Steel bridges and structures often need strengthening due to increased life loads, or repair due to corrosion or fatigue cracking. This study explored the use of adhesively bonded Carbon Fibre Reinforced Polymers (CFRP) flexible sheets and rigid plates in retrofitting steel columns and girders, through experimental and analytical investigations. The first part of the research program investigated the behaviour of CFRP-strengthened steel columns comprised of square Hollow Structural Sections (HSS). Fifty columns, 175 mm to 2380 mm long (i.e. with slenderness ratios ranging from 4 to 93), were tested under axial compression loads to examine the effects of number and type of CFRP layers, fibre orientation, and slenderness ratio. Transverse wrapping was shown to be suitable for controlling outwards local buckling in HSS short columns, while longitudinal layers were more effective in controlling overall buckling in slender columns. The maximum increases in axial strength observed in the experiments were 18 and 71 percent, for short and slender columns, respectively. An analytical fibre-element model and a non-linear finite element model were developed for slender columns. The models account for steel plasticity, geometric non-linearities, and residual stresses. The models were verified using experimental results, and used in a parametric study. It was shown that CFRP effectiveness increases for columns with larger out-of-straightness imperfections and higher slenderness ratios. The second part of the research program investigated w-section steel-concrete composite girders retrofitted using CFRP materials. Three girders, 6100 mm long, were tested to study strengthening of intact girders using CFRP plates. Eleven girders, 2030 mm long, including girders artificially damaged by completely cutting their tension flanges at mid-span, were tested to study the effectiveness of repair using CFRP sheets. The parameters considered were the CFRP type, number of layers, number of retrofitted sides of the tension flange, and the length of CFRP repair patch. The strength and stiffness of the intact girders have increased by 51 and 19 percent, respectively. For the repaired girders, the strength and stiffness recovery ranged from 6 to 116 percent and from 40 to 126 percent, respectively. Unlike flexural strength, the stiffness was not much affected by the bond length. Analytical models were developed, verified, and used in a parametric study, which showed that the higher the CFRP modulus, the larger the gain in stiffness and yielding moment, but the lower the gain in strength and ductility. In general, this study demonstrated that steel structures can indeed be successfully strengthened or repaired using CFRP material. / Thesis (Ph.D, Civil Engineering) -- Queen's University, 2007-11-15 18:35:59.552

Esse trabalho apresenta a validação do método numérico dos elementos finitos para estimar a resistência ao cisalhamento da interface entre camadas de um compósito polimérico de fibra de carbono. Foram realizados ensaios de Resistência ao Cisalhamento Interlaminar (ILSS, interlaminar shear strength) para validação do modelamento numérico. O método numérico consistiu no desenvolvimento de dois modelos em elementos finitos utilizando um programa comercial (ANSYS Rev. 10). O primeiro usando elementos finitos de casca tridimensional e o segundo, usando elementos finitos planos para simular o ensaio ILSS. O modelo numérico que apresentou resultados mais próximos aos experimentais, o modelo tridimensional de casca, apresentou um erro de apenas 5,6%, indicando uma aproximação bastante satisfatória. / This work presents the validation of the numerical method of finite elements to estimate the interlaminar shear strength in a carbon fiber reinforced polymeric composite. ILSS (interlaminar shear strength) tests were performed to validate the numerical modeling. The numerical method consisted of two different finite element models using a commercial software (ANSYS Rev. 10.0). The first model uses tridimensional shell finite elements and the second model, plane finite elements to simulate the ILSS test. The numerical method that presented the closest results to those from the experimental method was the tridimensional shell model, with an error deviation of only 5.6%, which indicates very good precision

Esse trabalho apresenta a validação do método numérico dos elementos finitos para estimar a resistência ao cisalhamento da interface entre camadas de um compósito polimérico de fibra de carbono. Foram realizados ensaios de Resistência ao Cisalhamento Interlaminar (ILSS, interlaminar shear strength) para validação do modelamento numérico. O método numérico consistiu no desenvolvimento de dois modelos em elementos finitos utilizando um programa comercial (ANSYS Rev. 10). O primeiro usando elementos finitos de casca tridimensional e o segundo, usando elementos finitos planos para simular o ensaio ILSS. O modelo numérico que apresentou resultados mais próximos aos experimentais, o modelo tridimensional de casca, apresentou um erro de apenas 5,6%, indicando uma aproximação bastante satisfatória. / This work presents the validation of the numerical method of finite elements to estimate the interlaminar shear strength in a carbon fiber reinforced polymeric composite. ILSS (interlaminar shear strength) tests were performed to validate the numerical modeling. The numerical method consisted of two different finite element models using a commercial software (ANSYS Rev. 10.0). The first model uses tridimensional shell finite elements and the second model, plane finite elements to simulate the ILSS test. The numerical method that presented the closest results to those from the experimental method was the tridimensional shell model, with an error deviation of only 5.6%, which indicates very good precision

