Dissertations / Theses on the topic 'Flexural loading'

Thesis (M. Phil.)--Hong Kong University of Science and Technology, 2004.
Includes bibliographical references (leaves 138-142). Also available in electronic version. Access restricted to campus users.

The main objective of this work is to study the long-term and residual flexura! strength of Near Surface Mounted (NSM) strengthened Reinforced Concrete (RC) beams with Carbon Fiber Reinforced Polymers (CFRP) strips when subjected to sustained loading. This work involved twenty-eight RC beams divided into two series, A and B, with two concrete batches of different compressive strength. In each series, sorne of the beams were strengthened with CFRP strips using the NSM strengthening technique and the others were un-strengthened. Series A was divided into two groups, Al and A2, while series B was divided into three groups, B1, B2, and B3. The beams of the first group in each series were tested at age of 55 days to determine the short-term flexural behavior of un-strengthened and strengthened beams. Other groups were subjected to long term test with different sequences.
El objetivo principal de este trabajo es estudiar la resistencia a la flexión residual y a largo plazo de las vigas HA reforzadas con NSM con tiras de CFRP cuando se someten a cargas sostenidas. Este trabajo involucró veintiocho vigas RC divididas en dos series, A y B, con dos lotes de hormigón de diferente resistencia a la compresión. En cada serie, algunas de las vigas se reforzaron con tiras de CFRP utilizando la técnica de refuerzo NSM y las otras no se reforzaron. La serie A se dividió en dos grupos, Al y A2, mientras que la serie B se dividió en tres grupos, Bl, B2 y B3. Las vigas del primer grupo de cada serie se probaron a la edad de 55 días para determinar el comportamiento de flexión a corto plazo de las vigas. Otros grupos fueron sometidos a pruebas a largo plazo con diferentes secuencias

In this study, a total of twelve beams continuous over two spans of 2,800 mm each were constructed and tested to failure. The beams were divided into two series. Series 1 included six T-beams under symmetrical loading, while Series 2 dealt with six rectangular beams under unsymmetrical loading conditions. In Series 1, the test variables included material type, assumed percentage of moment redistribution, spacing of lateral reinforcement in flange, arrangement of shear reinforcement, and serviceability requirements. In Series 2, three different loading cases were considered, I) loading both spans equally, II) loading both spans maintaining a load ratio of 1.5 and III) loading one span only. Under the loading case II, the parameters of reinforcing material type, assumed percentage of moment redistribution and serviceability requirements were investigated. The test results of both series showed that moment redistribution from the hogging to the sagging moment region took place in GFRP-RC beams which were designed for an assumed percentage of moment redistribution. In Series 1, the decrease of the stirrups spacing from 0.24d to 0.18d enhanced the moment redistribution percentage. Also, decreasing the spacing of lateral reinforcement in the flange from 450 to 150 mm improved the moment redistribution through enhancing the stiffness of the sagging moment region. In Series 2, the unsymmetrical loading conditions (loading case II and III) reduced the moment redistribution by reducing flexural stiffness in the heavily loaded span due to extensive cracking. Regarding serviceability in both series, the GFRP-RC beam designed for the same service moment calculated from the reference steel-RC beam, was able to meet the serviceability requirements for most types of the structural applications.
February 2017

Aluminium foam has a range of properties that are desirable in many applications. These properties include good stiffness and strength to weight ratios, impact energy absorption, sound damping, thermal insulation and non combustibility. Many of these characteristics are particularly attractive for core materials within sandwich structures. The combination of aluminium foam cores with thermoplastic composite skins is easily manufactured and has good potential as a multifunctional sandwich structure useful in a range of applications. This thesis has investigated the flexural behaviour of such structures using a combination of experimental and modelling techniques. The development of these structures towards commercial use requires a thorough understanding of the deformation and strain mechanisms of the structure, and this will, in turn, allow predictions of their structural behaviour in a variety of loading conditions. ¶ The experimental research involved the use of an advanced 3D optical measuring technique that produces realtime, full-field strain evolution during loading. This experimental characterisation of strain evolution in this class of sandwich structure under flexural loading is the first of its kind in the world. The experimental work studied the sandwich structure undergoing four-point bend testing. Initial studies compared the behaviour of the aluminium foam structure with a more traditional polymer foam sandwich structure. The aluminium foam structure was found to have equivalent or improved mechanical properties including more ductile deformation and an enhanced energy absorption. An investigation was conducted on the effect of core and skin thickness on the metal structure and a range of flexural behaviours were observed. Analysis of the strain distribution showed a complex development including localised effects from the non-uniform cellular structure of the material. An understanding of the variation with size is important in establishing design methods for utilising these structures. In particular, it is desirable that finite element simulations can be used to predict behaviour of these structures in a diverse range of loading conditions. This aspect was considered in the second half of this study. An existing constitutive model for aluminium foam, developed for use in compression energy absorption studies, was used to investigate finite element simulations of the flexural behaviour of the sandwich structure. The FE model was able to predict the general deformation behaviour of the thinner skinned structures although the magnitude of the load-displacement response was underestimated. It is suggested this may be related to the size effect on the input parameter characterisation. The strain distribution corresponded well with the experimental strain measurements. It was found a simple increase in the material model input parameters was able to more closely match the magnitude of the load-displacement response while maintaining the appropriate strain distribution. The general deformation shape of the model with the thicker skin corresponded reasonably well with the experimental observations. However, further work is necessary on the element failure criterion to capture the shear cracking observed. The strain distributions of the model predicted this failure with high strain concentrations matching those of the experimental contours. The last part of the thesis describes a parametric study on the effect of the foam material model input parameters on the flexural behaviour of the sandwich structure model. An important conclusion of this work is that this material model for aluminium foam can, with some development, be utilized to provide a viable method for simulating aluminium foam composite sandwich structures in flexural loading situations.

This thesis investigates the flexural behavior of interlocking compressed earth block (ICEB) shear walls. In-plane cyclic tests were conducted to evaluate the performance of three flexure dominant large scale ICEB specimens: a slim wall with a 2:1 height to width aspect ratio, a flanged wall, and a wall with an opening at the center. Following the experimental investigation, two types of analyses were conducted for calculating the ultimate strength of flexure dominant ICEB walls: a nonlinear static analysis model assuming lumped plasticity and a plastic analysis model. In addition, incremental dynamic analysis was conducted to address the seismic performance of flexure dominant ICEB buildings. Based on the database from the incremental dynamic analysis, the collapse potential of demonstration ICEB buildings were compared for the countries of interest.

