The use of near surface mounted (NSM) carbon fibre reinforced polymer (CFRP) reinforcement is a recent and a promising technique for increasing the flexural capacity and the fatigue life of reinforced concrete (RC) flexural members. Prestressing the NSM CFRP rod may be utilized for a further enhancement in the monotonic and fatigue flexural response of RC beams. The aim of this study is to investigate the effectiveness of strengthening RC beams with non-prestressed and prestressed CFRP rods to increase the monotonic and fatigue flexural strength of the beams. Twenty-two RC beams were fabricated. Five beams were not strengthened and acted as control to simulate an existing structural member. The other beams were divided into groups that were strengthened with non-prestressed CFRP rod (0% prestressed), and prestressed CFRP rod (40%, or 60% prestressed of the CFRP rod tensile strength). A beam from each group was tested under monotonic load and acted as a reference beam for those tested under cyclic loads. The test results showed that strengthening the RC beams with NSM CFRP rods increased both the monotonic flexural capacity and the fatigue strength. An increase in the yield and ultimate load of 26% and 50% was achieved, when the beams were strengthened with non-prestressed CFRP rod compared to the control beam. Also, the flexural stiffness of the strengthened beam was slightly enhanced by 16% over that of the control beam. When the beams were strengthened with prestressed CFRP rod (40% and 60%), considerable improvements in the cracking, yield, and ultimate loads were achieved as well as the flexural stiffness (serviceability). In a comparison to the control beam, an increase up to 91% in the yield load and 79% in the ultimate load were obtained, in addition to 52.6% improvement in the flexural stiffness (pre-yielding) when a prestressed NSM CFRP rod was applied. A model to predict the flexural behaviour of the beams (control, non-prestressed, 40%, and 60% prestressed strengthened beams) under monotonic loading using section analysis is presented. It includes a model for flexural crack spacing considering the effect of the CFRP reinforcement, and the transfer length model. For an easy use, the monotonic flexural behaviour model is adopted in a computer language (Visual Basic 6). A model based on strain-life approach is also utilized to predict the fatigue life of the beams at various load ranges for all tested RC beams. For a given load range, by obtaining the nominal maximum and minimum stresses using the monotonic flexural model, the fatigue life of a beam is estimated by accounting for the effect of notch (ribs of the reinforcing bars), and the effect of mean stress. In summary, this study presents the first North American experience by using prestressed NSM CFRP rod for strengthening RC beams. Using such high prestressing levels of 40% and 60% with NSM strengthening method is considered the original contribution for monotonic flexural behaviour. Under cyclic loading, investigating the fatigue behaviour and constructing the fatigue life curves for RC beams strengthened with non-prestressed NSM CFRP rod is a considerable contribution to the very limited information available in the literature. This study also includes the inventiveness of testing the fatigue response of the RC beams strengthened with prestressed NSM CFRP rod. A monotonic flexural model of strengthened RC beams with non-prestressed and prestressed NSM CFRP strengthened beams was developed to predict load versus deflection, strain in the concrete, strain in the tension and compression steel reinforcement, and strain in CFRP rod. The model is verified with the experimental results with excellent agreement. A model using strain-life approach was also developed to predict the fatigue life of non-prestressed and prestressed beams with a reasonable accuracy.

