Dissertations / Theses on the topic 'TRC strengthening'

Für das Funktionieren von Verstärkungsschichten aus Textilbeton ist eine sichere Kraftübertragung zwischen den einzelnen Verbundbaustoffen sicherzustellen. Aufgrund der sehr hohen Garnzugfestigkeiten sind besonders bei Verwendung textiler Bewehrungen aus Carbon sehr effektive Verstärkungen herstellbar. In Textilbetonbauteilen sind hierbei im Regelfall Übergreifungsstöße der textilen Bewehrungslagen nicht zu vermeiden. Der vorliegende Beitrag befasst sich daher mit der experimentellen und analytischen Bestimmung der Übergreifungslängen textiler Bewehrungsstrukturen innerhalb von Textilbetonverstärkungsschichten
A safe introduction and transmission of the acting forces is crucial for the functioning of composite materials. Because of the very high yarn tensile strengths of textile reinforcements made of carbon, the manufacturing of very effective TRC strengthening layers is possible. In TRC members, overlap joints within the textile layers usually cannot be avoided. This contribution deals with the experimental and analytical determination of the lap lengths of textile fabrics within a textile reinforced concrete strengthening layer

Textilbewehrter Beton zur Verstärkung von Stahlbetonbauteilen ist neben den klassischen und etablierten Verfahren eine äußerst interessante Alternative, die die Vorteile der leichten Kohlenstofffaserklebeverstärkungen mit denen von Spritzbeton mit Bewehrung verbindet. Aus den theoretischen und experimentellen Untersuchungen in dieser Arbeit können wichtige Erkenntnisse zum gemeinsamen Tragverhalten von Betonstahl und textiler Bewehrung sowie zu den Auswirkungen der verbundbedingten Unterschiede abgeleitet werden. Mit den theoretischen Betrachtungen werden das gemeinsame Tragverhalten und der Einfluss des unterschiedlichen Verbundverhaltens auf die Zugkraftaufteilung gezeigt und qualifiziert. Die Behandlung der verbundbedingten Unterschiede bei gemischt mit Betonstahl und Textil bewehrten Zuggliedern ist analog dem Vorgehen bei gemischter Beton- und Spannstahlbewehrung bzw. Klebebewehrung mit Verbundbeiwerten darstellbar. Zur Ableitung entsprechender Kennwerte werden verschiedene Möglichkeiten diskutiert. Zudem wird eine vereinfachte Bemessung vorgeschlagen. Insgesamt sind die Ergebnisse ein wesentlicher Schritt auf dem Weg zur baupraktischen Anwendung von Textilbetonverstärkungen und ermutigen bereits zum umsichtigen Einsatz unter Beachtung der Sicherheitsaspekte. Noch offene Fragen und notwendiger Klärungsbedarf sollten die Wissbegier anregen und vertiefende Forschungsvorhaben und weitere experimentelle Untersuchungen ermöglichen
Textile reinforcement represents an excellent alternative to existing techniques for strengthening of concrete structures, combining the benefits of lightweight fiber reinforced polymer strengthening with those of shotcrete with reinforcement. The theoretical and experimental studies in this thesis provide essential insights into the common load bearing behaviour of reinforcing steel and textile reinforcements as well as on the impact of the different bond characteristics of both types of rein-forcement. With the theoretical investigations, the combined load bearing behaviour and the influence of the different bond characteristics on distribution of the forces could be shown and qualified. The inter-action of both reinforcement types, taking into account the different bond characteristics, can be represented by bond coefficients analogous to the approach to mixed steel and pre-stressing-steel reinforcements. So as to derive the appropriate parameters, several options were discussed. Moreover, a simplified approach to design a TRC-strengthening-layer was proposed. Overall, the results are an essential step towards the practical application of textile reinforced con-crete for the strengthening of concrete structures and should already be encouraging the prudent use while considering the necessary safety aspects. Remaining issues and necessary clarifications should stimulate curiosity and in-depth research projects and allow further experimental studies

Textile Bewehrungen stellen eine hervorragende Alternative zu bisherigen Verstärkungsmethoden dar. Die Wirksamkeit von Textilbetonverstärkungen konnte bereits eindrucksvoll nachgewiesen werden. Um sowohl die vorhandene Bausubstanz, als auch die Verstärkung optimal auszulasten, ist es erforderlich, das Zusammenwirken beider Bewehrungsarten unter Berücksichtigung der unterschiedlichen Verbundeigenschaften zu beschreiben. In diesem Beitrag wird das gemeinsamen Tragverhalten von Betonstahl und textiler Bewehrung eingehend erläutert. Zur Veranschaulichung wird daher vor allem die Verbundtragwirkung und deren Einfluss auf gerissene Zugglieder genauer untersucht.

Experimentelle Untersuchungen an Plattenbalken zeigen, dass Querkraftverstärkungen auch außerhalb der Biegedruckzone verankert werden können. Entscheidend dabei ist, dass alle in der Verbundfuge von Altbeton und Verstärkung auftretenden Beanspruchungen durch die Haftzug- und Scherfestigkeit des Alt- und Feinbetons übertragen werden können. Ein Verbundversagen führt durch das Ablösen der Verstärkungsschicht zu deren Ausfall. Der Beitrag befasst sich mit den Beanspruchungen und Versagensmechanismen des Verankerungsbereiches, die anhand von Versuchsergebnissen dargestellt werden. Als Versagenskriterium für die Verankerung sind zwei flächige Versagensarten – der Altbetonuntergrund und die Ebene der textilen Bewehrung – zu berücksichtigen. Als weiteres Versagenskriterium der Verankerung ist der innere Verbund zwischen den Multifilamentgarnen und der sie umgebenden Feinbetonmatrix zu betrachten. Für die Bemessung des Verankerungsbereiches einer Verstärkung wird der jeweils ungünstigste Wert dieser drei Versagensarten maßgebend.

Ces travaux portent sur la réparation et le renforcement de structures béton armé par matériaux composite. Dans ce domaine, la solution de type carbone-époxy appliqué sur les faces extérieures des structures occupe une place prépondérante, mais reste perfectible. L'objectif principal de cette thèse est de proposer des solutions alternatives à ces matériaux, tels que les composites de type textile-mortier (Textile Reinforced Concrete, « TRC ») et d'en juger la faisabilité, les performances et le comportement. Une approche expérimentale et analytique, aux échelles micro, méso et macroscopiques, est menée en s'appuyant notamment sur la technique de mesure de champs de déplacements par corrélation d'images. À l'égard de l'étude du matériau, une procédure d’essai de caractérisation en traction directe des TRC a été conçue et validée. La conduite de 98 essais par cette procédure, a permis de mieux appréhender le comportement de ces composites, notamment l’articulation entre les mécanismes locaux et leur traduction à l’échelle macroscopique. Les principaux leviers permettant l'optimisation des TRC ont ainsi été déterminés. À l'échelle structurelle, l'étude de 11 poutres réparées vis-à-vis de l'effort tranchant, par collage de plats préfabriqués ou moulage à même la poutre, a été conduite. Il en ressort que les solutions TRC se comparent favorablement à celles de type carbone-époxy. Aussi, le comportement local a été finement évalué, notamment, l'évolution des efforts repris par le renfort TRC ainsi que la validité du modèle analytique du treillis. Un comportement de type multifissurant ou pull-out du TRC sensible à son procédé de mise en oeuvre a également été mis en avant
This research focuses on repairing and strengthening concrete structures with composite materials. In this particular domain, carbon-epoxy composites are of considerable interest, but still room for improvement. The main objective of this thesis is to show alternatives to these composites, such as Textile Reinforced Concrete (TRC). Feasibility, performances and behavior of this alternative composite are examined. An experimental and analytical approach, at the micro-, meso- and macroscopic scale are conducted, notably thanks to the technique of digital image correlation for in-plane displacement measurement. Regarding the study of the material, a rather handy, reliable and efficient procedure of a direct tensile test was designed and validated. To enable a better understanding of the TRC behavior, 98 different TRC configurations were tested thanks to this procedure. The links between local mechanisms and macroscopic scale behavior were notably studied. Finally, key levers for optimizing the TRC were determined. On the structural level, a study was conducted on 11 beams shear strengthened by bonding of prefabricated plates or by contact molding. It shows that TRC solutions compare favorably with carbon-epoxy composites. Also, the local behavior was thoroughly assessed, notably the change of forces carried by the composite material and the truss model validity. A multi-cracking or pull-out behavior of the TRC was put forward depending on its application process

Im Beitrag werden drei Methoden für den Entwurf und die Bemessung von Textilbetonverstärkungen vorgestellt. Für eine Vorbemessung wird die Variantenuntersuchung angewendet, z.B. für die Bestimmung der Anzahl an Textillagen. Für die Festlegung von Realisierungen mehrerer kontinuierlicher Entwurfsvariablen unter Berücksichtigung unterschiedlicher Entwurfsziele und Entwurfsnebenbedingungen werden die Fuzzy-Optimierung und die direkte Lösung der Entwurfsaufgabe skizziert. Mit der Fuzzy-Optimierung werden Kompromisslösungen für die multikriterielle Entwurfsaufgabe ermittelt. Die direkte Lösung basiert auf der explorativen Datenanalyse von Punktmengen, die als Ergebnis einer unscharfen Tragwerksanalyse vorliegen, und liefert Bereiche – sog. Entwurfsteilräume – als Grundlage für die Auswahl des Entwurfs.

