Dissertations / Theses on the topic 'Concrete plasticity damaged model'

Because of an eventual ban of creosote-impregnated products, alternative materials for poles used in the electrical grid are needed. Concrete is one alternative and spun concrete poles have been manufactured for the Swedish grid before. These poles are still in use since the high strength and good functioning. However, they weigh too much in terms of the way that poles are assembled on the grid today. Therefore, a study comparing the capacity of different geometries, resulting in lower weight, is of interest.  In this Master’s Thesis, crack initiation and compressive failure in concrete poles are examined by creating FE-models in the software BRIGADE/Plus, using concrete damage plasticity. Thus, guidance is provided about how thin the concrete walls can be made without risking failure – which also means how low the weight of such a pole can be. The failure most likely to occur is a compressive failure in the concrete with a ductile behavior. The result shows that a geometry change, which implies a thinner concrete wall, is possible. This means a weight reduction between 30-75 % or even more, depending on which network the poles are designed for.

Implementing pre-stressing cables is a viable option aiming at controlling deformation and cracking of concrete flat slabs in serviceability limit state. The pre-stressing cables also contribute to punching shear capacity of the slab when they are located in vicinity of the column. The positive influence of pre-stressing cables on punching capacity of the concrete slabs is mainly due to the vertical component of inclined cables, compressive in-plane stresses and counter acting bending moments near the support region. The method presented in Eurocode 2 to determine the punching capacity of the pre-stressed concrete flat slabs considers the in-plane compressive stresses but totally neglects the effect of counter acting moments. The effect of vertical forces introduced by inclined cables is only considered when they are within the distance 2d from the face of the column. This area is called basic control area in the Eurocode 2. In this master thesis nonlinear finite element analysis is carried out to study the effect of pre-stressing cables on punching shear capacity of concrete slabs respecting the distance of cables from the face of the column. To attain this objective, the concrete damage plasticity model is implemented to model the concrete. The results indicate that until the distance of 6d from the face of the column the contribution of pre-stressing cables in punching shear capacity of slabs is significant. Furthermore, comparing the numerical results with the punching shear capacity of slabs predicted by Eurocode 2 reveals that Eurocode tremendously underestimates the punching shear capacity when the cables are located outside the basic control area.

Characterizing the full range of damage and plastic behaviour of asphalt mixtures under varying strain-rates and stress states is a complex and challenging task. One reason for this  is partly due to the strain rate and temperature dependent nature of the material as well as the variation in the properties of the constituent materials that make up the composite asphalt mixture. Existing stress-based models for asphalt concrete materials are developed based on mechanics principles, but these models are, however, limited in their application for actual pavement analysis and design since rate dependency parameters are needed in the constitutive model to account for the influence of the strain rate on the stress-based yield and evolution criteria. Till date, we are yet to arrive at simple and comprehensive constitutive models that can be used to model the behaviour of asphalt mixture over a wide range of strain-rate which is experienced in the actual pavement sections. The aim of this thesis is to develop an increased understanding of the strength and deformation mechanism of asphalt mixtures through multi-scale modeling and to develop simple and comprehensive continuum models to characterize the non-linear behaviour of the material under varying stress-states and conditions. An analysis framework is developed for the evaluation of the influence of asphalt mixture morphology on its mechanical properties and response using X-Ray CT and digital image processing techniques. The procedure developed in the analysis framework is then used to investigate the existence of an invariant critical energy threshold for meso-crack initiation which serves as the basis for the development of a theory for the development of energy-based damage and plastic deformation models for asphalt mixtures. A new energy-based viscoelastic damage model is developed and proposed based on continuum damage mechanics (CDM) and the thermodynamics of irreversible processes. A second order damage variable tensor is introduced to account for the distributed damage in the material in the different principal damage directions. In this way, the material response in tension and compression can be decoupled and the effects of both tension- and compression stress states on the material behaviour can be accounted for adequately. Based on the finding from the energy-based damage model, an equivalent micro-crack stress approach is developed and proposed for the damage and fracture characterization of asphalt mixtures. The effective micro-crack stress approach takes account of the material stiffness and a critical energy threshold for micro-crack initiation in the characterization of damage and fracture properties of the mixture. The effective micro-crack stress approach is developed based on fundamental mechanics principles and it reduces to the Griffith's energy balance criterion when purely elastic materials are considered without the need for the consideration of the surface energy and a crack size in the determination of the fracture stress. A new Continuum Plasticity Mechanics (CPM) model is developed within the framework of thermodynamics to describe the plastic behaviour of asphalt concrete material with energy-based criteria derived for the initiation and evolution of plastic deformation. An internal state variable termed the "plasticity variable" is introduced to described the distributed dislocation movement in the microstructure. The CPM model unifies aspects of existing elasto-plastic and visco-plastic theories in one theory and shows particular strength in the modeling of rate-dependent plastic behaviour of materials without the need for the consideration of rate dependency parameters in the constitutive relationships. The CPM model is further extended to consider the reduction in the stiffness properties with incremental loading and to develop a unified energy-based damage and plasticity model. The models are implemented in a Finite Element (FE) analysis program for the validation of the models. The result shows that the energy-based damage and plastic deformation models are capable of predicting the behaviour of asphalt concrete mixtures under varying stress-states and strain-rate conditions. The work in this thesis provides the basis for the development of more fundamental understanding of the asphalt concrete material response and the application of sound and solid mechanics principles in the analysis and design of pavement structures.
En heltäckande karakterisering av skador och plastiska beteende hos asfaltblandningar under varierande belastningshastighet och spänningstillstånd är en komplex och svår uppgift. En orsak till detta är relaterat till materialets belastningshastighet- och temperaturberoende, såväl som variationen i materialegenskaperna hos de ingående komponenterna i den sammansatta asfaltblandningen. Befintliga spänningsbaserade modeller för asfaltbetongmaterial är utvecklade baserade på mekanikprinciper, men dessa modeller är begränsade när det gäller analys och design av verkliga asfaltsbeläggningar eftersom hastighetsberoende parametrar behövs i den konstitutiva modellen även med hänsyn till töjningshastighetens inverkan på kriterier för gränser och utveckling av spänningstillstånd. Det finns därför behov av att utveckla enkla men ändå heltäckande konstitutiva modeller som kan användas för att modellera beteendet hos asfaltmassan över ett brett spektrum av belastningshastigheter för olika av sektioner asfaltsbeläggningar. Syftet med denna avhandling är att öka förståelsen av hållfasthets- och deformationsmekanismer för asfaltblandningar genom multi-modellering. Målet är att utveckla enkla och heltäckande kontinuummodeller som karakteriserar materialets olinjära beteende under varierande spänningstillstånd och betingelser. Ett analysramverk har utvecklats för utvärdering av påverkan av asfaltmassans morfologi på dess mekaniska egenskaper och beteende med hjälp av röntgendatortomografi och digital bildbehandlingsteknik. Detta förfarande har sedan använts för att undersöka förekomsten av inneboende kritiska tröskelvärden för brottenergin för mesosprickinitiering vilket i sin tur ligger till grund för utvecklingen av en teori för modellering av energibaserade skador och plastisk deformation hos asfaltblandningar. En ny energidensitet baserad viskoelastisk skademodell utvecklas och föreslås utgå från kontinuum-skade-mekanik (CDM) och termodynamik för irreversibla processer. En andra ordningens skadevariabeltensor införs för att ta hänsyn till  skadedistributionen i materialen i de olika principiella skaderiktningarna. På detta sätt kan materialets respons i drag- och tryckbelastning separeras och effekterna av spänningstillstånd i både drag och tryck kan beaktas på ett adekvat sätt. Baserat på resultaten från den energibaserade skademodellen utvecklas och föreslås en motsvarande metod för mikrosprickspänning gällande skade- och brottkarakteriseringen av asfaltblandningar. Metoden för den effektiva mikrosprickspänningen tar hänsyn till materialets styvhet och en kritisk tröskelenergi för mikrosprickinitiering för karakteriseringen av skador och brottegenskaper hos blandningen. Denna metod är utvecklad baserat på grundläggande mekanikprinciper och kan för rent elastiska material reduceras till Griffiths energibalanskriterium utan hänsyn till ytenergi och sprickstorlek vid bestämningen av brottspänningen. En ny termodynamikbaserad modell för kontinuumplasticitetsmekanik (CPM) utvecklas för att beskriva det plastiska beteendet hos asfaltbetongmaterial med energibaserade kriterier härledda för initiering och progression av plastisk deformation. En intern tillståndsvariabel kallad "plasticitetvariabeln" införs för att beskriva den fördelade dislokationsrörelsen i mikrostrukturen. CPM-modellen förenar befintliga elasto-plastiska och visko-plastiska teorier i en teori och visar sig vara särskilt effektiv i modelleringen av hastighetsberoende plastiskt beteende hos material utan att behöva beakta hastighetsberoende parametrar i de konstitutiva sambanden. CPM-modellen utvidgas ytterligare för att kunna beakta reduktionen av styvheten med stegvis ökad belastning och för att utveckla en enhetlig energibaserad skade- och plasticitetmodell. Modellerna är implementerade i ett finit element (FE)-analysprogram för validering av modellerna. Resultatet visar att de energibaserade modellerna för skador och plastisk deformation kan förutsäga beteendet hos asfaltbetongblandningar under varierande spänningstillstånd och töjningshastighetsförhållanden. Arbetet i denna avhandling utgör grunden för utvecklingen av mer grundläggande förståelse av asfaltbetongmaterialets respons och tillämpningen av sunda och robusta mekanikprinciper i analys och design av asfaltstrukturer.

