Dissertations / Theses on the topic 'Permanent deformation model'

FundaÃÃo Cearense de Apoio ao Desenvolvimento Cientifico e TecnolÃgico
Permanent deformation or rutting is a major distress in asphalt pavements. To predict permanent deformation of asphalt mixtures the dynamic creep test is often used in laboratory, with the result presented in terms of the so called flow number. However, for this work it was performed the triaxial repeated permanent deformation load test, a confined test that better represents field conditions. The models that incorporate the flow number do not represent the main zone of the dynamic creep test result, denoted secondary region, in which the permanent deformation rate of growth is constant. In this work the Shift Model was used, which is a viscoplastic model that accesses the permanent deformation from the superposition principles, i.e., time-temperature superposition and time-stress superposition. Thus, the asphalt mixtures were tested under different loading conditions, temperature, load time and rest period, in order to assess three parameters of the test: parameter C, which indicates where the secondary region begins (parameter that governs the primary region of the test); the parameter α (alpha) is the slope of the secondary region; and the parameter B represents the level of permanent deformation of the secondary region. The results show that the TRLPD test is more severe than the conventional dynamic creep test. Nevertheless, the use of TRLPD test represents an advance in the understanding of the behavior of asphalt mixtures with respect to rutting performance, and has the advantage of allowing the use of results in computational simulations.
A deformaÃÃo permanente à um dos principais defeitos em pavimentos asfÃlticos. Para prever esta falha em revestimentos, por meio de ensaios laboratoriais, à frequentemente utilizado o ensaio de creep dinÃmico cujo resultado final à apresentado em termos do chamado flow number. No entanto, para este trabalho foi realizado o triaxial repeated load permanent deformation (TRLPD) test, que à um ensaio sob condiÃÃes de confinamento, a fim de melhor se aproximar das condiÃÃes encontradas em campo. Os modelos que incorporam o flow number nÃo representam a principal regiÃo de ensaio de creep dinÃmico, denominada regiÃo secundÃria, na qual o incremento de deformaÃÃo permanente cresce em valor constante. No presente trabalho utilizou-se o Shift Model, o qual à um modelo viscoplÃstico que avalia a deformaÃÃo permanente a partir da superposiÃÃo dos efeitos tempo-temperatura e tempo-tensÃo. Dessa forma, as misturas asfÃlticas foram testadas sob diferentes condiÃÃes de carregamento, temperatura, tempo de aplicaÃÃo de carga e perÃodo de repouso. Foram avaliados trÃs parÃmetros do ensaio em questÃo: o parÃmetro C, que fornece os dados de onde a regiÃo secundÃria se inicia (parÃmetro que governa a regiÃo primÃria do ensaio); o parÃmetro α (alfa), que à o aclive da regiÃo secundÃria; e o parÃmetro B, que representa o nÃvel de deformaÃÃo permanente da regiÃo secundÃria. Os resultados obtidos mostram que o ensaio TRLPD à mais severo do que o ensaio convencional de creep dinÃmico, porÃm considera-se que a utilizaÃÃo de ensaios confinados representa um avanÃo para o entendimento do comportamento das misturas asfÃlticas quanto à resistÃncia à deformaÃÃo permanente das mesmas, e este traz a vantagem de poder ser usado em simulaÃÃes computacionais.

