Dissertations / Theses on the topic 'Repeated loading'

The main aim of the research was to study the behaviour of a silty clay under two-way cyclic loading. Equipment was developed for the application of a sinusoidally varying deviator stress to a sample in the triaxial cell. The equipment was designed to apply deviator stresses in both compression and extension during each cycle. ii A programme of monotonic and two-way cyclic triaxial tests has been performed on samples of Keuper Marl, isotropically consolidated to a range of stress histories. The build-up of strain and pore pressure during repeated loading is discussed. A model is developed, within the framework of the critical state theory of soil mechanics, to predict the amount of pore pressure produced by a given number of loading cycles at a known stress level. An extension of the model is suggested whereby the varied loading, more appropriate to offshore foundation conditions, may be analysed. In addition, a programme of monotonic and cyclic simple shear tests has been performed. The equipment has been developed, during the course of the research, to enable the direct measurement of pore pressure during shear. At attempt has also been made to monitor the change in lateral stress during shear by means of an instrumented membrane. The results of the simple shear tests have been analysed and are presented in terms of horizontal shear stress and effective vertical stress. An attempt has been made. to deduce the principal stresses present in a sample subject to simple shear loading and a method of relating the results from monotonic tests using simple shear and triaxial devices is discussed.

The primary aim of this research was to investigate the behaviour of a clay subjected to a loading regime similar to that experienced by a road subgrade under traffic loading in Great Britain. The material used was Keuper Marl. The samples were anisotropically consolidated in a triaxial apparatus from a slurry which allowed careful control over the stress history and produced uniform samples. The samples were fully instrumented and the apparatus was capable of applying repeated axial and radial stresses. The test programme was designed to investigate the resilient and permanent response of the samples to a variety of stress pulse magnitudes and time periods. The main conclusions were: i) The material exhibited a marked stress softening. ii) The mean normal effective stress remained constant under a variety of total stress paths over the range of frequencies tested. iii) The resilient response was found to depend on the magnitude of the applied stress pulse and the mean normal effective pressure, and to be independent of the preconsolidation pressure. iv) The material exhibited significant thixotropy. A smaller parallel series of tests was carried out on compacted triaxial samples of three clays (Keuper Marl, Gault clay and London clay) in a simple pneumatic repeated load triaxial rig. The test programme was designed to investigate the resilient response of the samples over a range of repeated deviator stresses. The suction moisture content relationship for each clay was established, and the resilient response of the clay was found to be controlled by the magnitude of the stress pulse and the suction. A series of California Bearing Ratio tests was carried out on compacted samples of the three clays, and on anisotropically consolidated samples of Keuper Marl, to allow a comparison to be made between the resilient modulus and CBR. A review of previous work is presented.

Unsaturated soils constitute a large proportion of the foundation materials supporting infrastructure throughout the world and they are subject to various loading conditions. The research into the behaviour of unsaturated soils has been ignored for many centuries; however the recent years have witnessed a surge of research activities looking into various aspects. The present research reported in this thesis places emphasis on the perfomlance of unsaturated soils under repeated loading. As part of the research, a series of monotonic and repeated load triaxial tests were perfonned on samples of kaolin clay prepared to various compaction water contents, 22%, 25%, '28% and 31% and two different compression pressures, 400kPa and 800kPa. Undrained tests were conducted in a newly developed simple triaxial cell for testing unsaturated soil under repeated loading with hydraulic loading system, hall-effect transducers for on-sample strain measurements and thennocouple psychrometer for suction measurements. Drained tests were conducted in twin-cell stress path apparatus with controlled suction by axis translation teclmique. The main findings of the research provide a remarkable insight into the influence of suction, and more imp011antly the degree of saturation, on the permanent defonnation and resilient behaviour of unsaturated compacted kaolin. At high suctions repeated loading was found to have a positive effect on the soil pelfoIl1lance. However, at low suction, repeated loading had a detrimental effect on the strength and stiffness of unsaturated soil, under both drained and undrained conditions. An important outcome of the research is the progression of permanent defoIl11ation throughout repeated loading with no asymptotic value ever being reached, particularly at loading amplitudes of more than 70% of the failure load.

Structures deform at high strain rates and temperatures when exposed to impulsive loads. To accommodate the macro change there are microstructural changes that occur, i.e., grain morphology and shear banding. Most studies report on macroscopic response, i.e., large inelastic deformation and tearing of the structure, while limited studies have reported on microscopic changes that develop in the structure. The microstructure is directly related to the mechanical properties and performance of the material. Therefore, understanding the effect of high strain rate loadings on the microstructural evolution and subsequent mechanical properties of metals and alloys is necessary for mechanical design. The main objective of this research was to investigate microstructural changes to characterise the strain distribution and plastic deformation, owing to impulsive loading. Features within the microstructure that could be used to characterise deformation included grain size morphology changes, the presence of shear bands and sub-grain networks. The electron backscatter diffraction (EBSD) technique, which used Kikuchi patterns to characterise the strain distribution in the crystal of the deformed material, was also used as a characterisation tool. The first step in the experimental procedure was to select the appropriate material to investigate these microstructural changes. There was also the systematic investigation into the use of single and double heat treatments. These were used to achieve a large equiaxed grain structure, which was desirable from a microstructural point of view but was not desirable for blast-resistant material selection. The two-step heat treatment was concluded to be the most suitable heat treatment for the annealing and homogenisation of the AISI 430 stainless steel plates. The AISI 430 stainless steel plates used were 244 mm by 244 mm in size and had a circular exposed area of 106 mm. These plates were subjected to repeated explosive blasts, using a plastic explosive (PE4). The charge mass was varied for each test and the stand-off distance was kept constant at 150 mm for uniform loads and 13 mm for localised loads. Two plates were selected to investigate the uniform loading scenario. The first plate, a torn plate, used a charge mass of 30 g and one blast and the second plate, an inelastically-deformed plate, used a charge mass of 10 g and was exposed to three blasts. These two plates offered the same overall charge load with a different strain path. A further two plates were chosen for the investigation into the localised loading scenario. One plate, a petalled plate, used a 6 g charge mass and was exposed to two blasts and the second plate, an inelastically-deformed plate, used a 5 g charge mass and was also exposed to two blasts. The latter two plates offered an investigation into the effect of an increased charge load, where charge load affected the strain rate of the deformation resulting from the blast load. All four plates were sectioned across the midline of the dome and then ground and polished to a mirror finish, using OP-S. The polished samples were analysed, using optical microscopy and EBSD. In addition, Vickers hardness tests were carried out along the midline of the sectional plate profiles, in order to evaluate the extent of strain hardening. All the plates showed either a response of inelastically deforming or of complete or partial tearing failures when subjected to blast loads. For inelastic deformation failures, a global dome was characteristic of the uniform loading condition and an inner dome superimposed by the global dome was characteristic of the localised loading condition. Variation of charge mass and the number of blasts showed an increasing linear relationship between the impulse and midpoint deflection. The macrostructure showed a large variation of failures in the localised condition. The microstructural characterisation results produced micrographs showing regions of long, flat grains with multiple sub-grain networks, indicating deformed microstructures of the blast loaded plates. Parts of the microstructures displayed equiaxed/recrystallised grains characteristic of restoration processes, owing to high temperatures. Vickers hardness tests indicated an increase in material hardness as the number of blasts was increased, with a maximum hardness in the central region of the plates. In the first investigation, into uniform loading, the material characterisation results, combined with the fractography results, indicated brittle failure modes typical of high strain rate failures in strain rate sensitive materials, such as the chosen AISI 430 stainless steel plates. In the second investigation, into localised loading, the material characterisation results, combined with the fractography results, indicated a more ductile failure, owing to a 1 g incremental increase of charge mass, which confirmed the strain rate sensitivity of this material.