Anhand von Versuchsergebnissen wird gezeigt, dass Stahlbetonbauteile mit textilbewehrtem Beton verstärkt werden können. Sowohl die Torsionstragfähigkeit als auch die Gebrauchstauglichkeit werden durch die textilbewehrte Verstärkungsschicht deutlich verbessert. Vergleichsrechnungen zeigen, dass die Torsionstragfähigkeit mit bereits bekannten Stabwerksmodellen ermittelt werden kann.

Zur Prognose des Langzeitverhaltens textilbetonverstärkter Tragwerke wird ein modellfreies Vorgehen auf Basis rekurrenter neuronaler Netze vorgestellt. Das Vorgehen ermöglicht die Prognose zeitveränderlicher Strukturantworten unter Berücksichtigung der gesamten Belastungsgeschichte. Mit unscharfen Größen aus Messungen an Versuchstragwerken werden rekurrente neuronale Netze trainiert. Anschließend ist die unscharfe Prognose des Tragverhaltens möglich.

An innovative strengthening technique is applied for the first time in this study to provide flexural strengthening in two-way reinforced concrete (RC) slabs supported on edge beams. The technique comprises external bonding of textiles on the tension face of RC slabs through the use of polymer-modified cement- based mortars. The textiles used in the experimental campaign comprised fabric meshes made of long stitch-bonded fibre rovings in two orthogonal directions. The specimens measured 2 x 2 m in plan and were supported on hinges at the corners. Three RC slabs strengthened by textile reinforced mortar (TRM) overlays and one control specimen were tested to failure. One specimen received one layer of carbon fibre textile, another one received two, whereas the third specimen was strengthened with three layers of glass fibre textile having the same axial rigidity (in both directions) with the single-layered carbon fibre textile. All specimens failed due to flexural punching. The load-carrying capacity of the strengthened slabs was increased by 26%, 53%, and 20% over that of the control specimen for slabs with one (carbon), two (carbon) and three (glass) textile layers, respectively. The strengthened slabs showed an increase in stiffness and energy absorption. The experimental results are compared with theoretical predictions based on existing models specifically developed for two-way slabs and the performance of the latter is evaluated. Based on the findings of this work the authors conclude that TRM overlays comprise a very promising solution for the strengthening of two-way RC slabs.

Academic and public policy interest in the role of local resource users in the management of forests has grown in recent decades. While much attention has focused on the self-organisation of user groups, with autonomy as a precondition for successful collective action, there has been relatively little research into the influence of external factors on the role of so-called induced grassroots organisations – organisations created through donor or government funding – in natural resource management (NRM). Nonetheless, it is evident that external influences are of critical importance to these organisations in authoritarian countries, and the establishment of grassroots organisations is a common approach to encouraging local participation in NRM. Moreover, in studies on NRM devolution policies, community property rights are often seen as a potential option. What these studies do not bring to light, however, is how different types of property rights can be mixed and arranged through different layers in the organisational structures of grassroots organisations. This study responds to these gaps in the literature, and drawing on learning from three case studies in Quang Tri province, Vietnam. It employs a qualitative and participatory approach, involving semi-structured interviews, focus group discussions, seasonal calendars, natural resource mapping and transect walks. The study’s findings highlight the dominance of the technocratic position in the roles played by induced forest-based grassroots groups. This results from the ambition of the Party-state to keep the rural population dependent on it, and the reluctance of international donors and INGOs, while operating within the current state structures, to use their leverage to effectively support grassroots organisations. The findings of the research also emphasise the need for induced grassroots organisational structures and property rights that combine village-wide, household-group and individual arrangements.

This diploma thesis analyze reinforced concrete construction, which is loaded by new steel superstructure with brick cladding. The necessary strengthening of construction is solved by using carbon fibre reinforced polymer plates. Software RFEM 5 is used for calculation of internal forces. All checks are made in Excel.

Textilbewehrter Beton zur Verstärkung von Stahlbetonbauteilen ist neben den klassischen und etablierten Verfahren eine äußerst interessante Alternative, die die Vorteile der leichten Kohlenstofffaserklebeverstärkungen mit denen von Spritzbeton mit Bewehrung verbindet. Aus den theoretischen und experimentellen Untersuchungen in dieser Arbeit können wichtige Erkenntnisse zum gemeinsamen Tragverhalten von Betonstahl und textiler Bewehrung sowie zu den Auswirkungen der verbundbedingten Unterschiede abgeleitet werden. Mit den theoretischen Betrachtungen werden das gemeinsame Tragverhalten und der Einfluss des unterschiedlichen Verbundverhaltens auf die Zugkraftaufteilung gezeigt und qualifiziert. Die Behandlung der verbundbedingten Unterschiede bei gemischt mit Betonstahl und Textil bewehrten Zuggliedern ist analog dem Vorgehen bei gemischter Beton- und Spannstahlbewehrung bzw. Klebebewehrung mit Verbundbeiwerten darstellbar. Zur Ableitung entsprechender Kennwerte werden verschiedene Möglichkeiten diskutiert. Zudem wird eine vereinfachte Bemessung vorgeschlagen. Insgesamt sind die Ergebnisse ein wesentlicher Schritt auf dem Weg zur baupraktischen Anwendung von Textilbetonverstärkungen und ermutigen bereits zum umsichtigen Einsatz unter Beachtung der Sicherheitsaspekte. Noch offene Fragen und notwendiger Klärungsbedarf sollten die Wissbegier anregen und vertiefende Forschungsvorhaben und weitere experimentelle Untersuchungen ermöglichen.
Textile reinforcement represents an excellent alternative to existing techniques for strengthening of concrete structures, combining the benefits of lightweight fiber reinforced polymer strengthening with those of shotcrete with reinforcement. The theoretical and experimental studies in this thesis provide essential insights into the common load bearing behaviour of reinforcing steel and textile reinforcements as well as on the impact of the different bond characteristics of both types of rein-forcement. With the theoretical investigations, the combined load bearing behaviour and the influence of the different bond characteristics on distribution of the forces could be shown and qualified. The inter-action of both reinforcement types, taking into account the different bond characteristics, can be represented by bond coefficients analogous to the approach to mixed steel and pre-stressing-steel reinforcements. So as to derive the appropriate parameters, several options were discussed. Moreover, a simplified approach to design a TRC-strengthening-layer was proposed. Overall, the results are an essential step towards the practical application of textile reinforced con-crete for the strengthening of concrete structures and should already be encouraging the prudent use while considering the necessary safety aspects. Remaining issues and necessary clarifications should stimulate curiosity and in-depth research projects and allow further experimental studies.

碩士
國立臺北科技大學
材料科學與工程研究所
97
TiC is often used as reinforcement phase to improve wear-resistant properties and hardness of tool steels and metal matrix composites (MMCs). In present study, synthesized TiC is formed via mechanical alloying (MA) by planetary ball milling Ti and carbon black powders. It is observed that very fine and spherical in-situ TiC powders can be synthesized by high energy ball milling at the condition longer than 8 hrs at 400 rpm. These TiC and tool steel powders are then sintered by combining two powder metallurgy routes, vacuum sintering and hot isostatic pressing (HIP). HIPping is beneficial in reducing internal voids of vacuum sintered composites and thus increases composite mechanical properties. Up to 99.9% sintering density is achieved without encapsulation. It is found that the fine in-situ TiC particles distribute uniformly with the ball milled tool steel powders. The amount of TiC can be added up to 44 vol.%. And the composite such formed can achieve hardness as high as 71.6 HRC. In present study, composite tool steels containing TiC are produced by a novel process which combines in-situ and powder metallurgy techniques.