Doctor of Philosophy / Department of Civil Engineering / Hayder A. Rasheed / The use of carbon fiber reinforced polymer (CFRP) anchors can improve the performance of reinforced concrete (RC) beams strengthened in flexure with CFRP sheets. This improvement results from delaying or controlling the debonding of FRP sheets at failure. In this research, six full-scale T beams and six full-scale rectangular beams are prepared and tested as two separate series. All the specimens are strengthened identically using three layers of unidirectional CFRP sheets and one layer of bidirectional CFRP sheet. The first strengthened beam in each series is anchored with side GFRP bars inserted longitudinally to both sides of the beam. The second strengthened beam in each series is anchored with GFRP patches applied to both sides of the beam. CFRP spike anchors are utilized for the other beams in the two series. The third beam in each series is secured with CFRP spike anchors of 16 mm diameter at 140 mm spacing along the shear span. The fourth strengthened beam in each series is anchored with CFRP spike anchors of 19 mm diameter at 203 mm spacing along the shear span. Four CFRP anchors are applied to each shear span of the fifth beam in each series with 16 mm- diameter (spaced at 406 mm) to secure the flexural CFRP sheets. An end CFRP anchorage technique is considered for the last beam in each series, which includes installing one CFRP spike anchor placed at 76 mm from the free edge of CFRP sheets. The beams were tested under four-point bending until failure and the results for each series are evaluated. In addition, the outcome is compared with other anchorage techniques that have been examined by some researchers utilizing the same beam geometry and properties. The experimental testing and nonlinear analysis showed improvement in the flexural performance of anchored beams compared with those strengthened beams without anchorage. By attaining debonding or rupture failure modes for the T beams and concrete crushing failure mode for the rectangular specimens, the ultimate sectional force capacity is achieved. Accordingly, the results prove that the anchors offer an effective solution against premature debonding failure.

The Casimiro Ulloa Hospital is a confined masonry structure more than 60 years old that does not satisfy the requirements of the Peruvian seismic code E.030 and it is located at high seismic zone. Therefore, this hospital is susceptible to collapse and becomes an essential deficient structure. Therefore, the present study is based on a comparative analysis between reinforced concrete wall and CFRP sheets through the nonlinear Push Over method in order to obtain which is the best reinforcement in structural capacity. The reinforcement with eight L-shaped concrete walls of 15 cm thick located at the corners of the structure, increased the strength of the hospital by 115% in longitudinal direction (Axis X) and 108% in transversal direction (Axis Y), and also increased the ductility by 3% and 117% in the directions respectively. The other reinforcement was carried out with CFRP sheets and anchors. The sheets were designed with a width of 9 inches and were placed in an X-shape in the masonry load-bearing walls and the anchors were implemented in the corners of the laminate walls in order to ensure adequate load transfer between the sheets and the surface. This reinforcement increased the strength of the structure by 345% in axis X and 150% in axis Y and increased the ductility by 59% in longitudinal direction and 331% in transversal direction.