This dissertation presents the development of an anisotropic viscoplastic continuum damage model to describe the permanent deformation of asphalt pavements. The model is developed to account for several phenomena that influence the permanent deformation of Asphalt Concrete (AC) at high temperatures. These phenomena include strain rate dependency, confining pressure dependency, dilation, aggregate friction, anisotropy, and damage. The model is based on Perzyna's theory of viscoplasticity with Drucker-Prager yield function modified to account for the microstructure anisotropy and damage. A parametric study was conducted to study the effect of key factors such as inherent anisotropy and damage on the model response. A preliminary investigation was conducted to demonstrate the capabilities of the model and its sensitivity to changes in the microstructure distribution and loading conditions. The model was used to describe laboratory experimental measurements obtained from the Federal Highway Administration (FHWA) Accelerated Loading Facility (ALF). The model had a good match with these experimental measurements. In particular, using the damage parameter, the model was able to capture the point at which AC experienced tertiary creep in a static creep test. A comprehensive experiment was conducted to systematically determine the model parameters and the evolution laws that describe AC hardening, anisotropy, and damage. The experiment consisted of a set of compressive triaxial strength tests conducted at three confining pressures and five strain rates. Based on these experimental measurements, the model was modified to include a nonassociated flow rule. The model was shown to capture the experimental measurements very well. Furthermore, an experiment was conducted to capture and characterize damage evolution in AC due to permanent deformation. AC specimens were loaded using a triaxial compression setup to four predefined strain levels at three confining pressures. X-Ray computed tomography and image analysis techniques were used to capture and characterize the evolution of cracks and air voids in the deformed specimens. Damage was found to be a localized phenomenon in the sense that there exists a critical section in an AC specimen that is mainly responsible for failure. The results of the damage experiment supported the damage evolution function proposed in the viscoplastic model.

Unbound Granular Materials (UGMs) are used in the base/subbase layers of flexible pavements for the majority of roads around the world. The deterioration of pavements increases with the increase of traffic loadings. To ensure the long-term performance and serviceability of pavement structures through a realistic design, the precise evaluation and comprehensive characterisation of the resilient and permanent deformation behaviour of pavement materials are essential. The present PhD study aims to investigate the characterisation of the resilient and permanent deformation behaviour of four road base UGMs sourced from quarries in Victoria, Australia, using Repeated Load Triaxial (RLT) testing. The triaxial system used in this study is instrumented with four axial deformation measurement transducers to achieve highly precise measurements and to evaluate the effect of instrumentation on the resilient modulus of UGMs. The resilient Poisson’s ratio of the studied UGMs is also determined using a radial Hall-Effect transducer. Moreover, a series of permanent deformation tests is performed to precisely characterise the axial and radial permanent deformation behaviour of UGMs and investigate the factors that may significantly influence the accumulated axial and radial permanent deformations. Finally, three permanent deformation models incorporated with a time-hardening procedure are employed to predict the magnitude of permanent strain for multiple stress levels of the RLT test. The predictions using the employed models are then compared against the measured values to evaluate the suitability of the models and to identify the model that best predicts the strain accumulation behaviour of the tested UGMs. While this study focuses on the resilient and permanent deformation behaviour of four Victorian UGMs under repeated loading, the knowledge generated from this comprehensive investigation will contribute towards the global development of more reliable methods for evaluating the long-term performance of pavement structures and minimising road maintenance and repair costs.
Doctor of Philosophy