碩士
國立臺北科技大學
材料及資源工程系所
93
In this study, we mixed AISI 440C high chromium stainless steel powders with different amounts (25, 33 and 40 wt.%) of TiC powder. The mixing was done by one of following methods, ball milling in laboratory and granulation. The mixed powders were sintered at 1200、1300、1400℃, followed by a series of heat treatments and HIP processes. The heat treatment included quenching at 1100℃, tempering three times at 520℃ for 2.5 hours. The HIP treatments were low and high pressures (1200 bar and 1500 bar at1250℃) with one HIP treatment (1500bar at 1250℃) followed by heat treatment (tempering three times at 200℃ for 3 hours). Various materials characterization techniques were used in order to evaluate the materials properties and microstructures, including apparent porosity, hardness test, transverse rupture strength (TRS) test, OM and SEM. The results show that a high TRS value of 1502.6MPa was obtained when the 25wt% TiC mixed powder was sintered at 1400℃. The 40wt% TiC mixed powder had the highest hardness (HRC 70.7 or HRA 86.9) after sintering at 1400℃ and HIP treatment (1500bar at 1250℃). The microstructural evaluation revealed that the matrix had small needle-like structure after HIP treatment, resulting in increased hardness. For the powder added with 40wt% TiC powder and sintered at 1400℃ followed by HIP treatment, numerous needle-like structures were seen with TiC uniformly dispersed in the high Chromium stainless steel matrix and thus the highest hardness (HRA 86.9 or HRC 70.7) and TRS 1104.93 MPa ( 160.21×103 psi) were achieved. The results were better than those reported for Ferro-Tic® ( HRC 68、TRS 149×103 psi). On the other hand, the powders prepared by the granulation method exhibited poor properties presumably because of the closed-pore effect.

碩士
國立臺北科技大學
材料及資源工程系碩士班
92
ABSTRACT Title：Strengthening of fine TiC powder added high vanadium tool steel by H.I.P. Pages：85 School：National Taipei University of Technology Department：Materials & Mineral Resources Engineering Time：July, 2004 Degree：Master Researcher：P.Y.Tzeng Advisor：T.P.Tang Keywords：high vanadium tool steel、TiC、H.I.P.、dispersion strengthening We selected high vanadium tool steel to be the matrix and high-hardness TiC powder as the additive to prepare a new material with high toughness and hardness via powder metallurgy route. The result shows that the composite consisting of steel powder with wide powder size range and 35 wt % TiC powder have 678.5 MPa. of TRS (Transverse Rupture Strength) after sintering at 1400℃.Using 25μm steel powders matrix，the TRS increase to 868.6 MPa. Various post heat treatment have been carried out. It is found that the composite possesses good TRS of 1059.3 MPa after 850℃ annealing ，followed by quenching at 1030℃ and tempering at 200℃. TRS of composite increase to 1180.4 MPa when the sintering at 1400℃ and HIP at 1250℃，1500 bar are performed. The hardness is also increased to HRC 71.7，which is better than that (HRC 69) of Ferro-Titanit. As HIPed specimens have poor strength and hardness after tradition heat treatment，the composite of high vanadium tool steel(25μm) with 35wt% TiC sintered at 1400℃ followed by HIPing would have combined good properties of TRS and hardness.

碩士
國立屏東科技大學
機械工程系所
100
Added appropriate amount of TiC powder to 316L stainless steel (the best amount to add was 2wt%) during the press molding of powder metallurgy (PM for short) as well as transferred the atmosphere control from H2 to 50%H2 plus 50%N2 at the moderate temperature when sintering(the wonderful atmosphere transferable temperature was 1200℃), and gained the conclusive result that the grain growth was under control, the phase was reinforced, the content of Nitrogen reached the maximum, and the most of the mechanical properties of 316L stainless steel were enhanced. On the other hand, also found the ductility and corrosion resistance of the matrix became lower for the reason that some chemical compound precipitated on the grain boundary bringing hard and brittle phases. Therefore, Cu is added in this new experiment in hope of improving the sintering property between 316L stainless steel and TiC, decreasing the hard and brittle phases and enhancing the ductility and corrosion resistance. Four groups of specimens are made for this experiment: specimen A(316L stainless steel+2 wt%TiC), specimen B(316L stainless steel+2 wt%TiC plated with Cu of 0.5wt%), specimen C(316L stainless steel+2 wt%TiC plated with Cu of 1.5wt%) and specimen D(316L stainless steel+2 wt%TiC plated with Cu of 3wt%). The experimental results show that there is hardly precipitation on the grain boundary due to the effect of copper, thus reaching the target of decreasing the hard and brittle phases. There is also apparent improvement in density, ductility &; corrosion resistance. The hardness, wear resistance and strength become slightly weaker as the amount of copper plated is raised but is still within the acceptable range.

碩士
國立臺北科技大學
材料及資源工程系研究所
102
AISI 440C, which possesses the high carbon of martensitic stainless steel, is widely used in applications in the tool industry which require good hardness, corrosion resistance and mechanical strengthening. The primary strengthening mechanisms include solid-solution strengthening and precipitation-hardening effects of chromium and molybdenum carbides. As the main strengthening phases of M23C6 and M7C3 are precipitated in the matrix and grain boundary, respectively, the distribution and particle size of the carbides are important for AISI 440C steel. In addition, the metal matrix composites (MMC) are well known for its excellent wear resistance. For instance, many investigations have depended on the characteristic of carbide as a reinforcing medium in a ferrous metal matrix in order to enhance performance. Tantalum carbide (TaC) has proven efficacy due to its high hardness, high melting temperature and chemical stability with Fe-based alloys; research has shown that adding various mounts of TaC into AISI 440C steel also improves these properties, as well as the carbide precipitation. In this study, we added and mixed different ratios of TaC powders (10, 20 and 30 wt%) to AISI 440C alloy powders (25-45 μm and below 25 μm) by the mechanical alloying process. After the compaction and forming processes, 440C-TaC alloy powder was sintered at 1270, 1280 and 1290°C by vacuum sintering, respectively. Furthermore, a series heat treatment process (quenching followed by tempering) was performed, by which the samples were heated to 1100°C and maintained at that temperature for 40 min for quenching, and 0.5 MPa of N2 for quenching media. Meanwhile, the tempering temperature was 480°C for 150 min, and repeated three times. Various material characterization techniques were used to evaluate the specimens’ properties, including porosity, hardness and transverse rupture strength (TRS), as well as corrosion tests. Moreover, the microstructures were analyzed using XRD, OM, SEM and EDS techniques. The experimental results showed that the porosity of 440C-TaC was decreased by less than 2% by the liquid-phase sintering process. Excess TaC hindered the liquid diffusion of the Fe elements, which resulted in the T30 still having 6.56% porosity. In addition, the 1270°C-sintered T10(S) specimens possessed the highest TRS value (2260 MPa), while the 1290°C-sintered T20(S) specimens obtained the highest hardness value (HRA 85.2) and lowest corrosion current density（1.14×10-3 A‧cm-2）. The microstructural evaluation revealed that the M7C3 carbides located on the grain boundary were gradually replaced and even disappeared after TaC particles were added. Meanwhile, all the rod-shaped M7C3 carbides transformed to M23C6 carbides, and precipitated on the matrix as a strengthening phase. Therefore, the TRS value of the T10(S) was obviously increased(2260 MPa → 2458 MPa) after heat treatment, while retaining its higher hardness (HRA 83.8). The chief concerns and factors were the hexagonal-shaped M23C6 carbides which decomposed and re-precipitated, resulting in the enhanced strength. The results showed that heat treatment effectively improved the particle size of the carbides and the strengthening of the matrix phase of 440C-TaC steel.