The use of near surface mounted (NSM) carbon fibre reinforced polymer (CFRP) reinforcement is a recent and a promising technique for increasing the flexural capacity and the fatigue life of reinforced concrete (RC) flexural members. Prestressing the NSM CFRP rod may be utilized for a further enhancement in the monotonic and fatigue flexural response of RC beams. The aim of this study is to investigate the effectiveness of strengthening RC beams with non-prestressed and prestressed CFRP rods to increase the monotonic and fatigue flexural strength of the beams. Twenty-two RC beams were fabricated. Five beams were not strengthened and acted as control to simulate an existing structural member. The other beams were divided into groups that were strengthened with non-prestressed CFRP rod (0% prestressed), and prestressed CFRP rod (40%, or 60% prestressed of the CFRP rod tensile strength). A beam from each group was tested under monotonic load and acted as a reference beam for those tested under cyclic loads. The test results showed that strengthening the RC beams with NSM CFRP rods increased both the monotonic flexural capacity and the fatigue strength. An increase in the yield and ultimate load of 26% and 50% was achieved, when the beams were strengthened with non-prestressed CFRP rod compared to the control beam. Also, the flexural stiffness of the strengthened beam was slightly enhanced by 16% over that of the control beam. When the beams were strengthened with prestressed CFRP rod (40% and 60%), considerable improvements in the cracking, yield, and ultimate loads were achieved as well as the flexural stiffness (serviceability). In a comparison to the control beam, an increase up to 91% in the yield load and 79% in the ultimate load were obtained, in addition to 52.6% improvement in the flexural stiffness (pre-yielding) when a prestressed NSM CFRP rod was applied. A model to predict the flexural behaviour of the beams (control, non-prestressed, 40%, and 60% prestressed strengthened beams) under monotonic loading using section analysis is presented. It includes a model for flexural crack spacing considering the effect of the CFRP reinforcement, and the transfer length model. For an easy use, the monotonic flexural behaviour model is adopted in a computer language (Visual Basic 6). A model based on strain-life approach is also utilized to predict the fatigue life of the beams at various load ranges for all tested RC beams. For a given load range, by obtaining the nominal maximum and minimum stresses using the monotonic flexural model, the fatigue life of a beam is estimated by accounting for the effect of notch (ribs of the reinforcing bars), and the effect of mean stress. In summary, this study presents the first North American experience by using prestressed NSM CFRP rod for strengthening RC beams. Using such high prestressing levels of 40% and 60% with NSM strengthening method is considered the original contribution for monotonic flexural behaviour. Under cyclic loading, investigating the fatigue behaviour and constructing the fatigue life curves for RC beams strengthened with non-prestressed NSM CFRP rod is a considerable contribution to the very limited information available in the literature. This study also includes the inventiveness of testing the fatigue response of the RC beams strengthened with prestressed NSM CFRP rod. A monotonic flexural model of strengthened RC beams with non-prestressed and prestressed NSM CFRP strengthened beams was developed to predict load versus deflection, strain in the concrete, strain in the tension and compression steel reinforcement, and strain in CFRP rod. The model is verified with the experimental results with excellent agreement. A model using strain-life approach was also developed to predict the fatigue life of non-prestressed and prestressed beams with a reasonable accuracy.

The Near Surface Mounted (NSM) strengthening is an emerging retrofitting technique, which involves bonding Fibre Reinforced Polymer (FRP) reinforcement into grooves cut along the surface of a concrete member to be strengthened. This technique offers many advantages over external bonding of FRP reinforcement, for example, an increased bond capacity, protection from external damage and the possibility of anchoring into adjacent concrete members. To date, significant research has been conducted into the NSM FRP strengthening technique. However, there are still some areas which need further research in order to fully characterise bond and anchorage of NSM FRP bars. Lack of experimental data, design tools and analytical models addressing these areas create obstacles for the efficient use of these advanced polymer materials. The particular objectives of the research are; to investigate bond behaviour between NSM FRP bars and concrete, to understand the critical failure modes involved and their mechanics, and to develop a rational analytical model to predict bond strength and anchorage length requirements for NSM FRP bars. Several significant variables affecting bond, such as bond length, size, shape and type of bar, resin type, groove dimensions and concrete strength, have been considered. In particular, attention has been focussed on the effect of bar shape on bond behaviour. A comprehensive set of laboratory testing and their results, including the effect of the investigated parameters are presented. Various modes of anchorage failure of NSM FRP bars are identified and the underlying mechanics are investigated. Analytical models are developed to predict bond capacity and anchorage length requirements of NSM FRP bars, and are verified with experimental results.

