PhD Theses (Civil Engineering)

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Fuzzy neural network modelling for hydrological studies
(2003) Deka, Paresh Chandra
Water resources related studies involve variables, which are highly random and uncertain in nature. Most hydrological variables exhibit a high degree of temporal and spatial variability. These studies are very essential to the mankind for providing a warning of the extreme flood or drought conditions and help to optimize the operation of systems like reservoirs and power plants etc. For better hydrological design, we need proper modelling of the system using these variables. Many approaches were suggested in the past. In this research study, a new modelling approach that uses artificial neural network and fuzzy logic concepts together is proposed for modelling hydrological problems.
DEVELOPMENT OF OPTIMAL OPERATING POLICY FOR PAGLADIA MULTIPURPOSE RESERVOIR
(2004) Ahmed, Juran Ali
Pagladia multipurpose reservoir, located on the river Pagladia, a major north bank tributary of Brahmaputra, proposes to serve three purposes, namely, flood control, irrigation and power generation. In order to achieve these, a proper operating policy of the reservoir is imperative. Recent researches have revealed the potential of heuristic methods in deriving reservoir-operating policy. In this study, the potential of Genetic Algorithm (GA) and Artificial Neural Network (ANN) in deriving an optimal operating policy has been explored through their application in the Pagladia multipurpose reservoir. Efficiency of the policies derived by these recent techniques has been assessed through their critical comparison with policies derived by some long-established techniques. To have the advantage of using a long streamflow series in the development of a reservoir operating policy, an ANN based synthetic streamflow generation model has been developed and compared with the Thomas-Fiering and Autoregressive Moving Average (ARMA) models. Synthetic streamflow series generated by the ANN based model has been used in the development of operating policies, as its statistics have been found to be in better agreement with those of the observed historic series. For solving the reservoir optimization problem for Pagladia multipurpose reservoir, deterministic Dynamic Programming (DP) has first been solved. Both multiple linear regression and ANN have been used to infer general monthly operating policy from the DP results, and these models are being termed as DPR and DPN models respectively in this study. Stochastic Dynamic Programming (SDP) model, which uses an explicit stochastic optimization technique, has been developed next for deriving monthly optimal operating policy for the Pagladia multipurpose reservoir. Finally, GA, which is of recent origin and has the capability of solving complex optimization problem, has been used to derive optimal monthly operating policy for the reservoir. Performance of all the operating policies developed by different models has been analyzed on the basis of the reservoir simulation results for 228 months of historic streamflow series (1977-1996). For making a fair comparison among all the models, a total of eight performance criteria covering different aspects of reservoir operation, have been used. The study has shown that GA, which is a robust optimization technique, is quite capable of developing multipurpose reservoir operating policy and has been found to give the most efficient operating policy for the Pagladia multipurpose reservoir. Policies derived by SDP and GA have been found to be competitive in respect of some of the performance criteria. GA out performs the DPR and the DPN models developed in this study. Although performances of different models vary with different performance criteria, considering overall performance and giving priority to irrigation, the application of operating policy derived by GA model has been suggested to be the most appropriate for the Pagladia multipurpose reservoir.
Geotechnical and environmental performance of residual lateritic soil atabilised with fly ash and lime
(2004) Goswami, Rajib Kumar
Application of fly ash for soil atabilisation has been the focus of many researchers due to its role in facilitating pozzolanic reactions and the possibility of bulk utilisation. Residual lateritic soils, with typical inherent properties, exhibit a number of constructional difficulties related to their workability, field compaction and strength that may be overcome with fly ash stabilisation. The present research was aimed at understanding the behaviour of a highly weathered residual lateritic soil modified with fly ash and lime, with respect to their geotechnical and environmental performance. Preceded by the study of physical and chemical properities of the axperimental soil and fly ash, a series of investigation were conducted to study the effects of particle aggregation upon drying as well as grain size distribution on the index and compaction properties in order to finalize ...