QC 20161220

Les techniques de renforcement de structures en béton armé (BA) par collage de polymères renforcés de fibres (PRF) trouvent un important champ d'applications dans le renforcement des poteaux en BA. Le chemisage par PRF confine le noyau du poteau et permet d'augmenter sa résistance et sa ductilité. Bien que de nombreux travaux expérimentaux aient été consacrés à l'étude de l'effet de confinement du PRF sur le comportement des poteaux en BA, la réalisation d'une simulation réaliste de la réponse structurelle de tels éléments présente de nombreuses difficultés liées aux modèles de comportement peu appropriés à reproduire précisément la réponse mécanique du béton confiné. Dans cette recherche, un modèle de comportement élasto-plastique endommageable est développé pour reproduire la réponse mécanique du béton sollicité suivant un chemin triaxial de contraintes. Ce modèle prend en compte différents mécanismes de comportement du béton tels que les déformations irréversibles, l'endommagement dû à la microfissuration, la sensibilité au confinement et les caractéristiques de dilatation. Un processus d'identification des paramètres du modèle est proposé sur la base d'essais classiques. La validation de ce modèle est ensuite démontrée en comparant des résultats de simulations à des données expérimentales de la littérature sur des bétons confinés activement puis des bétons confinés par des PRF présentant une large gamme de rigidité. Le modèle proposé est également comparé à différentes modélisations de la littérature. Les capacités du modèle sont illustrées et analysées sur des applications tridimensionnelles de poteaux en BA de taille réelle, non confinés et confinés par PRF
For the past two decades, externally bonded Fiber Reinforced Polymers (FRP) has gained much popularity for seismic rehabilitation of reinforced concrete (RC) columns. In this technique, FRP wrap installed on the surface of a column acts as lateral confinement and enhance the strength and deformation capacity of the concrete element. Although many experimental works have been devoted to the study of confining effect of FRP on the behavior of RC columns, the numerical simulation of FRP-jacketed RC columns remains a challenging issue due to the lack of appropriate constitutive model for confined concrete. In this study, a damage plastic model is developed to predict the behavior of concrete under triaxial stress states. The proposed model takes into account different material behavior such as irreversible strain, damage due to microcracking, confinement sensitivity and dilation characteristic. A straightforward identification process of all model’s parameters is then presented. The identification process is applied to different normal strength concrete. The validity of the model is then demonstrated through confrontation of experimental data with simulations considering active confined concrete and FRP confined concrete with a wide range of confinement stiffness. The proposed constitutive model is also compared with other models from the literature and the distinguishing features of this new model are discussed. Furthermore, the capacity of the model in the three-dimensional finite element analysis of full-scale RC columns is demonstrate and discussed

O confinamento de pilares de concreto por meio de camisas de aço ou compósitos possui uma função importante na preservação, recuperação e reforço de estruturas, pois proporciona aumento de resistência e ductilidade desses elementos estruturais. Porém, grande parte dos modelos existentes apresenta limitações na previsão do comportamento do concreto confinado, principalmente por serem dependentes do tipo de confinamento. Portanto, este trabalho apresenta um modelo para descrição do comportamento tensão-deformação do concreto submetido a qualquer tipo de confinamento uniforme, ativo ou passivo, e confinado com diferentes materiais confinantes - aço ou compósitos. O modelo constitutivo associa plasticidade e dano a fim de prever adequadamente a resistência, deformabilidade e redução de rigidez elástica do concreto confinado. O modelo é desenvolvido para um processo incremental explícito de implementação, permitindo, portanto, o seu desenvolvimento em qualquer tipo de planilha. Finalmente, o modelo foi validado por meio de um conjunto representativo de experimentos encontrados na literatura.
Confinement of concrete columns through steel or composites jackets has an important function in the preservation, recovery and strengthening of structures, because it provides increased strength and ductility of these structural elements. However, most of the existing models have limitations in the prediction of the behavior of confined concrete, mainly because they are dependent on the type of confinement. This work presents a model for the description of the stress-strain behavior of the concrete submitted to any type of uniform confinement, active or passive, and confined with different confinement materials, steel or composites. The constitutive model associates plasticity and damage in order to predict with accuracy the strength, ultimate strain and reduction of elastic stiffness of the confined concrete. The model is developed by an explicit incremental implementation process allowing, therefore, its development in any type of spreadsheet. Finally, the model was validated through a representative set of experiments found in the literature.

This thesis comprises of two different kinds of work. The first part is focussed on existing experimental data. Investigations and observations of the behaviour of plain concrete under triaxial and multiaxial compression following cyclic loading and a variety of stress paths has been presented. The behaviour of concrete with different constituents was also investigated. The directions of the plastic strain vectors were identified. Two loading surface were also identified: (i) the Peak Nominal Stress surface (PNS) which was identified from the peak stresses recorded from stress control tests and (ii) the Volume Transition Stress surface (VTS) which determines the onset of the volumetric dilation. The plastic VTS is the surface which was identified from plastic strain components only. At this surface, the directions of the plastic strain vectors are purely deviatoric. A proposal for the shapes of the yield surface for concrete is given. These shapes were identified by the plastic work contours and also from the directions of the plastic strain vectors assuming the associated flow rule. This assumption has been verified by examining the normality of the plastic strain vectors to the PNS surface. Following the investigation of the experimental data, an examination of various advanced plasticity models for concrete revealed the need to develop a new constitutive model with a suitable shape of the loading surfaces and with a better prediction for the stress-strain response. A new constitutive model for plain concrete has been developed using the previous work in this field at the University of Sheffield. The new yield surface was developed as a combination of a reflection of part of the peak nominal stress surface (PNS) and a quartic function. The continuity, the convexity and the normality of the yield surfaces were ensured. The model was calibrated and the optimum values of the thirteen material constants are presented. This is followed by a sensitivity study with simulations of a wide range of existing experimental data. Simulations of concrete with different constituents are also presented. The formulation of the model was simplified and verified by using numerical derivatives. A comparative study between the analytical and numerical derivatives of the constitutive model is presented. The sensitivity study and the simulations of experimental tests showed that the new constitutive model is: (i) easy to calibrate using only data from uniaxial compression tests and one triaxial compression test, and (ii) gives very good predictions of stressstrain response of different types of concrete under triaxial compression stresses and at different levels of confinement all the way to the peak stress state.