In recent years, a modified method to strengthen reinforced concrete (RC) structures has emerged involving application of fibre reinforced polymers (FRPs) in the ‘near surface’ of a member. The near surface mounted (NSM) method entails placing a pre-cured FRP bar, rod, strip, or plate, along with an adhesive into a pre-cut groove or slot in the cover of a member. Advantages of the NSM technique over externally bonded (EB) systems include minimal surface preparation and installation time, the ability to anchor the FRP into an adjacent member, superior protection from mechanical and environmental damage, and superior bond properties. Although a number of laboratory studies, field applications, and experimental field projects have employed the NSM FRP strengthening technique, none of these have been performed in a climate where cold environments and freeze-thaw cycling could cause adverse effects. This thesis presents the results of an experimental program to investigate the flexural and bond performance and freeze-thaw durability of a specific NSM carbon/vinylester FRP tape strengthening system through a series of tests on strengthened slab strips and a series of pull-out bond tests. The effects of adhesive type (cementitious or epoxy) and exposure condition (room temperature, freeze-thaw, sustained load, or freeze-thaw under sustained load) are examined. The results indicate no discernable negative impacts on the performance of the grout strengthened members after exposure to freeze-thaw cycles and/or sustained load. The slab strips strengthened with epoxy adhesive displayed minor changes in ultimate load (less than three percent) after exposure to freeze-thaw cycles or a period of sustained load, while the combined effect of freeze-thaw cycles and sustained load produced an average reduction in ultimate load of eight percent. The epoxy adhesive strengthened pull-out bond tests experienced a 27% average drop in ultimate load after 150 freeze-thaw cycles. These results suggest that additional research on the combined effects of sustained load and freeze-thaw cycling are warranted, particularly for NSM strengthening applications using epoxy adhesives. / Thesis (Master, Civil Engineering) -- Queen's University, 2010-04-30 18:11:56.424

O uso de Carbon Fiber Reinforced Polymer (CFRP) como reforço em estruturas de concreto armado tem evoluído com o avanço das técnicas e com a melhora das fibras, principalmente com um novo método: o Near Surface Mounted (NSM), em que os laminados de fibra são inseridos no cobrimento do concreto. Uma análise da eficiência dos sistemas de reforço ao cisalhamento em vigas de concreto armado foi realizada por meio de ensaios experimentais. As vigas foram reforçadas nas configurações íntegra e com carregamento prévio de 40% e 70% da força máxima. O programa experimental compreende ensaios de flexão em prismas e vigas de concreto armado além de ensaios não destrutivos de análise de vibrações para a determinação das frequências naturais e dos modos de vibração. A análise modal foi realizada com uso de um método de identificação modal estocástica, em que na sua formulação não é usada força de excitação. Nestas, foram analisadas as variações nas frequências naturais e dos modos de vibração, utilizando MAC, COMAC, DCM e ID. Como resultados, todas as vigas com sistemas de reforço obtiveram acréscimos na capacidade de carga, alterando suas formas de ruptura de cisalhamento para destacamento da camada de concreto adjacente aos laminados de CFRP e para ruptura por esmagamento do concreto à flexão, independente da ocorrência de carregamento prévio. Na análise modal foi possível identificar a presença e local do dano nas vigas na maioria dos métodos utilizados, mas a identificação do sistema de reforço não foi significativa. / The use of Carbon Fiber Reinforced Polymer (CFRP) in concrete structures has enhanced with the advancement of techniques and the improvement of fiber, especially with the usage of the new method: the Near Surface Mounted (NSM) when the fiber laminates are inserted to cover thickness the concrete. An analysis of the efficiency of these shear reinforcements in reinforced concrete beams was performed by destructive and non-destructive experimental tests. The beams were reinforced intact and preloading of 40% and 70% of maximum load. The experimental program includes flexural tests on reinforced concrete beams as well as non-destructive testing to determine the natural frequencies and vibration modes. The modal analysis was done use of method stochastic modal identification, which in its formulation is not used excitation force. The variations were analyzed in the natural frequencies and vibration modes, using MAC, COMAC, DCM and ID. In the results are obtained increase in load capacity in all beams with reinforcement systems, regardless of the occurrence of preloading, changed the form of shear break for rupture due detachment off cover concrete adjacent to the laminate and crushing of concrete in flexion. In modal analysis, it was possible to identify the presence and local damage in the beams on most of methods used, but the identification of reinforcements systems was not significant.