Throughout the ocean basins many broad regions of anomalously shallow topography exist that do not fit the widely accepted model of conductive plate cooling and subsidence as a function of lithospheric age. These ‘swells’ often coincide with positive geoid, Free-air gravity and heat flow anomalies as well as groups of ocean islands and seamounts. Various mechanisms have been proposed to explain how this anomalous topography is isostatically supported at depth, including increased crustal buoyancy and dynamic asthenospheric support. The Cape Verde Swell is the largest oceanic mid-plate swell on Earth at ~1800 km in diameter, with a crest ~2.2 km high, and positive geoid, gravity and heat flow anomalies of 8 m, 30 mGal and 10-15 mW m-2, respectively. These characteristics and its location on the slow-to-stationary African Plate, which concentrates the volcanism and associated geophysical anomalies within a relatively small areal extent, makes the Cape Verde Swell an ideal location to test the various proposed mechanisms for swell support. Wide-angle seismic refraction data along an ~474 km profile, extending from the Cape Verde Swell crest, is analysed and modelled to produce a 2-D velocity-depth model of the crustal structure. The resulting model reveals no widespread thickening of the lower oceanic basement, despite evidence for localised thickening beneath the islands from other studies. Subsequent 3-D ‘whole plate’ lithospheric flexure modelling reveals that, on a regional scale, the plate is stronger than expected based on its age, with some evidence for localised weakening around the islands. Overall, the results of this study suggest that the anomalously shallow topography of the Cape Verde Swell is primarily maintained by a dynamic upwelling of hot, low density material impinging on the base of the lithosphere. Over time, conduction from this hot column has thermally rejuvenated the lithosphere on a local scale, leading to additional uplift, melting and volcanism associated with the islands.

Thesis (Ph. D.) -- University of Maryland, College Park, 2007.
Thesis research directed by: Dept. of Mechanical Engineering. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.

The design of metal building roof and wall systems under uplift and suction wind loading is complicated because the laterally unbraced purlin and girtâ s free flange is compressed, and the cross-section rotates due to the shear flow. The objective of this thesis is to introduce a Direct Strength Method (DSM) prediction approach for simple span purlins and girts with one flange through-fastened under uplift or suction loading. This prediction method is also applicable for the case when rigid board insulation is placed between the metal panel and through-fastened flange. The prediction method is validated with a database of 62 simple span tests. To evaluate the prediction for the case when rigid board is used, 50 full-scale tests with rigid board insulation are conducted by the author of this thesis. In the experimental study panel failure, connection failure and member (purlin and girt) failure are observed, and they all limit the systemâ s capacity. Another important contribution of this thesis is that it builds the foundation for future study of a general, mechanics-based limit state design approach for metal building roof and wall systems that can accommodate uplift and gravity loads, simple and continuous spans, and through-fastened and standing seam roofs.
Ph. D.

Magister Scientiae Dentium - MSc(Dent)
Statement of the problem: Fibre reinforcement of polymethyl methacrylate (PMMA) denture base material is known to improve the strength, as well as the fatigue behavior, of the material. The powder liquid (P/L) ratio of PMMA is often changed to modify the handling properties of the material. Little is known about the effect of this deviation from manufacturer’s guidelines on the fatigue behaviour of the fibre reinforced product. Purpose: This study compared the flexural strength (FS) of PMMA reinforced with glass fibre using different P/L ratios, before and after cyclic loading. Methods and materials: Three groups, with 50 glass fibre reinforced (everStick nonimpregnated fibers) heat-cured PMMA resin (Vertex Rapid Simplified) specimens each, were prepared using a custom-made template (dimensions 10x9x50mm). Each group had a different P/L ratio: the control group (100%) had the manufacturer’s recommended ratio; the 90% and 80% groups had reduced P/L ratios (by weight).Twenty five specimens from each group were subjected to a 3-point bending compression test using a universal testing machine. The remaining 25 specimens from each group were subjected to cyclic loading (104 cycles) before compression testing. The (FS) was calculated using the highest force (Fmax) before specimen failure. Flexural strength was calculated using the equation: FS=3WL/2bd2. Within each group, median FS values before and after cyclic loading were compared by means of a non-parametric analysis of variance. The Aligned Ranks Transform method was used for the analysis. Statistical significance was set at p=0.05. Results: The Fmax (N) of the control (100%), 90% and 80% groups fatigued and unfatigued were 100%: 1665 (fat), 1465 (unfat); 90%: 1679 (fat), 1548 (unfat) and 80%: 1585 (fat), 1467 (unfit) respectively. There was no significant interaction between Mix ratio and Fatigue state, and the 80% mix had a significantly higher mean than either the 90% or 100% mix (with differences of about 0.3 units for both). The Fatigued state had a higher mean than the Un- fatigued state by about 6.0 units. Using FS (MPa) it was found that the fatigued 80% mix specimens had the highest value. The FS MPa of the control (100%), 90% and 80% groups fatigued and un-fatigued were 64.3, 60.6; 66.9, 65.6 and 70.2, 69.3 respectively. The fact that fatiguing strengthened the specimens merits further research. When observing the broken specimens it was found that there was a complete debonding of the fibres and the PMMA. Conclusion and clinical relevance: a) Fibre: The benefit of using glass fibre bundles to reinforce prostheses fabricated using heat cured PMMA is questionable due to problems with bonding between the fibre bundles and the heat cured PMMA resin. b) Fatiguing: An average person chews 107 times during a 3 year period. A limited period of average masticatory forces should not have a detrimental effect on prostheses made from heat cured PMMA resin. c) Mix ratio: Within the normal parameters of laboratory techniques the mix ratio of PMMA resin had no significance on the fracture resistance of the prostheses. Due to the high cost of the fibres used for the reinforcement and the limited success and insignificant results achieved in this study, this researcher cannot recommend using Stickbond or Stick fibers for the reinforcement of dentures made with heat cured PMMA resin.