Corrosion damage reduces the load-carrying capacity of bridges which poses a threat to passenger safety. The objective of this research was to reduce the resources involved in conventional bridge inspections which are an important tool in the condition assessment of bridges and to help in determining if live load testing is necessary. This research proposes a framework to link semi-automated damage detection on prestressed concrete bridge girders with the estimation of their residual flexural capacity. The framework was implemented on four full-scale corrosion damaged girders from decommissioned bridges in Virginia. 3D point clouds of the girders reconstructed from images using Structure from Motion (SfM) approach were textured with images containing cracks detected at pixel level using a U-Net (Fully Convolutional Network). Spalls were detected by identifying the locations where normals associated with the points in the 3D point cloud deviated from being perpendicular to the reference directions chosen, by an amount greater than a threshold angle. 3D textured mesh models, overlaid with the detected cracks and spalls were used as 3D damage maps to determine reduced cross-sectional areas of prestressing strands to account for the corrosion damage as per the recommendations of Naito, Jones, and Hodgson (2011). Scaling them to real-world dimensions enabled the measurement of any required dimension, eliminating the need for physical contact. The flexural capacities of a box beam and an I-beam estimated using strain compatibility analysis were validated with the actual capacities at failure sections determined from four destructive tests conducted by Al Rufaydah (2020). Along with the reduction in the cross-sectional areas of strands, limiting the ultimate strain that heavily corroded strands can develop was explored as a possible way to improve the results of the analysis. Strain compatibility analysis was used to estimate the ultimate rupture strain, in the heavily corroded bottommost layer prestressing strands exposed before the box beam was tested. More research is required to associate each level of strand corrosion with an average ultimate strain at which the corroded strands rupture. This framework was found to give satisfactory estimates of the residual strength. Reduction in resources involved in current visual inspection practices and eliminating the need for physical access, make this approach worthwhile to be explored further to improve the output of each step in the proposed framework.
Master of Science
Corrosion damage is a major concern for bridges as it reduces their load carrying capacity. Bridge failures in the past have been attributed to corrosion damage. The risk associated with corrosion damage caused failures increases as the infrastructure ages. Many bridges across the world built forty to fifty years ago are now in a deteriorated condition and need to be repaired and retrofitted. Visual inspections to identify damage or deterioration on a bridge are very important to assess the condition of the bridge and determine the need for repairing or for posting weight restrictions for the vehicles that use the bridge. These inspections require close physical access to the hard-to-reach areas of the bridge for physically measuring the damage which involves many resources in the form of experienced engineers, skilled labor, equipment, time, and money. The safety of the personnel involved in the inspections is also a major concern. Nowadays, a lot of research is being done in using Unmanned Aerial Vehicles (UAVs) like drones for bridge inspections and in using artificial intelligence for the detection of cracks on the images of concrete and steel members. Girders or beams in a bridge are the primary longitudinal load carrying members. Concrete inherently is weak in tension. To address this problem, High Strength steel reinforcement (called prestressing steel or prestressing strands) in prestressed concrete beams is pre-loaded with a tensile force before the application of any loads so that the regions which will experience tension under the service loads would be subjected to a pre-compression to improve the performance of the beam and delay cracking. Spalls are a type of corrosion damage on concrete members where portions of concrete fall off (section loss) due to corrosion in the steel reinforcement, exposing the reinforcement to the environment which leads to accelerated corrosion causing a loss of cross-sectional area and ultimately, a rupture in the steel. If the process of detecting the damage (cracks, spalls, exposed or severed reinforcement, etc.) is automated, the next logical step that would add great value would be, to quantify the effect of the damage detected on the load carrying capacity of the bridges. Using a quantified estimate of the remaining capacity of a bridge, determined after accounting for the corrosion damage, informed decisions can be made about the measures to be taken. This research proposes a stepwise framework to forge a link between a semi-automated visual inspection and residual capacity evaluation of actual prestressed concrete bridge girders obtained from two bridges that have been removed from service in Virginia due to extensive deterioration. 3D point clouds represent an object as a set of points on its surface in three dimensional space. These point clouds can be constructed either using laser scanning or using Photogrammetry from images of the girders captured with a digital camera. In this research, 3D point clouds are reconstructed from sequences of overlapping images of the girders using an approach called Structure from Motion (SfM) which locates matched pixels present between consecutive images in the 3D space. Crack-like features were automatically detected and highlighted on the images of the girders that were used to build the 3D point clouds using artificial intelligence (Neural Network). The images with cracks highlighted were applied as texture to the surface mesh on the point cloud to transfer the detail, color, and realism present in the images to the 3D model. Spalls were detected on 3D point clouds based on the orientation of the normals associated with the points with respect to the reference directions. Point clouds and textured meshes of the girders were scaled to real-world dimensions facilitating the measurement of any required dimension on the point clouds, eliminating the need for physical contact in condition assessment. Any cracks or spalls that went unidentified in the damage detection were visible on the textured meshes of the girders improving the performance of the approach. 3D textured mesh models of the girders overlaid with the detected cracks and spalls were used as 3D damage maps in residual strength estimation. Cross-sectional slices were extracted from the dense point clouds at various sections along the length of each girder. The slices were overlaid on the cross-section drawings of the girders, and the prestressing strands affected due to the corrosion damage were identified. They were reduced in cross-sectional area to account for the corrosion damage as per the recommendations of Naito, Jones, and Hodgson (2011) and were used in the calculation of the ultimate moment capacity of the girders using an approach called strain compatibility analysis. Estimated residual capacities were compared to the actual capacities of the girders found from destructive tests conducted by Al Rufaydah (2020). Comparisons are presented for the failure sections in these tests and the results were analyzed to evaluate the effectiveness of this framework. More research is to be done to determine the factors causing rupture in prestressing strands with different degrees of corrosion. This framework was found to give satisfactory estimates of the residual strength. Reduction in resources involved in current visual inspection practices and eliminating the need for physical access, make this approach worthwhile to be explored further to improve the output of each step in the proposed framework.

En el presente trabajo se aborda la tesis “Estudio paramétrico con FEM del refuerzo a punzonamiento de losas de hormigón armado”. Se trata de todo lo relacionado con el fenómeno resistente de punzonamiento en estructuras, especialmente en forjados construidos mediante hormigón armado. Se trata de cuatro apartados bien diferenciados. En este, el primero, se desarrolla la síntesis de la tesis, donde se marcan unos objetivos, seguido de una explicación detallada y descripción de este fenómeno mediante su estado del arte, que abarca el grueso de éste primer apartado, en el cual se describen, entre otros aspectos, las diferentes patologías producidas por el punzonamiento y casos de sucesos catastróficos que provocaron, la historia de los forjados y los principales estudios llevados a cabo sobre este fenómeno, y acabando con las principales resultados y conclusiones de la tesis. Después, el segundo y tercer apartado contienen los artículos publicados y no publicados, respectivamente, por capítulos. Por último, se desarrollan las conclusiones en el último y cuarto apartado.

This thesis describes a non-linear finite element model suitable for the analysis of reinforced concrete, or steel, structures under general three-dimensional states of loading. The 20 noded isoparametric brick element has been used to model the concrete and reinforcing bars are idealised as axial members embedded within the concrete elements. The compressive behaviour of concrete is simulated by an elasto-plastic work hardening model followed by a perfectly plastic plateau which is terminated at the onset the . crushing. In tension, a smeared crack model with fixed orthogonal cracks has been used with the inclusion of models for the retained post-cracking stress and the reduced shear modulus. The non-linear equations of equilibrium have been solved using an incremental-iterative technique operating under load control. The solution algorithms used are the standard and the modified Newton-Raphson methods. Line searches have been implemented to accelerate convergence. The numerical integration has been generally carried out using 15 point Gaussian type rules. Results of a study to investigate the performance of these rules show that the 15 point rules are accurate and computationally efficient compared with the 27(3X3X3) point Gaussian rule. The three- dimensional finite element model has been used to investigate the problem of elasto-plastic torsion of homogeneous members. The accuracy of the finite element solutions obtained for beams of different cross-sections subjected to pure and warping torsion have been assessed by comparing them with the available exact or approximate analytical solutions. Because the present work is devoted towards the analysis of reinforced concrete members which fail in shear or torsional modes, the computer program incorporates three models to account for the degradation in the compressive strength of concrete due to presence of tensile straining of transverse reinforcement. The numerical solutions obtained for reinforced concrete panels under pure shear and beams in torsion and combined torsion and bending reveal that the inclusion of a model for reducing the compressive strength of cracked concrete can significantly improve the correlation of the predicted post-cracking stiffness and the computed ultimate loads with the experimental results. Parametric studies to investigate the effects of some important material and solution parameters have been carried out. It is concluded that in the presence of a compression strength reduction model, the tension-stiffening parameters required for reinforced concrete members under torsion should be similar to those used for members in which bending dominates.