Little effort has been made to apply the Critical State Soil Mechanics concept to the prediction of pavement response. The aim of this research is to apply soil mechanics principles, particularly the kinematic hardening concept, to the prediction of the response of lightly trafficked pavements to repeated loading. For this purpose, the finite element critical state program CRISP is used. A comparison is made between the predictions given by the three-surface kinematic hardening (3-SKH) model and a layered elastic analysis BISAR for the resilient deformation produced by repeated loading of a thinly surfaced pavement, and the models are found to be in good agreement. The ability of the 3-SKH model to predict soil behaviour under cyclic loading, and under one-dimensional loading, unloading and reloading is also evaluated. A comparison between model predictions and experimental data obtained by other researchers shows that the 3-SKH model over-predicts the value of K0,nc and hence shear strain during monotonic loading. This problem is magnified when the model is applied to cyclic loading behaviour where large numbers of cycles are involved. The model also predicts an accumulation of negative shear strain with increasing number of cycles under some stress conditions. This will lead to unrealistic predictions of rutting in pavements. However, the model is suitable for obtaining resilient parameters for input to a layered elastic analysis program. A new model, which is a modified version of the 3-SKH model, is therefore proposed by modifying the flow rule and the hardening moduli. This model can correctly predict the value of K0,nc and reduce the amount of shear strain predicted. The model also eliminates the problem of accumulation of negative shear strain with increasing number of cycles. The new model introduces two additional parameters, one of which can be determined by one-dimensional normal compression test, and the other by fitting a set of cyclic loading data. The new model is used to design the required thickness of granular material using the permissible resilient subgrade strain and permanent rut depth criteria during construction. It is found that the new model predicts a realistic granular layer thickness required to prevent excessive rutting, thus showing much promise for use in design of thinly surfaced pavements.

Repeated undrained load tests were carried out under the application of cyclic deviator stresses at a frequency that varies from 0.0001 Hz up to 0.001 Hz. For a specific amplitude of applied stress, a critical level of repeated loading (CLRL) was evaluated for both kaolinite and crust clays. The strength of the soil is affected by the frequency, cyclic fluctuation of water table, and the amount of axial strain developed during cycling. The decrease in postcyclic strength is strain-dependent. It is further shown that cycling below the CLRL causes an increase in the overconsolidation of the clayey soils. The effect of cycling in behaviour of soils increases with increasing the OCR. This thesis also describes a method for the determination of in situ horizontal stresses of heavily overconsolidated sands using a stress-path triaxial apparatus. This method was proposed by Garga and Khan (1991) who applied it for overconsolidated clays. The proposed method is based on the concept that if the radial stress exceeds the in situ horizontal stress, while maintaining the axial stress constant and equal to the in situ vertical effective stress, only then will the sample experience significant axial strain. In this investigation, the above method is applied to the samples of known stress histories of overconsolidated sand. The effect of the complex stress history undergone by soils on the estimation of K$\sb0$ by the proposed method is investigated in laboratory. It is found that the proposed method replicated the imposed "in situ" horizontal stress exactly. Also this method is capable of estimating $\rm K\sb0$ of an overconsolidated soil irrespective of the previously imposed stress history. (Abstract shortened by UMI.)

Este trabalho descreve o comportamento da aderência do concreto armado sob ações monotônicas e repetidas através de uma revisão bibliográfica e de ensaios de arrancamento padronizados. A influência de alguns parâmetros foi analisada, como diâmetro da armadura, tipo e amplitude de carregamento. Os resultados dos ensaios monotônicos foram comparados com as recomendações do CEB-FIP MC 1990, EUROCODE 2 e NB-1/78. Também foi realizada a análise numérica da aderência monotônica por meio de elementos finitos. Considerou-se a barra lisa, elementos de contato entre o aço e concreto e comportamento elástico-linear dos materiais; pois a ruína experimental da ligação ocorreu pelo corte do concreto entre as nervuras. A resistência monotônica da ligação ficou compreendida entre condições boas e ruins de aderência. Os resultados calculados de acordo com as normas foram muito diferentes em relação aos valores experimentais, e apresentaram uma dispersão muito grande. A força repetida ocasionou a perda de aderência pelo crescimento progressivo dos deslizamentos. Os modelos numéricos não representaram o comportamento experimental, devido à resposta força-deslizamento não-linear.
This research describes the bond behaviour in reinforced concrete under monotonic and repeated loading through a state-of-art and standard pull-out tests. The influence of some parameters was analysed as deformed bar diameter, type and amplitude of loading. The monotonic test results were compared with recommendations of CEB-FIP MC 1990, EUROCODE 2 and NB-1/78. The numerical analysis of monotonic bond was realized through finite elements. It was considered smooth bar, contact elements between the steel and concrete, and materials as of linear-elastic behaviour, because the experimental degradation of bond was caused by concrete between the ribs sheared off. The monotonic bond resistance resulted between good and bad bond conditions. The results calculated according to the codes were very different from the experimental values and very disperse. The repeated loading causes bond degradation by progressive increase of slip. The numerical specimens did not represent the experimental behaviour because of the non-linear load-slip response.

Static stretching is commonly performed by athletes and clinicians on the assumption that it increases joint range of motion (ROM). However, observations from our laboratory indicate that there is an apparent inter-individual variance in the change in ROM in response to static stretching. Furthermore, prolonged repetitive loading has also been shown to affect ROM of a joint or series of joints. In particular, runners have a significantly decreased hamstring ROM. The aim of this study was to investigate the factors which are associated with a change in ROM in response to 1) a static stretch session and 2) prolonged repetitive loading. The findings showed that there is a variable response in the change in ROM following both a SSS intervention and in response to participation in a 42.2 or 56 km road race. More specifically, about 10% of the participants had a reduction in ROM after the SSS while the majority of participants had a reduced ROM after completing the marathon or ultra marathon.