Abstract : Deterioration of concrete structures reinforced with steel bars can be seen daily in regions with aggressive weather as steel-corrosion problems worsen. Fiber-reinforced-polymers (FRP) reinforcement has proven its feasibility through different civil structural elements. Present guidelines for FRP structures in North-America and Europe have not yet handled axially loaded members, due to the lack of research and experiments. This research takes charge of providing experimental database as well as extensive analyses and design recommendations of circular concrete columns reinforced totally with different FRP bars and spirals/hoops (FRP-RC columns). Full-scale columns were tested under monotonic loading with different levels of eccentricity. Test variables included the eccentricity-to-diameter ratio (e/D); reinforcement type (GFRP and CFRP vs. steel); concrete strength; longitudinal and transverse reinforcement ratio; and confinement configuration. All specimens measured 305 mm diameter and 1500 mm height. Test results indicated that specimens reinforced with glass-FRP (GFRP) or carbon-FRP (CFRP) reached their peak strengths with no damages to GFRP or CFRP rebar on either side of specimens. Specimens with CFRP reinforcement (CFRP-RC) behaved very similarly to their steel counterparts, and achieved almost the same nominal axial forces. Specimens with GFRP reinforcement (GFRP-RC) exhibited, however, reduced stiffness and achieved lower nominal axial forces than their steel or CFRP counterparts. Failure of GFRP-RC and CFRP-RC specimens was dominated by concrete crushing at low levels of eccentricity (e/D ratios of 8.2% and 16.4%). Experimental strain results revealed that GFRP bars developed high levels of strains and stresses on the compression and tension sides and hence the GFRP-RC specimens could sustain constant axial load after peak for some time up to the limit of concrete crushing at higher levels of eccentricity (e/D ratios of 8.2% and 16.4%), which help to delay the full damage. At these levels, flexural–tension failure initiated in the GFRP-RC specimens resulting from large axial and lateral deformations and cracks on the tension side until secondary compression failure occurred due to strain limitations in concrete and degradation of the concrete compressive block. The failure of CFRP-RC specimens at higher levels of eccentricity (e/D ratios of 8.2% and 16.4%) was characterized as flexural–compression in which it took place in a less brittle manner. On the other hand, this research also included different studies to analyze the test results, evaluate rebar efficiency, and provide recommendations for analysis and design. It was, therefore, indicated that the axial and flexural capacities of the tested FRP-RC specimens could be reasonably predicted using plane sectional analysis, utilizing the equivalent rectangular stress block (ERSB) parameters given by the ACI 440.1R-15 or CSA S806-12. All predictions underestimated the actual strength with variable levels of conservatism ranged between 1.05 to 1.25 for the GFRP-RC specimens and between 1.20 to 1.40 for the CFRP-RC specimens. These levels were noticeably reduced to critical limits in specimens with high-strength concretes. An elaborate review was made to the available ERSB parameters in the present steel and FRP design standards and guidelines. Modified expressions of the ERSB given in ACI 440.1R-15 and CSA S806-12 were developed. The results indicated good correlation of predicted and measured strength values with enhanced levels of conservatism. Additionally, sets of axial force–bending moment (P-M) interaction diagrams and indicative bar charts are introduced, and recommendations drawn. The compressive-strength contribution of FRP reinforcement was thoroughly reviewed and discussed. The minimum GFRP and CFRP reinforcement ratios to avoid rebar rupturing were broadly examined. Finally, the flexure stiffness (EI) of the tested specimens was analytically determined and compared with the available expressions using experimental and analytical M-ψ responses. Proposed equations are developed and validated against the experimental results to represent the stiffness of GFRP-RC and CFRP-RC columns at service and ultimate levels.
La détérioration des structures en béton armé avec des barres d’armature d’acier peut être observée quotidiennement dans les régions à climat agressif. Le renforcement interne en polymères renforcés de fibres (PRF) a démontré sa faisabilité grâce à différents éléments structuraux en génie civil. Les lignes directrices actuelles pour les structures en béton armé de PRF en Amérique du Nord et en Europe n'ont pas encore gérées les sections soumises à des efforts axiaux excentrique, en raison du manque de recherches et d'expériences. Cette recherche permet d’augmenter la base de données expérimentales ainsi établir des analyses approfondies et des recommandations de conception pour les colonnes circulaires en béton armé complètement renforcées de PRF (barres et spirales). Des grandeur-nature colonnes ont été testées sous charge monotone avec différents niveaux d'excentricité. Les variables de test comprenaient le rapport excentricité / diamètre (e/D) ; le type de renfort (PRFV et PRFC comparativement à l’acier); la résistance du béton en compression; le taux d’armature longitudinal et transversal; et la configuration de l’armature de confinement. Tous les échantillons mesuraient 305 mm de diamètre et 1500 mm de hauteur. Les résultats des tests ont indiqué que les spécimens renforcés avec des PRF de verre ou des PRF de carbone atteignaient leur résistance maximale sans endommager les barres d’armature. Des deux types de renforcement, les spécimens de PRFCCFRP se comportaient de manière très similaire à leurs homologues en acier et atteignaient presque les mêmes résistances axiales. Cependant, les spécimens avec renforcement en PRFV ont présenté une rigidité réduite et des forces axiales nominales inférieures à celles de leurs homologues en acier ou en PRFC. Le mode de rupture des spécimens de PRFC et de PRFV a été dominé par l’écrasement du béton à de faibles niveaux d'excentricité (rapports e/D de 8,2% et 16,4%). Les résultats ont révélé que les barres de PRFV ont développé des niveaux élevés de déformations et de contraintes sur les faces en compression et en tension et, par conséquent, les spécimens de PRFVC pourraient supporter une charge axiale constante après la résistance ultime pendant un certain temps jusqu'à la limite de la rupture en compression du béton du noyau à des niveaux supérieurs d'excentricité (rapport e/D de 8,2% et 16,4%), ce qui contribue à retarder la dégradation. À ces niveaux, une rupture en tension a été initiée dans les spécimens de PRFV résultant à de grandes déformations axiales et latérales et des fissures du côté de la face en tension jusqu'à ce que la rupture en compression du béton. La rupture des spécimens de PRFC à des niveaux supérieurs d'excentricité (rapport e/D de 8,2% et 16,4%) a été caractérisé comme étant en compression du béton dans laquelle il s'est déroulé de manière moins fragile. D'autre part, cette recherche comprenait également différentes études pour analyser les résultats des tests, évaluer l'efficacité des barres d'armature et fournir des recommandations pour l'analyse et la conception. Il a donc été indiqué que les capacités axiales et de flexion des spécimens en PRF testées pourraient être raisonnablement prédites en utilisant une analyse en section plane, en utilisant les paramètres du bloc de contrainte rectangulaire équivalent (BCRE) donnés par l'ACI 440.1R-15 ou la CSA S806- 12. Toutes les prédictions ont sous-estimé la résistance réelle avec des niveaux de variabilité conservateur entre 1,05 et 1,25 pour les spécimens de PRFC et entre 1,20 et 1,40 pour les spécimens de PRFC. Ces niveaux ont été nettement réduits à des limites critiques dans les spécimens avec des bétons à haute résistance. Un examen approfondi a été effectué sur les paramètres du BCRE disponibles dans les normes et les directives de conception actuelles en acier et en PRF. Les expressions modifiées du BCRE fournies dans ACI 440.1R-15 et CSA S806-12 ont été développées. Les résultats indiquent une bonne corrélation entre les valeurs de résistance prédites et mesurées avec des niveaux accrus de conservatisme. La contribution de la résistance à la compression du renforcement en PRF a été soigneusement examinée et discutée. Le taux d’armature minimum de PRFV et de PRFC pour éviter la rupture de l'armature ont été largement examinés. Enfin, la rigidité en flexion (EI) des spécimens testés a été déterminée de manière analytique et comparée aux expressions disponibles dans la littérature en utilisant les réponses expérimentales et analytiques M-ψ. Les expressions modifiées de la rigidité en flexion EI apportées dans l’ACI 440.1R ont été développées et validées.