Materially non-linear analysis of reinforced concrete frame structures with infill walls requires appropriate mathematical models to be adopted for the beams and the columns as well as the infill walls. This study presents a mathematical model for frame elements based on a 3D Hermitian beam/column finite element and an equivalent strut model for the infill walls. The spread-of-plasticity approach is employed to model the material nonlinearity of the frame elements. The cross-section of the frame element is divided into triangular sub regions to evaluate the stiffness properties and the response of the element cross-section. By the help of the triangles spread over the actual area of the section, the bi-axial bending and the axial deformations are coupled in the inelastic range. A frame super-element is also formed by combining a number of frame finite elements. Two identical compression-only diagonal struts are used for modeling the infill. The equivalent geometric and material properties of the struts are determined from the geometry of the infill and the strength of the masonry units A computer code is developed using the object-oriented design paradigm and the models are implemented into this code. Efficiency and the effectiveness of the models are investigated for various cases by comparing the numerical response predictions produced by the program with those obtained from experimental studies.

Submitted by Cássia Santos (cassia.bcufg@gmail.com) on 2017-01-30T09:49:46Z No. of bitstreams: 2 Dissertação - Wanessa Mesquita Godoi Quaresma - 2016.pdf: 2901974 bytes, checksum: fcac435f9dfd087f8402d916a36a5f05 (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5)
Approved for entry into archive by Luciana Ferreira (lucgeral@gmail.com) on 2017-01-30T10:04:13Z (GMT) No. of bitstreams: 2 Dissertação - Wanessa Mesquita Godoi Quaresma - 2016.pdf: 2901974 bytes, checksum: fcac435f9dfd087f8402d916a36a5f05 (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5)
Made available in DSpace on 2017-01-30T10:04:13Z (GMT). No. of bitstreams: 2 Dissertação - Wanessa Mesquita Godoi Quaresma - 2016.pdf: 2901974 bytes, checksum: fcac435f9dfd087f8402d916a36a5f05 (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Previous issue date: 2016-07-06
Conselho Nacional de Pesquisa e Desenvolvimento Científico e Tecnológico - CNPq
This work deals with the study of the concrete mechanical behavior using a two-dimensional numerical modeling in mesoscopic scale. The material is considered to be composed of three phases consisting of the interface zone matrix and inclusions, where each constituent is modeled properly. In the representative volume element (RVE) inclusions of as various shapes and randomly arranged are considered. The interface zone is modeled by finite elements where a model of fracture and contact recently proposed is incorporated. On the other hand, the transition zone is modeled by triangular finite elements where the Mohr-Coulomb model with lower strength characteristics compared to the mortar, is used. Inclusion is modeled as a linear elastic material and the matrix is considered as elastoplastic materials governed by the Mohr-Coulomb model. Our main goal is to show that a formulation based on computational homogenization is an alternative to complex macroscopic constitutive models for the mechanical behavior of brittle materials using a procedure based on the Finite Element Method and a multiscale theory. Examples changing the form of aggregate, their volume fraction and distribution in RVE, as well as various strategies for modeling the transition zone are shown to illustrate the performance of the proposed model. The results evidence that the proposed modeling leads to are promising results for employment in a multiscale modeling. Also, this work shows the importance of parametric identification of fracture and contact model in the microstructural analysis of concrete.
Este trabalho trata do estudo do comportamento mecânico do concreto utilizando uma proposta de modelagem numérica bidimensional em escala mesoscópica. O material é considerado como composto por três fases consistindo de zona de interface, matriz e inclusões, onde cada constituinte é modelado adequadamente. O Elemento de Volume Representativo (EVR) consiste de inclusões idealizadas como de várias formas e aleatoriamente dispostas no EVR. Uma das abordagens permite que a zona de interface seja modelada por meio de elementos finitos coesivos de contato, onde um modelo de fratura e contato recentemente proposto é incorporado ao elemento. Por outro lado, a zona de transição pode ser modelada por elementos finitos triangulares onde o modelo de Mohr- Coulomb com características de menor resistência em relação à argamassa, é utilizado. A inclusão é modelada como sendo um material elástico linear, já a matriz é considerada como material elastoplástico obedecendo ao modelo de Mohr-Coulomb. O principal objetivo é mostrar que uma formulação baseada na homogeneização computacional é uma alternativa aos modelos constitutivos macroscópicos complexos para o comportamento mecânico de matérias frágeis usando um procedimento baseado no Método dos Elementos Finitos no âmbito de uma teoria multiescala. Uma série de exemplos envolvendo a mudança de forma de agregados, sua fração volumétrica e sua distribuição no EVR, assim como diferentes estratégias de modelagem da zona de transição, é apresentada de modo a ilustrar a performance da modelagem proposta. Os resultados encontrados evidenciam que as modelagens propostas apresentam resultados promissores para o emprego numa modelagem multiescala. Também, este trabalho mostra a importância da identificação paramétrica do modelo de fratura e contato na análise microestrutural do concreto.

La compaction des bétons se rencontre le plus souvent dans le cas de choc ou d'impact sur structure en béton. Sous l'effet de fortes sollicitations de compression triaxiales, le matériau béton, initialement poreux, se densifie par réduction de la porosité initiale. L'énergie dissipée au cours de cette densification est tres importante : le matériau est fortement plastifie et endommage. Au cours d'un impact, d'autres phénomènes entrent en jeu : du cisaillement provoque par la perforation du missile, et de l'écaillage provoque par réflexion des ondes de compression sur la face non-impactée en ondes de traction. Nous proposons dans la première partie de cette thèse une modélisation de ces phénomènes basée sur la mécanique des milieux poreux, la mécanique de l'endommagement et la plasticité. Le modèle phénoménologique que nous proposons est apte à représenter les divers phénomènes physiques qui interviennent au cours d'un impact. Les comportements obtenus tant en traction qu'en compaction sont comparables avec des résultats expérimentaux. De plus le modèle propose à des propriétés de régularisation intéressantes en vue de calculs numériques par éléments finis. Dans une deuxième partie, nous proposons une stratégie expérimentale en vue de caractériser la compaction de bétons et de mortiers. Ce processus expérimental s'appuie sur deux essais statiques de compaction. Le premier de ces essais est dénommé essai uniaxial confine. Le principe de cet essai est de solliciter axialement une éprouvette cylindrique ayant un diamètre de 5 cm pour une hauteur de 10 cm, et d'empêcher son gonflement radial par une cellule cylindrique métallique de forte épaisseur. Les sollicitations maximales de compression atteintes sont alors de 1275 mpa axialement sur l'éprouvette pour une contrainte radiale de 260 mpa environ. Cet essai permet de caractériser la compaction de béton sur un trajet oedometrique. Le deuxième essai est dénommé essai triaxial hydrostatique : il résulte de l'adaptation aux matériaux très poreux d'une cellule a confinement fluide mis au point pour les matériaux métalliques. Les éprouvettes testées sont alors des mortiers et des micro-bétons. La sollicitation maximale atteinte est une pression hydrostatique de 400 mpa. Cet essai permet de caractériser des mortiers sur un trajet hydrostatique.

