Fiber Effects

Transitioning from Shear to Flexural Failure of UHPC Beams by Varying Fiber Content

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Abstract

Ultra High Performance Concrete (UHPC) is a new class of cementitious materials that has been developed recently. Compared to normal reinforced concrete, it has very high compressive strength,durability, and long-term stability. However, the presence of high volumetric content of fibers along with the very small maximum aggregate size set its behavior apart from both regular and fiber reinforced concrete, especially in shear. While many experimental campaigns were directed towards understanding UHPC beams behavior, those which considered shear failure were mostly performed by using beams with non-rectangular cross sections. This limits the applicability of their findings in other cases. In addition, many tests did not track the the effects of including fibers compared to having no fibers at all. In this study, an experimental campaign was performed which included twelve reinforced prismatic UHPC beams in addition to multiple companion specimens for characterizing the material properties. Fiber volumetric contents were 0%, 1% and 2%. Rebar reinforcement was either one or two #3 Grade 60 rebars. Beams were 3 in x4 in (76 mm x 101.5 mm) in cross section and were tested in 3 point bending setup over 18 in (457 mm) span. For each fiber content, splitting tension, compression and notched 3 point bending tests were performed to characterize the material strength. Beam testing showed a transition from diagonal shear failure at 0% fiber content to full rebar rupture at 2% fiber content. At 1% fiber content, very small diagonal shear cracks were observed with 2 rebars but not with 1 rebar, yet, fiber crack bridging prevented the development of critical shear cracks. Results show an interplay between reinforcement ratio and fiber content that is not a simple addition of their individual effects which calls for considering their effects on strength and ductility in a coupled manner.

Keywords: Fiber crack bridging, Reinforce UHPC beams, Diagonal Shear

How to Cite:

Gomaa, S. & Alnaggar, M., (2019) “Transitioning from Shear to Flexural Failure of UHPC Beams by Varying Fiber Content”, International Interactive Symposium on Ultra-High Performance Concrete 2(1). doi: https://doi.org/10.21838/uhpc.9731