Concrete is a very weak and brittle material in tension. It has been shown in previous researches that the addition of steel fibers to a concrete matrix can improve this behavior. The ability of fibers to control and redistribute stresses after cracking results in a number of improvements in the structural behaviour of concrete. A review of existing literature shows that the addition of steel fibers enhances concrete’s tensile resistance, crack control properties, ductility and damage tolerance. In beams, fibers can transform brittle shear response into a flexural response and promote ductility, thereby allowing for a full or partial replacement of traditional shear reinforcement. The enhanced shear capacity, ductility and damage tolerance of Steel Fiber Reinforced Concrete (SFRC) can also potentially be used to relax seismic detailing requirements in frames by partially replacing the required transverse reinforcement in the plastic hinge regions of RC beams. One of the drawbacks associated with SFRC is that the addition of steel fibers to a traditional concrete mix at high fiber contents can result in workability problems. The combined use of Self-Consolidating Concrete (SCC) and fibers can solve this problem and facilitate placement for a wider range of structural applications. Although several studies have been conducted on the behaviour of SFRC beams subjected to monotonic loading, there is limited research on the behaviour of SFRC beams under cyclic or reverse-cyclic loading. This thesis presents the results of an experimental and analytical study conducted on nine SFRC beam specimens tested under load reversals. The main objective of this research program was to investigate the effect of fibers on structural behaviour and to examine the ability of steel fibers to replace transverse reinforcement. The experimental and analytical results show that use of fibers results in several improvements in behaviour, including enhanced damage tolerance and post-peak ductility. The results also show that steel fibers can potentially be used to allow for a reduction of transverse reinforcement in beams, however further research is required.

Current analysis procedures for new reinforced concrete structures are typically based on linear-elastic principles. However, under certain conditions, it may be necessary to analyze a structure to more accurately predict its structural behaviour. Such an analysis can be performed using nonlinear analysis procedures which typically require specialized software. This type of software is limited in number and most available programs do not adequately capture shear-related influences, potentially severely overestimating strength and ductility in shear-critical structures. The purpose of this study is to develop and verify an analytical procedure for the nonlinear analysis of frame structures with the aim of capturing shear-related mechanisms as well as flexural and axial effects. A previously developed analysis program, VecTor5, is further developed for this purpose. Originally formulated in the early 1980s at the University of Toronto, VecTor5 is based on the Modified Compression Field Theory (MCFT) and is capable of performing nonlinear frame analyses under temperature and monotonic loading conditions. Although providing generally satisfactory simulations, there are a number of deficiencies present in its computational algorithms. This study consists of three major parts: improvement of the original analysis procedure for monotonic loading conditions, expansion of the procedure for general loading conditions including the special cases of cyclic and reversed-cyclic loading, and further development of the procedure for dynamic loading conditions including time-varying base accelerations, impulse, impact and blast forces, initial mass velocities, and constant mass accelerations. Each part is supported by verification studies performed on a large number and variety of previously tested structures available in the literature. In addition, considerations in nonlinear modelling are discussed with the aim of providing guidelines for general modelling applications. Analyses of 63 previously tested structures, half of which are shear-critical, demonstrate that the developed analytical procedure is highly successful in simulating the experimental responses in terms of load-deflection response, reinforcement strains, crack widths, failure mode, failure displacement, total energy dissipation, displacement ductility ratio, and post-peak vibrational characteristics.

Minimum impact construction for bridge building is a growing demand in modern urban environments. Pre-cast segmental construction is one solution that offers low-impact, economical, and aesthetically pleasing bridges. The standardization of pre-cast concrete sections and segments has facilitated an improved level of economy in pre-cast construction. Through the development of high performance materials such as high strength fibre-reinforced concrete (FRC), further economy in pre-cast segmental construction may be realized. The design of pre-cast bridges using high-strength FRC and external unbonded tendons for cantilever construction may provide an economical, low-impact alternative to overpass bridge design. This thesis investigates the feasibility and possible savings that can be realized for a single cell box girder bridge with thin concrete sections post-tensioned exclusively with external unbonded tendons in the longitudinal direction. A cantilever-constructed single cell box girder with a curtailed arrangement of external unbonded tendons is examined.