Mise au point d'un modèle non linéaire caractérisant la tenue ultime des structures constituées de poutres en béton armé. Analyse critique des théories actuelles (plasticité globale et endommagement). Nécessité d'une formulation nouvelle incluant les deux non-linéarités. Formulation d'un modèle complet applicable aux situations accidentelles les plus courantes en particulier aux sollicitations sismiques. Après son implémentation dans un programme de calcul par éléments finis, on effectue deux calculs de démonstration dans le cas d'une poutre en flexion 4 points avec dilatation de membrane libre ou bloquée.

Cette thèse traite de rupture localisée de structures construites en matériau composite hétérogène, comme le béton, à deux échelles différentes. Ces deux échelles sont connectées par le biais de la mise à l'échelle stochastique, où toute information obtenue à l'échelle méso est utilisée comme connaissance préalable à l'échelle macro. À l'échelle méso, le modèle de réseau est utilisé pour représenter la structure multiphasique du béton, à savoir le ciment et les granulats. L'élément de poutre représenté par une poutre Timoshenko 3D intégrée avec de fortes discontinuités assure un maillage complet indépendance de la propagation des fissures. La géométrie de la taille des agrégats est prise en accord avec la courbe EMPA et Fuller tandis que la distribution de Poisson est utilisée pour la distribution spatiale. Les propriétés des matériaux de chaque phase sont obtenues avec une distribution gaussienne qui prend en compte la zone de transition d'interface (ITZ) par l'affaiblissement du béton. À l'échelle macro, un modèle de plasticité multisurface est choisi qui prend en compte à la fois la contribution d'un écrouissage sous contrainte avec une règle d'écoulement non associative ainsi que des composants d'un modèle d'adoucissement de déformation pour un ensemble complet de différents modes de défaillance 3D. Le modèle de plasticité est représenté par le critère de rendement Drucker-Prager, avec une fonction potentielle plastique similaire régissant le comportement de durcissement tandis que le comportement de ramollissement des contraintes est représenté par le critère de St. Venant. La procédure d'identification du modèle macro-échelle est réalisée de manière séquentielle. En raison du fait que tous les ingrédients du modèle à l'échelle macro ont une interprétation physique, nous avons fait l'étalonnage des paramètres du matériau en fonction de l'étape particulière. Cette approche est utilisée pour la réduction du modèle du modèle méso-échelle au modèle macro-échelle où toutes les échelles sont considérées comme incertaines et un calcul de probabilité est effectué. Lorsque nous modélisons un matériau homogène, chaque paramètre inconnu du modèle réduit est modélisé comme une variable aléatoire tandis que pour un matériau hétérogène, ces paramètres de matériau sont décrits comme des champs aléatoires. Afin de faire des discrétisations appropriées, nous choisissons le raffinement du maillage de méthode p sur le domaine de probabilité et la méthode h sur le domaine spatial. Les sorties du modèle avancé sont construites en utilisant la méthode de Galerkin stochastique fournissant des sorties plus rapidement le modèle avancé complet. La procédure probabiliste d'identification est réalisée avec deux méthodes différentes basées sur le théorème de Bayes qui permet d'incorporer de nouvelles bservations générées dans un programme de chargement particulier. La première méthode Markov Chain Monte Carlo (MCMC) est identifiée comme mettant à jour la mesure, tandis que la deuxième méthode Polynomial Chaos Kalman Filter (PceKF) met à jour la fonction mesurable. Les aspects de mise en œuvre des modèles présentés sont donnés en détail ainsi que leur validation à travers les exemples numériques par rapport aux résultats expérimentaux ou par rapport aux références disponibles dans la littérature
This thesis deals with the localized failure for structures built of heterogeneous composite material, such as concrete, at two different scale. These two scale are latter connected through the stochastic upscaling, where any information obtained at meso-scale are used as prior knowledge at macro-scale. At meso scale, lattice model is used to represent the multi-phase structure of concrete, namely cement and aggregates. The beam element represented by 3D Timoshenko beam embedded with strong discontinuities ensures complete mesh independency of crack propagation. Geometry of aggregate size is taken in agreement with EMPA and Fuller curve while Poisson distribution is used for spatial distribution. Material properties of each phase is obtained with Gaussian distribution which takes into account the Interface Transition Zone (ITZ) through the weakening of concrete. At macro scale multisurface plasticity model is chosen that takes into account both the contribution of a strain hardening with non-associative flow rule as well as a strain softening model components for full set of different 3D failure modes. The plasticity model is represented with Drucker-Prager yield criterion, with similar plastic potential function governing hardening behavior while strain softening behavior is represented with St. Venant criterion. The identification procedure for macro-scale model is perfomed in sequential way. Due to the fact that all ingredients of macro-scale model have physical interpretation we made calibration of material parameters relevant to particular stage. This approach is latter used for model reduction from meso-scale model to macro-scale model where all scales are considered as uncertain and probability computation is performed. When we are modeling homogeneous material each unknown parameter of reduced model is modeled as a random variable while for heterogeneous material, these material parameters are described as random fields. In order to make appropriate discretizations we choose p-method mesh refinement over probability domain and h-method over spatial domain. The forward model outputs are constructed by using Stochastic Galerkin method providing outputs more quickly the the full forward model. The probabilistic procedure of identification is performed with two different methods based on Bayes’s theorem that allows incorporating new observation generated in a particular loading program. The first method Markov Chain Monte Carlo (MCMC) is identified as updating the measure, whereas the second method Polynomial Chaos Kalman Filter (PceKF) is updating the measurable function. The implementation aspects of presented models are given in full detail as well as their validation throughthe numerical examples against the experimental results or against the benchmarks available from literature

Liquefied natural gas (LNG) is stored at a cryogenic temperatures ≤ -160°C and around atmospheric pressure to insure the minimum storage volume in tanks. The demand for LNG has been increasing as a primary source of energy. Therefore, there is significant interest in the construction of LNG tanks to achieve low cost and safe storage. Three systems are typically used to store LNG: single containment, double containment, and full containment. Concrete is used in these containment systems, and consequently, understanding concrete behavior and properties at cryogenic temperatures is important. The research documented in this thesis deals with computational analysis of the behavior of concrete subjected to cryogenic temperatures. The analysis focuses on the effect of aggregate sizes, coefficient of thermal expansion, volume fraction, and the shape of aggregate on damage of concrete subjected to cryogenic temperatures. The analysis is performed by developing a computational model using the finite element software ABAQUS. In this model, concrete is considered as a 3- phase composite material in a meso-scale structure: mortar matrix, aggregate, and interfacial transmission zone (ITZ). The Concrete Damage Plasticity model in ABAQUS is used to represent the mortar and ITZ phases of concrete. This model has the advantage of accounting for the effect of temperature on material properties. The aggregate phase is modeled as a linear-elastic material. The model parameters are selected based on comprehensive literature review of material properties at different temperatures. The finite element results provide very useful insight on the effects of concrete mixture design and properties on resistance to damage. The most important factor that affected damage development was the difference in the coefficient of thermal expansion between the mortar and aggregates. Models in which the mortar and aggregate had close values of positive coefficients experienced less damage. The model with irregular shape particles experienced more localized damage than the model with circular shape particles. The model was successful in demonstrating the effect of using air entrained concrete in reducing damage. The damage results predicted by the model for air entrained and non-air entrained concrete are validated by comparing them with experimental data from the literature. The analysis validated the capabilities of the mode in simulating the effect of reduction in temperature on damage. The modeling results and the findings from the literature review were used to put forward recommendations regarding the characteristics of concrete used in LNG storage.