Dynamic response of ageing concrete gravity dams with unbounded reservoir
(2006) Gogoi, Indrani
The assessment of response of an aged concrete dam is important for the prediction of its behavior during earthquakes, so that remedial measures can be taken at the right time to withstand future earthquakes. The Assassment is necessary, as the analyses procedures may become obsolete and the state of the art may change since the time of construction and the structural material may deteriorate due to harsh environmental conditions. At the same time, the sediment will be accumulated at the reservoir bottom on the upstream side of the dam. The decision of retrofitting or strengthening the aged dam necessitates accurate analysis....
Response of Horizontally Curved Thin-Walled Box-Girder Bridge to Vehicular Loads
(2006) Nallasivam, K.
The curved girder bridges have become popular due to the increased demand for curved roadway alignment for the smooth discrimination of congested traffic along with advancement in fabrication and creation technology...
Simulation of Dam Break Hydraulics in Natural Flood Plain Topography
(2007) Saikia, Mimi Das
Catastrophi floods caused by dam failures always lead to a great amount of property damage and even loss of human and wild life. several dames are proposed in north east region of indi, to harness the existing hydropower to facilitate electricity. irrigation, water supply, navigation, recreation and to achieve flood and erosion control. while multi-objective dam can provide immense benefite, its failure or improper operation may lead to devastating flood downstream. one of the ....
Updating of finite element model of cable-stayed bridges for improved dynamic characteristization and active seismic response control implementation
(2007) Dutta, Atanu Kumar
The present work deals with the model updating of two cable stayed bridges,viz, the Quincy Bayview bridge of Illinois, USA and the Bill Emerson Memorial Bridge, Missouri, USA and subsequently studies on active response of these bridges subjected to seismic excitations have been carried out. The finite element models for both the bridges have been updated so as to reproduce the experimentally observed modal characteristicsto the closest possible extent....
Study of rheological behavior of high performance concrete
(2008) Laskar, Aminul Islam
High performance concrete has become indispensable in construction of modern high rise buildings, long span bridges, nuclear structures, off shore structures and in many other applications. This is generally preferred for high strength and high durability. To achieve these objectives, production of concrete should be given due consideration in terms of proper workability. Principles of fluid rheology have been found to describe workability of high performance concrete in a more scientific way than conventional empirical rules do. Rheology of fresh concrete is recognized as difficult subject due to the fact that concrete is a complex material with time dependent properties and includes wide range of particle sizes. It has been found that concrete can be considered as Bingham fluid with good accuracy where flow is described by two parameters: yield stress and plastic viscosity. Two types of rheometers viz. coaxial and parallel plate type are in use to determine rheological parameters of cementitious materials and concrete. While the rheometers for cement pastes and cementitious material are more or less established in terms of its functioning, concrete rheometers still today present challenge in design and operation because of large size of coarse aggregate. The present study undertakes the design and construction of a new rheometer with parallel plate geometry. Frictional resistance between concrete and vertical wall of cylindrical container has been taken into account while deriving expression for total torque. Measures have been taken to prevent wall slip by providing ribs in the cylindrical container of the rheometer. Concrete is subjected to torsion where the shear rate is not uniform in all areas of material. This non-uniform variation of shear rate has been taken in to account while deriving the expression for the torque. For practical use, shear stress versus torque and overall shear strain rate versus rotational frequency relationships have been established for the given geometry of the rheometer. Calibration of torque in the present rheometer has been performed by rotor blocking method. Calibration of torque was validated by testing a magneto-rheological fluid (MRF 132DG) with the present rheometer and comparing these test results with the results independently obtained by HAAKE RS1 rheometer. It was observed that measured values of MRF properties by the present rheometer and HAAKE RS1 are comparable. Repeatability of the tests has been judged by statistical approach. The presently developed rheometer has been used to investigate rheology of high performance concrete without using any mineral admixtures and then using different mineral admixtures and steel fibers. In concrete without mineral admixtures, experiments have been conducted to examine the influence of some basic parameters such as percentage sand, aggregate gradation, chemical admixture dosage and elapsed time on rheological properties of high performance concrete (HPC). It was observed that different parameters affected rheological parameters in different manners. Optimum values exist for percent sand, sand zone and HRWRA dose. It was also observed that, in addition to water-cement ratio, cement paste volume/aggregate volume ratio affect the rheological parameters of concrete.
Water quality modeling in an untreated effluent dominated urban river
(2008) Girija, T.R.