碩士
國立臺北科技大學
材料及資源工程系研究所
99
Cobalt-based superalloys are used extensively in applications requiring good wear resistance, corrosion resistance and heat resistance. Many of the properties of these alloys arise from the crystallographic nature of cobalt, the solid solution strengthening and carbide precipitation effects of chromium, tungsten and molybdenum. Metal matrix composites are known to exhibit exceptional wear resistance; therefore, several investigators have used titanium carbide (TiC) as a reinforcing medium in a ferrous metal matrix in order to enhance this property. TiC has proved its suitability in Fe or Fe-based alloys due its high hardness, low density and chemical stability with Fe-based alloys. In this study, we have mixed and added different amounts of TiC powders (10, 15 and 20 wt %) to the Cobalt-based superalloy powders. The mixing processed was finished by ball milling and granulation in a laboratory. In addition, the mixing powders (Cobalt-based superalloy and TiC) were sintered at 1260, 1270, 1280 and 1290°C, and then a series of HIP processes and heat treatments were performed. Meanwhile, the parameter of HIP treatment was 1250°C, 125 MPa and 100 min. The heat treatment processes were heating to 1100°C and maintaining for 40 min for quenching; aging at 760°C and soaking time was 6, 9, 12 h, respectively. Various materials characterization techniques were used to evaluate the materials’ properties and microstructures, including: apparent porosity, hardness test, transverse rupture strength (TRS) test, OM, and SEM microstructral examinations. The experimental results show that the highest TRS value of 1566.7 MPa was obtained by the 15 wt% TiC additive powder, which was sintered at 1280°C and then followed by HIP process and solid solution heat treatment. It also has been proved that the closed pores can be effectively eliminated (1.2% → 0.86%) by HIP treatment; in addition, the M6C carbides can produce more uniform precipitation on the grain-boundary and matrix after heat treatment. Furthermore, the highest hardness value of HRA 80.4 was obtained by the 20 wt% TiC additive powder, which was only sintered at 1290°C.

Dissertação de mestrado integrado em Engenharia Civil (área de especialização em Perfil de Estrutura e Geotecnia)
Atualmente, têm-se registado inúmeros eventos sísmicos que comprovaram a vulnerabilidade das paredes de enchimento inseridas em pórticos de betão armado. A vulnerabilidade é essencialmente devida à inexistência de regras de dimensionamento e à não utilização de detalhes construtivos adequados durante a construção. Por isso, é importante avaliar técnicas de reforço que possam ser implementadas nas paredes existentes ou a ser construídas, de maneira a melhorar o seu desempenho, evitando as roturas frágeis, e por outro lado possam potenciar benefícios ao nível do comportamento global do edifício à ação sísmica. Este trabalho apresenta uma sugestiva adaptação da técnica de reforço de paredes de alvenaria designada na literatura inglesa por Textile Reinforced Mortar (TRM) com vista ao melhoramento das paredes a ações fora do plano. A malha é constituída por varões compósitos cujo núcleo é ocupado por fibras resistentes que são envolvidas numa estrutura de entrançado têxtil, sendo uma alternativa ao uso de materiais compósitos aplicados através de diferentes técnicas. Esta técnica apresenta a vantagem da possibilidade de dimensionamento da constituição da malha de acordo com determinadas exigências mecânicas, através de processos de baixa tecnologia e baixo custo na sua produção. Para além da definição e otimização experimental dos varões de material compósito em termos de aderência com a argamassa de reboco, foi efetuado um estudo alargado para avaliação do desempenho como material de reforço da alvenaria sujeita a esforços de flexão. Os resultados obtidos permitiram concluir que as malhas constituídas pelos varões compósitos inseridos no reboco de alvenaria possuem boa aderência, resistência mecânica favorável e comportamento muito dúctil quando comparadas com malhas comerciais equivalentes, evitando assim a rotura brusca e potenciando o comportamento dúctil essencial ao bom desempenho sísmico.
In the recent past numerous seismic events have demonstrated the important vulnerability of masonry infill walls enclosed in reinforced concrete frames. This vulnerability is attributed to the inexistence of design rules and to the non-adequate constructive details during the construction. Therefore, it is important to evaluate strengthening techniques that can be implemented on existing walls or to be built aiming at improving the seismic behavior by preventing fragile failure modes and that can potentiate the good global seismic behavior of reinforced concrete frames structures. This study provides a suggestive adaptation of the technique known as Textile Reinforced Mortar (TRM), aiming at improving the out-of-plane behavior of the masonry infill walls. The fabric comprises textile composite rods with a reinforced nucleus and is an alternative technique to the use of other composite materials applied with distinct techniques. This technique has the advantage of designing the constitution of the mesh according to certain mechanical requirements, involving of low production technology and low cost production. Besides the definition and experimental optimization of the of the textile reinforced composite material in terms of adherence to the involving mortar, an enlarged experimental program was carried out for the evaluation of its mechanical performance as a strengthening material of masonry infill subjected to flexure. The results showed that the meshes formed by composite rods embedded in the mortar plastering have good adhesion, mechanical strength and a very ductile behavior, when compared to equivalent commercial meshes, thus avoiding the sudden collapse and promoting the ductile behavior, which is essential to the good seismic behavior.

Dissertação de mestrado em Structural Analysis of Monuments and Historical Constructions
Earthen constructions constitute a considerable part of the existing heritage and a large percentage of the World population is still living or working in buildings built with this structural system. Like other types of masonry structures, rammed earth constructions are acceptably stable under gravity loads, although they are significantly vulnerable to earthquakes. Therefore, a precise understanding of their behavior in case of being subjected to ground motions and the proposing of effective strengthening techniques achieved a great interest both in research and practice. Strengthening methods should be not only to enhance capacity and ductility of the building, but also to satisfy a variety of criteria such as being compatible with the substrate, economical and reversible. Considering all, the low-cost textile reinforced mortar (LC-TRM) strengthening is introduced, and its efficiency on rammed earth walls is studied numerically in the present thesis. In the current study, the seismic performance of both unstrengthened and strengthened rammed earth structural components is investigated. In this regard, in-plane and out-of-plane behaviors are studied by means of different constructed nonlinear finite element models. At first, pushover analysis by massbased lateral load pattern is conducted on unstrengthened walls to evaluate their capacity and understand possible failure mechanisms. Furthermore, the outcomes of these analyses are employed to select the most proper modeling approach from shell or solid elements and the walls with appropriate geometrical dimensions. In the following, pushover analyses are conducted on strengthened walls to choose between different strengthening materials and assess the effectiveness of the adopted strengthening technique. Furthermore, the frequency change of the walls with the damage states (lateral displacement levels) is studied to represent the initiation and propagation of damage in unstrengthened walls and to evaluate the effectiveness of TRM strengthening method. Finally, an artificially generated ground motion record was applied to both unstrengthened and strengthened walls to perform nonlinear time-history analyses. The outcomes were used to compare the dynamic behavior of the walls against the results of the pushover analyses.
As construções de terra constituem uma parte considerável do património construído e uma grande parte da população mundial ainda vive ou trabalha em edifícios construídos com este sistema estrutural. Como outros tipos de estruturas de alvenaria, as construções de terra são estáveis face a cargas gravíticas, embora sejam significativamente vulneráveis a sismos. Portanto, a compreensão do seu comportamento perante a ocorrência de movimentos do solo e a proposta de técnicas efetivas de reforço despertam um grande interesse, tanto a nível da investigação como na prática. Os métodos de reforço devem ser adequados não só para aumentar a capacidade e a ductilidade da construção, mas também para satisfazer uma variedade de critérios, como a compatibilidade com o substrato, custo económico e reversibilidade. Considerando todos estes aspetos, apresenta-se uma técnica baseada em argamassa reforçada com malhas têxteis de baixo custo (LC-TRM), cuja eficiência em paredes de terra é estudada na presente tese do ponto de vista numérico. No presente trabalho, investiga-se o desempenho sísmico de componentes estruturais de taipa não reforçados e reforçados. A este respeito, estudam-se os comportamentos no plano e fora do plano, por meio de diferentes modelos de elementos finitos não lineares. Em primeiro lugar, realiza-se a análise pushover proporcional à massa em paredes não reforçadas para avaliar sua capacidade e compreender possíveis mecanismos de colapso. Adicionalmente, estes resultados são utilizados para selecionar a técnica de modelação mais apropriada (elementos de casca ou sólidos) e as dimensões geométricas mais apropriadas. De seguida, realiza-se a análise pushover em paredes reforçadas para escolher de entre diferentes materiais de reforço e avaliar a eficácia da técnica de reforço adotada. Além disso, a variação das frequências das paredes com os estados de dano (níveis de deslocamento lateral) é estudada para identificar o início e a propagação de dano em paredes não reforçadas e avaliar a estabilidade do método de reforço baseado na técnica TRM. Finalmente, selecionou-se um registro sísmico artificial para realizar análises temporais não lineares de paredes simples e reforçadas. Os resultados são utilizados para comparar o comportamento dinâmico das paredes com os resultados da análise pushover.
This present work was developed within the framework of SAHC Erasmus Mundus Master Course (www.msc-sahc.org) and the project of POCI-01-0145-FEDER-016737 (PTDC/ECM-EST/2777/2014), financed by FEDER funds through the Competitivity Factors Operational Programme - COMPETE and by national funds through FCT – Foundation for Science and Technology. They are both kindly acknowledged.