Coupling beams are structural elements used to connect two or more shear walls. The most common material used in the construction of coupling beam is reinforced concrete. The use of coupling beams along with shear walls require them to resist large shear forces, while possessing sufficient ductility to dissipate the energy produced due to the lateral loads. This study has been undertaken to produce a computational model to replicate the behavior of conventionally reinforced coupling beams subjected to cyclic loading. The model is developed in the finite element analysis software ABAQUS. The concrete damaged plasticity model was used to simulate the behavior of concrete. A calibration model using a cantilever beam was produced to generate key parameters in the model that are later adapted into modeling of two coupling beams with aspect ratios: 1.5 and 3.6. The geometrical, material, and loading values are adapted from experimental specimens reported in the literature, and the experimental results are then used to validate the computational models. The results like evolution of damage parameter and crack propagation from this study are intended to provide guidance on finite element modeling of conventionally reinforced concrete coupling beams under cyclic lateral loading.

In reinforced concrete (RC) structures, adequate bond between the reinforcement and concrete is required to achieve a true composite system, in which reinforcing steel carries tensile stress, once concrete cracks, and concrete and reinforcing steel carry compression. Determining bond strength and required development length for shear transfer between concrete and reinforcement is an ongoing research subject in the field of reinforced concrete with advances in the concrete and reinforcement materials requiring continuous experimental efforts. Finite element analysis (FEA) provides opportunities to explore structural behavior of RC structures beyond the limitations of experimental testing. However, there is a paucity of research studies employing FEA to investigate the reinforcement-concrete bond-zone behavior and related failure mechanism. Instead, most FEA-based research associated with RC bond has centered on developing a bond (or interface) constitutive model for use in FEA that, by itself, can characterize bond-zone behavior, typically represented by the bond stress-slip displacement relationship. This class of bond models is useful for simulating the global behavior of RC structures but is limited in its ability to simulate local bond resistance for geometries and material properties that differ substantially from those used to calibrate the model. To fill this gap in research, this study proposes a finite element (FE) modeling approach that can simulate local bond-zone behavior in reinforced concrete. The proposed FE model is developed in a physics-based way such that it represents the detailed geometry of the bond-zone, including ribs on the deformed reinforcement, and force transfer mechanisms at the concrete-reinforcement interface. The explicit representation of the bond-zone enables simulation of the local concrete compression due to bearing of ribs against concrete and subsequent hoop tension in the concrete. This causes bond failure either due to local concrete crushing (leading to reinforcement pullout) or global concrete splitting. Accordingly, special attention is given to the selection and calibration of a concrete model to reproduce robust nonlinear response. The power of the proposed modeling approach is its ability to predict bond failure and damage patterns, based only on the physical and material properties of the bond area. Thus, the successful implementation and application of this approach enables the use of FEA simulation to support the development of new design specifications for bond zones that include new and improved materials.

A three dimensional nonlinear finite element model has been developed to study the behaviour of composite beams with profiled sheeting oriented perpendicular to its axis. The analysis of the push test was carried out using ABAQUS/Explicit with slow load application to ensure a quasi-static solution. Both material and geometric nonlinearities were taken into account. Elastic¿plastic material models were used for all steel components and the Concrete Damaged Plasticity model was used for the concrete slab. The post-failure behaviour of the push test was accurately predicted, which is crucial for realistic determination of shear capacity, slip and failure mode. The results obtained from finite element analysis were verified against the experimental push tests conducted in this research and also from other studies. After validation, the model was used to carry out an extensive parametric study to investigate the effect of transverse spacing in push tests with double studs placed in favourable and staggered positions with various concrete strengths. The results were also compared with the capacity of a single shear stud. It was found that shear connector resistance of pairs of shear connectors placed in favourable position was 94% of the strength of a single shear stud on average, when the transverse spacing between studs was 200 mm or more. For the same spacing, the resistance of staggered pairs of studs was only 86% of the strength of a single stud. The strength of double shear studs in favourable position was higher than that of the staggered pairs of shear connectors.

Reinforced concrete frames, infilled with brick/concrete block masonry, are the most common type of structures found in multi-storeyed constructions, especially in developing countries. Usually, the infill walls are considered as non-structural elements even though they alter the lateral stiffness and strength of the frame significantly. Approximately 80% of the structural cost from earthquakes is attributable to damage of infill walls and to consequent damages of doors, windows and other installations. Despite the broad application and economical significance, the infill walls are not included in the analysis because of the design complexity and lack of suitable theory. But in seismic areas, ignoring the infill-frame interaction is not safe because the change in the stiffness and the consequent change in seismic demand of the composite structural system is not negligible. The relevant experimental findings shows a considerable reduction in the response of infilled frames under reverse cyclic loading. This behaviour is caused by the rapid degradation of stiffness, strength, and low energy dissipation capacity resulting from the brittle and sudden damage of the unreinforced masonry infill walls. Though various national/international codes of practice have incorporated some of the research outcomes as design guidelines, there is a need and scope for further refinement. In the initial part of this work, a numerical modelling and linear elastic analysis of masonry infilled RC frames has been done. A multi-storey multi-bay frame infilled with masonry panels, is considered for the study. Both macro modelling and micro modelling strategies are adopted. Seismic loading is considered and an equivalent static analysis as suggested in IS 1893, 2002 is done. The results show that the stiffness of the composite structure is increased due to the obvious confinement effects of infill panels on the bounding frame. A parametric study is conducted to investigate the influence of size and location of openings, presence/absence of infill panels in a particular storey and elevation irregularity in terms of floor height. The results show that the interaction of infill panel changes the seismic response of the composite structure significantly. Presence of openings further changes the seismic behaviour. Increase in openings increases the natural period and introduce newer failure mechanisms. Absence of infill in a particular storey (an elevation irregularity) makes it drift more compared to adjacent storeys. Since the structural irregularities influence the seismic behaviour of a building considerably, we should be cautious while construction and renovation of such buildings in order to take the advantage of increased strength and stiffness obtained by the presence of infill walls. A nonlinear dynamic analysis of masonry infilled RC frames is presented next. Material non linearity is considered for the finite element modelling of both masonry and concrete. Concrete damage plasticity model is employed to capture the degradation in stiffness under reverse cyclic loading. A parametric study by varying the same parameters as considered in the linear analysis is conducted. It is seen that the fundamental period calculation of infilled frames by conventional empirical formulae needs to be revisited for a better understanding of the real seismic behaviour of the infilled frames. Enhancement in the lateral stiffness due to the presence of infill panel attracts larger force and causes damage to the composite system during seismic loading. Elevation irregularities included absence of infill panels in a particular storey. Soft storey shows a tendency for the adjacent columns to fail in shear, due to the large drift compared to other storeys. The interstorey drift ratios of soft storeys are found to be larger than the limiting values. However this model could not capture the separation at the interfaces and related failure mechanisms. To improve the nonlinear model, a contact surface at the interface is considered for a qualitative analysis. A one bay one storey infilled frame is selected. The material characteristics were kept the same as those used in the nonlinear model. Contact surface at the interface was given hard contact property with pressure-overclosure relations and suitable values of friction at the interface. This model could simulate the compressive diagonal strut formation and the switching of this compressive strut to the opposite diagonal under reverse cyclic loading. It showed an indication of corner crushing and diagonal cracking failure modes. The frame with central opening showed stress accumulation near the corners of opening. Next, the micro modelling strategy for masonry suggested by Lourenco is studied. This interface element can be used at the masonry panel-concrete frame interface as well as at the expanded masonry block to block interface. Cap plasticity model (modified Drucker – Prager model for geological materials) can be used to describe the behaviour of masonry (in terms of interface cracking, slipping, shearing) under earthquake loading. The blocks can be defined as elastic material with a potential crack at the centre. However, further experimental investigation is needed to calibrate this model. It is required to make use of the beneficial effects and improve upon the ill-effects of the presence of infills. To conclude, infill panels are inevitable for functional aspects such as division of space and envelope for the building. Using the lateral stiffness, strength contribution and energy dissipation capacity, use of infill panels is proposed to be a wiser solution for reducing the seismic vulnerability of multi-storey buildings.