The procedure presented builds a bridge between computational intelligence and ecologic modeling by aoolying fuzzy rule-based model, artificial neural network, multiple linear regression for the prediction of dissolved oxygen which is one of the most important water quality indicators in an urban tributary of river brahmaputra, assam, india The study was aimed at evaluating application of three data- driven models in predicting dissolved oxygen and developing an ANN-based Do management strategy. by analyzing the key physical, chemical and biological parameters for samples drawn from key location, an assessment of the dissolved load and pollution levels at different segments in the river was made.
(A) STUDY ON PERFORMANCE IMPROVEMENT OF EXPANSIVE SOIL USING RESIDUAL SOIL AND LIME EXPANSIVE SOIL USING RESIDUAL SOIL AND LIME
(2009) Hussain, Md. Monowar
The soils which show volumetric changes due to changes in their moisture content are referred to as expansive soils. With increase in moisture content, these soils swell and with decrease in moisture content undergo shrink. This leads to seasonal movements causing heave in rainy season and subsidence in summer, giving rise to high differential settlement in the structures founded on them thereby causing distress and damage to it. Stabilization of expansive soils with additives has been used with great success. In the recent past several investigations have been reported highlighting the beneficial use of lime for performance improvement of clay soils (Davidson and Handy, 1959; Thompson, 1966; Bhasin, 1978; Bell, 1988; Sivapullaiah et al., 1998, 2000; to name a few). In spite of these studies there is still need of further investigation to understand the mechanism of lime induced modifications of soils more clearly. From literature review it is observed that lime generally improves the performance of clayey soils in terms of reduced swelling and increased strength. However, in some cases, depending on the type of soil, amount of lime added, curing period etc. the performance improvement reduces. In view of this an attempt is made to carry out a systematic study through careful variation of above parameters, to develop an understanding of the mechanisms involved.Primarily an expansive soil (ES) and a residual soil (RS) that represent the extreme types of soil are used in the present study. The non swelling and high strength residual soil was added to the expansive soil to improve its performance. Besides to cover a wide range of plasticity these two soils are mixed in different proportion (i.e. 100%ES, 80%ES + 20%RS, 60%ES + 40%RS, 40%ES + 60%RS, 20%ES + 80% RS, 100%RS) to prepare six different soil samples. Subsequenty these soils were treated with lime of varied quantity under varied curing period. The test results indicate that the liquid limit continues to reduce till 3% lime content, beyond which the increased lime content has marginal effect on it. However, at very high lime content (i.e. 13%) and long curing period (i.e. 28 days) the liquid limit of the expansive soil has shown an increasing trend. This increasing trend gradually grows more prominent with increased percentage of residual soil and curing period. It is of interest to note that irrespective of soil type the liquid limit is large for increased curing period. The plastic limit increases with increases in lime content. The increase is relatively faster till lime content reaching about 3%. From 3 to 5% of lime content the rate of increase in plastic limit is relatively slow. Beyond 5% lime content visible increase in plastic limit is noticed only for increased percentage of residual soil and higher curing period. In general soils have shown an immediate decrease in plasticity index upon addition of lime. For 100%ES, increasing the lime content beyond 5% had a marginal effect in further reducing the plasticity index. This is in line with earlier observations that immediately upon addition of lime the liquid limit reduces and plastic limit increases. In general the plasticity index increases with increase in curing period however it is more prominent for the increased percentage of residual soil. This is attributed to the silica gel that enhances the...
Application and evaluation of amine based polymers for heavy metals adsorption and recovery from wastewater
(2009) Kumar, Potsangbam Alibion
The impact of heavy metal pollution on environment due to industrial effluent is a global concern. adsorption technique is one of the well proven metal removal techniques due to its several advantages over conventional methods like simple and easy operation, low cost, recovery of metal ions etc. Employment fo functionalized polymers containing several functional groups such as amines, carboxylate, ether, hydroxyl, sulphate, cyanide, chloride, acetate etc., as adsorbent for removel of metal ions has become a recent trend. However many of the reported functionalized polymers have complex synthesis procedure and cost ineffective. Therefore development of low cost functional polymer with easy synthesis procudere, moderate to high metal removal, rapid adsorption kinetics and reusability is necessary...