Unbound granular materials (UGMs) used in the base and sub-base layers of flexible pavements play a significant role in the overall performance of the structure. Proper understanding and characterization of the deformation behaviour of UGMs in pavement structures are, therefore, vital for the design and maintenance of flexible pavements. In this study, the resilient deformation (RD) and the permanent deformation (PD) behaviour of UGMs were investigated for the better understanding and improved modelling of these deformation characteristics. The study is based on a series of repeated-load triaxial (RLT) tests carried out on several UGMs commonly used in pavement structures. Here, the influences of stress level and moisture content - two of the most significant factors affecting the deformation behaviour of UGMs - were analysed. The effects of the grain size distribution and the degree of compaction were also considered. The study on the RD behaviour indicated that the resilient stiffness (MR)of UGMs increases with the increased bulk stress level, which can be satisfactorily described by the k-θ model. Moisture was found to negatively impact the MR as long as the deformation was mostly resilient with a negligible amount of accumulated PD. Analysis of the influence of moisture on the parameters k1 and k2 of the k-θ model showed that k1 decreases with increased moisture and k2 is relatively insensitive to moisture. Based on these observations, a simple model was developed for the impact of moisture on MR. The performance of this model was comparable to an existing moisture dependent MR model. In contrast, it was further observed that at the later stages of the RLT tests, after a relatively large number of load applications, the MR increased with increased moisture up to the optimum moisture content. This occurred when the RD was accompanied by a significant amount of PD. Further investigation suggested that moisture aided the post-compaction (PC) and possible particle rearrangement that resulted in the increased PD and increased MR. In this case k1 decreased, whereas k2 increased, with increased moisture. The existing MR-moisture model did not work for this behaviour. This suggests that the effect of PC on MRshould be considered in modelling. However, although not explored in this study, it may be possible to simulate this effect of increase in MR with increased moisture due to PC using the proposed model if k2 is expressed as a function of moisture. The PD characteristics of UGMs were investigated based on the multistage (MS) RLT test. In contrast with the single stage (SS) RLT test, the MS RLT test accounts for the effect of stress history and enables a comprehensive study of the material behaviour under cyclic stresses of various magnitudes. Since the existing PD models cannot be directly applied for the MS loading procedure, a general formulation based on the time hardening concept was derived that can be used to extend the models for the MS loading conditions. Based on this formulation, some of the current models were calibrated and their performance in predicting the PD behaviour in MS RLT tests was compared. The investigation regarding the impact of moisture on PD showed that moisture significantly increases the accumulation of PD. Generally, materials with finer grading showed more sensitivity to moisture with regards to both PD and RD. To characterize the impact of moisture, moisture sensitivity of different grain size distributions and the impact of the degree of compaction on PD with reduced effort, a simple model was proposed. Unlike some of the well-performing existing models, this model can be calibrated using a single MS RLT test without requiring any separate static failure triaxial tests. This model was validated using the MS RLT test data with satisfactory results. The sensitivity of the parameters of this model was studied with respect to moisture content, degree of compaction and grain size distribution. Some reasonable trends for the sensitivity of the parameters to these influential factors were obtained, which suggests that these may be further developed to incorporate into the model.

QC 20150325

Recently, there has been growing interest on the behaviour of unbound granular material in road base layers. Researchers have studied that the design of a new pavement and prediction of service life need proper characterization of unbound granular materials, which is one of the requirements for a new mechanistic design method in flexible pavement. Adequate knowledge of the strength and deformation characteristics of unbound layer in pavements is a prerequisite for proper thickness design, residual life determination, and overall economic optimization of the pavement structure. The current knowledge concerning the granular materials employed in pavement structures is limited. In addition, to date, no general framework has been established to explain satisfactorily the behaviour of unbound granular materials under the complex repeated loading which they experience. In this study, a conceptual method, packing theory-based model is introduced; this framework evaluates the stability and performance of granular materials based on their packing arrangement. In the framework two basic aggregate structures named as Primary Structure (PS), and Secondary Structure (SS). The Primary Structure (PS) is a range of interactive grain sizes that forms the network of unbound granular materials. The Secondary Structure (SS) includes granular materials smaller than the primary structure. The Secondary Structures fill the gaps between the particles in the Primary Structure and larger particles essentially float in the skeleton. In this particular packing theory-based model; the Primary Structure porosity, the average contact points (coordination number) of Primary Structure, and a new parameter named Disruption Potential are the key parameters that determine whether or not a particular gradation results in a suitable aggregate structure. Parameters mentioned above play major role in the aggregate skeleton to perform well in terms of resistance to permanent deformation as well as load carrying capacity (resilient modulus). The skeleton of the materials must be composed of both coarse enough and a limited amount of fine granular materials to effectively resist deformation and carry traffic loads.
QC 20120601