O uso de Carbon Fiber Reinforced Polymer (CFRP) como reforço em estruturas de concreto armado tem evoluído com o avanço das técnicas e com a melhora das fibras, principalmente com um novo método: o Near Surface Mounted (NSM), em que os laminados de fibra são inseridos no cobrimento do concreto. Uma análise da eficiência dos sistemas de reforço ao cisalhamento em vigas de concreto armado foi realizada por meio de ensaios experimentais. As vigas foram reforçadas nas configurações íntegra e com carregamento prévio de 40% e 70% da força máxima. O programa experimental compreende ensaios de flexão em prismas e vigas de concreto armado além de ensaios não destrutivos de análise de vibrações para a determinação das frequências naturais e dos modos de vibração. A análise modal foi realizada com uso de um método de identificação modal estocástica, em que na sua formulação não é usada força de excitação. Nestas, foram analisadas as variações nas frequências naturais e dos modos de vibração, utilizando MAC, COMAC, DCM e ID. Como resultados, todas as vigas com sistemas de reforço obtiveram acréscimos na capacidade de carga, alterando suas formas de ruptura de cisalhamento para destacamento da camada de concreto adjacente aos laminados de CFRP e para ruptura por esmagamento do concreto à flexão, independente da ocorrência de carregamento prévio. Na análise modal foi possível identificar a presença e local do dano nas vigas na maioria dos métodos utilizados, mas a identificação do sistema de reforço não foi significativa. / The use of Carbon Fiber Reinforced Polymer (CFRP) in concrete structures has enhanced with the advancement of techniques and the improvement of fiber, especially with the usage of the new method: the Near Surface Mounted (NSM) when the fiber laminates are inserted to cover thickness the concrete. An analysis of the efficiency of these shear reinforcements in reinforced concrete beams was performed by destructive and non-destructive experimental tests. The beams were reinforced intact and preloading of 40% and 70% of maximum load. The experimental program includes flexural tests on reinforced concrete beams as well as non-destructive testing to determine the natural frequencies and vibration modes. The modal analysis was done use of method stochastic modal identification, which in its formulation is not used excitation force. The variations were analyzed in the natural frequencies and vibration modes, using MAC, COMAC, DCM and ID. In the results are obtained increase in load capacity in all beams with reinforcement systems, regardless of the occurrence of preloading, changed the form of shear break for rupture due detachment off cover concrete adjacent to the laminate and crushing of concrete in flexion. In modal analysis, it was possible to identify the presence and local damage in the beams on most of methods used, but the identification of reinforcements systems was not significant.

Master of Science / Department of Civil Engineering / Hayder A. Rasheed / Nowadays, using the technology of FRP strengthening has become acknowledged by engineers and has reached a full acceptance. However, researchers are always looking for improvement in performance. In this study, external bonding of GFRP and near surface mounting of regular steel bars are combined to improve the behavior, delay the failure and enhance the economy of the strengthening. E-Glass FRP is selected due to its inexpensive cost and non-conductive properties to shield the NSM steel bars from corrosion. On the other hand, the use of NSM bars gives redundancy against vandalism and environmental deterioration of GFRP. An experimental program was conducted in which four full scale T beams were designed and built. All four specimens were fabricated with Grade 70 steel reinforcement and 8000 psi concrete. Only one beam was loaded beyond first cracking then exposed to highly concentrated deicing salt water to accelerate the corrosion process. All beams were tested by monotonic loading until failure. The load rate was 1 kips/min. The first specimen is tested as a control beam failing at about 15 kips. The second specimen is strengthened using two #5 steel NSM bars and 1 layer of GFRP, both extending to the support. This beam failed at 38.4 kips by GFRP debonding. The third specimen is strengthened with the same system used for the second beam. However, the NSM steel bars were cut short covering only 30% of the shear-span while the GFRP was extended to the support. This beam failed at 25.9 kips by GFRP debonding and NSM delamination due to the lack of sufficient development of the NSM steel bars and the shear stress concentration at the steel bar cut off point. Nevertheless, the fourth beam is strengthened with the same system used for the third beam. The fourth specimen was exposed to severe attack of deicing salt by immersing it in concentrated deicing salt solution for three continuous months. In order to accelerate the corrosion process, the beam was loaded beyond its cracking load before the corrosion procedure. After the completion of the three months, the beam was tested monotonically to failure. It failed at 23.2 kips indicating that some deterioration might have taken place. The failure mode was by GFRP debonding and NSM delamination like the case of Beam 3.However, it was observed after failure that the NSM bars were very well protected by the surrounding epoxy.