The flexural performance of composite systems made of reinforced concrete, Fibre Reinforced Polymers (FRPs) and adhesives was studied during the current research. The experimental investigation was principally concentrated on the potential use of Kevlar® 49 (aramid fibre) for RC beam strengthening. The main aims of research have been; (a) to investigate the relative merits of using Aramids in comparison to other FRPs, (b) strength optimisation of systems to prevent excessive losses of ductility, (c) to examine the failure mode and crack patterns, together with salient strength factors at ultimate limit state and (d) to carry out analytical modelling using a commercial FE package. The experimental investigation comprised of testing 55 simply supported RC beams of either 1.5m or 2.6m length. In addition to the parametric studies included in points (a)-(d) above (to assess the section characteristics), further experimentation was conducted to investigate the beam performance by varying the factors of; (e) beam shear span, (f) FRP anchorage length, (g) concrete surface preparation, (h) FRP end-anchoring, (i) beam precracking, (j) introduction of air-voids within the bond line of FRP/concrete, (k) influence of cyclic loading and, (1) exposure to aggressive environment. The results from current tests confirm elements of reports from other researchers (by thorough review of literature) that all FRPs have great potential for flexural strengthening of RC members. This is valid even in cases where additional environmental degradation and/or cracking (due to serviceability loads), had taken place. Aramid fibres were found to result in favourable outcomes concerning both strength and ductility enhancements. It was determined, both from experiments and non-linear modelling, that the amount of FRP fibre content is an important factor in every strengthening application. Experimentation showed that depending on the existing condition of the structure (concrete strength, internal reinforcement ratio, section dimensions, degradation level and load configuration), there seems to be a unique level of optimum fibre content. The FRP levels in excess of the optimum were seen to lead to premature brittle tearing-off failure modes. It was also found that to prevent premature beam failure (due to incompatibility of stress at concrete and FRP interface), a maximum possible anchorage length should be considered in order to deliver an optimum section performance. The results from the analytical modelling indicated a most satisfactory agreement with the experimental data after the initial mechanical properties were calibrated. It was found that actual representation of material properties (e.g. steel constitutive law) are of great significance, for an accurate modelling of RC element loaded behaviour. The bond developed between the FRP and concrete is one of the key parameters for achieving good performance of the systems. It was determined that concrete surface preparation and priming is beneficial, while the introduction of air-voids due to poor workmanship can reduce the section load bearing capabilities. Cyclic loading on FRP strengthened sections was found to curtail the full rotational capacity utilisation of the beam. However, even the above mentioned curtailed behaviour was more advantageous than cyclically loaded beam performance without FRP strengthening.

Calcium phosphate cements (CPCs) are used as bone void fillers and as complements to hardware in fracture fixation. The aim of this thesis was to investigate the possibilities and limitations of the CPCs’ mechanical properties, and find out if these ceramic bone cements can carry application-specific loads, alone or as part of a construct. Recently developed experimental brushite and apatite cements were found to have a significantly higher strength in compression, tension and flexion compared to the commercially available CPCs chronOS™ Inject and Norian® SRS®. By using a high-resolution measurement technique the elastic moduli of the CPCs were determined and found to be at least twice as high compared to earlier measurements, and closer to cortical bone than trabecular bone. Using the same method, Poisson's ratio for pure CPCs was determined for the first time. A non-destructive porosity measurement method for wet brushite cements was developed, and subsequently used to study the porosity increase during in vitro degradation. The compressive strength of the experimental brushite cement was still higher than that of trabecular bone after 25 weeks of degradation, showing that the cement can carry high loads over a time span sufficiently long for a fracture to heal. This thesis also presents the first ever fatigue results for acidic CPCs, and confirms the importance of testing the materials under cyclic loading as the cements may fail at stress levels much lower than the material’s quasi-static compressive strength. A decrease in fatigue life was found for brushite cements containing higher amounts of monetite. Increasing porosity and testing in a physiological buffer solution (PBS), rather than air, also decreased the fatigue life. However, the experimental brushite cement had a high probability of surviving loads found in the spine when tested in PBS, which has previously never been accomplished for acidic CPCs. In conclusion, available brushite cements may be able to carry the load alone in scenarios where the cortical shell is intact, the loading is mainly compressive, and the expected maximum stress is below 10 MPa. Under such circumstances this CPC may be the preferred choice over less biocompatible and non-degradable materials.

Numerical methods aid significantly the engineering efforts towards the conservation of existing masonry structures and the design of new ones. Among them, macro-mechanical finite element methods based on the smeared crack approach are commonly preferred as an affordable choice for the analysis of large masonry structures. Nevertheless, they usu-ally result in a non-realistic representation of damage as smeared over large areas of the structure, which hampers the correct interpretation of the damage pattern. Additionally, a more critical pathology of this approach is the mesh-dependency, which influences nota-bly the safety and stability predictions. To overcome these limitations, this thesis proposes a novel computational tool based on the {enrichment} of the classical smeared crack approach with a local tracking algorithm. The objective of this localized damage model is the realistic and efficient non-linear anal-ysis of masonry structures with an enhanced representation of cracking. The non-linear behaviour of masonry is simulated through the adoption of a continuum damage mechanics model with two damage indices, allowing the differentiation between the tensile and compressive mechanical responses of masonry. In this context, a novel explicit formulation for the evolution of irreversible strains is proposed and implemented. Two new expressions are derived for the regularization of the tensile and compressive softening responses according to the crack-band approach, ensuring the mesh-size objec-tivity of the damage model. The simulation of the structural behaviour of masonry structures under versatile loading and boundary conditions necessitates some developments in the context of local tracking algorithms. To this end, this thesis presents the enhancement of local tracking algorithms with novel procedures that make possible the simulation of multiple, arbitrary and inter-secting cracking under monotonic and cyclic loading. Additionally, the effect of different crack propagation criteria is investigated and the selection among more than one potential failure planes is tackled. The proposed localized damage model is validated through the simulation of a series of structural examples. These vary from small-scale tests on concrete specimens with few dominant cracks, to medium and large-scale masonry structures with multiple tensile, shear and flexural cracking. The analyses are compared with analytical, experimental and numerical results obtained with alternative methods available in the literature. Overall, the localized damage model developed in this thesis largely improves the mesh-independency of the classical smeared crack approach and reproduces crack patterns and collapse mech-anisms in an efficient and realistic way.
Los métodos numéricos son decisivos en la ingeniería para la conservación de estructuras de mampostería existentes y el diseño de estructuras nuevas. Entre ellos, los métodos macro-mecánicos de elementos finitos, basados en el concepto de fisuras distribuidas, son habitualmente los preferidos como opción asequible para el análisis de grandes estructuras de mampostería. Sin embargo, suelen resultar en a una representación poco realista del daño, distribuido en grandes áreas de la estructura, lo que impide la correcta interpretación del patrón de daño. Además, esta metodología presenta una patología más crítica, la dependencia de la malla, que influye notablemente en las predicciones de seguridad y estabilidad. Para superar estas limitaciones, esta tesis propone una nueva herramienta numérica basada en el enriquecimiento del clásico enfoque de fisuras distribuidas con un algoritmo de trazado local. El objetivo de este modelo de daño localizado es el análisis no-lineal de las estructuras de mampostería de manera realista y eficiente con una representación mejora-da de fisuras. El comportamiento no lineal de la mampostería se simula a través de la adopción de un modelo de mecánica de daño continuo con dos índices de daño, permitiendo la diferenciación entre las respuestas mecánicas de tensión y compresión de la mampostería. En este contexto, se propone e implementa una nueva formulación explícita para la evolución de deformaciones irreversibles. Se derivan dos nuevas expresiones para la regularización del ablandamiento de tracción y compresión según el ancho de banda de la fisura, garantizan-do la objetividad del modelo de daño al respecto del tamaño de la malla. La simulación del comportamiento estructural de las estructuras de mampostería en condiciones de carga y contorno generales precisa de algunos desarrollos en el contexto de los algoritmos locales de trazado. Con este objetivo, se presenta la mejora de los algoritmos locales de trazado con nuevos procedimientos que posibilitan la simulación de fisuración múltiple, arbitraria e secante bajo cargas monótonas y cíclicas. Además, se investiga el efecto de diferentes criterios de propagación de fisuras y se aborda la selección entre más de un plano de falla posible. El modelo de daño localizado propuesto se valida mediante la simulación de una serie de ejemplos estructurales. Éstos van desde pruebas a pequeña escala en probetas de hormigón, con pocas fisuras dominantes, hasta estructuras de mampostería de mediana y gran escala con fisuración múltiple de tracción, de cortante y de flexión. Los análisis se comparan con los resultados analíticos, experimentales y numéricos obtenidos con métodos alternativos disponibles en la literatura. El modelo de daño localizado mejora en gran medida la independencia de la malla del clásico método de fisuras distribuidas y reproduce patrones de daño y mecanismos de colapso de una manera eficiente y realista

