Behavior of Rc Beams Strengthened in Shear with FRCM Composites

Interventions for strengthening, repairing, and upgrading of existing reinforced concrete (RC) structures are aimed to increase/restore their structural capacity to withstand flexural, shear, torsional, and axial loads. Reasons to carry out such interventions vary from the need to upgrade the structure to current guidelines, overcome design and construction mistakes, and allow an increment in load due to a change in use. In addition, unexpected overloading events, such as earthquakes, might damage the structure, reducing its original performance. The same behavior can be expected in the case of fire or lack of adequate maintenance. In the previous decades the use of fiber reinforced polymer (FRP) composites has gained worldwide popularity to carry out such interventions due to some of their properties such as high strength-to-weight ratio, ease of application, and good corrosion resistance. However, the use of organic resin matrix in FRP composites has been associated with some limitations of their use such as inability to apply onto wet surfaces, low resistance to relatively high temperatures, and difficulty to carry out post-earthquake assessment. For this reason, in recent years, an important research effort has been developed in order to study composites known as fiber reinforced cementitious matrix (FRCM) composites, in which the organic resin is replaced by an inorganic matrix. In this thesis, the behavior of RC beams strengthened in shear with externally bonded FRCM composites is studied. The first part of this thesis summarizes the state of research on the topic of shear strengthening of RC beams using externally bonded FRCM composites with the goal of serving as a reference point for the development of future research. A detailed bibliographical review of the literature on the shear strengthening of RC beams using FRCM composites is carried out, and the major findings and main aspects that should be addressed in future research are indicated. The collected experimental evidence shows that FRCM composites are able to increase the shear strength of RC beams, modifying in some cases the type of failure from shear to a flexural mode. Then, the results of an experimental campaign on shear strengthening of RC beams with externally bonded FRP and FRCM composites are presented. FRP and FRCM composites with two different fiber types are examined. Two different stirrup spacings were employed to investigate the internal-external shear reinforcement interaction. Considering the limited experimental evidence on the use of anchors for RC beams strengthened in shear with FRCM composites, the performance of FRCM strengthened beams with and without anchors is also compared. Results show that the effectiveness of the FRCM system depends on the spacing of theinternal shear reinforcement. In addition, internal-external shear reinforcement interaction was witnessed, but the intereaction appears to be less pronounced than in beams strengthened with FRP composites. Design models proposed to predict the contribution of the FRCM composite to the shear strength of RC beams are assessed using the database of experimental results collected and compiled by the author and the experimental results included in this thesis. Results show that the performance of the models is highly influenced by the type of failure mode attained by the strengthened beams. In addition, the use of the FRCM composite properties instead of the bare fiber mechanical characteristics does not result in an increase in the accuracy of the models. Strains measured by strain gauges mounted onto the internal (stirrups) and external (FRCM system) transverse reinforcement of the tested beams are used to compute the individual contributions of the concrete, steel, and fibers to the overall shear strength of the FRCM strengthened beams, and to study the possible interaction among them. It was found that the concrete contribution to the shear resistance starts to decrease after first cracking of the concrete is achieved. After this point, the stirrup and fiber contributions start to increase until the peak load is attained. Lastly, a new analytical model based on the bond behavior of the FRCM composites applied onto concrete substrates is introduced and discussed. Although additional tests are required to calibrate the model, initial results show that the assumptions and hypothesis used during its development are appropriate

Evaluation of Mechanical Properties of existing reinforced concrete bridges.

When performing numerical evaluations on concrete bridges, the Fracture Energy (GF) plays a very important role, and this Fracture Energy value is calculated using empirical formulas derived from compressive strength tests. In order to perform such experiments, methods for obtaining the fracture energy have been carried out on concrete belonging to a 55-year-old bridge located in the city of Kalix, northern Sweden. For this purpose, cylindrical concrete samples were taken from the bridge and other bridges and tested in uniaxial tensile tests. In this Thesis, different methods for determining the Fracture Energy of concrete will be discussed, and recommendations for evaluative procedures will be given. Firstly, a literature review will be carried out, in which the different methods for obtaining the Fracture Energy experimentally will be studied in depth. In addition, these methods will be compared with each other to check for possible discrepancies, and the different factors that affect the Fracture Energy results will be discussed. Secondly, the methodology of the experiments will be explained in more detail.Thirdly, all the experimental work that has been carried out in the laboratory will be discussed, i.e., all the work performed, both the preparation prior to the tests and the tests themselves, will be described. Fourthly, the results obtained from the experiments will be put on paper and analyzed in order to check how reliable they are and whether they meet the established expectations. Finally, a conclusion will be made about all the work done, both outside and inside the laboratory, and the study carried out on the Fracture Energy in concrete bridges will be evaluated.<br /