Batch and Column adsorption studies for simultaneous removal of Iron. Arsenc and Fluoride by Wooden Charcoal and river sand used as filter media in Indigenous Household Iron filter Units of Rural and semi-Urban Assam(India) : Author
(2010) Ahamad, Kamal Uddin
Groundwater is the major source of domestic water for people living in rural and semi-urban area of Assam D a northeastern hilly province of India. However, it contains excessive amounts of fluoride (F-), arsenic [As(III)] and iron [Fe(II)] D much higher than the permissible limits of drinking water. The rural and semi-urban population of Assam use different variants of indigenous household iron filter units D developed over last few generations using locally available materials such as community prepared wooden charcoal (CPWC) and river sand (RS) to reduce concentration of Fe(II) from the groundwater. No efforts are being made by the rural and semi-urban population to reduce concentrations of FD and As(III) from the groundwater before using it. Research efforts of past few decades have yielded many techniques and methods to remove Fe(II), FD and As(III) from groundwater in developing countries including India which have been tested for community level use especially in rural area. However, none of the techniques and methods developed has found application in rural and semi-urban areas of Assam; and people are still dependant on different variants of indigenous household iron filtrer units. There are very scanty scientific study available showing the effectiveness of the filter units in reducing Fe(II) as well as FD and As(III) from groundwater. The Government of India has launched DWater Technology InitiativeD as well as DWAR for WaterD to promote research and development activities to provide safe drinking water at affordable cost and in adequate quantity using appropriate science and technological interventions. The focus of work is directed towards assessing the potential of CPWC and RS D media used in the indigenous household filter units for removal of Fe(II), F- and As(III) through kinetics (batch mode), equilibrium (batch mode) and column (continuous mode) studies from mono-, binary- and ternary-metal ion systems comprising of Fe(II), FD and As(III) ions. The ultimate aim of this work is to design an improved filter unit for simultaneous removal of Fe(II), As(III) and FD. The procured CPWC and RS were processed to the required size ranges which were termed as processed wooden charcoal (PWC) and processed sand (PS). Potential of PWC and PS for metal uptake were evaluated through various batch and continuous mode column studies from mono- [comprising of either Fe(II), or F-, or As(III)], binary- [comprising of Fe(II)+As(III) and Fe(II)+FD] and ternary- [comprising of Fe(II)+FD+As(III)] metal ion systems using synthetic water samples in the laboratory. The effects of variation in different parameters such as pH, shaking speed, contact time, adsorbent dose and initial metal concentrations were investigated through batch studies. Continuous mode column studies were carried out using 3 cm internal diameter PVC columns to investigate the impact of bed depths and flow rates on metal adsorption by PWC and PS beds from mono-, binary- and ternary-metal ion systems to generate breakthrough profiles with bed depths of 5, 10 and 15 cm operated at flow rates of 1.5, 2.5 and 3.5 mL/min. The column data were used to carry out bed depth service time (BDST) analysis. Co-precipitation experiments were conducted with binary- and terna....
STOCHASTIC EROSION IN THE COMPOSITE BANKS OF ALLUVIAL RIVER BENDS
(2010) Karmaker, Tapas
The present research study is focused to find out the dominated bank erosion processes prevailing in the braided Brahmaputra river by conducting in-situ hydrodynamic and morphological observations. Better understanding of these bank erosion mechanisms is essential for designing a cost-effective bank protection system(s), which is one of major challenging tasks for river engineers. River bank erosion occurs mainly due to three processes: fluvial entrainment, subaerial erosion and mass failure due to poor strength of the bank materials. One or the combination of these processes is responsible for the bank erosion. The nature of the erosion for a cohesive river bank is different from cohesionless (sandy) river bank. In a cohesive river bank, the erosion takes place as crumbs of soil rather than individual particles, as they are bound tightly by the electromechanical cohesive forces. The erosion of composite river banks is even more complex. Banks of the alluvial river reaches are mostly composed of stratified soil layers with varying grain sizes. A lot of uncertainty in defining these causative
Seismic Microzonation of Imphal City and Probabilitc Seismic Hazard Assessment of Manupur State
(2010) Kumar, Pallav
Insrease in damages due to earthquqkes in the recent past viz, Bhuj(2001) , Sumatra92004) , kashmir earthquakes(2005) etc.,has woken up engineers and planners to the possibility of seismic risk in densely populated Indian cities such as Imphal city. Imphal city, the capital of manipur state, lies in one of the most seismically active regions( i.e Northeast region of India) of the world and hence it is of paramount important to understand the existing earthquakes hazard of Imphal city on an engineering basis. ........