Thesis (MScEng)--Stellenbosch University, 2013.
ENGLISH ABSTRACT: Different types of live loading due to traffic may act on bridges. The focus of this study is on normal traffic loading according to the South African specification of TMH7. Heavy vehicles are not included in normal traffic loading. TMH7 represents the code of practice for the design of highway bridges and culverts in South Africa. The aim of the study is to provide an insight into the flexural analysis of skew bridges, under the effects of normal traffic loading. The need for the study arose since the specification of TMH7 does not explicitly specify application patterns for normal traffic loading. Only the intensity of normal traffic loading is specified and it should be applied to yield the most adverse effects. For these reasons, a set of so-called standard application patterns are investigated and developed through the course of this study. The envelope of the values from the standard application patterns are compared to the most adverse application pattern for flexural effects in certain design regions of the bridge deck. Flexure, as in the context of this study, translates into the bending and twisting of the bridge deck under loads. A number of numerical experiments are performed for typical single span and multi-span continuous carriageways, where the standard application patterns are compared to the most adverse application patterns. The results from the numerical experiments are documented and compared as the angle of skew of the bridge deck increases in plan-view. For this purpose, the development of effective and specialized software was necessary. It was found that the set of standard application patterns can be used as a preliminary approximation for the most adverse effects of normal traffic loading, for specific flexural resultants in certain design regions of a bridge deck. However, for a large number of secondary flexural effects, the set of standard application patterns did not represent a good approximation for the most adverse values.
AFRIKAANSE OPSOMMING: Verskillende tipes lewendige belasting, as gevolg van verkeer, kan op brûe inwerk. Die fokus van die studie is op normale verkeers-belasting volgens die Suid-Afrikaanse spesifikasie van TMH7. Swaar-voertuie word nie ingesluit by normale verkeers-belasting nie. TMH7 verteenwoordig die kode vir die ontwerp van padbrûe en duikers in Suid-Afrika. Die doel van die studie is om insig te verskaf in die buig-analise van skewe brûe, as gevolg van die werking van normale verkeers-belasting. Die rede vir hierdie studie ontstaan aangesien die spesifikasie van TMH7 nie eksplisiet aanwendingspatrone vir normale verkeers-belasting voorskryf nie. Slegs die intensiteit van normale verkeersbelasting word voorgeskryf en dit moet aangewend word om die negatiefste effekte te verkry. Vir hierdie redes word 'n versameling van sogenaamde standaard aanwendings-patrone deur die loop van die studie ondersoek en ontwikkel. Die omhullings-kurwe van die waardes wat deur die standaard patrone gelewer word, word vergelyk met die waarde van die aanwendings-patroon wat die negatiefste buig-effek in sekere ontwerp-areas van die brugdek veroorsaak. Buig-effekte, soos van toepassing op hierdie studie, verwys na buig en wring van die brugdek as gevolg van belastings. 'n Aantal numeriese eksperimente, vir enkel-span sowel as multi-span deurlopende brugdekke, word uitgevoer en die standaard aanwendings-patrone word vergelyk met die aanwendings-patrone wat die negatiefste waardes lewer. Die resultate van die numeriese eksperimente word gedokumenteer en vergelyk soos die hoek van skeefheid van die brugdek in plan-aansig toeneem. Vir hierdie doel is die ontwikkeling van effektiewe en gespesialiseerde sagteware dus nodig. Daar is gevind dat die standaard aanwendings-patrone, vir spesifieke buig-resultante in sekere ontwerp-areas van die brugdek, as 'n voorlopige benadering vir die negatiefste effekte van normale verkeers-belasting gebruik kan word. Dit was egter verder gevind dat vir 'n groot aantal sekondêre buig-effkte, die versameling standaard aanwendings-patrone nie as 'n goeie benadering vir die negatiefste waardes dien nie.

In order to predict the inelastic hysteretic behavior of reinforced concrete (RC) structural walls under lateral cyclic loading, robust and reliable numerical tools are required. The Shear-Flexure-Interaction Multiple-Vertical-Line-Element-Model (SFI-MVLEM) proposed by Kolozvari et al. (2015) incorporates important material characteristics and behavioral response features, therefore it promises excellent capabilities. In reference to the SFI-MVLEM approach, this study investigates the global response (i.e. lateral load versus lateral top displacement) sensitivity to some input parameters, in order to evaluate which input parameters are influential and which ones are not. Seven RC structural wall specimens with a moderate aspect ratio are considered for the parametric sensitivity study. The predicted load-displacement responses are compared with the experimental ones, in order to assess variations in analytical responses. The input parameters here analyzed are the number of SFI-MVLEM elements used for the wall discretization, the concrete tensile strength, the dowel stiffness coefficient for steel reinforcing bars, and the cracks closure mechanism. The study shows that the number of SFI-MVLEM elements does not affect the predicted global response, while the concrete tensile strength and the dowel stiffness coefficient for steel reinforcing bars affect the simulated global response in terms of both lateral load capacity and energy capacity dissipation. In addition, the study indicates that the assumption of sudden crack closure provides more accurate results in terms of energy capacity dissipation than the assumption of gradual cracks closure.

Reinforced concrete (RC) structures constitute a significant portion of the building inventory in earthquake-prone regions of the United States. Accurate analysis tools are necessary to allow the quantitative assessment of the performance and safety offered by RC structures. Currently available analytical approaches are not deemed adequate, because they either rely on overly simplified models or are restricted to monotonic loading. The present study is aimed to establish analytical tools for the accurate simulation of RC structures under earthquake loads. The tools are also applicable to the simulation of reinforced masonry (RM) structures. A new material model is formulated for concrete under multiaxial, cyclic loading conditions. An elastoplastic formulation, with a non-associative flow rule to capture compression-dominated response, is combined with a rotating smeared-crack model to capture the damage associated with tensile cracking. The proposed model resolves issues which characterize existing concrete material laws. Specifically, the newly proposed formulation accurately describes the crack opening/closing behavior and the effect of confinement on the strength and ductility under compressive stress states. The model formulation is validated with analyses both at the material level and at the component level. Parametric analyses on RC columns subjected to quasi-static cyclic loading are presented to demonstrate the need to regularize the softening laws due to the spurious mesh size effect and the importance of accounting for the increased ductility in confined concrete. The impact of the shape of the yield surface on the results is also investigated. Subsequently, a three-dimensional analysis framework, based on the explicit finite element method, is presented for the simulation of RC and RM components under cyclic static and dynamic loading. The triaxial constitutive model for concrete is combined with a material model for reinforcing steel which can account for the material hysteretic response and for rupture due to low-cycle fatigue. The reinforcing steel bars are represented with geometrically nonlinear beam elements to explicitly account for buckling of the reinforcement. The strain penetration effect is also accounted for in the models. The modeling scheme is validated with the results of experimental static and dynamic tests on RC columns and RC/RM walls. The analyses are supplemented with a sensitivity study and with calibration guidelines for the proposed modeling scheme. Given the computational cost and complexity of three-dimensional finite element models in the simulation of shear-dominated structures, the development of a conceptually simpler and computationally more efficient method is also pursued. Specifically, the nonlinear truss analogy is employed to capture the response of shear-dominated RC columns and RM walls subjected to cyclic loading. A step-by-step procedure to establish the truss geometry is described. The uniaxial material laws for the concrete and masonry are calibrated to account for the contribution of aggregate interlock resistance across inclined shear cracks. Validation analyses are presented, for quasi-static and dynamic tests on RC columns and RM walls.
Ph. D.