This study is intended to provide researchers with empirically derived guidelines for conducting factor analytic studies in research contexts that include dichotomous and continuous levels of measurement. This study is based on the hypotheses that ordinary least squares (OLS) factor analysis will yield more accurate parameter estimates than maximum likelihood (ML) and principal axis factor anlaysis (PAF); the level of improvement in estimates will be related to the proportion of observed variables that are dichotomized and the strength of communalities within the data sets. To achieve this study's objective, maximum likelihood, ordinary least squares, and principal axis factor extraction models were subjected to various research contexts. A Monte Carlo method was used to simulate data under 540 different conditions; specifically, this study is a four (sample size) by three (number of variables) by three (initial communality levels) by three (number of common factors) by five (ratios of categorical to continuous variables) design. Factor loading matrices derived through the tested factor extraction methods were evaluated through four measures of factor pattern agreement and three measures of congruence. To varying degrees, all of the design factors, as main effects, yielded significant differences in measures of factor loading sensitivity, agreement between sample and population, and congruence. However, in all cases, the main effects were components of interactions that yielded differences in values of these measures that were at least medium in effect size. The number of factors imbedded in the population was a component in six interactions that resulted in medium effect size differences in measures of agreement between population and sample factor loading matrices. of factor loading sensitivity, general pattern agreement, per element agreement, congruence, factor score correlations, and factor loading bias; in terms of the number of interactions that yielded at least medium effect size differences in measures of sensitivity, agreement, and congruence. The number of factors design factor exerted a larger influence than any of the other design factors. The level of communality interacted with the number of factors, number of observed variables, and sample size main effects to yield at least medium effect size differences in factor loading sensitivity, general pattern agreement, per element agreement, congruence, factor score correlations, factor loading bias, and RMSE; in terms of the number of factors that included communality as a component, this design factor exerted the second largest amount of influence on the measures of sensitivity, agreement, and congruence. The level of dichotomization, sample size, and number of observed variables were included in smaller numbers of interactions; however, these interactions yielded differences in all of the outcome variables that were at least medium in effect size. Across the majority of interactions among the manipulated research contexts, the ordinary least squares factor extraction method yielded factor loading matrices that were in better agreement with the population than either the maximum likelihood or the principal axis methods. In three of the four measures of congruence, the ordinary least squares method yielded factor loading matrices that exhibited less bias and error than the other two tested factor extraction methods. In general, the ordinary least squares method yielded factor loading matrices that correlated more strongly with the population than either of the other two tested methods. The suggested use of ordinary least squares factor analytic techniques represents the major, empirically derived recommendation derived from the results of this study. In all tested conditions, the ordinary least squares factor extraction method identified common factors with a high degree of efficacy. Suggested studies for future would incorporate the limiting constraints associated with this dissertation into methodological studies to extend the generalizability of conclusions and recommendations into areas that are beyond the scope of this dissertation.

Im Mittelpunkt der vorliegenden Arbeit steht die gezielte Analyse des Verbundverhaltens zwischen Bewehrungsstahl und Beton unter kombinierter Beanspruchung aus Ermüdung und Querzug. Den Hintergrund bilden Stahlbetonbauteile, wie z. B. Fahrbahnplatten von Verbundbrücken, welche einen zweiaxialen Lastabtrag unter nicht vorwiegend ruhenden Belastungen aufweisen. Die Untersuchungen für normal- und hochfesten Beton erfolgten an Ausziehkörpern mit einem durch Querzugspannungen hervorgerufenen Längsriss entlang des Bewehrungsstabes. Das Versuchsprogramm beinhaltete hochzyklische Schwellversuche mit unterschiedlichen Schwingspielen und variierenden Längsrissbreiten bis zu einer Million Lastwechseln. Anhand der Entwicklung des Schlupfes zwischen Bewehrungsstab und Beton konnte eine deutliche Abhängigkeit des Verbundwiderstandes vom Querzug beobachtet werden. Aufbauend auf der Schlupfentwicklung erfolgt die Ableitung von normierten Wöhlerlinien der Verbundermüdung. Diese Wöhlerlinien können direkt in Beziehung zu den Wöhlerlinien der Betonstahlermüdung gesetzt werden und vereinfachen die Erstellung von Dauerfestigkeitsdiagrammen für Bemessungszwecke. Es wird deutlich, dass die Ermüdungsfestigkeit des Verbundes durch das Vorhandensein eines Längsrisses gegenüber der Betonstahlermüdung verstärkt an Bedeutung gewinnt
The main focus of the present work is the specific analysis of the bond behaviour between reinforcement and concrete under combined loading due to fatigue and transverse tension. The background is formed by reinforced concrete elements such as bridge decks of steel-concrete composite bridges, which show a biaxial load bearing behaviour under not predominantly monotonic loading. The investigations for both normal strength and high performance concrete were conducted on pull-out specimens with a longitudinal crack along the reinforcing bar caused by transverse tensile stresses. The experimental program included high cyclic tests with different stress ranges and varying longitudinal crack widths up to one million load cycles. By means of the slip development, a definite dependency of the bond strength on the transverse tension could be observed. Based on the slip development, normalised S-N curves for bond fatigue have been deduced. These S-N curves can be set in direct relation to the S-N curves for steel fatigue and simplify creating constant life diagrams for design purposes. It becomes clear that the bond fatigue strength, due to an existing longitudinal crack, gains in importance in comparison to the fatigue strength of the reinforcing steel

Abstract Compaction of Soil by Repeated Loading Rouzbeh Roudgari Construction of roads is usually made by stripping the top soil (600 to 1000 mm), which often contains organic materials, and replacing it with a layer of subgrade material (crushed stones, well-graded sand). One of the main design requirements is that the subgrade material must be compacted up to a minimum of 95% of the Proctor maximum dry density, as determined from laboratory test results (AASHTO T99). This requirement is usually specified as a norm in any contract document involving field compaction. Soils can be compacted by repeated, systematic application of high energy using hammer. The imparted energy is transmitted from the ground surface to the deeper soil layer by propagating shear and compression waves types, which force the soil particles into a denser state (R. Massarsch, 1999) Research in this field has been directed to establish relationships between the water content, the dry density and the compacting effort, the type of soils which allow a higher level of compaction, and to develop field equipment and techniques which would be more effective in performing field compaction. Nevertheless, there are reports to confirm that achieving 95 % of the Proctor maximum dry density in the field compaction is impossible in some cases. The role of the surrounding soils, in particular the underlying layer, in determining the level of compaction, is a paramount parameter in achieving high level of compaction. This thesis presents a plane-strain numerical model using PLAXIS computer software to simulate shallow compaction of a subgrade layer underlain by a deep deposit of various stiffness levels. The compaction effort is applied by means of repeated loading on the ground and modeled as a static load applied to the soil through a rigid plate having similar properties of roller material. Based on the results obtained in this study, it can be stated that the level of compaction achieved in the field depends on the thickness of the subgrade layer, stiffness of the lower layer, the number of load cycles, and the magnitude of the load applied. The results of this study are presented in the form of compression curves of the subgrade and lower layer, and accordingly, the level of compaction for a given soil/load/geometry conditions can be predicted. Design guidelines are presented for practitioners.