An experimental program was carried out to investigate the effect of post-tensioning on timber beams and the performance of timber bridge decks with post-tensioned stringers. The experimental program contains three phases. As part of the first phase, twenty shear tests were performed to determine the ultimate capacity of lag screws that could be used in the post-tensioning process. Results showed that six lag screws with a diameter of 12.7 mm were adequate for the anchorage system. The second phase included testing 22 full scale timber beams. Six beams were control without any reinforcement. The remaining sixteen beams were post-tensioned with either draped or straight carbon fiber reinforced polymer (CFRP) tendons (Groups CD and C) or steel cables (Groups SD with draped cables and S with straight cables).The results revealed that the strength and the stiffness for Group CD were increased on average by 70% and 10%, respectively, while the strength for Group C was increased on average by 56%. In contrast, the strength and the stiffness for Group SD were increased on average by 45% and 4%, respectively, while the strength for Group S was increased on average by 49%. The bending strength of the post-tensioned timber beams was predicted using analytical model. The third phase of the research included the construction of four timber bridge decks: control deck (BD-CO), deck with stringers post-tensioned with draped CFRP tendons (BD-DC), deck with stringers post-tensioned with draped steel tendons (BD-DS), and a deck with stringers strengthened with near-surface mounted glass fibre-reinforced polymer bars (NSM-GFRP) referred to as BD-G. Post-tensioning the stringers of BD-DS and the stringers of BD-DC increased the apparent stiffness on average by 2% and 3%, respectively. In contrast, the apparent stiffness for the stringers of BD-G increased on average by 29%. SECAN program was used to analyze the four timber bridge decks. It was found that SECAN can predict the behaviour of the timber bridge deck based on the experimental stiffness of the individual tests. Cost analysis was done for the three strengthening techniques. It was found that post-tensioning stringers with draped steel cables can be cost effective.

The use of fibre-reinforced polymer (FRP) as an internal reinforcement for concrete has many advantages over steel, most notably lack of corrosion which is considered to be a major problem for structures incorporating steel. In Europe alone, it is estimated that the annual repairing and maintenance costs associated with steel corrosion in infrastructure are around £20 billion (Nadjai et al., 2005). Despite of its corrosion resistance, the widespread use of FRP as an internal reinforcement for concrete was hindered due to its relatively weak performance at elevated temperatures, such as in the event of fire. Under heating, the polymer matrix in FRP softens, which causes bond degrading between reinforcement and concrete. The softening of polymer matrices occurs around their glass transition temperatures, which is typically in the range of 65– 150 °C. The sensitivity of FRP bond to temperature is recognised in design guidelines, therefore many advise against utilising FRP as an internal reinforcement for concrete in structures where fire performance is critical. On the other hand, fibres, the other component of FRP, can tolerate temperatures much higher than polymer matrices. This research investigates a new design for FRP internal reinforcement, which exploits the fact that the FRP fibres in general and carbon fibres in particular are capable of sustaining a large proportion of their original strength at high temperatures. Instead of the traditional way of using separate bars, FRP reinforcement was made as closed loops produced through the continuous winding of carbon fibre tows. When the surface bond degrades at elevated temperatures, interaction with concrete can still be provided through bearing at loop ends. The concept of FRP loops was investigated through a series of experimental work. Firstly, the performance of carbon FRP (CFRP) loops was evaluated through a series of push-off tests in which specimens consisting of CFRP loops bridging two concrete cubes were tested in pull-out using hydraulic jacks. Specimens with straight and hooked reinforcement were produced as well for comparison. A total number of 18 specimens were tested at ambient temperature, glass transition temperature (Tg), and above Tg. Results showed that while at ambient temperature there was no distinction in performance. At elevated temperatures, CFRP loops developed strength about three times higher than specimens with straight or hooked bars. Also, while failure mode occurred due to de-bond in the case of straight and hooked reinforcement, rupture failure occurred with CFRP loops. For better demonstration of the concept in more realistic conditions, four-point bending tests were conducted upon 28 beam specimens reinforced either with CFRP loops or straight bars as flexural reinforcement. Beams were tested under monotonic loading at ambient temperature, or under sustained loads with localised heating over the midspan region that contained the reinforcement overlaps. The benefit of CFRP loops became evident in the elevated temperature tests. Beam specimens with spliced straight bars failed due to debonding after a short period (up to 15 minutes) of fire exposure. Conversely, the fire endurance increased four to five times when CFRP loop reinforcement was used. Unlike straight bars, debonding failure was avoided as failure occurred due to reinforcement rupture. The overlap length of the CFRP loops was found to be important in the order for the loop to develop full capacity. Premature failure can occur with short overlap length due to shear off concrete within the overlap zone. The presence of transverse reinforcement increases confinement levels for reinforcement, so the bond failure of straight bars at ambient temperature testing was eliminated when stirrups were provided. However, at elevated temperatures straight bars failed by pull-out even in presence of transverse reinforcement. To facilitate design with CFRP loops, a numerical analysis tool was developed to calculate the bond stress-slip response of reinforcement at ambient and elevated temperatures. A Matlab programme was designed based on a one-dimensional analytical model for steel. The bond law was modified to be used for CFRP reinforcement. Other analytical models from the literature to account for bond degradation with temperature and tensile strength of curved FRP were also utilised. The developed Matlab code has the capability of producing slip, axial stress, and bond stress distribution along reinforcement. The novel FRP loop reinforcement was demonstrated to be a promising solution for enhancing the fire performance of CFRP internal reinforcement at elevated temperatures. It contributes to removing a major obstacle preventing widespread use of FRP-reinforced concrete, and paves the way for CFRP reinforcement to be used in situations where fire performance is critical.

