14- 16 Nevertheless, a large scatter in experimental data has been observed and a comprehensive theory that is able to predict thoroughly the plastic rotation capacity developed by RC members has not been still provided. 13 In this framework, a decrease in the plastic rotation capacity together with an increase in specimen depth and/or reinforcement percentage has been recognized. More recently, an extended version of the Bridged Crack Model 11, 12 was applied to investigate the scale-transitional role of the shearing failure in RC beams.Įxtensive experimental tests have demonstrated that the parameters influencing the ductility of RC elements may be summarized into three main groups: construction material structural geometry static system. In the study of RC fracturing process, the Bridged Crack Model 5, 7- 10 proved to be able to capture the loading drops due to cracking, particularly in the case of lightly reinforced or high-performance concrete elements. Structural behavior of a reinforced concrete beam subjected to bending
In this way, a rational and quantitative definition of over-reinforcement is provided as a steel percentage depending on the beam depth. In particular, the maximum steel percentage results to be inversely proportional to h 0.25, h being the beam depth. Thus, a scale-dependent maximum reinforcement percentage beyond which concrete crushing occurs prior to steel yielding is demonstrated to exist.
In this context, the application of the Cohesive/Overlapping Crack Model highlights that the ductility, which is represented by the plastic rotation capacity of a reinforced concrete element subjected to bending, decreases as reinforcement percentage and/or beam depth increase. Moreover, this model is able to investigate local mechanical instabilities occurring in the structural behavior of reinforced concrete structures: tensile snap-back and snap-through, which are due to concrete cracking or steel fracture, and the compressive snap-back occurring at the end of the plastic plateau, which is generated by the unstable growth of the crushing zone. Within this Nonlinear Fracture Mechanics model, the tensile and compressive ultimate behaviors of the concrete matrix are modeled through two different process zones that advance independently one of another. The Cohesive/Overlapping Crack Model is able to describe the transition between cracking and crushing failures occurring in reinforced concrete beams by increasing beam depth and/or steel percentage.
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