Dissertação de mestrado integrado em Engenharia Civil
Estima-se que cerca de 25% do património construído tenha a terra crua como material de construção principal, de onde se destacam várias construções listadas com Património Mundial pela UNESCO. Este tipo de construções é conhecido pela sua elevada vulnerabilidade sísmica, devido ao seu elevado peso próprio, baixas propriedades mecânicas (resistência à tração muito baixa) e fracas ligações entre elementos estruturais. De facto, este tipo de construções encontrase também edificado sobre zonas de perigosidade sísmica não negligenciável, pondo em risco a vida dos seus moradores e a preservação das mesmas. Este é o caso concreto de várias construções de taipa edificadas no Sul de Portugal. Existe a necessidade de se desenvolverem técnicas de reforço de forma a minimizar-se a vulnerabilidade sísmica das construções de taipa. Nos últimos anos, tem sido desenvolvida alguma investigação sobre a aplicação da técnica TRM (Textile Reinforced Mortar) na construção em adobe. Os resultados obtidos demonstraram um aumento do desempenho estrutural, através de uma maior capacidade resistente e de dissipação de energia. Pensa-se que esta técnica possa ser aplicada também em construções de taipa, no entanto, devido à pouca investigação existente sobre os princípios de conservação e reforço estrutural, esta tarefa tornase mais difícil. Assim sendo, o desenvolvimento desta solução requer a investigação de materiais de baixo custo e compatíveis com este tipo de construções, bem como da caracterização do seu comportamento mecânico. Com esta dissertação pretende-se contribuir para o desenvolvimento do conhecimento sobre o reforço de paredes de taipa com LC-TRM (Low Cost Textile Reinforced Mortar), através da execução de um programa experimental. Os resultados obtidos permitiram caracterizar o comportamento mecânico isolado de potenciais componentes da solução, bem como da sua interação.
The percentage of the built heritage using raw earth as main building material is estimated to be of about 25%, from where are highlighted several constructions listed as World Heritage by UNESCO. The high seismic vulnerability of this type of construction is acknowledged by their high dead-weight, low mechanical properties (very low tensile strength) and poor connections between structural elements. In fact, many of these construction are built on region with nonnegligible seismic hazard, putting in risk the life of their inhabitants and of their preservation. Several rammed earth constructions built in Southern Portugal are identified within this situation. The development of strengthening techniques is required to mitigate seismic vulnerability of rammed earth constructions. In the last years, some research has been carried out regarding the application of the TRM (Textile Reinforced Mortar) technique to adobe construction. The results obtained showed an improvement of the structural performance, by means of improved load capacity and energy dissipation. The application of this technique is expected to provide a similar effect on rammed earth constructions, but the little investigation on conservation principles and structural strengthening difficult its implementation. Thus, the development of this strengthening solution requires researching for compatible materials with low cost, as well as for the characterisation of their mechanical behaviour. This dissertation intends to contribute for the development of the knowledge on the strengthening of rammed earth walls with LC-TRM (Low Cost Textile Reinforced Mortar), by means of the execution of an experimental program. The results obtained allowed characterising the individual mechanical behaviour of potential components of the solution, as well as of their interaction.
O presente trabalho foi executado no âmbito do projeto SafEarth - Proteção sísmica do património construído em terra POCI-01-0145-FEDER-016737 (PTDC/ECMEST/2777/2014);
Financiado por fundos do FEDER através do Programa Operacional Fatores de Competitividade (COMPETE) e por fundos nacionais através da Fundação para a Ciência e a Tecnologia (FCT).