Infrared thermography was used to evaluate Carbon Fiber Reinforced Panels (CFRP) and optimize the inspection process so that a set of guidelines can be established in order to be efficient and effective. It has been shown in previous work that when a material is heated up the heat will diffuse through the material at a constant rate. However, if there is a defect in the material, such as a delamination, this defect will act like an insulator. When this happens the heat cannot penetrate as quickly as the rest of the material so the surface above the defect shows up hotter than the rest of the material. An operator looks for inconsistent temperatures in the sample to determine the quality of the piece. Samples with simulated defects were made and modeled using a finite element program. Heat will be applied to the models and the temperature profiles analyzed. Along with changing the heat and time, different post-processing techniques were used to improve the method in determining defects in the sample. Once this has been optimized, actual CFRP with the same simulated defects was experimentally tested using the conditions from the analytical model. The analytical and experimental data was compared to insure that the testing process has been optimized. A standardized process was developed for evaluating the CFRPs using infrared thermography.

Le polymère renforcé de fibres de carbone (CFRP) est l'une des solutions courantes pour réparer/renforcer/ fortifier/ rétrofiter les structures en génie civil en raison de ses avantages dans les propriétésmécaniques, la durabilité et la maniabilité. Cependant, des problèmes d'incendie récents ont soulevédes inquiétudes quant à la performance au feu du CFRP et des structures renforcées par CFRP. Dansla littérature, il existe plusieurs études sur l'évolution de la performance mécanique de CFRP et desstructures renforcées par CFRP pendant ou après l'exposition à différents niveaux de température quisont proches des températures obtenus durant un feu. Cependant, les résultats sont dispersés en raisonde la diversité des matériaux utilisés, de la différence dans les protocoles d'essai et de la limitation del'installation d'essai pour une utilisation à température élevée. Des études analytiques et numériquessont également menées avec une étude paramétrique pour observer, améliorer et proposer desrecommandations pour les directives de conception. Cependant, le manque de données expérimentalesa une influence significative sur applicabilité des résultats disponibles.Cette recherche caractérise les comportements des CFRP et de la structure renforcée avec du matériauCFRP dans trois conditions distinctes concernant la température élevée et la charge mécanique quisont proches des différents cas d'application au feu. Les méthodes expérimentales et numériques sontutilisées pour mener cette recherche afin d'étudier plus en détail l'état de chaque matériau au cours desétudes de cas. En particulier, l'essai résiduel est utilisé pour étudier la performance mécanique desspécimens refroidis après exposition à température élevée en respectant l'évaluation du comportementrésiduel des structures renforcées en CFRP en situation post-incendie à des fins de réparation /renforcement. Deux essais thermomécaniques sont utilisés pour étudier la performance mécanique deséchantillons à différentes températures élevées et leur performance thermique à différents étatsmécaniques en respectant la situation d'incendie pour la prédiction et la conception. Les deux dernierscas portent sur l'influence de l'ordre de chargement sur les résultats pour confirmer la validité desdonnées mécaniques expérimentales obtenues à différentes températures lors de l'évaluation de laperformance au feu de la structure renforcée par CFRP où les effets mécaniques et puis les effetsthermiques sont combinés.Dans la première partie expérimentale, 86 essais sur deux types de CFRP (un préfabriqué en usine etun fabriqué manuellement en laboratoire) ont été étudiés dans la plage de température de 20°C à712°C. La performance du matériau CFRP est généralement réduite lorsque la température augmente.Les résistances thermomécaniques et résiduelles du P-CFRP diminuent graduellement de 20°C à700°C, tandis que le module de Young varie de moins de 10% de 20°C à 400°C et ensuite diminuesignificativement à 600°C. La performance thermomécanique identifiée de CFRP a été inférieure quesa performance résiduelle, en particulier à une température supérieure à 400°C. En outre, latempérature élevée et la charge mécanique sont expérimentalement pertinentes et l'ordre dechargement a donc un faible effet sur les performances du matériau dans des conditionsthermomécaniques. Un nouveau modèle analytique, proposé pour l'évolution de la résistance ultimethermomécanique en fonction de la température, a montré sa capacité à s'adapter à deux CFRP étudiéset à ceux testés dans des conditions thermomécaniques similaires dans la littérature [etc...] / Carbon fibre reinforced polymer (CFRP) is one of common