conducted using the validated numerical model. An analytical model to calculate the catenary forces and critical temperature of the beam for design purposes is also proposed.
Snow/Glacier Dynamics of Himalayan Ranges and Associated Hazards
(2023) Mondal, Sandeep Kumar
The Himalayan cryosphere, also termed “the Third Pole, " acts as a natural storehouse to several mega river systems, such as the Ganges, Indus, and Brahmaputra, serving billions of people with fresh water. However, the high mountain ranges of the Himalayas are also susceptible to various categories of hazards, such as snow/rock-ice avalanches, landslides, earthquakes, and glacial lake outburst floods (GLOFs). The present study attempts to perform a series of investigations to better understand the dynamics of snow/glaciers in the Himalayan region and their contribution to perennial river streams. It also includes studying the major types of Himalayan hazards that have occurred in the recent past.
Assessment and Modelling of River Water-Sediment Pollution Load based on Spatial and Temporal Variations
(2022) Goswami, Ankit Pratim
This doctoral thesis attempts to understand the interrelationship between the two critical components of river ecosystem, i.e., its surface water and benthic sediments, as sediments are said to source and sink many contaminants in a river. In order to fully understand the aspects of the river ecosystem, the study has been divided into five objectives to get a better understanding of pollution load in surface water and benthic sediments, their sources and the need for monitoring and treatment. In the first part of Objective I, a survey of the probable catchment area of the river was carried out to select the sampling locations from which surface water and benthic sediment samples were collected. Sampling and analysis of surface water were carried out for 21 parameters at 18 different sites, whereas sampling and analysis of benthic sediments were carried out for 9 parameters, particularly heavy metals, at 9 different sites. The analysis of surface water samples revealed that with respect to pollution load, heavy metals present a higher risk to the consumer of surface water of Kolong river. The aim of the second part of Objective I was to use the analysed surface water samples to evaluate the drinking water quality using fuzzy logic and information entropy. Fuzzy logic based index, i.e., fuzzy water quality index (FWQI) results are more stringent than information entropy based index, i.e., entropy weighted water quality index (EWQI), as it is more sensitive to parameter variation. The aim of Objective II was to assess the benthic sediment quality or load in the river using total metal concentration and metal speciation fractions based indices. Total metal concentration based indices include geoaccumulation index (Igeo), pollution load index (PLI), enrichment factor (EF), potential ecological risk of individual metal (Eir), potential ecological risk index (PERI), and metal speciation fractions based indices, include pollution index (IPOLL), mobility factor (MF), individual (ICF) and global contamination factors (GCF), modified ecological risk index (MRI). After comparing both types of indices, it was found that the speciation-based index quantifies the risk associated with heavy metal contamination better as the indices developed using this approach gave consistent results and gel well with the variation of the
Global Damage Indices for RC Structures: A Numerical Response-Driven Training Approach
(2024) Naskar, Subhadip
Any seismic damage index model can be used to compute earthquake-induced structural damage of a building. Most researchers prefer combined damage index models (e.g., modified Park and Ang-type damage indices) due to their ability to consider the effect of both maximum and cyclic deformations on structural damage. All such combined damage models require section-level responses through nonlinear time-history analysis and cannot compute the global damage index (GDI) using global-level responses alone. Utilising the structural dynamic responses recorded by modern sensors, there is a scope for developing a new combined GDI evaluation method which uses such recorded data and avoids the requirement of numerically obtained sectional responses. On the other hand, the acceptability of the computed damage of a building utilising any damage index model through the output of a representative finite element model depends on the authenticity of the experimental data with which the finite element model is calibrated. The lateral output of any finite element model is usually calibrated with experimental results of axially loaded cantilever columns subjected to unidirectional horizontal quasi-static loading. For most of the conventional experimental setups, the true lateral behaviour of a cantilever column is altered because of the undesirable orientations of the actuators and the fixing arrangements between the actuator heads and the column tip. Therefore, the results obtained from such experiments must be rectified to generate true lateral load-deformation behaviour before being used directly for the calibration of any finite element model. Many previous research works also emphasised the need to rectify such experimental data. Therefore, a novel mechanics-based formulation to reproduce the true lateral load-deformation curve of cantilever columns from experimental data and a novel combined GDI evaluation method incorporating recorded floor-displacement responses for instrumented RC buildings during any seismic event are explored in the present study. Using the new GDI evaluation methodology, four different GDI formulae based on either displacement ductility or curvature ductility of columns are introduced to estimate the damage to 2D frames and 3D buildings. Explicit expressions of global damage coefficients available in those formulae are formulated in terms of some basic structural properties and local soil conditions. For wider applicability of the new GDI formulae, the limiting ranges of computed GDI values associated with post-earthquake restoration-based different global damage states (e.g., no damage, repairable, irreparable and collapse) are also studied

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