The aim is to propose solutions to the new bridge construction due to its unsatisfactory compared to the existing bridge reconstruction project . There are three studies bridging and selected variant trapezoidal plate further processed static opinion. The design was judged by the ultimate limit states and usability. Partial assessments were made for the anchoring system, anchorage area , unravels notched bars and store design to support .

碩士
國立臺灣大學
土木工程學研究所
101
Reinforced concrete shear walls are commonly used to resist the actions imposed on buildings due to earthquake loading. To resist such actions, properly proportioned and detailed slender walls are designed to yield in flexure, and to undergo large flexural deformations without loss of lateral load capacity. ACI 318-11 uses displacement-based design to ensure that the shear wall will have adequate deformation capacity. The basis of the approach is to use displacement as the primary design parameter to relate overall system response to wall cross section behavior. Recent earthquake reconnaissance in Chile and New Zealand gave shocking results for buildings that use a shear wall system. The result indicates that many of these buildings did not have adequate deformation capacity. The typical damage that was found, includes crushing/spalling of concrete, buckling of vertical reinforcement, and global wall buckling. Based on these observations, some changes in the ACI 318-11 will be made related to design and detailing of shear wall for the next ACI series, ACI 318-14. A prototype building which incorporates with two different shear wall cross-sections (rectangular and T-shaped) were chosen to investigate this ACI 318 code change. Design procedures are presented by including the shear capacity design recommended by NEHRP (2011). In addition, the use of high-strength material in the slender walls design was also observed in this study.

碩士
國立中興大學
土木工程學系
91
The flexural behavior of reinforced lightweight aggregate concrete beam (R.L.C.) under cyclic loading is investigated in this study. The results are compared to corresponding reinforced concrete beam (R.C.). A total of 44 beam specimens were made. The parameters included concrete type, concrete strength, reinforcement ratio, spacing of shear reinforcement and section size. The test results show that R.L.C. beams have same or less ductility than R.C. beams. For specimens of reinforcement ratio smaller than 2.88%. Both R.L.C. and R.C. beams. increase of concrete strength will increase the ductility. For specimens of reinforcement ratio smaller than ρmax . Both at lower and higher concrete strength level, the decaying of strength and stiffness of R.L.C. beams appear milder than those of R.C. beams. By increase of concrete strength. The energy dissipation capacity of R.L.C. beams were obviously increased. When specimens were tend to compression fractured. The decaying of strength and stiffness of R.L.C. beams are similar or poor than those of R.C. beams. The energy dissipation capacity of R.L.C. beams are also similar or poor than those of R.C. beams. Different spacing of shear reinforcement have no obviously effect to the beams.

Aluminium foam has a range of properties that are desirable in many applications. These properties include good stiffness and strength to weight ratios, impact energy absorption, sound damping, thermal insulation and non combustibility. Many of these characteristics are particularly attractive for core materials within sandwich structures. The combination of aluminium foam cores with thermoplastic composite skins is easily manufactured and has good potential as a multifunctional sandwich structure useful in a range of applications. This thesis has investigated the flexural behaviour of such structures using a combination of experimental and modelling techniques. The development of these structures towards commercial use requires a thorough understanding of the deformation and strain mechanisms of the structure, and this will, in turn, allow predictions of their structural behaviour in a variety of loading conditions. ¶ ...

碩士
國立中興大學
土木工程學系
87
The purpose of this study is to investigate the flexural behavior of reinforced concrete columns with high strength shear reinforcement under cyclic lateral load. A total of fourteen column specimens were made in this study. The size of specimens was 300mm×300mm×4500mm . The variables included were concrete strength、level of axial load 、 strength of transverse reinforcement and volume of transverse reinforcement . The results showed that ultimate strengths predicted by ACI Code were conservative. Columns under higher axial load exhibited less strength﹐ductility﹐stiffness and capability of energy dissipation .With same amount of transverse reinforcement , columns contained high strength shear reinforcement showed better ductility . When designed by ACI 318-95 equation (21-4), due to larger spacing , columns with high strength shear reinforcement showed less ductility in this study.

Tese de mestrado, Medicina Dentária, Universidade de Lisboa, Faculdade de Medicina Dentária, 2018
Objectives: The aim of this study was to evaluate the influence of the concentration of chlorhexidine (CHX) on the flexural strength of three reline acrylic resins, Kooliner, Ufi Gel Hard and Probase Cold, after undergoing a thermal ageing process. Methods: Distinct proportions of CHX were selected for loading each reline resin. Kooliner had four groups (1%, 2.5%, 5%, 7.5% CHX), Ufi Gel Hard had five groups (1%, 2.5%, 5%, 7.5%, 10% CHX) and Probase Cold had three groups (1%, 2.5%, 5% CHX). Every material had also a control group (0% CHX). Specimens with 64x10x3.3mm were submitted to a thermocycling procedure consisting of 1000 cycles of thermal fluctuations between 5ºC and 55ºC. Afterwards they were tested for flexural strength values using a three point bending device. Results were submitted to nonparametric tests according to the Kruskal-Wallis method, followed by multiple comparisons using Mann-Whitney tests with Bonferroni corrections, being considered the 5% level of significance (α=0.05). Results: Regarding Kooliner and Ufi Gel Hard specimens, there were no statistical significant differences on flexural strength values among different CHX groups (p>0.05). Results for Probase Cold specimens showed that 5% CHX group had a lower flexural strength value compared to the control group (p= 0.033). Conclusions: The proportions of 1%, 2.5%, 5% and 7.5% CHX for Kooliner, 1%, 2.5%, 5%, 7.5% and 10% CHX for Ufi Gel Hard and 1% and 2.5% CHX for Probase Cold do not affect the flexural strength values of the acrylic resins after a thermal ageing process equivalent to one month in the oral cavity.

碩士
國立中興大學
土木工程學系
85
Abstract The purpose of this study is to investigate the flexural behaviorof concrete columns with welded wire fabric as shear reinforcement under constant axial load and cyclic lateral load . A total of ten column specimens were made in this study . The size of specimens was300mm×300mm×4500mm . The variables included were concrete strength、loading type、amount of transverse reinforcement、type of transversereinforcement、level of axial load and arrangement of transverse reinforcement . The results showed that strengths predicted by ACI Code were conservative . Cyclic loading on column would not reduce the maximumstrength but would reduce the ductility tremendously . Flexural strength、 ductility、crack control、strength and stiffness degradation of columns with welded wire fabric were about the same as columns withconventional transverse reinforcement . Capability of energy dissipationof columns with WWF was higher than that of conventional columns .WWFcan be adopted in concrete columns due to its construction ease .