solutions in repairing / reinforcing/strengthening/ retrofitting structures in civil engineering due to its advantages in mechanicalproperties, durability and workability. However, recent issues have raised concerns for fireperformance of CFRP and CFRP reinforced structures. Throughout the literature, there are severalinvestigations on the evolution of mechanical performance of CFRP and CFRP reinforced structuresduring or after exposing to different levels of temperature which are close to temperatures obtainedduring a fire. However, the results are scatter due to the diversity of materials used, the difference intest protocols, and limitation in test facility for elevated temperature use. Analytical and numericalstudies are also conducted with parametric investigation to observe, improve, and proposerecommendations for design guideline. Additionally, missing gap in experimental data has asignificant influence on the applicability of the available results.This research characterizes the behaviours of CFRPs and of concrete structure reinforced with CFRPmaterial under three separated conditions concerning elevated temperature and mechanical loadingthat are close to different cases of fire application. The experimental and numerical methods used inthis research are to further investigate the status of each material during the case studies. Particularly,residual test is used to study the mechanical performance of specimens cooled after exposing toelevated temperature respecting the evaluation of the remained behaviour of CFRP reinforcedstructures at post-fire situation for repairing/ retrofitting purpose. Two thermo-mechanical tests areused to study the mechanical performance of specimens at different elevated temperatures and theirthermal performance at different mechanical statuses respecting the fire situation for predicting anddesigning purpose. The two final cases focus on the influence of loading order on the results toconfirm the validity of experimental mechanical data obtained at different temperatures whenapplying for evaluating the fire performance of CFRP reinforced structure where mechanical effectsand then temperature effects are combined.In the first experimental part, 86 tests on two types of CFRP (one pre-fabricated in factory and onemanually fabricated in laboratory) were studied in the temperature range from 20°C to 712°C. Theperformance of CFRP material is generally reduced as the temperature increases. The thermomechanicaland residual ultimate strengths of P-CFRP gradually decrease from 20°C to 700°C, whileits Young’s modulus varies less than 10% from 20°C to 400°C and then significantly decreases at600°C. The identified thermo-mechanical performance of CFRP was lower than its residualperformance, especially at temperature beyond 400°C. Furthermore, the elevated temperature andmechanical load are experimentally shown to be relevant and thus the loading order has a small effecton the material performance under thermo-mechanical conditions. A new analytical model, proposedfor the evolution of thermo-mechanical ultimate strength in function of temperature, has shown theability to fit with two studied CFRPs and with those tested under similar thermo-mechanical conditionin the literature [etc...]

Steel bridges and structures often need strengthening due to increased live loads, or repair due to corrosion or fatigue cracking. This thesis explores the use of adhesively bonded prestressed carbon fibre reinforced polymers (CFRP) strips in retrofitting intact steel girders, through experimental and analytical investigations. The first part of the research program investigates the behaviour of CFRP-strengthened steel beams comprised of W Structural Sections (W ) with cover plates welded to the tension flange. Six beams, 2000 mm long, were tested under cyclic loads to examine the effects of CFRP strip strengthening on the fatigue life. The CFRP strip prestressing process, type of CFRP strip, level of prestressing, and the location of the CFRP strips were the main parameters examined in this study. Debonding at the end of strip was a significant problem that can be controlled by applying a proper end clamp. The maximum increase in fatigue life observed in the experiments was 125 percent, for a specimen strengthened using high modulus CFRP strips bonded onto the cover plates with the highest level of prestressing. An analytical model and a finite element model were developed for analyzing the strengthened beams. A fracture mechanic analysis was performed to investigate the effects of prestressing on the crack growth rates at the critical weld toe. The models were verified using experimental results, and then used to perform parametric studies. It is shown that the effectiveness of reinforcement is greatest for beams with strips on the cover plate, higher CFRP elastic modulus, and higher prestressing level. In general, this study demonstrates that steel beams can indeed be successfully strengthened or repaired using prestressed CFRP materials.