A combined experimental and analytical program was conducted to investigate the effects of Alkali-Silica Reaction (ASR) and Delayed Ettringite Formation (DEF) on D-regions in reinforced concrete (RC) bridge bents. Four large-scale RC specimens, which represent cantilever and straddle bents in Texas bridges in each specimen, were constructed. The first specimen represented the unexposed control specimen, while the other three were conditioned in the field with supplemental watering to promote ASR/DEF and served as the exposed specimens. The control and two exposed specimens with various levels of ASR/DEF, after eight months and two years of field conditioning, were load tested to failure. The last specimen remains in field with additional exposure to promote ASR/DEF and will be load tested in future studies. The width and length of preload-induced cracks and developing cracks that initiated in the exposed specimens and grew over time, indicating concrete expansion due to ASR/DEF mechanisms, were measured. Petrographic analysis results of concrete cores extracted from the exposed specimens after their load testing confirmed the formation of ASR gel and minimum accumulation of ettringite. The structural testing results showed that the failure mechanism in all three tested specimens was due to a brittle shear failure in the beam-column joint. However, slightly greater stiffness, strength, and ductility were observed in the exposed specimens as a result of the activation of the reinforcing steel in the specimens due to the expansion of the concrete primarily from ASR, which effectively prestressed and confined the core concrete. Sectional analysis and Strut-and-Tie Modeling (STM) of the experimental specimens were applied. Three-dimensional nonlinear Finite Element Analyses (FEA) were also conducted to numerically simulate the overall structural performance, internal response, and out-of-plane behavior of the experimental specimens. The effects of varying constitutive relations of the concrete in tension on models of the specimens were compared with the measured experimental response. A method to mimic ASR/DEF effects on exposed specimens was proposed and incorporated into the FEA approach. As a result, forces that prestress and confine the core concrete were effectively applied through the reinforcing steel prior to subsequent structural loading. The three-dimensional FEA approach was able to simulate the out-of-plane behavior of the beam-column joint and the proposed method yielded comparable results with the measured overall and internal behavior of specimens.

When the huge building stock in Turkey is considered, it is practically impossible to carry out detailed structural analyses for all of the buildings. In order to cope with the seismic safety evaluation of a large number of existing buildings, it is necessary to use simplified techniques, which can predict the seismic vulnerability of the existing buildings in a relatively short time. The comprehensive structural data compiled for the 48 different reinforced concrete buildings contain full information on their structural characteristics before and after retrofitting and are used in this study. The first basic goal of the study is to develop a procedure through which the building stock under consideration can be classified as &ldquo / safe&rdquo / or &ldquo / unsafe&rdquo / according to the current Turkish Seismic Code. The classification procedure is based on discriminant analysis. The cross-sectional area of the load-bearing members of a building and its preliminary assessment score are selected as the discriminator variables. The second and ultimate basic goal of the study is to propose a method through which the minimum retrofitting cost for satisfying the provisions of the Turkish Seismic Code can be estimated. A quick and uncostly assessment of retrofitting cost estimates based on the procedure described in this thesis will provide a useful input for decisions concerning whether a seismically &ldquo / unsafe&rdquo / building should be rebuilt or retrofitted. Such a situation will save time, labor and money, when it is used for the evaluation of building stocks involving large number of buildings and also in urban transformation operations.

Minimum impact construction for bridge building is a growing demand in modern urban environments. Pre-cast segmental construction is one solution that offers low-impact, economical, and aesthetically pleasing bridges. The standardization of pre-cast concrete sections and segments has facilitated an improved level of economy in pre-cast construction. Through the development of high performance materials such as high strength fibre-reinforced concrete (FRC), further economy in pre-cast segmental construction may be realized. The design of pre-cast bridges using high-strength FRC and external unbonded tendons for cantilever construction may provide an economical, low-impact alternative to overpass bridge design. This thesis investigates the feasibility and possible savings that can be realized for a single cell box girder bridge with thin concrete sections post-tensioned exclusively with external unbonded tendons in the longitudinal direction. A cantilever-constructed single cell box girder with a curtailed arrangement of external unbonded tendons is examined.

Current analysis procedures for new reinforced concrete structures are typically based on linear-elastic principles. However, under certain conditions, it may be necessary to analyze a structure to more accurately predict its structural behaviour. Such an analysis can be performed using nonlinear analysis procedures which typically require specialized software. This type of software is limited in number and most available programs do not adequately capture shear-related influences, potentially severely overestimating strength and ductility in shear-critical structures. The purpose of this study is to develop and verify an analytical procedure for the nonlinear analysis of frame structures with the aim of capturing shear-related mechanisms as well as flexural and axial effects. A previously developed analysis program, VecTor5, is further developed for this purpose. Originally formulated in the early 1980s at the University of Toronto, VecTor5 is based on the Modified Compression Field Theory (MCFT) and is capable of performing nonlinear frame analyses under temperature and monotonic loading conditions. Although providing generally satisfactory simulations, there are a number of deficiencies present in its computational algorithms. This study consists of three major parts: improvement of the original analysis procedure for monotonic loading conditions, expansion of the procedure for general loading conditions including the special cases of cyclic and reversed-cyclic loading, and further development of the procedure for dynamic loading conditions including time-varying base accelerations, impulse, impact and blast forces, initial mass velocities, and constant mass accelerations. Each part is supported by verification studies performed on a large number and variety of previously tested structures available in the literature. In addition, considerations in nonlinear modelling are discussed with the aim of providing guidelines for general modelling applications. Analyses of 63 previously tested structures, half of which are shear-critical, demonstrate that the developed analytical procedure is highly successful in simulating the experimental responses in terms of load-deflection response, reinforcement strains, crack widths, failure mode, failure displacement, total energy dissipation, displacement ductility ratio, and post-peak vibrational characteristics.