Στα πλαίσια της παρούσας διατριβής διερευνήθηκε – τόσο σε πειραματικό όσο και σε αναλυτικό επίπεδο – η ενίσχυση των τοιχοπληρώσεων σε πλαίσια ΟΣ με μια νέα τεχνική που κάνει χρήση ενός προηγμένου σύνθετου υλικού γνωστού ως «Ινοπλέγματα σε Ανόργανη Μήτρα (ΙΑΜ)». Η τεχνική αυτή αποτελεί εναλλακτική πρόταση ενίσχυσης έναντι άλλων, συμβατικών και μη, τεχνικών και χαρακτηρίζεται από την ευκολία εφαρμογής της, τις εξαιρετικές ιδιότητες του υλικού καθώς και τα συγκριτικά πλεονεκτήματα του τελευταίου έναντι ανταγωνιστικών υλικών για τον ίδιο σκοπό, όπως τα ινοπλισμένα πολυμερή. Για τη διερεύνηση της αποδοτικότητας της νέας τεχνικής σχεδιάσθηκε και εκτελέστηκε ένα πολύπλευρο πειραματικό πρόγραμμα. Αρχικά αναπτύχθηκε ένα νέου είδους αγκύριο με βάση τα πλέγματα ινών, το οποίο δοκιμάσθηκε ως μέσο σύνδεσης μεταξύ στοιχείων τοιχοποιίας και σκυροδέματος. Όπως έδειξαν πειραματικές δοκιμές για τη σύνδεση τοιχοποιίας-στοιχείων σκυροδέματος, τα αγκύρια που αναπτύχθηκαν αποδείχθηκαν επαρκώς αποτελεσματικά ώστε να χρησιμοποιηθούν στο δεύτερο - και κυρίως μέρος - του πειραματικού προγράμματος, το οποίο περιελάμβανε δοκιμές σε τριώροφα τοιχοπληρωμένα πλαίσια. Στα πλαίσια του δεύτερου μέρους του πειραματικού προγράμματος κατασκευάσθηκαν και δοκιμάσθηκαν, σε εντός επιπέδου ανακυκλιζόμενη φόρτιση, δύο τοιχοπληρωμένα πλαίσια μεγάλης κλίμακας (2/3). Το ένα εξ αυτών δοκιμάσθηκε χωρίς να ενισχυθεί και απετέλεσε το δοκίμιο αναφοράς, ενώ το άλλο δοκιμάσθηκε μετά την ενίσχυσή του με μανδύες ΙΑΜ και την υλοποίηση αγκύρωσης/σύνδεσης της τοιχοπλήρωσης με τα περιμετρικά μέλη του πλαισίου. Επιπλέον των δοκιμών κυκλικής φόρτισης, πραγματοποιήθηκαν και δοκιμές ελεύθερης ταλάντωσης για τη μελέτη της επιρροής των τοιχοπληρώσεων – ενισχυμένων και μη – στα δυναμικά χαρακτηριστικά του πλαισίου. Τα αποτελέσματα των δοκιμών στα τριώροφα τοιχοπληρωμένα πλαίσια κατέδειξαν τη συμβολή της νέας τεχνικής στη βελτίωση της απόκρισης του πλαισίου με αύξηση της αντοχής του σε πλευρική φόρτιση, της ικανότητας παραμόρφωσής του και της ικανότητας ανάλωσης ενέργειας. Το τρίτο μέρος της έρευνας επικεντρώθηκε στην ανάπτυξη αναλυτικού προσομοιώματος, το οποίο βασίσθηκε στη χρήση γραμμικών στοιχείων θλιπτήρα-ελκυστήρα για την προσομοίωση της απόκρισης των τοιχοπληρώσεων (ενισχυμένων και μη). Για τον υπολογισμό των ιδιοτήτων του θλιπτήρα έγινε χρήση αναλυτικών σχέσεων από τη βιβλιογραφία, ενώ για τον υπολογισμό των ιδιοτήτων του ελκυστήρα αναπτύχθηκε κατάλληλη αναλυτική μεθοδολογία. Για τον προσδιορισμό συγκεκριμένων παραμέτρων που απαιτούνταν για το αναλυτικό προσομοίωμα της ενισχυμένης τοιχοπλήρωσης, διεξήχθησαν πρόσθετες δοκιμές και συγκεκριμένα, δοκιμές εφελκυσμού ΙΑΜ, δοκιμές κεντρικής θλίψης τοιχοσωμάτων – ενισχυμένων και μη – και δοκιμές διαγώνιας θλίψης τοιχοσωμάτων – ενισχυμένων και μη. Οι πειραματικά προσδιορισμένες ιδιότητες του υλικού της ενίσχυσης (όπως η εφελκυστική του αντοχή και το μέτρο ελαστικότητας) καθώς και οι ιδιότητες των τοιχοσωμάτων (όπως η θλιπτική αντοχή, η διατμητική τάση ρηγμάτωσης, το μέτρο ελαστικότητας και το μέτρο διάτμησης) χρησιμοποιήθηκαν ως τιμές των αντίστοιχων παραμέτρων του αναλυτικού προσομοιώματος. Τα παραπάνω στοιχεία ενσωματώθηκαν σε λογισμικό ανοικτού κώδικα για τη μη-γραμμική ανάλυση κατασκευών, στο οποίο τα μέλη του πλαισιακού φορέα (δοκοί και υποστυλώματα) προσομοιώνονται με γραμμικά στοιχεία συγκεντρωμένης ανελαστικότητας στα άκρα τους. Για την προσομοίωση των δύο πειραματικών δοκιμίων (μη ενισχυμένο και ενισχυμένο τοιχοπληρωμένο τριώροφο πλαίσιο) πραγματοποιήθηκαν σειρές αναλύσεων με στόχο την βαθμονόμηση-επαλήθευση του αναλυτικού προσομοιώματος. Βάσει των αναλύσεων προέκυψε ότι το αναλυτικό προσομοίωμα μπορεί να αναπαράγει με καλή ακρίβεια την απόκριση των πειραματικών δοκιμίων. Η διατριβή χωρίζεται σε επτά κεφάλαια. Στο Κεφάλαιο 1 πραγματοποιείται η εισαγωγή στο αντικείμενο της εργασίας και στο πρόβλημα το οποίο επιχειρεί να αντιμετωπίσει. Στο πλαίσιο της περιγραφής του προβλήματος παρουσιάζονται συνοπτικά οι υφιστάμενες τεχνικές αντιμετώπισης, οι οποίες είτε εφαρμόζονται στο πεδίο είτε έχουν διερευνηθεί πειραματικά. Στο Κεφάλαιο 2 περιγράφεται συνοπτικά το υλικό το οποίο χρησιμοποιείται στη νέα τεχνική που αναπτύσσεται στην παρούσα εργασία, δηλαδή τα «Ινοπλέγματα σε Ανόργανη Μήτρα (ΙΑΜ)», μαζί με μία σύντομη ανασκόπηση των ερευνητικών εργασιών της διεθνούς βιβλιογραφίας που κάνουν χρήση των ΙΑΜ σε εφαρμογές ενισχύσεων στοιχείων οπλισμένου σκυροδέματος (ΟΣ) και τοιχοποιίας. Το Κεφάλαιο 3 αποτελεί ένα μικρό κεφάλαιο στο οποίο περιγράφεται εποπτικά το σύνολο του πειραματικού προγράμματος το οποίο χωρίζεται σε τρία μέρη. Το πρώτο μέρος παρουσιάζεται στο Κεφάλαιο 4 και διερευνά τη σύνδεση μεταξύ μελών ΟΣ και τοιχοποιίας μέσω ΙΑΜ και ειδικά διαμορφούμενων αγκυρίων ινών. Στο Κεφάλαιο 5, το οποίο αποτελεί τον κορμό της παρούσας εργασίας, παρουσιάζεται το δεύτερο μέρος του πειραματικού προγράμματος που αποτελείται από δοκιμές σε τριώροφα τοιχοπληρωμένα πλαίσια μεγάλης κλίμακας. Η περιγραφή του τρίτου μέρους του πειραματικού προγράμματος, το οποίο περιλαμβάνει συμπληρωματικές δοκιμές για την υποστήριξη των αναλύσεων, ενσωματώνεται στο Κεφάλαιο 6 μαζί με την περιγραφή του αναλυτικού προσομοιώματος και των αριθμητικών αναλύσεων. Τέλος, στο Κεφάλαιο 7 πραγματοποιείται η σύνοψη της εργασίας και η παράθεση των συμπερασμάτων που προκύπτουν από αυτή.
The subject of the present thesis is the experimental and analytical investigation of strengthening masonry infilled reinforced concrete (RC) frames with Textile-Reinforced Mortar (TRM). The proposed strengthening technique comprises the application of externally applied TRM layers on the infills surfaces and the connection to the surrounding RC frame members. TRM is a composite material which comprise fibers in form of textiles in combination with inorganic matrices (such as cement based mortars). The experimental campaign includes tests on small-scale specimens (i.e. masonry subassemblies) as well as on large-scale specimens (3-story masonry infilled RC frames). In the framework of the first part of the experimental campaign different methods of masonry infill-concrete connection are examined by developing and testing textile-based anchors. The parameters under investigation include mainly the type of boundary conditions at the masonry-concrete interface, the geometry and fiber volume of anchors and the type and number of layers of the textile. It is concluded that the anchors developed in this study enable the transfer of substantial tensile forces between masonry and concrete. The second part of the experimental campaign includes the application of TRM on nearly full-scale, as-built and retrofitted, 3-storey frames, subjected to in-plane cyclic loading. The results of testing a 2:3 scale, as-built frame representing typical structures with non-seismic design and detailing characteristics and of a companion frame retrofitted via TRM jacketing are compared in terms of the efficiency of the proposed technique to enhance the strength and deformation characteristics. Additionally, in order to determine the dynamic characteristics of the frames free vibration tests are performed in three different stages of their construction (bare frame; infilled-frame; retrofitted-infilled frame). It is concluded that the proposed strengthening technique is very effective in increasing the lateral strength, the deformation capacity, the initial elastic stiffness as well as the dissipating energy of the infilled frames. The last part of the thesis presents an analytical approach for modeling the behavior of TRM-retrofitted infilled RC frames under seismic loading. The model falls into the discrete diagonal-element type and is based on the use of a single-strut and single-tie elements to represent the infill panel and it builds on the results of the experimental campaign. The model is implemented in a nonlinear finite-element code, with the parameters of the diagonal elements being determined from a series of tests on TRM coupons and masonry specimens. The results of the numerical analyses are compared with the experimental data and is concluded that the model adequately accounts for the TRM-strengthening contribution to the global response of masonry-infilled frames.