Rut formation has long been recognized as a distress mechanism in flexible pavements. One of the causes of rut formation in flexible pavements is permanent deformation of uppermost asphalt concrete layers due to repeatedly applied traffic loading. The long term permanent deformation of asphalt concrete under repeated load is commonly called as dynamic creep. The primary objective of this thesis is to examine dynamic creep behavior of asphalt concrete specimens tested in laboratory and also study some suitable mathematical models for representing dynamic creep behavior. In this study, a set of uniaxial repeated load creep tests were performed on standard Marshall specimens prepared at three different bitumen contents. The effects of bitumen content and test condition parameters on dynamic creep behavior are examined. Among several mathematical creep models suggested by researchers, two well known models and a model proposed by the author are selected for representing the laboratory creep behavior. For each of these models, the interactions of the model parameters with varying bitumen content and test conditions are studied to detect probable definite trends, and to evaluate whether some relations for the model parameters as functions of bitumen content and test conditions can be developed or not. The results of analyses showed that all three mathematical models used in this study are successful in representing the laboratory dynamic creep behavior of asphalt concrete. The Power Model which has only two parameters is found to be the most stable and suitable model for parametric study among the three selected models. More consistent and definite interactions are observed between the parameters of this model and test conditions. However, within the scope of this study, no relations could be developed for the parameters of selected models as functions of bitumen content and test conditions because of limited test data.