Reservoir Operation Considering Downstream Impact of A Hydroelectric Project
(2010) Ray, Maya Rajnarayan
With the increasing demand of power, hydropower projects are coming up at a much faster rate the developing countries of the world. theses projects are generally operated to meet the power demand during peak hours, which induces significant diurnal variations downstream of the dam ........
Geocell-Sand Mattress overlying soft clay subgradei: Behaviour under circular loading
(2010) Rai, Minaxi
The soft soil often poses design, construction and maintenance hazards to civil engineering structures, so any development activities on such areas are generally avoided. However, the advancement of technology has led to the emergence of numerous ground improvement techniques that render such sites suitable for constructional purposes. Among others, soil reinforcement technique is a viable alternative to enhance the strength of the soft soils. The latest adaptation of this technique involves the use of geocell mattress which is a three dimensional, polymeric, honeycomb like structure interconnected at joints. The geocells provide an all round confinement to the material by virtue of their interconnected cells and prevent their lateral spreading on the application of load, thus resulting in a much stiffer material with higher load carrying capacity. Available literature on geocell reinforcement indicates that substantial improvement in performance can be obtained with the provision of geocell reinforced sand mattress over soft clay subgrade. However, the influence of various key parameters on the overall performance and behaviour of geocell-sand mattress reinforced clay subgrade system are not well understood. Under the present investigation, a detailed parametric study through a series of experiments has been carried out to develop an understanding of the behaviour of the soft clay subgrade supported geocell-sand mattress system under circular loading. The influence of various parameters pertaining to geocell-soil configuration such as depth of placement of geocell mattress from the base of the footing, pattern of formation of geocells, pocket size of geocells, height of geocell mattress and relative density of the infill sand in geocells have been studied extensively in a systematic manner. Tests have also been carried out with an additional layer of geogrid placed at the base of the geocell mattress. The influences of the height of geocell mattress, pocket size of geocells and iv relative density of infill sand on the overall performance of the geocell-geogrid composite system have been evaluated. The results of the model load tests show that the stiffness and the load carrying capacity of the clay subgrade improve substantially with the provision of geocell reinforcement. The load carrying capacity of the reinforced foundation bed is found to be influenced by the depth of placement of geocell mattress, pocket size of geocells, height of geocell mattress and relative density of infill sand in geocells. Based on the analysis of the test data, the critical values of the geocell-sand mattress giving maximum beneficial effect are determined. The heaving on the fill surface is found to reduce due to increased confinement provided by the geocell reinforcement to the infill sand. The reduction is relatively more with geocell mattress of higher height and of smaller pocket sizes. An additional geogrid layer at the base of the geocell mattress further enhances the load carrying capacity of the foundation bed. The beneficial effect of the basal geogrid layer is, however, dependent on the pocket size of geocells, height of geocell mattress and relative density of the infill sand. Multiple-variable regression analysis has been performed on the experimental data to develop models in order to predict the bearing capacity of the reinforced foundation bed as a func...