碩士
國立成功大學
土木工程學系碩博士班
94
The purpose of this study is to incorporate the residual mechanical properties of fire damaged concrete and steel into the rotating-angle softened truss model (RA-STM) and variable-angle truss model for the prediction of shear and flexural strengths of reinforced concrete beams after fire exposure. Both models can reasonably predict the shear strengths for beams with span-to-depth ratio a/d≧2.5 under room temperature, within the orientations of diagonal strut between 30 degree and 45 degree. The RA-STM slightly over estimated shear strengths of beams with 2.0≦a/d≦2.5. The variable-angle truss model, assuming the inclined angle of diagonal strut of 30 deg, gives a good agreement with the test results. The compressive strain ε0 corresponding to peak strength of concrete subjected to fire test less than 400℃ did not increase significantly. Applying these two models to predict the shear and bending strength of fire damaged concrete beams, good agreements were found between the analytical and experimental results. The full-scale reinforced concrete beam-column assemblage specimens were employed to assess the strengths after fire damage. Analytical results of RA-STM theory show that specimen under the constant applied load exhibits greater shear and bending strength deterioration in the hogging region than in the sagging region. After fire testing, the strengths predicted by the RA-STM and the variable-angle truss model are very close.

A plasticity model to predict the behavior of confined concrete is developed. The model is designed to implicitly account for the increase in strength and ductility due to confining a concrete member. The concrete model is implemented into a finite element (FE) model. By implicitly including the change in the strength and ductility in the material model, the confining material can be explicitly included in the FE model. Any confining material can be considered, and the effects on the concrete of failure in the confinement material can be modeled. Test data from a wide variety of different concretes utilizing different confinement methods are used to estimate the model parameters. This allows the FE model to capture the generalized behavior of concrete under multiaxial loading. The FE model is used to predict the results of tests on reinforced concrete members confined by steel hoops and fiber reinforced polymer (FRP) jackets. Loading includes pure axial load and axial load-moment combinations. Variability in the test data makes the model predictions difficult to compare but, overall, the FE model is able to capture the effects of confinement on concrete. Finally, the FE model is used to compare the performance of steel hoop to FRP confined sections, and of square to circular cross sections. As expected, circular sections are better able to engage the confining material, leading to higher strengths. However, higher strains are seen in the confining material for the circular sections. This leads to failure at lower axial strain levels in the case of the FRP confined sections. Significant differences are seen in the behavior of FRP confined members and steel hoop confined members. Failure in the FRP members is always determined by rupture in the composite jacket. As a result, the FRP members continue to take load up to failure. In contrast, the steel hoop confined sections exhibit extensive strain softening before failure. This comparison illustrates the usefulness of the concrete model as a tool for designers. Overall, the concrete model provides a flexible and powerful method to predict the performance of confined concrete.

Across the State of Texas and many other areas of the world, relatively young concrete structures have developed signs of premature concrete deterioration. Large cracks form on the surface of the concrete due to expansive forces from alkali-silica reaction (ASR) and delayed-ettringite formation (DEF). The goal of this project is to assess the effect of ASR/DEF on the trapezoidal box beam bridges in the US 59 corridor and Katy Central Business District (CBD) HOV lanes in Houston, TX. Five dapped-end beams were rejected during the casting process and have been in storage at a local precast yard for nearly fifteen years. These beams have been subject to accelerated deterioration and represent the potential severity of the ongoing ASR/DEF distress within the dapped end regions of the in-service trapezoidal box beams. The results from five load tests, corresponding strut-and-tie models, and forensic investigation are used to provide insights into the relationship between the severity of the deterioration and the capacity margin.
text

Yes
Nine continuous concrete deep beams reinforced with glass fibre reinforced polymer (GFRP) bars were experimentally tested to failure. Three main parameters were investigated, namely, shear span-to-overall depth ratio, web reinforcement and size effect. The experimental results confirmed the impacts of web reinforcement and size effect that were not considered by the strut-and-tie method (STM) of the only code provision, the Canadian S806-12, that addressed such elements. The experimental results were employed to evaluate the applicability of the methods suggested by the American, European and Canadian codes as well as the previous studies to predict the load capacities of continuous deep beams reinforced with GFRP bars. It was found that these methods were unable to reflect the influences of size effect and/or web reinforcement, the impact of which has been confirmed by the current experimental investigation. Therefore, a new effectiveness factor was recommended to be used with the STM. Additionally, an upper-bound analysis was developed to predict the load capacity of the tested specimens considering a reduced bond strength of GFRP bars. A good agreement between the predicted results and the experimental ones was obtained with the mean and coefficient of variation values of 1.02 and 5.9%, respectively, for the STM and 1.03 and 8.6%, respectively, for the upper-bound analysis.
Higher Committee of Education Development in Iraq (HCED)

This paper presents a numerical investigation into the behaviour of headed shear stud in composite beams with profiled metal decking. A three-dimensional finite element model was developed using general purpose finite element program ABAQUS to study the behaviour of through-deck welded shear stud in the composite slabs with trapezoidal deck ribs oriented perpendicular to the beam. Both static and dynamic procedures were investigated using Drucker Prager model and Concrete Damaged Plasticity model respectively. In the dynamic procedure using ABAQUS/Explicit, the push test specimens were loaded slowly to eliminate significant inertia effects to obtain a static solution. The capacity of shear connector, load-slip behaviour and failure modes were predicted and validated against experimental results. The delamination of the profiled decking from concrete slab was captured in the numerical analysis which was observed in the experiments. ABAQUS/Explicit was found to be particularly suitable for modelling post-failure behaviour and the contact interaction between profiled decking and concrete slabs. It is concluded that this model represents the true behaviour of the headed shear stud in composite beams with profiled decking in terms of the shear connection capacity, load-slip behaviour and failure modes.