The "sustainability" concept relates to the prolonging of human economic systems with as little detrimental impact on ecological systems as possible. Construction that exhibits good environmental stewardship and practices that conserve resources in a manner that allow growth and development to be sustained for the long-term without degrading the environment are indispensable in a developed society. Past, current and future advancements in asphalt as an environmentally sustainable paving material are especially important because the quantities of asphalt used annually in Europe as well as in the U.S. are large. The asphalt industry is still developing technological improvements that will reduce the environmental impact without affecting the final mechanical performance. Warm mix asphalt (WMA) is a type of asphalt mix requiring lower production temperatures compared to hot mix asphalt (HMA), while aiming to maintain the desired post construction properties of traditional HMA. Lowering the production temperature reduce the fuel usage and the production of emissions therefore and that improve conditions for workers and supports the sustainable development. Even the crumb-rubber modifier (CRM), with shredded automobile tires and used in the United States since the mid 1980s, has proven to be an environmentally friendly alternative to conventional asphalt pavement. Furthermore, the use of waste tires is not only relevant in an environmental aspect but also for the engineering properties of asphalt [Pennisi E., 1992]. This research project is aimed to demonstrate the dual value of these Asphalt Mixes in regards to the environmental and mechanical performance and to suggest a low environmental impact design procedure. In fact, the use of eco-friendly materials is the first phase towards an eco-compatible design but it cannot be the only step. The eco-compatible approach should be extended also to the design method and material characterization because only with these phases is it possible to exploit the maximum potential properties of the used materials. Appropriate asphalt concrete characterization is essential and vital for realistic performance prediction of asphalt concrete pavements. Volumetric (Mix design) and mechanical (Permanent deformation and Fatigue performance) properties are important factors to consider. Moreover, an advanced and efficient design method is necessary in order to correctly use the material. A design method such as a Mechanistic-Empirical approach, consisting of a structural model capable of predicting the state of stresses and strains within the pavement structure under the different traffic and environmental conditions, was the application of choice. In particular this study focus on the CalME and its Incremental-Recursive (I-R) procedure, based on damage models for fatigue and permanent shear strain related to the surface cracking and to the rutting respectively. It works in increments of time and, using the output from one increment, recursively, as input to the next increment, predicts the pavement conditions in terms of layer moduli, fatigue cracking, rutting and roughness. This software procedure was adopted in order to verify the mechanical properties of the study mixes and the reciprocal relationship between surface layer and pavement structure in terms of fatigue and permanent deformation with defined traffic and environmental conditions. The asphalt mixes studied were used in a pavement structure as surface layer of 60 mm thickness. The performance of the pavement was compared to the performance of the same pavement structure where different kinds of asphalt concrete were used as surface layer. In comparison to a conventional asphalt concrete, three eco-friendly materials, two warm mix asphalt and a rubberized asphalt concrete, were analyzed. The First Two Chapters summarize the necessary steps aimed to satisfy the sustainable pavement design procedure. In Chapter I the problem of asphalt pavement eco-compatible design was introduced. The low environmental impact materials such as the Warm Mix Asphalt and the Rubberized Asphalt Concrete were described in detail. In addition the value of a rational asphalt pavement design method was discussed. Chapter II underlines the importance of a deep laboratory characterization based on appropriate materials selection and performance evaluation. In Chapter III, CalME is introduced trough a specific explanation of the different equipped design approaches and specifically explaining the I-R procedure. In Chapter IV, the experimental program is presented with a explanation of test laboratory devices adopted. The Fatigue and Rutting performances of the study mixes are shown respectively in Chapter V and VI. Through these laboratory test data the CalME I-R models parameters for Master Curve, fatigue damage and permanent shear strain were evaluated. Lastly, in Chapter VII, the results of the asphalt pavement structures simulations with different surface layers were reported. For each pavement structure, the total surface cracking, the total rutting, the fatigue damage and the rutting depth in each bound layer were analyzed.