Dissertação de mestrado em Structural Analysis of Monuments and Historical Constructions
The un-reinforced masonry structures (URM) represent an important percentage of the building heritage, but they have poor performance in seismic condition. Hence the construction industry has been extremely interested in their repair and rehabilitation. In the last decades, the innovative materials made of continuous fibres embedded in organic matrices (FRP) have been largely adopted to enhance the seismic performance of the constructions. Initially, these materials were designed to be applied to concrete structures, and only later they were adopted also in masonry structures. Although the advantages introduced by these composite products were undeniable, some drawbacks were also observed, mainly related to the organic matrices (e.g. epoxy). As a consequence, a new type of composite materials, where the organic substrate is substituted with an inorganic matrix (e.g. cementitious or lime-based mortar), were proposed as a solution. These materials on one hand kept the positive aspects of the FRPs (improvement of the shear-resistance and the deformability without increasing the weight of the structure) and on the other hand overcame their disadvantages (poor behaviour in condition of high temperatures or fire, vulnerability to the external agents, low permeability, low compatibility with the masonry substrate). Consequently, mortar-based composites resulted to be mechanically and physically more compatible with masonry substrates and able to satisfy issues related to conservation principles as reversibility and sustainability. The innovative composite materials made of continuous fibres embedded in thin mortar layers for externally bonded reinforcement of masonry structures, typically referred to as FRCM (Fibre Reinforced Cementitious mortar) or TRM (Textile Reinforced Mortar), have recently received attention from researchers. Despite the recent interest on the use of these materials, the available information regarding their performance when applied to structures or structural components is still scare. For instance, the effectiveness of TRM systems on the seismic performance of strengthened structures is not clear yet. Given the aforementioned research context, the present thesis has the aim to investigate the effectiveness of the implementation of TRM composite materials on the in-plane and out-of-plane response of a masonry wall. Therefore, different finite element models to study the in-plane and out-of-plane performance have been created. A comparison of their behaviour in unreinforced and reinforced conditions is carried out by means of non-linear analyses, under the effect of a lateral-monotonic load proportional to the mass (pushover) first and then under the effect of a real accelerogram recorded during the L'Aquiia earthquake, occurred the 6 t of April 2009. The results are presented and discussed critically.
As estruturas em alvenaria não reforçada (URM) correspondem a uma importante percentagem do património edificado existente, no entanto, apresentam uma débil resposta a eventos sísmicos. Assim sendo, a sua reparação e reabilitação é de extrema importância para a indústria da construção. Nas últimas décadas, foram amplamente adotados materiais inovadores à base de polímeros reforçados com fibras (FRP) para o melhoramento da resposta sísmica de edificações. Desenhados inicialmente tendo em vista a sua aplicação em estruturas de betão armado, apenas mais tarde foram também adotados para as estruturas de alvenaria. Apesar das inegáveis vantagens que estes materiais apresentam, foram também observados alguns aspetos negativos, essencialmente referentes às matrizes orgânicas (ex.: epoxy). Como consequência, foi proposto um novo tipo de materiais compósitos, nos quais a matriz polimérica é substituída por matrizes inorgânicas (ex.: argamassas à base de cal). Estes materiais, por um lado mantem os aspetos positivos dos FRPs (melhoramento da resistência ao corte e da deformabilidade, sem aumento de peso da estrutura), e por outro lado ultrapassaram a sua desvantagem (mau desempenho em condições de altas temperaturas ou fogo, vulnerabilidade aos agentes externos, baixa permeabilidade, baixa compatibilidade com o substrato em alvenaria). Assim sendo, estes novos materiais compósitos demonstraram ser mecânica e fisicamente mais compatíveis com substratos de alvenaria, e capazes de satisfazer questões relativas a princípios de conservação (ex: a reversibilidade e a sustentabilidade das intervenções) Materiais compósitos inovadores à base de fibras contínuas, embebidas em finas camadas de argamassa para reforço pelo exterior de estruturas de alvenaria, conhecidos por FRCM (argamassas comentícias reforçadas com fibras), ou TRM (argamassas reforçadas com têxteis), tem sido alvo de atenção por parte de vários investigadores. Apesar do recente interesse no uso destes materiais, a informação disponível referente ao seu desempenho quando aplicados em estruturas ou componentes estruturais é ainda escassa. A título de exemplo, a eficácia dos reforços aplicados em sistema TRM, em face de eventos sísmicos, ainda não é clara. Atendendo ao estado da arte apresentado acima, a presente tese tem como objetivo investigar numericamente a eficácia de implementação de materiais compósitos à base de TRM, na resposta de estruturas de alvenaria tradicional a ações no plano e para fora do plano. Para tal, foram criados diferentes modelos de elementos finitos para avaliar o desempenho destes materiais para ambos os tipos de ações. Comparou-se também o seu comportamento em situações com e sem reforço, recorrendo a análises não lineares, primeiro sob efeito de cargas monotónicas proporcionais à massa, aplicadas lateralmente, (pushover), e depois sob o efeito de cargas dinâmicas representadas por acelerogramas reais recolhidos durante o sismo de L'Aquila, ocorrido a 6 de Abril de 2009. Os resultados obtidos são apresentados e discutidos em detalhe.
Le strutture in muratura non rinforzate (URM) costituiscono una percentuale significativa del patrimonio costruito, ma non presentano deille buone performance in condizioni sismiche. Per questa ragione l'industria delle costruzioni si è dimostrata estremamente interessata agli interventi per la loro riparazione e riabilitazione. Negli ultimi decenni, questi materiali innovativi costituiti da fibre immerse in matrici organiche (FRP) sono stati ampiamente usati per migliorare il comportamento di queste strutture in condizioni sismiche. Inizialmente, tali materiali erano stati progettati per essere applicati prevalentemente su strutture in cemento e solo negli ultimi tempi il loro utilizzo è stato ampliato anche alla muratura. Nonostante gli indiscutibili miglioramenti introdotti dai materiali compositi, alcuni svantaggi sono emersi, dovuti principalmente alla natura organica delle resine (ad esempio epossidiche). Di conseguenza, un nuovo tipo di materiaii compositi, nei quali la matrice organica è sostituita da una inorganica (ad esempio malta a base di cemento o di calce), è stato proposto come soluzione. Questi materiali, se da un lato assicurno gli stessi risultati degli FRP (aumento della resistenza a taglio e delle capacità deformative senza incrementare il peso della struttura) dall'altro permettono di superare gli aspetti negativi (vulnerabilità alle alte temperature, al fuoco e agli agenti esterni, bassa permeabilità e ridotta compatibilità con Ia muratura sottostante). I materiali compositi a base di malta consentono il soddisfacimento dei principj del restauro, quali reversibilità e sostenibilità, poiché risultano più compatibili con il substrato in muratura, sia per quanto riguarda gli aspetti meccanici che fisici. I nuovi materiali compositi, costituiti da fibre immerse in un sottile strato di malta, per il rinforzo delle strutture in muratura, di souto definiti FRCM (Malta cementizia rinforzata con fibre) o TRM (Malta rinforzata con tessuto), hanno di recente ricevuto molto interesse dal mondo della ricerca. Nonostante il recente interesse nell'uso di questi materiali, le informazioni disponibili riguardo il loro funzionamento quando applicati a strutture reali o a componenti strutturali, sono ancora esigui. Ad esempio, l'efficienza dei sistemi TRM per il miglioramento della risposta, in condizioni sismiche, delle strutture rinforzate non è ancora totalmente chiaro. La presente tesi, inserendosi nell'ambito di ricerca descritto, ha lo scopo di determinare se l'utiiizzo di materiali compositi TRM sia valido o meno quando applicato suile strutture, in condizioni di sollecitazione nel piano e fuori dal piano. Pertanto, diversi modelli agli elementi finiti sono stati realizzati per studiare questi due tipi di risposta. Un confronto del loro funzionamento in condizioni non rinforzate e rinforzate è stato condotto in termini di analisi non-lineari, sia sotto l'effetto di un carico laterale-monotonico proporzionale alla massa (Push-over) che sotto l'effetto di un carico dinamico rappresentato da un accelerogramma reale, registrato durante li terremoto verificatosi a L'Aquila (6 Aprile 2009). I risultati ottenuti sono presentati e discussi criticamente.