The continual deterioration of infrastructure has motivated researchers to look for new ways of repairing and monitoring existing structures. A particularly challenging problem confronting engineers in the revival of the infrastructure is the rehabilitation of reinforced concrete (RC) structures. Traditionally, the repair of RC beams has been achieved by bonding steel plates to the structure. Although this technique has proven to be reasonably effective, it has several distinct disadvantages such as susceptibility of the steel plates to corrode and the excessive weight of steel plates when used in long-span beams. Recently, there has been an emergence of structural engineering applications employing fibre reinforced polymer (FRP) composites as an alternative to steel plates. FRP composites are well known for their high strength- and stiffness-to-weight ratios, corrosion resistance, durability, and ease of application. Numerous studies have been conducted to prove the efficiency of bonding FRP on structural elements. In spite of this, industrial practitioners are still concerned about premature debonding of the plates before reaching the desired strength or ductility. Premature debonding initiates from the ends of the plate or from intermediate cracks (IC) in the concrete. While end initiated debonding and peeling mechanisms have been researched extensively, researchers have unanimously recognized the lack of data for the FRP-RC structural members subjected to IC debonding. The scarcity of data compiled exemplifies the need to develop more refined numerical analysis tools to reduce the high cost and significant time required to conduct full-scale physical testing. In this study, the results of a comprehensive numerical investigation are presented to assess the failure mechanisms caused by different types of flexural and shear crack distributions in RC beams strengthened with FRP composites. The model is based on damage mechanics modeling of concrete and a bilinear bond-slip relationship with softening behaviour to represent the FRP-concrete interfacial properties. A discrete crack approach was adopted to simulate crack propagation through a nonlinear fracture mechanics based finite element analysis to investigate the effects of crack spacing and interfacial parameters such as stiffness, local bond strength, and fracture energy on the initiation and propagation of the debonding and structural performance. Results from the analysis reveal that the debonding behaviour and load-carrying capacity are significantly influenced by interfacial fracture energy and crack spacing. The debonding propagation is mainly governed by mode II fracture mechanisms. The results provide an insight on the long-term behaviour of a repair system that is gaining widespread use and will be of interest to researchers and design engineers looking to successfully apply FRP products in civil engineering applications.

The continual deterioration of infrastructure has motivated researchers to look for new ways of repairing and monitoring existing structures. A particularly challenging problem confronting engineers in the revival of the infrastructure is the rehabilitation of reinforced concrete (RC) structures. Traditionally, the repair of RC beams has been achieved by bonding steel plates to the structure. Although this technique has proven to be reasonably effective, it has several distinct disadvantages such as susceptibility of the steel plates to corrode and the excessive weight of steel plates when used in long-span beams. Recently, there has been an emergence of structural engineering applications employing fibre reinforced polymer (FRP) composites as an alternative to steel plates. FRP composites are well known for their high strength- and stiffness-to-weight ratios, corrosion resistance, durability, and ease of application. Numerous studies have been conducted to prove the efficiency of bonding FRP on structural elements. In spite of this, industrial practitioners are still concerned about premature debonding of the plates before reaching the desired strength or ductility. Premature debonding initiates from the ends of the plate or from intermediate cracks (IC) in the concrete. While end initiated debonding and peeling mechanisms have been researched extensively, researchers have unanimously recognized the lack of data for the FRP-RC structural members subjected to IC debonding. The scarcity of data compiled exemplifies the need to develop more refined numerical analysis tools to reduce the high cost and significant time required to conduct full-scale physical testing. In this study, the results of a comprehensive numerical investigation are presented to assess the failure mechanisms caused by different types of flexural and shear crack distributions in RC beams strengthened with FRP composites. The model is based on damage mechanics modeling of concrete and a bilinear bond-slip relationship with softening behaviour to represent the FRP-concrete interfacial properties. A discrete crack approach was adopted to simulate crack propagation through a nonlinear fracture mechanics based finite element analysis to investigate the effects of crack spacing and interfacial parameters such as stiffness, local bond strength, and fracture energy on the initiation and propagation of the debonding and structural performance. Results from the analysis reveal that the debonding behaviour and load-carrying capacity are significantly influenced by interfacial fracture energy and crack spacing. The debonding propagation is mainly governed by mode II fracture mechanisms. The results provide an insight on the long-term behaviour of a repair system that is gaining widespread use and will be of interest to researchers and design engineers looking to successfully apply FRP products in civil engineering applications.

Nach zwölf Jahren endete am 30.6.2011 die Förderung des Sonderforschungsbereiches 528 durch die Deutsche Forschungsgemeinschaft (DFG). Der Abschlussbericht fasst die zentralen Ergebnisse des Sonderforschungsbereiches auf dem Gebiet der Verstärkung und Instandsetzung mit textilbewehrtem Beton über die gesamte Laufzeit des SFBs zusammen. Dazu berichten die einzelnen Teilprojekte über ihre aktuellen Erkenntnisse aus der letzten Förderperiode.