Il concetto di “sostenibilità” si riferisce allo sviluppo dei sistemi di supporto per la vita umana che minimizzino l’impatto sul sistema ambientale. Le opere che si inseriscono bene nel contesto ambientale circostante e le pratiche che rispettano le risorse in maniera tale da permettere una crescita e uno sviluppo a lungo termine senza impattare sull’ambiente sono indispensabili in una società moderna. Il progressi passati, presenti e futuri che hanno reso i conglomerati bituminosi materiali sostenibili dal punto di vista ambientale sono particolarmente importanti data la grande quantità di conglomerato usato annualmente in Europa e negli Stati Uniti. I produttori di bitume e di conglomerato bituminoso stanno sviluppando tecniche innovative per ridurre l’impatto ambientale senza compromettere le prestazioni meccaniche finali. Per esempio il conglomerato bituminoso ad “alta lavorabilità” (WMA), pur sviluppando le stesse caratteristiche meccaniche, richiede un temperatura di produzione minore rispetto a quella di un tradizionale conglomerato bituminoso a caldo (HMA) riducendo sensibilmente l’invecchiamento del legante. Anche il conglomerato additivato con polverino di gomma, ottenuto dalla frantumazione di pneumatici dismessi, è risultata essere un’alternativa eco-sostenibile al conglomerato stradale convenzionale. Oltretutto, l’utilizzo di questo additivo non è rilevante solamente dal punto di vista ambientale, costituendo materiale di risulta difficile da smaltire, ma anche per le proprietà meccaniche che lo stesso è in grado di conferire al conglomerato. L’obbiettivo principale di questa tesi è quello di dimostrare il duplice valore meccanico-ambientale di questi materiali innovativi, sottolineando come il concetto di sostenibilità, applicato alla progettazione delle infrastrutture viarie, non dipenda esclusivamente dai materiali impiegati. L’uso di materiali a basso impatto ambientale rappresenta solamente il punto di partenza della progettazione sostenibile. L’approccio ecocompatibile deve essere esteso anche ai metodi progettuali e alla caratterizzazione in laboratorio dei materiali al fine di conoscerne il comportamento e conseguentemente sfruttarne le potenzialità. La caratterizzazione volumetrica (Mix Design) e meccanica (Deformazioni Permanenti e Comportamento a fatica) di un conglomerato bituminoso è fondamentale e necessaria per una realistica previsione delle performance di una pavimentazione stradale. Una metodo progettuale avanzato ed efficiente potrebbe essere rappresentato dall’approccio Empirico-Meccanicistico (M-E). La progettazione Empirico-Meccanicistica consiste di un modello strutturale capace di prevedere gli stati tenso-deformativi all’interno della pavimentazione sotto l’azione del traffico e in funzione delle condizioni atmosferiche e di modelli empirici, calibrati sul comportamento dei materiali, che collegano la risposta strutturale alle performance della pavimentazione. Nel 1996 in California, per poter effettivamente sfruttare i benefici dei continui progressi nel campo delle pavimentazioni stradali, fu iniziato un estensivo progetto di ricerca mirato allo sviluppo dei metodi di progetto Empirico-Meccanicistici per le pavimentazioni stradali. Il risultato finale fu la prima versione del software CalME che fornisce all’utente tre approcci diversi di l’analisi e progetto: un approccio Empirico, uno Empirico - Meccanicistico classico e un approccio Empirico - Meccanicistico Incrementale - Ricorsivo. Questo dissertazione si focalizza sulla procedura Incrementale - Ricorsiva del software CalME basata su modelli di danno da fatica e accumulo di deformazioni permanenti ottenuti sperimentalmente attraverso una accurata caratterizzazione dei materiali in laboratorio. Tale procedura funziona per incrementi temporali successivi e, usando i risultati di ogni incremento temporale, ricorsivamente, come input dell’incremento temporale successivo, prevede le condizioni di una pavimentazione stradale per quanto riguarda il modulo complesso dei diversi strati, le fessurazioni superficiali dovute alla fatica, le deformazioni permanenti e la rugosità superficiale. Al fine di verificare le proprietà meccaniche delle miscele oggetto di studio e le reciproche relazioni in termini di danno a fatica e deformazioni permanenti una volta inserite nella sovrastruttura stradale per fissate condizioni ambientali e di traffico, la procedura sopracitata è stata adottata. I conglomerati bituminosi studiati, due tiepidi ed uno additivato con rubber, sono stati impiegati nella pavimentazione stradale come strato superficiale. Le performance delle pavimentazioni sono poi state confrontate in riferimento ad una pavimentazione contenente conglomerati tradizionali. Le tre tipologie di conglomerato oggetto di studio sono: un conglomerato bituminoso ad “alta lavorabilità” a gradazione “chiusa” (DGWMA), un conglomerato bituminoso modificato con polverino di gomma a gradazione “aperta” (GGRAC) e un conglomerato bituminoso ad “alta lavorabilità” additivato con SBS a gradazione aperta (PGGWMA). I primi due Capitoli sintetizzano gli step necessari a soddisfare i principi fondamentali alla progettazione sostenibile delle infrastrutture viarie. Nel primo Capitolo è stato approfondito il tema delle miscele di conglomerato eco-compatibili. In particolare sono state descritte dettagliatamente le proprietà dei Conglomerati tiepidi ad “alta lavorabilità” e dei Conglomerati con polverino di gomma. Inoltre è stato introdotto il problema dei metodi di progettazione delle sovrastrutture stradali flessibili, dai metodi razionali ai metodi Empirico Meccanicistici. Nel Capitolo due si è sottolineata l’importanza della caratterizzazione in laboratorio dei materiali di uso stradale basata su una appropriata selezione degli stessi e su uno studio di performance. Nel Terzo Capitolo, è stato introdotto il Californian Mechanistic Empirical design Software (CalME) attraverso una dettagliata analisi dei modelli alla base delle differenti procedure di progettazione in dotazione. Il Capitolo Quattro introduce il programma sperimentale e descrive le procedure di prova adottate fini alla caratterizzazione meccanica dei materiali. I risultati sperimentali a Fatica ed a Rutting ed i modelli di performance delle miscele oggetto di studio sono stati estrapolati nei Capitoli Cinque e Sei. In ultimo, nel Capitolo Sette, attraverso l’ausilio del CalME e dei modelli comportamentali estrapolati nei capitoli precedenti, sono riportati i risultati delle simulazioni effettuate con le diverse pavimentazioni in esame. Per ogni sovrastruttura sono state analizzate le seguenti forme di ammaloramento: superficie totale fessurata, ormaiamento totale e danno da fatica e ormaiamento relativo ad ogni strati legato.

