Abstract
Torsional behavior and analysis of steel fiber reinforced concrete (SFRC) beams is investigated in this paper. The purpose of this study is twofold; to examine the torsion strength models for SFRC beams available in the literature and to address properly verified design formulations for SFRC beams under torsion. A total of 210 SFRC beams tested under torsion from 16 different experimental investigations around the world are compiled. The few strength models available from the literature are adapted herein and used to calculate the torsional strength of the beams. The predicted strength is compared with the experimental values measured by the performed torsional tests and these comparisons showed a room for improvement. First, a proposed model is based on optimizing the constants of the existing formulations using multi-linear regression. Further, a second model is proposed, which is based on modifying the American Concrete Institute (ACI) design code for reinforced concrete (RC) members to include the effect of steel fibers on the torsional capacity of SFRC beams. Applications of the proposed models showed better compliance and consistency with the experimental results compared to the available design models providing safe and verified predictions. Further, the second model implements the ACI code for RC using a simple and easy-to-apply formulation.
Highlights
The addition of fibers to the concrete mass leads to the creation of fiber reinforced concrete, a composite material
The torsional strength of the examined torsional beams calculated using the modified Narayanan and Kareem-Palanjian and Tegos (NKPT) model are depicted in the diagrams of Figure 6 in terms of torsion safety factor (TSF) values versus the parameters affecting the capacity of the steel fiber reinforced concrete (SFRC) beams
The less than 0.3 values of R indicate the ability of the proposed model to be less dependent on these parameters and, this weak correlation expresses that it can yield safe calculations concerning the torsional strength of SFRC beams
Summary
The addition of fibers to the concrete mass leads to the creation of fiber reinforced concrete, a composite material. Fibers are available in various shapes (straight, hooked, crimped, duoform, paddled, enlarged ends, and irregular), cross-sections (circular, rectangular, and irregular), and materials (steel, glass, or composite materials). When they are uniformly dispersed in different percentages in the concrete mix, the material properties improve. The gradual activation of the fibers results in the transformation of the overall behavior of the concrete from brittle to pseudo-ductile, enhance the energy dissipation capacity and reduce the width of the cracks [16,17]. The improved tensile behavior of fiber reinforced concrete leads to an enhancement of the structural element’s response under flexural, shear and torsional loading. Regarding the phenomenon of torsion, previous research revealed that the behavior of an element under pure torsion is fully influenced by the behavior of the material under direct tension [18,19]
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