Master of Science / Department of Civil Engineering / Hayder Rasheed / The technology of FRP strengthening has matured to a great extent. However, there is always room for performance improvements. In this study, external bonding of GFRP and near surface mounting (NSM) of regular steel bars is combined to improve the behavior, delay the failure, and enhance the economy of the strengthening. E-Glass FRP is selected due to its inexpensive cost and non-conductive properties to shield the NSM steel bars from corrosion. On the other hand, the use of NSM bars gives redundancy against vandalism and environmental deterioration of the GFRP. An experimental program is conducted in which four rectangular cross-section beams are designed, built, and tested in four-point bending. The first beam is tested as a control beam failing at about 12.24 kips. The second beam is strengthened using two #5 steel NSM bars and 1 layer of GFRP, both extending to the support. This beam failed at 31.6 kips. The third beam is strengthened with the same system used for the second beam. However, the NSM steel bars were cut short covering 26% of the shear-span only while the GFRP was extended to the support. This beam failed at 30.7 kips due to reaching the full flexural capacity of the section at the NSM bars cut off point and the shear stress concentration at the steel bar cut off point. The fourth beam was strengthened with same system as the third beam but then submerged in a highly concentrated saline solution for six months and then tested. This beam failed at a maximum applied load of 29.8 kips, which shows that the GFRP sheet provided good corrosion resistance from the saline solution.

Der vorliegende Band vereinigt Beiträge zu zentralen Bereichen des Public Managements. Dabei werden Fragestellungen und Herausforderungen für Wissenschaftler und Praktiker aufgezeigt, Entwicklungen im öffentlichen Sektor empirisch nachgezeichnet und Problem- sowie Erfolgsfelder der Verwaltungsmodernisierung beleuchtet. Im Mittelpunkt steht dabei die Frage, wie ein modernes Management von öffentlichen Dienstleistungen aussieht und aussehen kann. Die Autoren/innen nehmen die Entwicklungen der letzten Jahre im öffentlichen Sektor zum Anlass, ihre eigenen Forschungsarbeiten im Bereich eGovernment, Wissensmanagement, Nonprofit und Hochschulmanagement, Finanzmanagement sowie dem Management öffentlicher Dienstleistungen zu präsentieren. Jeder dieser Beiträge ist das Resultat langjähriger und empirischer Beschäftigung mit dem Phänomenbereich des Public Management.

The 21st century has brought with it myriad innovative construction techniques and structural systems; however reinforced masonry systems have gone virtually unchanged over the last decades. The innovative Surface-Reinforced Concrete Masonry Unit (SRCMU) system makes use of Near-Surface Mounted reinforcement to form a structurally efficient system. Preliminary analysis of this system shows the potential for improved moment resistance when compared to conventional masonry construction. There is also evidence for a potential decrease in embodied and operating energy for finished structures using the SRCMU system. Experimental work indicates similar axial compressive behaviour of the SRCMU when compared to conventional concrete masonry systems. Pull-out and flexural tests performed on reinforced SRCMU specimens indicate it is possible to achieve a good bond between the SRCMU system and the reinforcing bars; up to 60kN of pull out force was developed in 590mm of bonded length, and flexural specimens developed up to 20kNm/m of moment-resistance. / October 2015