Numerical Analysis of an FRP-Strengthened Masonry Arch Bridge

Historical masonry arch bridges are a fundamental part of the road and railway networks in Europe. Very often, due to factors such as lack of maintenance, increase of traffic loads, etc., these structures need interventions in order to guarantee their adequate structural performance. For this reason, an important research effort has been devoted in previous decades to study the behavior of masonry arches and to identify innovative techniques able to increase their ultimate capacity, such as fiber reinforced polymer (FRP) composites. In this paper, the results of an experimental campaign carried out on masonry arches strengthened with one FRP layer applied at the structure intrados are used to calibrate a numerical analysis model. Then, the model is used to predict the contribution that this type of strengthening would have had on the well-known Prestwood Bridge. The numerical results show that the hypothetical intervention of the Prestwood Bridge would imply an increase in the ultimate load of the structure, although it would be significantly lower than that usually obtained for the case of arches tested in laboratory

Behavior of Rc Beams Strengthened in Shear with FRCM Composites

Interventions for strengthening, repairing, and upgrading of existing reinforced concrete (RC) structures are aimed to increase/restore their structural capacity to withstand flexural, shear, torsional, and axial loads. Reasons to carry out such interventions vary from the need to upgrade the structure to current guidelines, overcome design and construction mistakes, and allow an increment in load due to a change in use. In addition, unexpected overloading events, such as earthquakes, might damage the structure, reducing its original performance. The same behavior can be expected in the case of fire or lack of adequate maintenance. In the previous decades the use of fiber reinforced polymer (FRP) composites has gained worldwide popularity to carry out such interventions due to some of their properties such as high strength-to-weight ratio, ease of application, and good corrosion resistance. However, the use of organic resin matrix in FRP composites has been associated with some limitations of their use such as inability to apply onto wet surfaces, low resistance to relatively high temperatures, and difficulty to carry out post-earthquake assessment. For this reason, in recent years, an important research effort has been developed in order to study composites known as fiber reinforced cementitious matrix (FRCM) composites, in which the organic resin is replaced by an inorganic matrix. In this thesis, the behavior of RC beams strengthened in shear with externally bonded FRCM composites is studied. The first part of this thesis summarizes the state of research on the topic of shear strengthening of RC beams using externally bonded FRCM composites with the goal of serving as a reference point for the development of future research. A detailed bibliographical review of the literature on the shear strengthening of RC beams using FRCM composites is carried out, and the major findings and main aspects that should be addressed in future research are indicated. The collected experimental evidence shows that FRCM composites are able to increase the shear strength of RC beams, modifying in some cases the type of failure from shear to a flexural mode. Then, the results of an experimental campaign on shear strengthening of RC beams with externally bonded FRP and FRCM composites are presented. FRP and FRCM composites with two different fiber types are examined. Two different stirrup spacings were employed to investigate the internal-external shear reinforcement interaction. Considering the limited experimental evidence on the use of anchors for RC beams strengthened in shear with FRCM composites, the performance of FRCM strengthened beams with and without anchors is also compared. Results show that the effectiveness of the FRCM system depends on the spacing of theinternal shear reinforcement. In addition, internal-external shear reinforcement interaction was witnessed, but the intereaction appears to be less pronounced than in beams strengthened with FRP composites. Design models proposed to predict the contribution of the FRCM composite to the shear strength of RC beams are assessed using the database of experimental results collected and compiled by the author and the experimental results included in this thesis. Results show that the performance of the models is highly influenced by the type of failure mode attained by the strengthened beams. In addition, the use of the FRCM composite properties instead of the bare fiber mechanical characteristics does not result in an increase in the accuracy of the models. Strains measured by strain gauges mounted onto the internal (stirrups) and external (FRCM system) transverse reinforcement of the tested beams are used to compute the individual contributions of the concrete, steel, and fibers to the overall shear strength of the FRCM strengthened beams, and to study the possible interaction among them. It was found that the concrete contribution to the shear resistance starts to decrease after first cracking of the concrete is achieved. After this point, the stirrup and fiber contributions start to increase until the peak load is attained. Lastly, a new analytical model based on the bond behavior of the FRCM composites applied onto concrete substrates is introduced and discussed. Although additional tests are required to calibrate the model, initial results show that the assumptions and hypothesis used during its development are appropriate.Gli interventi per il rafforzamento e la riparazione delle strutture esistenti in