碩士
國立中興大學
土木工程學系
84
Abstract The purpose of this study is to investigate the flexural behavior of reinforced concrete beams with welded wire fabric as shear reinforcement under cyclic loading. Atotal of fourteen beam specimens were made. Twelve contained welded wire fabric as shear reinforcement while the other two contained conventional shear reinforcement. The parameters included concrete strength, shear span to depth ratio, spacing of shear reinforcement, ratio of positive steel to negative steel, amount oftension reinforcement and loading history。 The results show that beams with welded wire fabric have less ductility than beams with conventional shear reinforcement. Beams with WWF have better crack control than those with conventional shear reinforcement. Beams with WWF showed faster deterioration than those with conventional shear reinforcement in strength and stiffness. Increase of amount of shear reinforcement and negative steel will increase the energy dissipation capacity。

Student Number : 0100677A - PhD thesis - School of Civil and Environmental Engineering - Faculty of Engineering and the Built Environment
This thesis presents the findings on empirical study of dry-stack masonry. Dry-stack masonry refers to a method of building masonry walls, where most of the masonry units are laid without mortar in the joints. Of late (since mid eighties) in modern construction, dry-stacking or mortarless technology is increasingly becoming popular because of its advantages. The construction industry is acknowledging the need to accelerate the masonry construction process, as the traditional method is labour intensive and hence slower due to the presence of a large number of mortar joints. Early attempts were made to increase the size of masonry units (block instead of brick), thereby reducing the number of mortar joints, wherein the use of bedding mortar imposed constraints on the number of courses to be constructed in a day. Elimination of bedding mortar accelerates construction; thereby reducing cost, variation due to workmanship and generally small pool of skilled labour is required in dry stacking. Dry-stack masonry is a relatively new technology not yet regulated in the code of practice and therefore very limited information on the structural behaviour of the masonry is available. This project is based on the investigation of the HYDRAFORM dry-stack system, which utilises compressed soil-cement interlocking, blocks. The system is now widely used in Africa, Asia and South America. The main objective of the project was to establish through physical testing the capacity of the system to resist lateral load (e.g. wind load), vertical load and dynamic load such as earthquake loading. In the first phase of the project investigations were conducted under static loading where series of full-scale wall panels were constructed in the laboratory and tested under lateral loading, and others were tested under vertical loading to establish the mode of failure and load capacity of the system. Series of control tests were also conducted by testing series of wallettes to establish failure mechanism of the units and to establish the flexural strength of the system. Finally the test results were used for modelling, where load prediction models for the system under vertical loading and under lateral loading were developed. The theoretical load prediction models were tested against the test results and show good agreement. After the load capacity was established the next step in the study was to further improve the system for increased capacity particularly under dynamic loading. The normal Hydraform system was modified by introducing a conduit, which allows introduction of reinforcements. Series of dry-stack seismic systems were constructed and initially tested under static lateral loading to establish the lateral load capacity. The second Phase of the project was to investigate the structural behaviour and performance of the Hydraform system under seismic loading. A shaking table of 20 tonnes payload, (4m x 4m) in plan was designed and fabricated. A full-scale plain dry-stack masonry house was constructed on the shaking table and subjected to seismic base motions. The shaking table test was performed using sine wave signals excitations starting from low to very severe intensity. A conventional masonry test structure of similar parameters was also constructed on the table and tested in a similar manner for comparison. The tests were conducted using a frequency range of 1Hz to 12Hz and the specimens were monitored for peak accelerations and displacements. For both specimens the initial base motion was 0.05g. The study established the mode of failure of the system; the structural weak points of unreinforced dry-stack masonry, the general structural response of the system under seismic condition and the failure load. The plain dry-stack masonry failed at 0.3g and the conventional masonry failed at 0.6g. Finally recommendations for further strengthening of system to improve its lateral capacity were proposed.

The following dissertation studies the behavior of flat slabs when subjected to constant vertical loads and cyclic horizontal displacements, as a continuation of previous studies developed at FCT/UNL. The main focus of this research is to study the influence of flexural reinforcement on the seismic response of flat slabs. Therefore, three reinforced concrete flat slabs with varying flexural reinforcement ratio were tested, two having the same top reinforcement ratio of !=0,64% and one with !=1,34%. One of the specimens with lower longitudinal ratio was reinforced with studs as specific punching shear reinforcement. All slabs had overall dimensions of 4,15 × 1,85 × 0,15 m3 and a gravity shear ratio, ratio between the gravity load and the punching shear resistance, approximately equal to 55%. For a more complete analysis the results obtained were compared to two other specimens from previous experimental campaigns also conducted at FCT/UNL. These two slabs were designed with top flexural reinforcement ratio (!=0,96%) that lies between the two tested in this dissertation, one with no shear-reinforcement and the other with headed studs. Results showed that the reduction of flexural reinforcement resulted in a more ductile behavior of the specimens and in a higher drift capacity. The high flexural ratio added to one specimen improved the maximum unbalanced moment capacity but also made the slab fail in a more brittle mode. As expected, the specimen with shear headed studs supported the highest drifts and ended up not failing during this experimental campaign, reaching the test setup upper limit.
A presente dissertação estuda o comportamento de lajes fungiformes submetidas a carga vertical constante e carregamento horizontal cíclico, sendo a continuação de trabalhos realizados anteriormente no Departamento de Engenharia Civil da FCT/UNL. O principal objetivo deste trabalho é estudar a influência da variação da taxa de reforço longitudinal na resposta sísmica de lajes fungiformes. Assim, três modelos de lajes fungiformes com variação da taxa de armadura longitudinal foram fabricados e testados, dois com a mesma taxa de !=0,64% e outro com !=1,34%. Um dos modelos com baixa taxa de armadura longitudinal foi reforçado com reforço específico ao punçoamento. Todas as lajes possuíam as mesmas dimensões de 4,15 × 1,85 × 0,15 m3 e razão entre a carga vertical e a resistência ao punçoamento aproximadamente igual a 55%. Para uma análise mais completa, os resultados obtidos foram comparados com outros dois modelos testados anteriormente na FCT/UNL. Estas duas lajes possuíam uma taxa intermédia de reforço longitudinal (!=0,96%), uma sem armadura específica de punçoamento e a outra contendo “shear studs”. Os resultados mostraram que a redução da taxa de armadura longitudinal resultou num comportamento mais dúctil das lajes e numa capacidade maior de deslocamentos horizontais. A utilização da taxa mais elevada de armadura longitudinal laje melhorou a capacidade máxima de momentos não balanceados, mas também fez com que a estrutura tivesse uma rotura mais frágil. Como esperado, o modelo com “studs” suportou os maiores “drifts” e acabou não rompendo durante o ensaio, devido a ter sido atingido o limite do sistema de ensaio.

