Infl uence of Transversal Reinforcement on Plastic Rotation Capacity of High-Strength Beams

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Title: Infl uence of Transversal Reinforcement on Plastic Rotation Capacity of High-Strength Beams

Author(s): L.F.A. Bernardo, L.A.P. Oliveira, and D.G. Pinto

Publication: Special Publication

Volume: 253

Issue:

Appears on pages(s): 305-322

Keywords: beam; high-strength concrete; plastic rotation capacity; transversal reinforcement

Date: 7/31/2008

Abstract:
During the last decade, the increase in knowledge about the potential of mixtures containing chemicals and mineral materials leads to the high-performance concretes, including high-strength concrete (HSC). When high strength, durability, and elevated service behavior are necessities high-strength concrete can be an economical solution. In general, it is known that increasing the compressive concrete strength leads to the deformability reduction resulting in a more brittle concrete. On the other hand, the low deformability of HSC doesn’t mean low deformability of the high-strength beams, because their behavior comes from a combined effect of concrete and reinforcement. One of the usual reinforcement elements is the stirrups (transversal reinforcement). By ensuring a suffi cient concrete confi nement in the compressive zone, and by its distribution along the beam length, this reinforcement can improve the plastic rotation capacity on the beam critical sections. This paper presents an experimental study about the infl uence of transversal reinforcement (stirrups) on the fl exure plastic rotation capacity of high-strength beams. Flexural tests on fi ve simply supported beams were carried out using a four-point bending load untill the failure load. The load position was favorable to create a central zone on the beam theoretically of pure fl exure behavior without shear stress influence. The beams failures were governed by the pure fl exure in the middle zone of the beams. In this study, only one solution of stirrups was used, corresponding to a transversal reinforcement ratio of 0.295%. The compressive concrete strength was between 75.0 and 90.6 MPa. The longitudinal reinforcement ratio was between 2.2 to 3.5%. The plastic rotation capacity in fl exure is characterized by the use and definition of a plastic trend parameter. From the results of this study, a well-known positive effect on plastic rotation capacity caused by confi nement with transversal reinforcement was shown. A bilinear law can induce the increment of plastic rotation capacity. This law states that the increment of plastic rotation capacity decreases in a large way as the longitudinal tensile reinforcement ratio increases, and becomes equal to zero from longitudinal reinforcement ratio 3.0 to 3.5%.