This work is focused on the design and determination of the properties of porous asphalt and asphalt concrete for very thin layers with TecRoad addition. The water sensitivity, particle loss, stiffness, fatigue and low temperature characteristics and resistance to permanent deformation are determined for a description of mixtures properties. Subsequently, the mixtures are compared and recommendations for use in maintenance and reconstruction of roads are prepared.

The diploma thesis deals with technology for the implementation and use of asphalt concrete for very thin layers (BBTM) with use of asphalt binder of high-polymer modification (HiMA). Further, there are described selected and performed functional tests. Thesis also contains design of a mixture for bituminous concrete type targeted for very thin layers with different types of binders. After a suitable design of the mixture, laboratory tests were carried out (stiffness modulus, resistance to permanent deformation, low temperature characteristics, water resistance and particle loss). The output of this work is a set of measured values and processed results with their interpretation.

This master's thesis deals with the possibility of special asphalt-rubber mixture using - Stress Absorbing Layer (SAL). In the theoretical part the SAL and test methods are described. In the practical part, several different mixtures are designed and selected mixtures were tested. Low-temperature characteristics, permanent deformations, bending tensile relaxation, stiffness modulus and fatigue properties were determined. Based on the test results the mixtures were compared and their benefit is evaluated according to Performance Pavement Design Method, the pavement structure was evaluated by using of computer programme LayEps.

Aim of this thesis is the usage of the open-graded asphalt concrete filled with a special cement grout in the road structures. Thesis defines the main concrete properties and explains related legislation and norms that apply. In addition, laboratory design of asfalt mixtures and a tree kind mortal filler and possibilities of mortal filler pigmentation are dealth with. Finally, thesis evaluates the results from various laboratory tests that were performed on the specimens made from final mixtures.

The thesis deals with the matter of usage of special asphalt binders for production of asphalt mixtures containing recycled materials in asphalt plant. For comparison analysis of characteristics of special binder used in roads is necessary to compose different mixtures of asphalt – one with binder containing R-materials, and another benchmark mixture with binder used in common mixtures without recycled materials. Investigation of features of mixtures with different binders is carried out by selected performance tests of asphalt mixtures. Evaluation and comparison of the results is described in the final section of the thesis.

碩士
國立成功大學
航空太空工程學系
87
The scope of the thesis is to study the thermo-elasto-plastic deformation response of a steel plate subject to hot working forming process. The laser heating device is adopted to heat the steel plate along a specific predefined heating path. We utilize a simplified thermo-elasto-plastic model to relate laser heating effect into the equivalent bending moment and shrinkage force exerted on the laser heated plate. These equivalent loadings are then introduced to a commercial finite element code-MARC. The resultant thermal induced permanent plate deformation can then be obtained. The purpose of using the simplified model is to reduce a large amount of finite element computational time. Notice that the given conditions of the present problem contain the size of specimen, laser power and the heating path and speed. In the line heating situation, the difference between the numerical simulated result and experiment finding is within 15 %. Moreover, the neural network is adopted to predict the deformation of a specific steel plate in question if the prescribed laser heating power, path and the speed of laser head are given. In this work, the back-propagation neural network with adaptive learning rate scheme is used. The heating conditions are used as the input in the input layer of neural network, and the network is expected to output the unknown deformation of steel plate. The result of leaning shows that the present neural network is efficient and is capable of simulating the deformation of steel plate in question.

Thesis (M.S.)--State University of New York at Buffalo, 2006.
Title from PDF title page (viewed Oct. 26, 2006). Available through UMI ProQuest Digital Dissertations. Thesis adviser: Bursik, Marcus I. Includes bibliographical references.

Thesis (Ph.D, Civil Engineering) -- Queen's University, 2011-01-31 20:52:11.162
One of the most severe hazards for buried pipelines, which are sometimes referred to as lifelines due to their essential role in delivering vital resources, is the hazard due to Permanent Ground Deformation (PGD). Earthquake induced PGD can be caused by surface faulting, landslides and seismic settlement. In this thesis, the behaviour of buried pipelines subject to normal faulting has been experimentally investigated through a series of centrifuge tests performed on both continuous and jointed pipelines. Both pipe and soil displacements were measured using image analysis. Signal processing techniques were then developed to filter this data so as to enable the calculation of curvature and other aspects of the response from the observed pipe deformations. First, a series of centrifuge tests was conducted on continuous pipelines of varying materials, representing a wide range of pipe stiffness relative to the soil and investigating the effect of pipe stiffness relative to the soil on soil-pipe interaction. The experimentally derived p-y curves at different locations along the pipe were compared to the recommended soil-pipe interaction models in the relevant guidelines. These p-y curves showed that the central shearing region was not captured well with independent soil springs. The response of the pipelines predicted by the ALA (2001) guideline, however, was shown to match the experimental data within 50%. Two new simplified design approaches were then developed. The first features calculations based on simplified pressure distributions. The second featured peak curvature normalized using a characteristic length, ipipe, the distance from peak to zero moment. A series of centrifuge tests using brittle pipes was also performed. The pipes were buried at three different depths, and the post-failure fracture angle of the pipe was measured to be used as an input for design of liners. Based on the experimental data, a computationally efficient approach was developed to estimate the initial fracture angle which occurs immediately after the pipe breaks. The last series of centrifuge tests was conducted on jointed pipelines with five different joint stiffnesses to investigate the flexural behaviour of jointed pipelines under normal faulting. Based on the observed pipe response, a simplified kinematic model was proposed to estimate the maximum joint rotation for a given geometry, pipe segment length, and the magnitude of the imposed ground displacement.
Ph.D