PERFORMANCE IMPROVEMENT OF WEAK CLAY FOUNDATION USING STONE COLUMN AND GEOCELL-SAND MATTRESS
(2010) Bora, Mukul Chandra
Due to the ever increasing demand for land space because of increased construction activity world wide, there is an increasing need to improve soft soil grounds which otherwise are deemed to be unsuitable. Ground improvement technique is a potential alternative to mitigate this problem. Amongst the various ground improvement techniques used for improving the in-situ ground conditions, geosynthetics reinforcement and stone column technique are the widely used ones. The three dimensional geocells are the latest adaptation in the avenues of geosynthetic reinforcements. It is a three dimensional, polymeric, honeycomb like structure of cells interconnected at joints. The reinforcement mechanism in the geocells is by all-round confinement of soil within its pockets. The stone columns are formed by compacting stones into the cylindrical hole formed in soft clay bed, generally by vibro-floatation technique. When load is applied the stone column develops end bearing and skin friction resistance as in piles. Their individual application of both these techniques has been studied well. However, combined application of both, has remained unexplored. Under the present study a series of experiments have been carried out to develop an understanding of the behaviour of foundation systems having geocell-sand mattress overlying stone column reinforced clay beds. The model tests were conducted in a test bed-cum-loading frame assembly in the laboratory. The influence of various parameters, such as; length and spacing of stone columns; pocket size, height, density of fill soil in geocell mattress; base geogrid and encasement of stone columns were The test results indicate that, with the provision stone columns, of adequate length and spacing, 3.5 fold increases in bearing capacity of soft clay foundations can be achieved. With geocell mattress of optimum geometry and dense soil infill, seven fold increase in bearing capacity of the clay foundation can be achieved. While, the geocell mattress-stone column composite reinforcement can increase the bearing capacity of clay bed by ten fold. The increase in the load carrying capacity and reduction in settlement, of the composite reinforced foundation bed, increases with increase in length of stone columns till 5dc, beyond which further improvement is marginal. The optimum spacing of stone columns in composite foundation beds is 2.5dsc. With further reduction in spacing, the stone columns do not produce much of additional performance improvement. The critical height of geocell mattress, giving optimum performance of stone columns in the composite foundation bed, is equal to about the diameter of the footing. A layer of planar geogrid at the interface between the geocell mattress and stone column reinforced clay bed can bring an improvement in bearing capacity as high as 30% more than that with the geocell mattress-stone column reinforcement alone. Encasement of stone columns further improves the performance, with the bearing capacity increasing with the increase in the length of encasement. However, with full length encasement of the floating stone columns the performance improvement reduces substantially. Combined application of base geogrid and encasement of stone columns is an added advantage that brings further improvement in load carrying capacity of the composite foundation bed. Dimensional analysis shows that, the ...........
Study on Size Effect of RC Beam-Column Joints with and without Retrofitting Under Cyclic Loading : Author , 2010.
(2010) Choudhury, Abdul Munim
During some of the past devastating earthquakes, it was observed that beam-column joint acts as one of the weakest links in moment resisting framed structures. The behaviour of reinforced concrete frame structures in earthquakes all over the world has highlighted the consequences of poor performance of beam-column joints. It was observed that during earthquakes, the exterior joints had suffered more in comparison to the interior ones. The failure of the beam-column joints during earthquakes gave a new thrust in the research for improving seismic behaviour of beam-column joint. Further, 1980 onward lot of researches were also done on strengthening of seismic deficient beam-column joints, especially the exterior joints. Several conventional methods of retrofitting were tried. These methods had many difficulties and problems. However, these difficulties and problems were reduced considerably with the introduction of Fibre-Reinforced Polymer (FRP). Hence, recent research efforts have been focused on the use of FRP for retrofitting of beam-column joints. Some of the researchers conducted tests on beam-column joint without varying the size of tested specimens. However, most of the investigators conducted tests on scaled down models. The results of scaled down models cannot be used directly for prototype implementation in actual field as the size of specimen plays an important role. Available theories of material behavior that predict size effects are receiving increasing attention in the technical literature. Concrete is a heterogeneous material, which is generally full of micro cracks. Upon loading, these micro cracks propagate and the accumulation of such micro cracks leads to failure of specimens. It is well established that the mathematical modeling of such behavior should be based on the theories of fracture mechanics. Material models based Literature survey shows that the experimental study of size effect was mainly done for basic RC structural elements. However, till today no study on size effect was reported for beamcolumn joint, which is a vital component of structural system and plays a very crucial role during earthquake. Hence, it is necessary to undertake study on size effect of structural behaviour of beam-column joints, particularly under cyclic loading. Further, very few researches were reported on size effect for retrofitted RC elements using FRP. Therefore, in the present research, experimental investigations were conducted for a detailed study on beam-column joints with three possible deficiencies to observe the change in various properties due to retrofitting under cyclic loading. With this motivation, the present research was initiated to study the size effect on RC beam-column joints with and without retrofitting. As the objective of the work is to strengthen beam-column joints against future earthquakes, all the specimens were tested under cyclic loading in this study. Three common types of deficiencies in beam-column joints were identified and corresponding three types of retrofitted specimens were also considered in this study. The deficient joints were properly retrofitted using Carbon Fiber Reinforced Polymer (CFRP) and Glass Fiber Reinforced Polymer (GFRP). Thus, six types of specimens with three geometrically similar specimens in each category were considered. Therefore, eighteen specimens were tested covering....