博士
國立中央大學
土木工程研究所
93
Construction specifications generally require that subgrade soils be compacted in the field at or near optimum moisture content (OMC). As such, subgrade soils should be treated as unsaturated soils. Soil suction is a fundamental physical property of unsaturated soils, since soil suction dictates the state of stress in unsaturated soils. It was known resilient modulus model is a function of stress state. Hence, this study developed a resilient model based on deviator stress and matric suction. This study was undertaken to evaluate the variations of soil suction with the moisture content for two soils. In particular, the effects of compaction energy on soil suction were investigated. The matric suctions were determined by the filter paper method on soil specimens after the resilient modulus test. Findings from these tests indicated that soil suction of compacted soil is influenced by the compaction energy and water content. Soil suction increases with decreasing water content. However, high compaction energy does not necessarily lead to high soil suction. Test results demonstrated that resilient modulus correlates better with the matric suction than with total suction. Matirc suction was found to be a key parameter when predicting the resilient modulus of cohesive subgrade soils. Also, a prediction model incorporating deviator stress and matric suction for subgrade soil resilient modulus, called the deviator stress-matric suction model was established. Based on the response of subgrade soil under repeated loading tests, a critical stress level can be defined. At stress levels higher than the critical level, the plastic strain of subgrade soil accumulates rapidly and an unstable condition occurs, and soil tends to soften after a specific number of load applications. Using the plastic strain data obtained at stress states below the critical level, a multiple regression plastic model for cohesive subgrade soils was developed. Taking both the deviator and confining stresses into account, the model can be used to predict the permanent deformation in the subgrade of flexible pavements under repeated loading in a reasonable way.

Key factors that influence the design of paved and unpaved roads are the strength and stiffness of the pavement layers. Among other factors, the strength of pavements depends on the thickness and quality of the aggregates used in the pavement base layer. In India and many other countries, there is a high demand for good quality aggregates and the availability of aggregate resources is limited. There is a need for the development of sustainable construction methods which can handle aggregate requirements with least available resources and provide good performance. Hence it is imperative to strive for alternatives to achieve improved quality of pavements using supplementary potential materials and methods. The strength of pavement increases with increase in the thickness of the base which has a direct implication on construction cost whereas decreasing the thickness of the base makes it weak which results in low load bearing capacity especially for unpaved roads. The use of different types of geosynthetics like geocell and geogrid are a potential and reliable solution for the lack of availability of aggregates and studies are conducted in this direction. To better understand the performance of any geosynthetically reinforced base layers, it is essential to characterize the pavement material by studying the behavior of these materials under static as well as repeated loading. For unpaved roads, the base layer, made of granular aggregates plays a crucial role in the reduction of permanent deformation of the pavements. The resilient modulus (Mr) of these materials is a key parameter for predicting the structural response of pavements and for characterizing materials in pavement design and evaluation. Usually, during the design of flexible pavements, pavement materials are treated as homogeneous and isotropic. The use of rollers in the field during pavement construction leads to a higher compaction of material in the vertical direction which introduces stress-induced anisotropy in the base material. The effect of stress-induced anisotropy on the properties of the granular material is studied and discussed in the first part of the research by conducting repeated load triaxial tests. Isotropic consolidated and anisotropically consolidated samples were prepared to investigate the behavior of base materials under stress induced anisotropic conditions. An additional axial load was applied on the isotropically consolidated sample to create anisotropically consolidated sample. The axial loading was provided such that the stress ratio (σ1/σ3), during anisotropic consolidation was kept constant for all the tests at different confining pressures. The effect of repeated loading on the permanent deformation and the resilient modulus for both isotropically and anisotropically consolidated samples, at different confining pressure and loading conditions, are discussed. The behavior of both anisotropically and isotropically consolidated samples has been explained using the record of the excess pore pressures generated during the experiments. The experimental studies show that the permanent strains measured in the vertical direction of the anisotropically consolidated samples are less compared to the results obtained for isotropically consolidated samples. The resilient moduli of the anisotropically consolidated samples were also observed to be higher than that of the isotropically consolidated sample. The study conducted on the pore pressure of both the samples explains better performance of the anisotropically consolidated samples. The studies showed that the isotropically consolidated samples showed higher pore pressures compared to the anisotropically consolidated specimens. Another factor which influences the resilient modulus of the pavement materials is the geosynthetic reinforcement. Geocell and geogrid reinforced triaxial samples were prepared to study the effect of reinforcement in the resilient modulus of the base materials. From the literature, it can be seen that most of the research in the triaxial testing equipment were carried out in the non-destructive range of confining pressure and deviatoric stress. Several studies have been conducted by the researchers to visualize the pavement response in the elastic range. However, the studies in the plastic creep range and incremental collapse range were highly limited. In the current study, testing is carried out on the triaxial samples for two different stress ranges. In the first sections, loading was applied in the elastic and elastic shakedown range as per AASTHO T-307. For various loading sequences, a comparative analysis has been done for the resilient modulus of the geogrid and geocell. In the next section, the loading was applied on the sample in the plastic shakedown range and incremental collapse range. The results of the permanent strains and resilient modulus of the sections are compared with the corresponding results of the unreinforced section. In the plastic shakedown and incremental collapse range also the permanent strains of reinforced samples were less than those observed in the unreinforced section. The performance of geosynthetically reinforced pavement layers can be better understood by studying the samples prepared under realistic field conditions. In the case of triaxial experiments the sample size is very less compared to the field conditions and the effect of other pavement layers on the performance of the base layers cannot be studied on triaxial samples. Samples were prepared in the laboratory by modeling the pavement sections in a cuboidal tank, in which different pavement layers are laid one over the other, and a static loading or repeated loading is applied to overcome the bottleneck of small sample size in the triaxial setup. The experiments were conducted on the unreinforced section; geocell reinforced section and geogrid reinforced section placed above strong and weak subgrade. The results of the study are examined regarding the resilient deformation, permanent deformation, pressure distribution and strain measurements for different thicknesses of base layers under repeated loading. The initial parts of the study present the results of experiments and analysis of the results to understand the behavior of geocell reinforced granular base during repeated loading. In this study, an attempt is made to understand the various factors which influence the behavior of geocell reinforced granular base under repeated loading by conducting plate load tests. The loads applied on the pavements are much higher than the standard axle loading used for the design of pavements. High pressure was applied on all the test sections to simulate these higher loading conditions in the field. The optimum width and height of the geocell to be provided, to get maximum reduction in permanent deformation is studied in detail. The effect of resilient deformation of reinforced and unreinforced base layers is quantified by calculating the resilient modulus of these layers. The studies showed that the geocell reinforcement was effective in reducing the permanent and resilient deformations of base layer when compared to the unreinforced samples. The resilient modulus calculated was higher for the reinforced sample with half of the thickness of the unreinforced sample. The effect of reinforcement in the stress distribution within the base layer is also studied by measuring the pressures at different depths of the base layer. The results showed that the pressure getting transferred to the subgrade level was much lower in the case of geocell reinforced base layer. The ultimate aim of any pavement design method is to reduce the distress in the subgrade level and thus leading to increased life of pavements. Pressures at the subgrade level for reinforced and unreinforced sections are studied in detail, the main parameter under study being the stress distribution angle, to investigate the distress in the subgrade level. It was observed that the geocell reinforced sample showed higher stress distribution angle when compared to its unreinforced counterpart. Another important factor that has to be studied is the strains at the subgrade level since it is the governing factor of causing rutting in the pavements. From the experiments conducted in the study, it was shown that the reinforcement is very effective in reducing the strains at the top of subgrades. The implications of the current study are brought out in terms of improved pavement performance as the carbon emission reductions. It is important to analyze the performance of reinforced section under realistic field conditions. To do that experiment were conducted on reinforced and unreinforced base layers placed on top of weak subgrade material. The study showed that the reinforcements are effective in reducing the deformations under weak subgrade conditions also but not as effective as it was under strong subgrade case. The experimental results were then validated with the two-dimensional mechanistic-empirical model for geocell reinforced unpaved roads for predicting the performance of pavements under a significant number of cycles. The modified permanent deformation model which incorporates the triaxial test results and strains measured directly from the base sections were used to model and validate. Plate load experiments were also conducted on base layers reinforced with geogrid to understand the behavior of these reinforced samples under repeated loading. Several factors like the width of the geogrid to be provided and the depth of placing the geogrid in the base layer were studied in detail to achieve maximum reduction in deformations. Permanent and resilient deformation studies were carried out for both reinforced and unreinforced sections of varying thicknesses, and a comparison was made to understand the effect of reinforcement. The geogrid reinforcement could effectively reduce the permanent and resilient deformations when compared to the unreinforced sections. A study was also carried out on the resilient modulus, which explained the better performance of the geogrid reinforced samples by showing higher resilient modulus for reinforced samples than the unreinforced specimens. The performance of the geogrid reinforced base layers was further verified by studying the pressure distribution at the subgrade level and by calculating the stress distribution angle corresponding to the reinforced and unreinforced samples. The strains at the subgrade level were also studied and compared with the unreinforced sample which showed a better performance of geogrid reinforced samples. The results from the strain gauges fixed in the geogrid were further used to model and validate the permanent deformation model. Experiments were conducted on geogrid-reinforced base layer placed above weak subgrade conditions. The results showed that the reinforcement was effective in reducing the deformations under weak subgrade conditions also. Apart from conducting the laboratory studies, experimental results were numerically modeled to accurately back-calculate the resilient moduli of the layers used in the study. 3D numerical modeling of the unreinforced and honeycomb shaped geocell reinforced layers were carried out using finite element package of ANSYS. The subgrade layer, geocell material, and infill material were modeled with different material models to match the real case scenario. The modeling was done for both static and repeated load conditions. The material properties were changed in a systematic fashion until the vertical deformations of the loading plate matched with the corresponding values measured during the experiment. The experimental study indicates that the geocell reinforcement distributes the load in the lateral direction to a relatively shallow depth when compared to the unreinforced section. Numerical modeling further strengthened the results of the experimental studies since the modeling results were in sync with the experimental data.