The introductions of large digital computers in the field of engineering have rendered possible the solution of a wide variety of problems without the need to violate the equilibrium and compatibility. The major requirement for such analysis is a good constitutive model that represents the stress strain behaviour of the materials in an accurate way. Nowadays for most of the geotechnical engineering applications the elastoplastic models like Mohr Coulomb model are widely used. All the existing constitutive models which represent the plastic behaviour of soil are developed from the fundamentals of classical theory of plasticity. The classical theory of plasticity is always associated with the concept of yield surface and potential surface to represent the plastic behaviour. The definition of yield surface depends on the location of the yield point. But in practical sense it is very difficult to find out the exact yield point for a material. The expression for yield and potential surfaces are simply mathematical expressions formulated for computational efficiency. Experimentally it is very difficult to find out the yield surface in the case of three dimensional stress spaces. The classical theory of plasticity is developed based on the mechanical process. It is believed that a theory which violates the thermodynamic principle is not able to represent the material behaviour accurately. the initial stage and combined to give the final state of stress. It was proved that the equation proposed by Wu and Wang (1983) can be used to represent the triaxial behaviour of sand very well. The dilation and densification behaviour can be predicted very well with the endochronic constitutive equations. The principal aim of this work is to implement the endochronic constitutive equation in the FLAC3D model library like any other constitutive model and validate it with the triaxial test data. After implementation and validation, the application of the particular constitutive model is extended to some practical geotechnical engineering problems like the stresses and displacements around an underground opening such as tunnels, surface settlement due to shallow tunneling, stress distribution below the footing, settlement analysis of footing on various foundation beds such as sand, clay and sand overlying clay bed, lateral displacement of the secant pile wall due to excavation and the force developed in the horizontal support etc. All the three problems validate the model with the analytical, experimental and field data respectively. The equation proposed by Wu and Wang (1983) is used for the present study. In order to validate the equation proposed by Wu and Wang (1983), MatLab programming is used. The hydrostatic, deviatoric and volumetric behaviour is obtained separately using the concerned equations. The equation is coded in the MatLab and analysis is done for a triaxial element test. Both drained and undrained analyses were done in order to study the behaviour. The pore pressure developed is captured separately with the equation proposed by Geoffrey et al (1975). The results obtained from the analysis of the MatLab were compared with that of the experimental results. The analysis shows that the equation captures the least plastic behaviour well for the triaxial element test. The dilation and densification behaviour obtained using the respective equation shows that it matches well with the experimental results. A parametric study is also conducted in MatLab to see how the parameters affect the stress strain and volumetric behaviour of the sand. The parametric study conducted with the MatLab shows that most of the parameters involved in the equation affect the plastic part of the stress strain curve rather than the initial elastic part. User defined constitutive model was written in visual C++ and compiled as DLL (Dynamic Link Library) files that will be loaded whenever it is needed in FLAC3D. In visual C++, header and source files were written by incorporating the constitutive equation proposed by Wu and Wang (1983), defining the variables and other functions etc, and a dynamic link library is created, which is then integrated into the 3D finite difference code FLAC3D using the CPPUDM module to simulate the stress strain behaviour of the materials. CPPUDM module is an additional option in FLAC3D to implement the user defined constitutive models. The visual C++ code was written in the form of incremental stress strain relationship. The model acts like any other constitutive model in the FLAC3D model library and can be loaded whenever it is required. For the validation of the model in FLAC3D, the data for the MatLab simulation were used. Both drained and undrained tests were simulated with the model. The results obtained from the analysis shows that by suitably selecting the parameters the model can simulate the stress strain behaviour of sand very well. The volumetric and deviatoric behaviour were observed and is matching well with the experimental data. In the case of the undrained test the pore pressure generation is well captured by the equation proposed by Geoffrey et al (1975). In urban areas the construction of shallow tunnels results in excessive settlements of the ground surface and thereby causes damage to the existing above ground structures. In order to minimize the settlements and to reduce the impact due to that, a prior analysis of the displacements and stresses around the opening is very important. Nowadays numerical analysis is widely used for the analysis of such structures. The most important requirement of such analysis is a constitutive model that can represent the unloading behaviour around the tunnel opening of sand very well. Here the endochronic constitutive model implemented in the FLAC3D model library is used to evaluate the stresses and displacements around the tunnel. In the analysis the tunnel is simulated as a cylindrical hole in an infinite medium with the in situ stress. The stresses at the springing line was observed and compared with the analytical solution. The results show that the results are matching well with the analytical results. The comparison of the results with that obtained using the Mohr Coulomb model is also done to see how the model differs from a widely used plastic model. By slightly adjusting the parameters the results obtained from both the models are in well agreement. The strain softening effect which is predominant around an underground opening due to the loosening of soil mass is well captured by the endochronic model compared to the Mohr Coulomb model. The settlement analysis shows that the model is almost in close agreement with the closed form solution proposed by Oteo & Sagaseta (1982) and the results obtained with the Mohr Coulomb model. The settlement trough formed for various shapes is wider and deeper than the Mohr Coulomb model. The vertical stress distribution around the opening of the tunnel is studied with varying the shape of the openings using the proposed constitutive model. The results obtained were compared with that of the Mohr Coulomb model. The slightly higher values in the case of endochronic model are basically due to its plastic nature. The displacement and stresses in the axial direction (along the excavation) is observed with the model. In the case of shallow tunnel the surface get influenced by the loosening of the soil mass which necessitates the use of the support system. The study shows that the model can be used for the simulation of underground opening like tunnel and will capture the behaviour well. Footings are structures used to support the buildings constructed above the ground. The settlement analysis of footings is very important when we consider the stability of the structures supported by it. The vertical stress distribution below the footing is studied using the endochronic constitutive model and compared with the analytical solution proposed by Boussinesq (1885). In the elastic range the model shows matching results with the Boussinesq’s solution. The settlement analysis of footing on various foundation beds such as sand, clay and sand overlying the clay bed were studied using the endochronic constitutive model implemented in the FLAC3D model library. The experimental data conducted in our lab (Sireesh (2006)) was used for the study. The results show that with the chosen parameters the results obtained with the endochronic model are in good agreement with the experimental data. The Mohr Coulomb model over predicts the results. This shows higher modulus value for the Mohr Coulomb model. By conducting the parametric study it was seen that by reducing the value of modulus for the Mohr Coulomb model, the results are in good agreement with the experimental value. The displacement and stress contours obtained for the two models were compared. By analyzing the displacement contours it is seen that the Mohr Coulomb model shows uniform settlement. In the case of endochronic model uniform settlement is observed for about 5% settlement that is in the elastic range. After a certain strain level the displacement contours are tilted more towards one side showing the rotational failure. Here the endochronic model captures the anisotropic behaviour associated with the materials like sand at higher strain level. This result is a concrete evidence that the model can capture the realistic behaviour very well compared to any other model. Even though the model developed is for sand its application can be extended to clay also. The size and shape of the footing is varied to study its effect on the pressure settlement curve. The analysis is done with square shape of 150mm side and circular shape of 150mm diameter. As there is not much variation in the area of influence, the shape has little influence on the pressure settlement curve. As the size of the footing increases the settlement increases for a given pressure. A parametric study is conducted by varying the modulus value used. The study shows that as the modulus value increases, the settlement reduces for a given bearing pressure. The endochronic model analysed with the lower modulus value shows that the model predicts the perfectly plastic behaviour, here the settlement increases for low value of bearing pressure. The application of endochronic model for the simulation of complex geotechnical engineering problems like footings is highly explored in the study. Nowadays most of the infrastructure facilities are concentrated towards the underground space. The excavation and construction of such structures in the urban areas results in damage to the existing above ground structures if the construction is done in close proximity to the structures. In the present study a staged excavation of an underground construction for the Bangalore metro project is simulated with the endochronic constitutive model. In the Bangalore metro project the excavation for the underground station is done at the cricket stadium site. At the site there are two major buildings such as the six storied Hindustan Aeronautical Limited building and 100 years old BSNL masonry building. To minimize the impact on these structures were a major concern during the construction of the work. A robust support system consists of secant pile walls, soldier piles and horizontal struts are installed at the site. The OSV method known as the Onsite Visualization and monitoring is conducted to minimize the damage to the existing structures and the accidents at the construction site. Sensors are connected to LEDs which show change in color when the displacements and forces cross the triggered value. The field instrumentation is done with inclinometers, tilt meters and strain gauges connected to the sensors to observe the lateral deformation of the secant pile wall, tilt of the HAL building and the forces developed in the horizontal struts. The monitoring of field data is done for a period of five months from July to November. From the analysis of the field observed data it is clear that the support system provided were strong enough to resist the forces due to unloading. The lateral deformation of the secant pile wall and the forces developed in the strut were numerically analysed using the endochronic constitutive model and the results were compared with the field monitored data. The results show that the model captures the behaviour very close to the field data for a slightly higher modulus than that reported in the geotechnical report (BMRC report). This may be due to the fact that the value of modulus calculated experimentally might have some error. The analysis with the Mohr Coulomb model shows that the model over predicts the results very close to the surface of the excavation. This indicates that the influence of load is more on that particular depth for the Mohr Coulomb model. But the stiffness of the lateral support system is uniform throughout the depth; the endochronic model predicts the result more accurately than the Mohr Coulomb model. The strut forces developed in the horizontal support system is observed using the two models. The strut forces in the field is affected by so many factors such as the temperature variation, stages of excavation and other live loads acting on the site, so an exact comparison with the field data is quite difficult. The analysis shows that even though it is difficult to simulate the exact three dimensional nature of the problem in the present study the endochronic constitutive model captures the behaviour very well. The results obtained shows that the endochronic constitutive model implemented in the FLAC3D model library provides a very promising solution like any other constitutive model. As the theory is based on the irreversible law of thermodynamics and the formulation of the constitutive equation are based on the internal energy concept it can represent the material behaviour in accordance with the laws of continuum mechanics. The anisotropic behaviour of soil at higher strain level is well represented through the footing problem. The endochronic constitutive model is a very simple one to simulate the stress strain behaviour of the materials without the concept of yield surface; the parameters used in the equation can be obtained directly from a single triaxial stress strain plot. This study highlights the importance of a model without the concept of yield surface to capture the stress strain behaviour of any materials. Since the model is of completely plastic nature it has its own uniqueness in capturing the material behaviour due to loading and unloading.