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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.
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.
"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.
Twelve specimens were tested to determine the local bond stress-slip characteristics of a No. 6 rebar embedded in a 3-inch diameter concrete cylinder. Radial confining stress around the concrete specimen and radial deformation were assumed to be fundamental variables, together with bond stress and slip, needed to properly describe the interface behavior. Configuration independent bond stress-slip, relationships for a short five-lug embedded length were obtained for various degrees of confining pressure. Maximum bond stresses could be increased almost threefold by increasing the confining stress from 500 to 4500 psi at the bar level. Two types of No. 6 bars with different deformations were investigated. In many reinforced concrete structures, the mode of failure is tensile cracking of the concrete. Where it is important to predict failure or severe damage, proper representation of bond is crucial. Principal gain from inclusion of actual bond-slip properties in the interface between steel rebar and concrete is a realistic prediction of cracking. The spacing, width, and extent of cracks in reinforced concrete are dependent on the assumed bond-slip characteristics. Critical Navy reinforced concrete structures, such as missile test cells and graving drydocks, are designed to withstand large deformations under severe blast and strong-motion earthquake loads. The development of design criteria for these structures requires evaluation of their response where severe deterioration of steel concrete interfaces takes place.
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.