碩士
國立交通大學
土木工程系所
102
Yunlin County is located in Central Western Taiwan, within the alluvial fan of Tsuo Shue river, where surface water resources are limited. Excessive ground water pumping in this region has caused ground subsidence. In order to evaluate the mechanisms of ground subsidence, the research team of National Chiao Tung University installed a 100m deep observation well at Guan Fu elementary school in Hu Wei Township of Yunlin County. Relationships between pore water pressure and ground subsidence (heaving) were observed using this monitoring system. 24 hour continuous readings showed that the pore water pressure fluctuated repeatedly in the morning and evening at depths between 30 and 40m. It was suspected that this fluctuation of pore water pressure was related to the on-and-off type of ground water pumping from wells nearby. To verify if this repeated effective stress variations induced by pore water pressure fluctuation was responsible for the accumulation of permanent strains, a series of pressuremeter tests (PMT) were performed. Relationships between the PMT repeated loading-unloading and the radial strain accumulation were evaluated. The thesis describes the background of this research, modifications of the PMT device and available test results.

碩士
國立中央大學
土木工程研究所
89
This study investigates behavior of cumulative permanent strain of subgrade soil under repeated loading at various stress levels. Results of the permanent strain test shows that the accumulated permanent strain of subgrade soil under repeated loading continues to build up with increasing load repetitions. If the tested soil approaches apparent shakedown state, the tested soil does not appear failures after the deviator stress of repeated load cycles. Approaching apparent shakedown state of the tested soils under high water content and high stress level needs more repeated load repetitions. The relationship of the resilient modulus and permanent strain of tested subgrade soil, at apparent shakedown state, is established using statistic regression. The relationship helps designers in predicting accumulated permanent strain as the tested soils reach apparent shakedown state with less testing times. This prediction model will enormously save the testing time needed as reaching the expected apparent shakedown state of tested soils. This prediction model also can evaluate the values of resilient modulus as the reference of designing the thickness of pavements of subgrade soil.

碩士
國立中央大學
土木工程研究所
83
After loading,the inner parts of cracking will occur bond failure.This bond failure will cause the stiffness degradation and the change of dynamic behavior. The thirty-eight beams were tested under both the one and repeated loading to investigate the effects of internal bond failure on the natural frequency of reinforced concrete beams.The principal variables were the loading cycles,bar diameter,span length/depth .It is the object to study the natural frequency,the crack width on the concrete surface under loading and unloading ,the cleavage length on the interface between the reinforced bar and the concrete cover under loading in each step. The paper provided an easy method of non-destruction testing for bridge in final chapter.This method was performed by the change of natrual frequency. So far the method subjected can't be used in filed right now,because it is not perfect and complete.

碩士
國立中興大學
土木工程學系所
94
This paper aims to investigate mechanical behavior of reinforced lightweight aggregate concrete (R.L.A.C.) walls under repeated loading. The test results were compared to those of corresponding reinforced normal aggregate concrete (R.N.A.C.) walls to evaluate the feasibility of R.L.A.C. walls in practical engineering. Three test parameters, such as spacing of reinforcing bars, types of coarse aggregates and sizes of reinforced concrete walls, were considered to research their effects on the failure modes of walls, the strength reduction, the stiffness reduction and the energy dissipation. The test results show that R.L.A.C. walls are very similar to R.N.A.C. walls in many properties under repeated loading. The R.N.A.C. walls basically all surpass the R.L.A.C. walls, but the difference not very obvious. Therefore, R.L.A.C. walls can replace R.N.A.C. walls in practical wall constructions. The energy dissipation of R.L.A.C. walls is about 25% less than that of R.N.A.C. walls when the lightweight aggregate is used to build short walls.

碩士
台北醫學院
口腔復健醫學研究所
90
Dental implants have become increasingly important in oral rehabilitation. However, implant treatments still fail frequently. The implant per se has to withstand stresses induced by intraoral forces. Abnormal loading, as well as fatigue under physiological loads, can lead to fractures of certain implant components. These problems are always complicated by cyclic fatigue. Fracture or loosening is most likely to occur in the screw. As for fracture problems, however, it is difficult to predict which component will suffer fatigue and the resulting effects on the entire system. Important aspects of implant design are related to biomechanics of implant systems and the different materials used for implants. However, a reliable method for dentist or manufacturer to evaluate the mechanisms of implant fracture was still unavailable. In this study proposal, a serious dynamic mechanical were carried out to assess the maximum dynamic loading and fatigue life of the implants. To provide the optimal testing parameters, preloading tests and static tests were performed first. After the pretests, dynamic tests were performed under the mode of loading control with a sinusoid force. To provide an indicator for assessing the fracture mechanisms of the fracture screw, the fracture surface of the failed screws were observed and recorded by SEM observation. The fatigue life as well as S-N curve of the sample implant were also obtained and further analyzed by numeric analysis with finite element method. The results showed the ratio of the length and area of the smooth portion on the fracture surface increased with decreased loading magnitude and increased loading cycles. It demonstrated linear relationships and the reliability is the highest between length ratio of the smooth area and loading magnitude (R2=0.8506, p<0.01). Besides, finite element analysis also demonstrated not only the stress concentrated area but the magnitude. The results obtained from this project will serve as important references for the future advance studies.