The work presented in this thesis is aimed at improving the accuracy of one of the components of a flexible pavement design procedure commonly used in South Africa, namely the South African Mechanistic- Empirical Design Method. This is achieved through the development of a new design approach and permanent deformation model for the pavement subgrade. The new distress model for the pavement subgrade was developed from a comprehensive Accelerated Pavement Testing (APT) database on subgrade behaviour and permanent deformation that was generated by a fleet of Heavy Vehicle Simulators (HVSs) over 20 years of testing in South Africa. A literature review of the origin of the current subgrade design model that is used by the South African Mechanistic-Empirical Design Method revealed that that model is based on very little actual subgrade performance data. The model was also developed from the AASHO road test data and adjusted for South African conditions, based on general observations of subgrade behaviour without any calibration. Previous researchers have illustrated the potential of using Heavy Vehicle Simulator data to develop structural pavement design models and it was decided to apply a similar process to the permanent deformation of the pavement subgrade. The present investigation consisted of two components, namely, the evaluation of the resilient and the permanent deformation response of the pavement subgrade, the emphasis in this thesis being more on the permanent deformation response. A general, multi-dimensional empirical model was formulated for the permanent subgrade deformation and the characteristics of the model investigated based on previously published permanent deformation data and mathematical assessment. A set of 35 HVS tests for which suitable data were available was identified and additional field and laboratory tests were done on selected sites to improve the classification of the subgrade materials at these sites. Standard procedures were developed to present the pavement, instrumentation and load sequence data of each HVS test. A process for doing the initial analysis of the deflection and permanent MDD displacement data and presenting the data was also developed. In terms of the resilient response of the subgrade, it was shown that the vertical depth deflection and vertical strain could be modelled accurately if an appropriate set of resilient modulus values was selected for the pavement layers. A detailed investigation of the resilient response of selected HVS sections did, however, clearly illustrate the stress-dependent behaviour of subgrade material, resulting in resilient modulus values being determined, which were well outside the range that would normally be expected for natural gravel subgrade material. This research needs to be continued to enable the development of a comprehensive set of stress-dependent resilient modulus models for South African subgrade materials. The selection of an appropriate critical parameter that can be used as a predictor of permanent subgrade deformation was done by an investigation of the relationship between potential critical parameters and several permanent deformation parameters. It was found that the subgrade elastic deflection showed the best correlation with the subgrade bearing capacity (the number of load repetitions that can be sustained before a terminal rut condition is reached). The vertical subgrade strain that is currently used in the South African Mechanistic-Empirical Design Method in fact correlates poorly with subgrade bearing capacity and has to be replaced with subgrade elastic deflection. A set of subgrade bearing capacity or design models was developed for different levels of permanent subgrade deformation. These models are referred to as S-N models and form contour lines on the general permanent deformation model that was formulated. The subgrade design model accommodates loading conditions ranging from a 40 kN dual wheel load to a 100 kN dual wheel load as well as subgrade materials ranging from a material quality one class better than that which would normally be used for a subgrade, to the lowest possible material class. The model is therefore very flexible in terms of its application.
Prof. P. Pretorius