Dissertação de mestrado integrado em Engenharia Civil
A presente dissertação aborda a investigação efetuada no âmbito do comportamento de lajes de betão armado reforçadas à flexão com a técnica da inserção (técnica NSM) de laminados de CFRP (Polímeros Reforçados com Fibras de Carbono) em entalhes efetuados no betão de recobrimento. Neste contexto, é estudado o efeito da pré-fendilhação do betão e do carregamento cíclico no comportamento à rotura de lajes de betão armado reforçadas à flexão com laminados de CFRP inseridos. Este trabalho é iniciado com a revisão bibliográfica, onde é apresentado o estado atual de conhecimento relativamente à utilização de materiais compósitos de CFRP no reforço à flexão de estruturas de betão armado no âmbito da temática da presente dissertação. De seguida, é apresentado o programa experimental no qual foi avaliado o efeito da pré-fendilhação e do carregamento cíclico no comportamento à rotura de lajes de betão armado reforçadas à flexão com laminados de CFRP inseridos. Foram analisados dois níveis de dano (pré-fendilhação) e dois níveis de carregamento cíclico. O comportamento à rotura das lajes pré-fendilhadas e reforçadas à flexão, com laminados de CFRP inseridos é comparado com o de uma laje semelhante, com a diferença de esta não ter sido pré-fendilhada. O comportamento à rotura das lajes reforçadas à flexão com laminados de CFRP inseridos e sujeitas a carregamento cíclico é comparado com o de uma laje semelhante, com a diferença de esta não ter sido submetida a carregamento cíclico. Por fim, são apresentadas as conclusões gerais obtidas com a realização desta dissertação, sendo posteriormente indicadas perspetivas de desenvolvimento futuro.
The current dissertation deals with the reasearch carried out on the behavior of reinforced concrete (RC) slabs flexural strengthened with CFRP (Carbon Fiber Reinforced Polymer) laminates according to the NSM (Near Surface Mounted) technique, which is based on introducing CFRP laminates into slits opened on the concrete of the slabs. Therefore, this work aims to study the effect of pre-cracking and cyclic loading on the behavior until failure of RC slabs flexural strengthened with NSM CFRP laminates. This work starts with the literature review about the current knowledge on the use of composite materials, such as CFRP, for the flexural strengthening of RC structures. Afterwards, the experimental program carried out on this work is described, which purpose is to evaluate the effect of pre-cracking and cyclic loading on the behavior until failure of RC slabs flexural strengthened with NSM CFRP laminates. It were analyzed two levels of damage (pre-cracking) and two levels of cyclic loading. The behavior until failure of pre-cracked RC slabs flexural strengthened with NSM CFRP laminates is compared with similar RC slab without pre-cracks before the CFRP application. The behavior until failure of RC slabs flexural strengthened with NSM CFRP laminates and subsequently subjected to a cyclic loading is compared with similar RC slab without cyclic loading. Finally, the most relevant conclusions obtained in this research are presented and the prospects for future developments are indicated.
Fundação para a Ciência e Tecnologia (FCT) - Projeto FCOMP-01-0124-FEDER-014844;
FEDER;
COMPETE.

碩士
國立高雄應用科技大學
土木工程與防災科技研究所
92
The main objective in this research is focused on the dynamic characteristics of the soil behind the flexural wall during earthquake. Moreover the mechanism of lateral spreading of the soil was also discussed when the decrease of the lateral pressure is happened due to the wall movement. The experimental shaking table(2m×2m), on which a sand tank(1.8m×0.9m×1.45m) wsa placed, was used in the article. To record soil behavior during shaking, earth pressure transducers, LVDTs and accelerometers are prepared in the suitable locations within the tank. Both of flexibility wall and relative density of the backfill soil were considered respectively in experiment. Results of shaking table showed that the lateral displacement of the wall decreases with increasing wall thickness and the relative density of the backfill. To simulate experimental results, the proper model was also developed in this study. The outcome of model is approximately close to the findings in the laboratory. The dynamic lateral earth pressure curve is less regular due to the wall movement. Noted that it has low and high area for medium dense or dense backfill sand. The dynamic earth pressure results of experiments are different with those calculated from M-O method, because of outside movement of the wall. The results in stress-strain diagram revealed that the shear strain becomes less when the position is near bottom, but the shear stress of the bottom is higher than that of the top.

Documentos apresentados no âmbito do reconhecimento de graus e diplomas estrangeiros
Glass Fiber Reinforced Polymer (GFRP) bars with significant corrosion resistance lead to an improvement in the performance of concrete structures and a significant reduction in costs. High ratio of tensile strength to weight, non conductive, and non-magnetic properties are other features of GFRP bars. Recent international design standards, such as ACI 440.1R-15 do not recommend including FRP reinforcement in compression, so they replace them by concrete in calculations. The purpose of this study was to investigate the effect of concentric and excentric axial loading on the axial capacity and ductility of GFRP reinforced concrete columns compared to steel reinforced concrete columns, comparison of flexural capacity of GFRP reinforced concrete beams with steel reinforced concrete beams, and also the effect of compressive bars on the bending capacity and ductility of GFRP reinforced concrete beams. In this study, concrete beams and columns were modeled using finite element software ,ABAQUS. Experimental data from previous studies were used as a criterion for numerical investigations and the model results were validated using the available experimental data. The results demonstrated that the average load carrying capacity of GFRP reinforced concrete columns is about 93.5 percent of steel reinforced concrete columns. GFRP reinforced concrete columns under concentric loading have greater load carrying capacity than GFRP reinforced concrete columns under eccentric loading which is more significant for steel reinforced concrete columns. The average flexural strength of steel reinforced concrete beam was about 90% of GFRP reinforced concrete beam. Also, the ductility of GFRP concrete beam specimens was greater than that for the steel beam specimen. Using GFRP compression reinforcement resulted in higher energy absorption and ultimately higher ductility of the GFRP concrete beams. Also, the results showed that GFRP compression reinforcement does not significantly increase the flexural strength of beams.

碩士
國立虎尾科技大學
動力機械工程研究所
92
The main research of this paper can be divided into two respects, the first is that development of flexure hinge based stack-type 5 DOF micro-stage for a heavy-loading machining process; the second is that development of a new nano-contouring measurement technique. In semiconductor manufacturing facility, the ability to etch the minimum line width of IC process depends on the positioning resolution of the fine motion stage. The construction of 5 DOF micro-stages in this paper is to complete assembly using the characteristic of distortion of flexible ware and provide high accuracy positioning in conjunction with the piezoelectric actuators. A 5 DOF micro-stage were designed, fabricated, and tested. For the validity of the derived theoretical model, the results of the theory and experiment are all examined. The comparison of the results by theory and experiment shows good agreement. The performance of the micro-stage has 52.76μm travel along the x-axis, 5l.79μm ravel along the y-axis, 12.08μm travel along the z-axis and lnm resolution, and 185μrad along θx-axis, and 277μrad along θy-axis, and resonance frequency of l.25kHz. The micro-stage also can support 12 kilograms to move. As with measurement system, there kinds of contouring measurement systems that can reach nano-level accuracy and be built by means of there different kinds of lens group placing methods are formulated in this paper. The resolution of the measurement is 1nm.