碩士
國立臺灣科技大學
營建工程技術學系
82
@　 混凝土品質對其內之鋼材腐蝕影響甚大， 所以施工品質為不可忽視 之一環， 為此本研究除使用傳統混凝土外，並特別採用了兼具高強度、 高流動、及高水密性之高性能混凝土， 探討其配比及一般鋼筋混凝土與 高性能預力混凝土等各項不同材料於海洋環境下其內部鋼材腐蝕之行為 ， 並於承受固定頻率單向性反覆荷重後，對其內部鋼材腐蝕產生之影響 。 根據材料之不同性質分別量測其載重前後之混凝土電阻系數、鋼材電 位，腐蝕速率及氯離子含量之變化，並佐以 SEM 、瞭解材料內部構造， 期能求得高性能混凝土與一般混凝土於相同環境下其材料性質對其內部鋼 材腐蝕之影響。 研究結果顯示，高性能混凝土較一般傳統混凝土具有較 高電阻係數， 裂縫發生前其氯離子含量及腐蝕速率皆較低，添加波索蘭 材料其電阻係數較未添加者大了近一倍。 預力混凝土在反覆載重下較鋼 筋混凝土有較小之變位及裂縫寬度， 且鋼材電位變化較小，添加鋼纖維 對混凝土電阻係數及鋼材腐蝕速率之影響初步顯示有偏大現象， 其實際 效果有待更準確之評估。 The corrosion behavior of the embadded steel in concrete is greatly affected by the quality of concrete, therefore, the quality of construction is important. One the basis of this reason, the study did not only apply traditional conventional concrete, but also adopted the high performance concrete (HPC) with the properties of high strength, high flowing and low permeability. The mixture proportion, the corrosion behavior of the embedded steel in ordinary RC beam and high performance prestressed concrete beam under marine circumstance and the influence on steel after suffering fix frequency cycle loading. The concrete electircal resistance, steel potential, corrosion rate and the change of concentration of the cl- ion are be measured according to the different properties of materials. Furthermore, aided try SEM micrographs of materials it is expect to find out the influence of the corrosion on steel of high performance concrete and conventional concrete under same circumstance. The study result indiacted that high performance concrete has higher electric resistance coefficient than ordinary traditional concrete, the content of cl- ion and corrosion rate are lower than that before cracked.The electric cofficient that adding with pozzloanic materials is about one time higher than that without addition. The prestressed dondrete has smaller deflection and crack's width and the change of electrical potential is smaller. Addition of steel fiber will has better effect for restrain the growth of corrosion of steel and the real effect of steel fiber is still future study.

The objective of this dissertation is to study the characteristics of subgrade soils under repeated loading and their influence on the design and performance of railway track. The roles of the subgrade as the track foundation are discussed. The mechanisms for different types of subgrade distress are examined. A method for the estimation of resilient modulus of subgrade soils is developed. This method takes into account the influence of soil physical state, stress state and soil type. The effect of soil physical state is quantified by combinations of two equations relating resilient modulus to moisture content. The effect of stress state is determined by equations relating resilient modulus at optimum moisture content to deviator stress. A method for the prediction of cumulative plastic strain of subgrade soils is developed which takes into account the influence of number of load cycles, stress state, soil physical state, and soil type. The stress state is represented by deviator stress. The influence of soil physical state is indirectly represented by the soil static strength. The parameters required for the prediction model are recommended for different soil classifications. Based on analysis with the GEOTRACK computer model, the effects of superstructure and substructure factors influencing track modulus are illustrated. The relationship between the track modulus and the track performance is analyzed. GEOTRACK is also used for analysis of the stress pulses generated in the subgrade under moving wheel loads. Two design methods are developed for the track granular layer thickness. The first one is intended to prevent the progressive shear failure of the subgrade and the other one is intended to prevent the excessive plastic deformation in the subgrade. The major considerations for these two methods include the magnitudes of the mix of dynamic wheel loads and the corresponding numbers of repeated loads, the soil type, the soil static strength, the subgrade thickness, the subgrade resilient modulus, and the resilient modulus for the granular layer. The granular layer thickness design method is evaluated by field test results. The field performance of the test track is reasonably interpreted by the design method developed in this dissertation.

All reinforced concrete (RC) design theories are based on the assumption that concrete exhibits a perfect bond with the steel reinforcement. The bond between steel and concrete is essential to the transfer of the load applied from the concrete to the steel reinforcement. When steel bars are corroded, the concrete cracks, and the strength of the bond between the steel bars and the concrete is decreased. Structures such as bridges and marine structures are prone to corrosion. These structures are usually also subjected to repeated loading. Repeated loading can initiate cracks in the concrete surrounding the steel bars that propagate as the number of load cycles increases leading to the destruction of the concrete-steel interface and slip of the steel bars inside the concrete. The combined effect of corrosion and repeated loading reduces the service life of RC structures. This study investigated the effect of anchorage length and confinement from supports, stirrups and carbon fibre reinforced polymer (CFRP) on the bond behaviour of corroded and uncorroded reinforced concrete beams subjected to monotonic and repeated loading. Fifty-seven large-scale reinforced concrete beams (152*254*2000 mm) were tested for the purpose of this study. The variables were stirrup spacing (75 mm and 150 mm), anchorage length (200 mm, 350 mm and 650 mm), corrosion level (mild corrosion and high corrosion level), repair condition (wrapped or unwrapped with FRP sheets in the anchorage zone) and the fatigue load range. From this study, it was found that the resistance to bond stresses (forces) between the steel and concrete were provided mainly by the concrete keys. The bond stresses increased with the number of the concrete keys engaged. The factors that affected the number of concrete keys engaged were: confinement from the supports, confinement from the stirrups, confinement due to wrapping with FRP sheets and change in anchorage length. Decreasing the stirrup spacing from 150 mm to 75 mm increased the number of concrete keys engaged thus increasing the bond capacity and changed the mode of failure under monotonic loading from splitting to pullout. The beams with the first stirrup spacing (150 mm c/c) when tested under repeated loading failed by bond fatigue while the beams with the second stirrup spacing (75 mm c/c) failed by flexure at the end of a debonded region that started from the support. The failure mechanism is discussed for each case. The change in anchorage length from 200 mm to 350 mm increased the static and fatigue bond capacity of the beams by 60% and 12.5% respectively. The debonding for this group of beams (200 mm and 350 mm anchorage length) subjected to monotonic loading started from the pocket and propagated towards the support while the debonding for the 350 mm anchorage length beams subjected to repeated loading started at the location of a crack that widened while fatiguing the beam and propagated towards the support. The change in anchorage length from 350 mm to 650 mm did not affect the monotonic bond capacity of the beams since in this case, debonding was initiated from the supports and the change in anchorage length had little effect. The confinement with FRP sheets caused the concrete keys at both the top and bottom of the bar to be crushed and increased the bond stress of the wrapped beams. The bond strength of the beams repaired with CFRP sheet was governed by the strength of the FRP sheets for all anchorage lengths and corrosion levels. The CFRP repair of the 200 mm anchorage length set of beams increased the capacity of the uncorroded beams by 80% and the capacity of the corroded beams by about 25% under static and repeated loading compared to the control (uncorroded and unrepaired) beam. The CFRP repair of the 350 mm anchorage length set of beams changed the mode of failure from bond to flexure. The fatigue life for the beams varied linearly on a logarithmic scale with the load range applied with a shallow slope. Corroding the 200 mm anchorage length set of beams to a mild corrosion level decreased their fatigue strength by 34% compared to the control beams. Corroding the 350 mm anchorage length set of beams to a mild corrosion level did not affect the fatigue strength for the single beam that failed in bond. Finally a probabilistic approach was used to allow the design engineers to estimate the design fatigue life for similar beams with 95% probability for a given normalized stress ratio.