calcestruzzo armato mirano ad aumentare e ripristinare la loro capacità strutturale per resistere a carichi flessionali, a taglio, torsionali e assiali. I motivi per fare tali interventi variano dalla necessità di aggiornare la struttura alle linee guida attuali, superare gli errori di progettazione e costruzione e consentire un incremento del carico a causa di un cambiamento nell'uso. Inoltre, eventi di sovraccarico inaspettati, come terremoti, potrebbero danneggiare la struttura, riducendo le prestazioni originali. Lo stesso comportamento può essere previsto in caso d’incendio o mancanza di manutenzione adeguata. Nei decenni precedenti l'uso di compositi polimerici rinforzati con fibre (FRP) ha guadagnato popolarità in tutto il mondo per fare tali interventi a causa di alcune delle loro proprietà come il rapporto tra forza-peso, facilità di applicazione e buona resistenza alla corrosione. Tuttavia, l'uso della matrice di resina organica dei compositi FRP è stato associato ad alcune limitazioni del loro uso, come l'incapacità di applicare su superfici bagnate, bassa resistenza a temperature relativamente alte e difficoltà nella valutazione post-terremoto. Per questo motivo, negli ultimi anni, è stato sviluppato un importante sforzo di ricerca per lo studio di compositi noti come compositi a matrice cementizia fibrorinforzata (FRCM), in cui la resina organica viene sostituita da una matrice inorganica. In questa tesi, è studiato il comportamento de travi di calcestruzo armato rafforzate a taglio con compositi FRCM. La prima parte di questa tesi riassume lo stato della ricerca sul tema del rinforzo a taglio delle travi RC utilizzando compositi FRCM con legami esterni con l'obiettivo di servire come punto di riferimento per lo sviluppo della ricerca futura. Viene effettuata una revisione bibliografica dettagliata della letteratura sul rafforzamento a taglio delle travi utilizzando i compositi FRCM, e vengono indicati i principali risultati e gli aspetti principali che dovrebbero essere affrontati nelle ricerche future. Le prove sperimentali raccolte mostrano che i compositi FRCM sono in grado di aumentare la resistenza al taglio delle travi, modificando in alcuni casi il tipo di cedimento da taglio a una modalità a flessione. Quindi, sono presentati i risultati di una campagna sperimentale sul rinforzo a taglio di travi con compositi FRP e FRCM. Vengono esaminati i compositi FRP e FRCM con due diversi tipi di fibre. Sono state impiegate due diverse spaziature delle staffe per studiare l'interazione di rinforzo di taglio interno-esterno. Considerando le limitate prove sperimentali sull'uso di elementi di ancoraggio travi rinforzate a taglio con materiali compositi FRCM, viene anche confrontata la prestazione di travi rinforzate FRCM con e senza ancoraggi. I risultati mostrano che l'efficacia del sistema FRCM dipende dalla spaziatura del rinforzo del taglio interno. Inoltre, è stata osservata l'interazione di rinforzo di taglio interno-esterno, ma l'interazione sembra essere meno pronunciata rispetto alle travi rinforzate con compositi FRP. I modelli di progettazione proposti per prevedere il contributo del composito FRCM alla resistenza al taglio delle travi sono valutati utilizzando il database dei risultati sperimentali raccolti e compilati dall'autore e i risultati sperimentali inclusi in questa tesi. I risultati mostrano che le prestazioni dei modelli sono fortemente influenzate dal tipo di modalità di rottura raggiunta. Inoltre, l'uso delle proprietà dei compositi FRCM al posto delle caratteristiche meccaniche delle fibre non comporta un aumento dell'accuratezza dei modelli. Le deformazioni misurati dagli estensimetri montati sulle armature interne (staffe) e esterne (sistema FRCM) delle travi sottoposte a prova vengono utilizzati per calcolare i singoli contributi del calcestruzzo, dell'acciaio e delle fibre alla resistenza complessiva al taglio delle travi rinforzate con i compositi FRCM, e per studiare la possibile interazione tra loro. Si è costatato che il contributo concreto alla resistenza al taglio inizia a diminuire dopo il primo crollo del calcestruzzo. Dopo questo punto, i contributi della staffa e della fibra iniziano ad aumentare fino al raggiungimento del picco di carico. Infine, è introdotto e discusso un nuovo modello analitico basato sul comportamento del legame dei compositi FRCM applicati su substrati in calcestruzzo. Sebbene siano necessari successivi test per calibrare il modello, i risultati iniziali mostrano che le ipotesi utilizzate durante il suo sviluppo sono appropriate

Bond behaviour of basalt FRCM composites applied on RC elements

In the last decades fibre reinforced polymers (FRP) composites have been extensively studied and used for strengthening and retrofitting existing reinforced (RC) concrete structures. A valid alternative to the use of FRP composites is represented by fibre reinforced cementitious matrix (FRCM) composites, which are comprised of high strength fibres embedded within a cementitious matrix. Although experimental and analytical studies about FRCM composites with carbon, glass, PBO, and steel fibre are available in the literature, very few studies concerning basalt FRCM composites can be found and their application is thus limited. In addition to their lower environmental impact, basalt fibres present suitable mechanical properties, good resistance to high temperature, and competitive costs. This paper shows the results of single-lap direct-shear tests on basalt FRCM-concrete joints employed to study the bond behaviour and mode of failure of this composite. Different composite bonded lengths were applied to investigate the presence of an effective bonded length, i.e. the length needed to fully develop the composite load-carrying capacity