Object-Oriented Nonlinear Finite Element analysis Framework for Implementing modified cam Clay Model
(2011) Devi, Dipika
Cam clay and modified Cam clay models are most widely used plasticity based constitutive models in soil mechanics. Finite element method is a powerful numerical tool which can model many complex conditions and popularly used to analyze geotechnical engineering problems. Traditionally procedure oriented programing, particularly in FORTRAN or C, has been used but recently object-oriented programming has gained wide attention and used by many investigators to develop finite element framework. In this present work an object-oriented finite element analysis framework for modified Cam clay model has been developed using C++ as programming language. In this framework, the whole finite element analysis class is divided into separate component classes to perform various tasks. Extensions to the design are presented in terms of inclusion of new integration algorithms for an existing constitutive model, inclusion of new constitutive models and inclusion of different nonlinear solution techniques and load stepping schemes with an existing integration algorithm of a constitutive model. In this study, firstly, an implicit integration algorithm for modified Cam clay model incorporating nonlinear elasticity is presented. The proposed implicit stress integration algorithm for the modified Cam clay model is based on the return mapping algorithm by making use of the both first order forward Euler scheme and the backward Euler scheme, considering associative flow rule. Secondly, some of the nonlinear solution techniques and load stepping schemes are presented and implemented with the modified Cam clay model. Their performances in some practical geomechanics problems are compared in terms of solution accuracy, number of global iteration and CPU time required to run the program. Thirdly, the context of interpreting the descretized form of the principle of virtual displacement and the ordinary differential equations of the constitutive model together as a system of differential.
Transient Analysis of Aged Concrete Damfoundation Coupled System
(2011) Burman, Avijit
The seismic behavior of concrete dams has been the subject of extensive research during the past decades because of concern for dam safety during earthquakes. Concrete dams are distinguished from other structures because of their huge size and their interactions with the adjacent reservoir and underlying foundation. The safety evaluation of the concrete gravity dams subjected to severe seismic excitations is really very complex as they create coupling effect with the underlying foundation. The interaction among dam, reservoir and its foundation may alter the actual behavior of the dam considerably than what is obtained from the consideration of the dam alone. Therefore, it is necessary to take into account the coupled dam-foundation-reservoir interaction effects for the sound design of the concrete dam. While the structural models are relatively simpler, foundation models are often complicated due to their unbounded nature and nonlinear stress-strain characteristics. Because of nonlinear stress-strain behavior of soil/rock material, it is important to consider its effect while carrying out soil-structure interaction analysis. An attempt is made here to develop a method to assess the effect of soil-structure interaction on the seismic response of dam to make its design more realistic. Due to ageing, the dams are subjected to severe environmental effects, which may lead to loss of stiffness as well as strength due to material degradation. Since the dam face is in constant contact with water, concrete degradation due to hygro-mechanical loading is inevitable and should be considered in the analysis procedure. This ageing process of concrete leads to loss of stiffness and strength of the material. Therefore, to assess the behavior of the dam at a later stage of its life, it is important to determine the proper strength of the concrete at a certain age. An approach to include the time dependent degradation of concrete owing to various environmental factors is presented. Both the aged dam and foundation domains are analyzed separately with the interaction effects at the dam-foundation interface enforced by a developed iterative scheme. In the present work, an appropriate method is presented to truncate infinite foundation domain with absorbing dampers. The finite element method is used to model both dam and foundation. The results obtained from present dam-foundation interaction analyses presents the trends to be expected for a concrete gravity dam at a later stage after construction which may help a designer in the decision making process..

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