碩士
國立中央大學
土木工程研究所
90
ABSTRACT The subgrade soil failures due to excessive permanent deformation produced by high stresses in the pavement. However, lack of reasonable mode distinguishes the critical stress in subgrade soil. This paper describes the shakedown behavior of cohesive subgrade soil under repeated loading. The main goal is to define the critical stress level of subgrade soil under repeated loading. According to the shakedown concept, this level is termed the shakedown limit, and it can be distinguish on bases of resilient, plastic, hysteretic, and shakedown behavior by repeated triaxial test. Besides, to select the deviatoric stress model and bilinear model predict the resilient modulus of subgrade soil. The test results show the bilinear model is better than the deviatoric stress model. The determination of critical stress can rely on the behavior of soil under repeated loading, such as dissipated energy and the type of plastic strain accumulation. Below the critical stress, the plastic strain is steady to accumulate, and the dissipated energy is more and more small as the number of load cycles increase. As the stress level advancing above the critical stress, the plastic strain is suddenly increases, and the dissipated energy rises again after specific load applications. Besides, the method of description for plastic strain rate versus plastic strain also can effectively distinguish the shakedown behavior. According to the shakedown concept, subgrade soil is from plastic creep shakedown to incremental collapse. The critical stress level is between two behaviors, and it decreases with increasing water content, increases with increasing confining pressure.

碩士
國立臺灣科技大學
營建工程技術學系
83
The Bridge structure may nave corrosion problem under external environment and loading condition. Therefore, its life cycle time may be reduced and needs further maintenance and repairing. Thus, life cycle cost of structure will be high. Recently, due to local HPC (High Performance Concrete) with high workability and high strength is successfully developed, such concrete is generally considered to have better durability. It needs further investigation on steel corrosion of HPC. Therefore, this research majors in studying the corrosion behavior of HPC beam with different mixture proportion containing pozzolans and steel fiber. Also, this research is taken to measure electronic potential and corrosion rate of rebar in HPC under repeated loading and marine enviornment. Macro-studies of mechanical property and permeability and chemical analysis are preceded at the seme time. Such results are matching with the micro- technology of MIP and SEM, the rebar corrosion behavior can be understood. Under repeated loading, no matter whether pozzolan or steel fiber is added or not, once the fatigue cracking initiates, the rebar electronic potential will drop from the range of uncorroded to corroded. HPC with additional pozzolans and steel fiber has high electronic potential and is expected to have better corrosion prevention result.

碩士
中原大學
土木工程研究所
86
Silting is a serious problems in most of the reservoirs in Taiwan. Dredging is frequently conducted to remove soils deposited in the reservoirs. On the other hand, back-fill materials are in serious shortage for engineering constructions. Thus, use of the dredged soils as a back-fill material has presented a great solution to the treatment of dredged soils. This study focuses on the use of dredged soils to construct road embankment. Soil samples were taken from Bai-Ho reservoir for laboratory tests. The soil was classified as CL based on the USCS classification system. Compressibility characteristics of compacted soil and soil-cement were investigated by conducting both static and repeated loading consolidation tests.Portland cement (type 1) of 0, 3, 6, 12, and 18% were mixed with the soil to prepare specimens of 1.91 cm in height and 6.35 cm in diameter. The specimens were cured for 28 and 90 days before the consolidation tests. Other testing conditions include a constant pressure increment of 50 kPa for repeated loading under static pressures of 25, 50 ,and 100 kPa to give load increment ratios of 0.5, 1, and 2, respectively. Furthermore, periods of both 20 and 100 seconds were used for applying the repeated loads. Results of this study include: (1) ratio of secondary compression indexes between improved soil and unimproved soil changes with the magnitudes of effective stress. The ratio is at its minimum value for stresses near the preconsolidation pressure. For stresses larger than the preconsolidation pressure, the ratio gradually increases with the effective stress with cement content smaller than 6% and keeps constant with the effective stress with cement content higher than 6%;(2) the average degree of improvement in secondary compression increases with cement content and reaches a peak value of 0.3 at 6% cement content; (3) the value of Cα/Cc increases with cement content, and an equation is proposed for predicting the value of Cα/Cc; (4) settlement under repeated loading is primarily affected by load increment ratio and cement content;(5) a prediction model for settlement of embankment under repeated loading. In summary, results of this study show that the compressibility of the soft dredged soil is greatly reduced by mixing with cement. Therefore, application of the soil-cement as a construction material for road embankment and foundation back-fill is highly feasible.