Experimental behavior of glass-FRCM Composites Applied onto Masonry and Concrete Substrates

The use of Fiber Reinforced Polymer (FRP) composites has become a popular solution for retrofitting and strengthening of existing concrete and masonry structures. However, some drawbacks of this technique, mainly associated with the use of organic resins, have been reported. To overcome such drawbacks, the development of composite materials in which the organic resins are replaced with inorganic matrices has recently caught the attention of the civil engineering industry. Among these newly developed systems, Fiber Reinforced Cementitious Matrix (FRCM) composites, which are comprised of high strength fibers embedded within an inorganic matrix, have shown promising results. However, research on this topic is still limited and important aspects, such as the bond behavior between the composite and the substrate, are not fully understood and require further study. This paper presents the results of an experimental campaign aimed at investigating the influence of the type of matrix and substrate on the bond behavior of FRCM composites. Glass-FRCM composite strips were applied onto concrete and masonry substrates and then tested by means of a classical push-pull single-lap direct-shear test set-up. A cementitious and a lime-based matrix were employed to apply the same type of fiber on concrete and masonry substrates, respectively. FRCM-concrete and FRCM-masonry joints reported the same failure mode. However, higher values of the peak load were obtained for the lime-based glass-FRCM composite applied onto masonry substrates than with the cementitious glass-FRCM composite applied onto concrete substrates

Assessment of an existing reinforced concrete (RC) prefabricated building: the case of the proc\ue9d\ue9 Camus

Prefabricated residential construction forms a large portion of the European building stock and needs to be upgraded to current living standards and, if applicable, to current seismic resistance requirements. In fact, as indicated by the European Union in 2011, the refurbishment of the structures built during the second half of the twentieth century is priority for the entire construction sector. However, this process is affected primarily by the lack of knowledge of the material and construction aspects of prefabricated buildings, which makes the development of economic and efficient refurbishment interventions difficult. Based on this need, this paper focuses on the assessment of the seismic structural behavior of residential buildings built using the prefabrication proc\ue9d\ue9 Camus, widely used in France and in many European countries, including Italy, during the 1960s. The analysis was carried out on a typological building placed in the city of Bologna, as this region concentrates an important number of prefabricated structures that had been recently affected by several earthquakes. Results show that due to the building layout, the analyzed structure has significantly higher lateral stiffness and better structural performance in the transverse direction than in the longitudinal direction. In fact, it was observed that the structural prefabricated walls located in the longitudinal direction will need to be strengthened in order to fulfill current requirements for shear strength and the combined effect of axial loads and bending moments

Bond behaviour and sustainability of fibre reinforced cementitious matrix composites applied to masonry elements

Fibre-reinforced polymers (FRP) have shown to be an effective solution for retrofitting and strengthening of existing masonry structures, although some drawbacks related with the use of organic resins have been found. A newly developed alternative to FRP, known as fibre reinforced cementitious matrix (FRCM) composites, may overcome the drawbacks. This paper provides a better insight into the bond behaviour of FRCM when applied to masonry substrates and highlights possible differences with the behaviour of FRP composites by means of push-pull single-lap direct-shear tests for two types of fibres (glass and basalt). Additionally, the sustainability of this strengthening system was evaluated by means of a life cycle assessment (LCA). The experimental data suggests that the effective bond length for basalt FRCM composites is lower than 260 mm and that for basalt and glass composites the initial response is highly dependent on the elastic behaviour of the fibres. The FRCM system provides environmental benefits in all the analysed categories with respect to the reference FRP technique, based on the analysis performed

Quantifying the Environmental Impact of Railway Bridges Using Life Cycle Assessment: A Case Study

As emission regulations in the EU are becoming stricter, the reduction of greenhouse gas emissions from the construction industry has become a pressing need. As part of the efforts related to this issue, it has been found that Environmental Life Cycle Analysis (LCA) approaches are required to optimize the design, construction, operation, and maintenance of buildings and infrastructure assets. In this paper, The Institution of Structural Engineers guidance on how to calculate the embodied carbon in structures is used as LCA model and evaluated in a case study. The guidance divides the structure´s life cycle into five stages (A1-A3: Product, A4-A5: Construction process, B1-B7: Use, C1-C4: End of live and D: Benefits and loads beyond the system boundary) and the environmental impact is measured in terms of carbon dioxide equivalent emissions (kgCo2e) or global warming potential (GWP). The model was applied to an existing reinforced concrete trough bridge, which is a structure type commonly used in Swedish railways. Results show that that the model was effective and simple for investigating the environmental impact of the studied structure.