Στην παρούσα διδακτορική διατριβή αναπτύσσεται μια νέα τεχνική ενίσχυσης υποστυλωμάτων οπλισμένου σκυροδέματος με βάση τη χρήση συνθέτων υλικών, τα οποία αποτελούνται από πλέγματα ινών σε ανόργανη μήτρα (π.χ. κονίαµα µε βάση το τσιμέντο), αποσκοπώντας στην επίλυση προβλημάτων που χαρακτηρίζουν τα Ινοπλισμένα Πολυμερή (ΙΟΠ) σχετικά µε τη χρήση εποξειδικών ρητινών. Τα Ινοπλέγματα σε Ανόργανη Μήτρα (ΙΑΜ) δοκιμάζονται στη μορφή μανδύα µε στόχο την περίσφιγξη και την αύξηση της πλαστιμότητας υποστυλωμάτων παλαιού τύπου, σχεδιασμένων δηλαδή χωρίς τις νέες αντισεισμικές λεπτομέρειες όπλισης. Εξετάζονται διάφορες παράμετροι, που περιλαμβάνουν τη χρήση ράβδων λείων ή με νευρώσεις, την πιθανή ένωση των ράβδων με υπερκάλυψη στον πόδα των υποστυλωμάτων και το μήκος υπερκάλυψης. Έτσι προσδιορίζεται η αποτελεσματικότητα των μανδυών ΙΑΜ και συγκρίνεται με αυτή τον ΙΟΠ ως μέσου περίσφιγξης στις κρίσιμες περιοχές υφισταμένων υποστυλωμάτων για όλες τις περιπτώσεις καμπτικών αστοχιών στην περιοχή της πλαστικής άρθρωσης. Το πειραματικό πρόγραμμα που ακολουθείται για την απόκτηση δεδομένων γύρω από τη συμπεριφορά υποστυλωμάτων οπλισμένου σκυροδέματος, ενισχυμένων με μανδύες ανόργανης (ΙΑΜ) ή οργανικής (ΙΟΠ) μήτρας, περιλαμβάνει συνολικά 28 δοκιμές επί δοκιμίων υποστυλωμάτων δύο τύπων: (α) 15 πρισματικά δοκίμια οπλισμένου σκυροδέματος που δοκιμάζονται σε κεντρική θλίψη και (β) 13 δοκίμια υποστυλωμάτων πλήρους κλίμακας, τα οποία δοκιμάζονται σε ανακυκλιζόμενη κάμψη με σταθερό αξονικό φορτίο. Καταδεικνύεται ότι η αποτελεσµατικότητα των µανδυών ΙΑΜ είναι υψηλή και γενικώς παρόµοια µε αυτή των µανδυών ΙΟΠ για όλες τις περιπτώσεις που εξετάστηκαν. Επιπροσθέτως, τα πειραματικά αποτελέσματα των 13 υποστυλωμάτων πλήρους κλίμακας που υποβλήθηκαν σε ανακυκλιζόμενη κάμψη (με σταθερό αξονικό φορτίο), συμβάλλουν στη διερεύνηση δύο ακόμα “θολών” μέχρι σήμερα πεδίων, όπως: (α) Ο λυγισμός των διαμήκων ράβδων σε περισφιγμένο με μανδύες ΙΑΜ ή ΙΟΠ σκυρόδεμα. Ιδιαίτερη έμφαση δίνεται στη μελέτη της αλληλεπίδρασης μεταξύ του μανδύα ΙΑΜ ή ΙΟΠ και των διαμήκων ράβδων, κατά την έναρξη και εξέλιξη του λυγισμού των τελευταίων. (β) Η αντοχή σε συνάφεια μεταξύ των ενωμένων με παράθεση ράβδων και του περισφιγμένου με μανδύες ΙΑΜ ή ΙΟΠ σκυροδέματος. Ιδιαίτερη έμφαση δίνεται στην πειραματική και αναλυτική μελέτη του μηχανισμού με τον οποίο η περίσφιγξη με μανδύες ΙΟΠ και ΙΑΜ συνεισφέρει στη βελτίωση των συνθηκών συνάφειας μεταξύ ράβδων οπλισμού και σκυροδέματος. Ακόμα στην παρούσα διδακτορική διατριβή διεξάγεται η πρώτη συστηματική μελέτη καμπτικής ενίσχυσης υποστυλωμάτων υπό ανακυκλιζόμενη κάμψη (και σταθερό αξονικό φορτίο) με Πρόσθετους Οπλισμούς νέου τύπου σε Εγκοπές (ΠΟΕ). Εξετάζονται υποστυλώματα που έχουν ενισχυθεί με πρόσθετο οπλισμό ινοπλισμένων πολυμερών (ελάσματα άνθρακα ή ράβδους γυαλιού) καθώς και με ράβδους ανοξείδωτου χάλυβα τοποθετημένων σε εγκοπές. Άλλη μια καινοτομία που εισαγάγει η παρούσα διατριβή είναι ο συνδυασμός του ΠΟΕ με τοπικούς μανδύες ινοπλεγμάτων σε ανόργανη μήτρα (IAM), οι οποίοι αποτελούν ένα εξαιρετικά αποτελεσματικό και πολλά υποσχόμενο σύστημα περίσφιγξης, όπως αναπτύσσεται και περιγράφεται λεπτομερώς στην παρούσα διδακτορική διατριβή. Η έρευνα που υλοποιείται για την απόκτηση δεδομένων γύρω από τη συμπεριφορά υποστυλωμάτων οπλισμένου σκυροδέματος ενισχυμένων σε κάμψη με ΠΟΕ, περιλαμβάνει τη διεξαγωγή 11 δοκιμών επί υποστυλωμάτων πλήρους κλίμακας, τα οποία υποβάλλονται σε ανακυκλιζόμενη κάμψη υπό σταθερό αξονικό φορτίο. . Καταδεικνύεται ότι μέσω ενός κατάλληλου σχεδιασμού, στα πλαίσια του οποίου ο ΠΟΕ συνδυάζεται με τοπικό μανδύα στα άκρα του υποστυλώματος (κορυφή και πόδα), είναι εφικτό η αύξηση της καμπτικής αντίστασης των υποστυλωμάτων να μην συνοδεύεται από μείωση της διαθέσιμης ικανότητας παραμόρφωσης. Τα χρήσιμα πειραματικά ευρήματα από τα ενισχυμένα με ΠΟΕ υποστυλώματα, συμπληρώνονται με την ανάπτυξη ενός αναλυτικού και υπολογιστικού προσομοιώματος, το οποίο έχει διττή συμβολή, καθώς επιτρέπει: (α) την εκτέλεση παραμετρικών αναλύσεων ώστε να μελετηθεί σε βάθος και χωρίς κόπο (πειραματικές δοκιμές) η επίδραση όλων σχεδόν των παραμέτρων, στην καμπτική αντίσταση των ενισχυμένων με ΠΟΕ υποστυλωμάτων. (β) Τη χρήση του ως πολύτιμου υπολογιστικού εργαλείου από το Μηχανικό για το σχεδιασμό καμπτικών ενισχύσεων υποστυλωμάτων με ΠΟΕ και / ή μανδύες συνθέτων υλικών. Η αξία της συμβολής του εν λόγω προσομοιώματος μεγιστοποιείται αν ληφθούν υπόψη ορισμένα χαρακτηριστικά του όπως: (1) Η μείωση των ροπών αντοχής ως προς τους δύο κύριους άξονες (ισχυρός και ασθενής), η οποία οφείλεται στην έντονη σύζευξή τους, για τα ενισχυμένα σε κάμψη υποστυλώματα που υποβάλλονται σε διαξονική κάμψη. (2) Η εφαρμογή ενός τραπεζοειδούς στερεού τάσεων για το σκυρόδεμα σε θλίψη, το οποίο σε σύγκριση με το κλασικό ορθογωνικό στερεό, προσομοιώνει με αρκετά μεγαλύτερη ακρίβεια τον όγκο του σκυροδέματος της θλιβόμενης ζώνης, ιδιαίτερα για τις ενισχυμένες διατομές. (3) Η ταυτόχρονη δράση της εξωτερικής περίσφιγξης με μανδύες συνθέτων υλικών στις ενισχυμένες σε κάμψη διατομές.
The effectiveness of a new structural material, namely Textile-Reinforced Mortar (TRM), was investigated experimentally in this PhD Thesis as a means of confining old-type reinforced concrete (RC) columns with limited capacity due to bar buckling or due to bond failure at lap splice regions. Comparisons with equal stiffness and strength fiber-reinforced polymer (FRP) jackets allow for the evaluation of the effectiveness of TRM versus FRP. Tests were carried out on nearly full scale non-seismically detailed RC columns subjected to cyclic uniaxial flexure under constant axial load. Thirteen cantilever-type specimens with either continuous or lap-spliced deformed longitudinal reinforcement at the floor level were constructed and tested. Experimental results indicated that TRM jacketing is quite effective as a means of increasing the cyclic deformation capacity of old-type RC columns with poor detailing, by delaying bar buckling and by preventing splitting bond failures in columns with lap-spliced bars. Compared with their FRP counterparts, the TRM jackets used in this study were found to be equally effective in terms of increasing both the strength and deformation capacity of the retrofitted columns. From the response of specimens tested in this study, it can be concluded that TRM jacketing is an extremely promising solution for the confinement of RC columns, including poorly detailed ones with or without lap splices in seismic regions. Moreover this PhD Thesis presents the results of a large-scale experimental program aiming to study the behavior of RC columns under simulated seismic loading, strengthened in flexure (of crucial importance in capacity design) with different types and configurations of near-surface mounted (NSM) reinforcing materials. The role of different parameters is examined, by comparison of the lateral load versus displacement response characteristics (peak force, drift ratios, energy dissipation, stiffness). Those parameters were as follows: carbon or glass fiber-reinforced polymers (FRP) versus stainless steel; configuration and amount of NSM reinforcement; confinement via local jacketing; and type of bonding agent (epoxy resin or mortar). The results demonstrate that NSM FRP or stainless steel reinforcement is a viable solution towards enhancing the flexural resistance of reinforced concrete columns subjected to seismic loads. With proper design, which should combine compulsory NSM reinforcement with local jacketing at column ends, it seems that column strength enhancement does not develop at the expense of low deformation capacity.