Efficient road network and connectivity play vital role in the development of any country. Majority of the rural roads are unpaved and connectivity of rural roads is always a major challenge. Unpaved roads are also used for temporary transportation facilities like access roads, haul roads for mines, forest roads and parking lots. Since these roads do not have asphalt surfacing, they are subjected to early failures due to distresses like rutting, pot holes and depressions . Stabilization of unpaved roads using geosynthetics has been proved to be promising in increasing the lifespan of these roads because they facilitate economical, aesthetic and effective design of the roads. Inclusion of geosynthetic layers at the interface of subgrade soil and granular sub-base, reduces the surface heave, ensures a better stress distribution and reduces the stresses transferred to the subgrade soil, as demonstrated by earlier researchers. Wide variety of geosynthetics like woven and nonwoven geotextiles, uniaxial and biaxial geogrids and geocells are used as reinforcement in road sections. Geotextiles improve the strength by interfacial friction, lateral restraint and membrane effect. Geogrids provide additional benefit of interlocking. Geocells are honeycomb shaped geosynthetic cellular confining systems filled with aggregates in which the reinforcement action is derived not only by friction and interlocking, but also by confinement. Load-deformation characteristics of reinforced soil-aggregate systems under static, repeated and cyclic loads is a potential topic of interest considering the fact that the design of geosynthetic reinforced unpaved roads is still under development and experimentation. The objective of the present study is to understand the beneficial use of geosynthetics in unpaved roads and to provide clear insight into the influence of geosynthetics on the cyclic loading characteristics of unpaved roads through laboratory experiments. California Bearing Ratio (CBR) tests were carried out on unreinforced and reinforced soil-aggregate systems to study the effect of various parameters such as type of reinforcement, form of reinforcement, quantity of reinforcement, and water content of the subgrade soil on the load-penetration response of the various systems. Modified CBR tests were also carried out to understand the influence of boundary of the mould and anchorage of reinforcement on the behavior of reinforced soil-aggregate systems. Behavior of unreinforced and reinforced soil-aggregate systems under repeated and cyclic loading is also studied to understand the resilience of the composite systems. From the measured stress-strain response, the elastic and plastic strains developed in various systems are compared. Different moduli such as secant modulus, cyclic modulus and resilient modulus are computed for different systems and compared. To investigate the effectiveness of geosynthetics in improving the load - bearing capacity, repeated load tests were carried out on model sections of unpaved road constructed in a steel test tank of size 750 mm × 750 mm × 620 mm. The effect of various parameters like the form of reinforcement, quantity of reinforcement, height of geocell layer and the position of geocell layer on the load-deformation behaviour of the unpaved model road sections was studied. Static and cyclic triaxial tests were carried out on unreinforced and reinforced granular sub-base materials to understand their stress strain behavior under static and cyclic loading conditions. The influence of quantity and form of reinforcement on the stress-strain behaviour of these materials was studied. From the studies it is observed that the use of reinforcement increases the CBR value of the soil-aggregate systems. Studies with two different sizes of CBR moulds indicated that the boundary effect in the standard CBR mould leads to the overestimation of the CBR value, resulting in unconservative design of road sections. Providing anchorage to the reinforcement in CBR tests did not produce an appreciable change in the load-penetration behavior. From the repeated load tests it was observed that the reinforced systems did not show any improvement in the load-deformation behaviour at low levels of rut depth. At higher rut depths, the reinforced systems developed less plastic settlements and more elastic settlements and low resilient modulus compared to unreinforced systems. From the model tests on unpaved road sections, it was observed that the improvement in the cyclic load resistance of the road due to the inclusion of geocell layer depends on the height of the geocell layer and its position. Increasing the height of geocell layer resulted in improved performance up to certain height of the geocell layer, beyond which, further increase in the height reduced the load resistance because of the inadequate granular overlay thickness and inadequate compaction of aggregate within the geocell pockets. Static and cyclic triaxial tests showed that the geogrid and geocell reinforced granular sub-base material sustained higher peak stresses and exhibited increase in modulus compared to the unreinforced specimens. Results of element and model tests carried out in this study gave important insight into the load-deformation characteristics of reinforced soil-aggregate systems under static, repeated and dynamic loads. The results provide guidelines regarding the selection of type, quantity and configuration of geosynthetic reinforcement while designing unpaved roads and the expected performance of these reinforced unpaved roads.

Im Mittelpunkt der vorliegenden Arbeit steht die gezielte Analyse des Verbundverhaltens zwischen Bewehrungsstahl und Beton unter kombinierter Beanspruchung aus Ermüdung und Querzug. Den Hintergrund bilden Stahlbetonbauteile, wie z. B. Fahrbahnplatten von Verbundbrücken, welche einen zweiaxialen Lastabtrag unter nicht vorwiegend ruhenden Belastungen aufweisen. Die Untersuchungen für normal- und hochfesten Beton erfolgten an Ausziehkörpern mit einem durch Querzugspannungen hervorgerufenen Längsriss entlang des Bewehrungsstabes. Das Versuchsprogramm beinhaltete hochzyklische Schwellversuche mit unterschiedlichen Schwingspielen und variierenden Längsrissbreiten bis zu einer Million Lastwechseln. Anhand der Entwicklung des Schlupfes zwischen Bewehrungsstab und Beton konnte eine deutliche Abhängigkeit des Verbundwiderstandes vom Querzug beobachtet werden. Aufbauend auf der Schlupfentwicklung erfolgt die Ableitung von normierten Wöhlerlinien der Verbundermüdung. Diese Wöhlerlinien können direkt in Beziehung zu den Wöhlerlinien der Betonstahlermüdung gesetzt werden und vereinfachen die Erstellung von Dauerfestigkeitsdiagrammen für Bemessungszwecke. Es wird deutlich, dass die Ermüdungsfestigkeit des Verbundes durch das Vorhandensein eines Längsrisses gegenüber der Betonstahlermüdung verstärkt an Bedeutung gewinnt.
The main focus of the present work is the specific analysis of the bond behaviour between reinforcement and concrete under combined loading due to fatigue and transverse tension. The background is formed by reinforced concrete elements such as bridge decks of steel-concrete composite bridges, which show a biaxial load bearing behaviour under not predominantly monotonic loading. The investigations for both normal strength and high performance concrete were conducted on pull-out specimens with a longitudinal crack along the reinforcing bar caused by transverse tensile stresses. The experimental program included high cyclic tests with different stress ranges and varying longitudinal crack widths up to one million load cycles. By means of the slip development, a definite dependency of the bond strength on the transverse tension could be observed. Based on the slip development, normalised S-N curves for bond fatigue have been deduced. These S-N curves can be set in direct relation to the S-N curves for steel fatigue and simplify creating constant life diagrams for design purposes. It becomes clear that the bond fatigue strength, due to an existing longitudinal crack, gains in importance in comparison to the fatigue strength of the reinforcing steel.

碩士
國立暨南國際大學
土木工程學系
104
The research present a finite element method to analyze elastic-plastic deformation of rolling elements under repeatedly contact loading. The finite element model is composed of four-node quadrilateral plane elements, and moving Hertzian contact stress used to simulate repeatedly rolling contact process. The Prager linear hardening model and Chaboche nonlinear model are used respectively in the elastic-plastic finite element analysis to simulate kinematic hardening behaviors of metals, and return mapping algorithm is used for the correction of stresses to yield surface. To verify the accuracy of the finite element results, numerical solutions of a cantilever beam under reversed loading and a two-dimension elastic contact problem are compared and shown a good agreement with ANSYS and analytical solutions. The results show that Prager model cannot be used to simulate ratchetting behavior for lack of a recall terms while Chaboche model is more effective to simulate cyclic deformation of materials under repeatedly contact loading. In the simulation of cyclic plastic deformation of contact components using Chaboche model, the results show that the elastic shakedown area remains at half-depth of plastic zone regardless the magnitude of contact loading. Friction coefficient may increase plastic deformation at contact surface but has limited effect on the depth of plastic zone and shakedown area. In shakedown analysis, the ratchetting rate of shear strain decreases with increasing number of contact cycles and the reduction rate increases with increasing magnitude of contact loading. In addition, the dimensionless maximum equivalent stress decreases with increasing magnitude of contact loading but increase with increasing coefficient of friction.

碩士
國立臺灣科技大學
營建工程技術學系
81
Bridge structures would usually corroded due to the existence of detrimental substances in exposed environment and loading codition, and that would increase the maintenance expenses and rebuilding cost. thus, this study focused on the corrosion behavior of prestress and single reinforced beams under repeated loading at a certain frequency before and after cracking. In addition. under dynamic loading, effect of different admixtures in concrete and coated bar was evaluated when specimens were soaked in artificial seawater. Simultaneously, chemical and physical properties were studied to reveal the corrosion mechanism and corrosion rate to find out the optimum auto-corrosion strategy.