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This study summarizes experimental results of the local bond stress-slip relationship of reinforcing bars embedded in fiber reinforced concrete (FRC). More than 70 bond specimens were tested and the effect of several parameters on the local bond stress-slip behavior was investigated. These include, size of reinforcing bar (#6 and #8); type of fibers (hooked steel, polypropylene); volume fraction of fibers Vf (between 0.9% and 1.4ft for the steel fibers, 1.5% for the polypropylene fibers); type of specimen (pullout, beam); and confinement (confined, unconfined). Whereas the primary emphasis was on the monotonic local bond stres3-slip response, some specimens were tested under large slip reversals to study the effect of fibers on the cyclic bond stress-slip behavior. The results showed that the addition of fibers to concrete matrixes improves the bond characteristics of ordinary reinforcing bar3. For specimens in which bond failure was by pull-out, adding steel fibers in 2% by volume fraction increased the maximum local bond resistance by about 15%. However, the intrinsic shape of the local bond stre33-slip behavior does not change in comparison with conventional concrete. Furthermore, the addition of fibers to concrete matrixes does not seem to influence the stiffness degradation characteristics of the local bond stress-slip response under cyclic 1oading compared to conventiona1 confined concrete reported in technical literature.
This study summarizes experimental results of the local bond stress-slip response of reinforcing bars embedded in fiber reinforced concrete (FRC) under splitting type failure. Pullout specimens were tested to study the effect of several parameters, namely, type, volume fraction, and aspect ratio of fibers, concrete cover to reinforcing bars (or splitting area surrounding the reinforcing bar), and size of reinforcing bar. The experimental results showed that the major contribution of fibers is in the post-splitting range. As compared to plain concrete, the bond behavior of fiber reinforced concrete is more ductile inasmuch as the post-splitting bond stresses are increased. This increase is function of the fiber reinforcing index and of the fiber bond characteristics. The results from the current study were combined with other results reported in technical literature and used to develop a model to describe the bond stress-slip relationship of reinforcing bars embedded in plain and FRC under splitting type failure. The model accounts for all of the important parameters that tend to influence the bond characteristics of reinforcing bar3 as observed in the experiment. It should be mentioned that this study consists the second pact of a two-phase experimental program dealing with the local bond stress-slip characteristics of reinforcing bars embedded in fiber reinforced concrete. While this current phase concentrates on the splitting type of failure, the first part of the study (Ref. 4) emphasized pullout failure.
"In 1993, the CEB Commission 2 Material and Behavior Modelling established the Task Group 2.5 Bond Models. It's terms of reference were ... to write a state-of-art report concerning bond of reinforcement in concrete and later recommend how the knowledge could be applied in practice (Model Code like text proposal)... {This work} covers the first part ... the state-of-art report."--Pref.
Ultra-High-Performance Steel Fiber Reinforced Concrete (UHP-SFRC) is an emerging concrete considered as an optimal, durable material that can substitute conventional concrete owing to its distinct fresh and hardened properties. Thus, it is essential to understand the mechanism of stress transfer between this concrete and conventional reinforcement that permits the composite action of both materials. A four-point bending test program (FPBT) was arranged and conducted on 19 beams designed for the bond development to occur in the constant moment region along a short embedment length in order to achieve a uniform distribution of bond stresses, enabling measurement of bond strength through reverse engineering of beam strength and deformation. Additional material testing was conducted on prisms under 4-point loading in order to extract the mechanical properties for all material mixes considered. The bond-specimens failed either by pullout or by cone formation with minimal deterioration of the concrete cover, illustrating the high confinement provided by the novel concrete surrounding the bar in tension. The bond strength was determined to be directly proportional to the tensile strength capacity of the design mix, where for the strongest material the bond strength was approximately 30 MPa. Moreover, the test results indicated a very ductile flexural beam response accompanied by significant mid-span deflection reaching 27 mm and substantial bar-slip values attaining 19 mm. Different UHP-SFRC mixes, concrete covers, and embedment lengths were considered. A numerical model was developed to simulate the FPBT using a nonlinear finite element analysis platform, VecTor2, with the ability to model this novel concrete. This high bond strength provided by the concrete cover enables a significant reduction in the design development length as compared to what is used today for conventional concrete.
monitored and the modes of bond failure were determined.
The International Federation for Structural Concrete (fib) is a pre-normative organization. 'Pre-normative' implies pioneering work in codification. This work has now been realized with the fib Model Code 2010. The objectives of the fib Model Code 2010 are to serve as a basis for future codes for concrete structures, and present new developments with regard to concrete structures, structural materials and new ideas in order to achieve optimum behaviour. The fib Model Code 2010 is now the most comprehensive code on concrete structures, including their complete life cycle: conceptual design, dimensioning, construction, conservation and dismantlement. It is expected to become an important document for both national and international code committees, practitioners and researchers. The fib Model Code 2010 was produced during the last ten years through an exceptional effort by Joost Walraven (Convener; Delft University of Technology, The Netherlands), Agnieszka Bigaj-van Vliet (Technical Secretary; TNO Built Environment and Geosciences, The Netherlands) as well as experts out of 44 countries from five continents.
Corrosion-resistant, electromagnetic transparent and lightweight fiber-reinforced polymers (FRPs) are accepted as valid alternatives to steel in concrete reinforcement. Reinforced Concrete with FRP Bars: Mechanics and Design, a technical guide based on the authors more than 30 years of collective experience, provides principles, algorithms, and pr