A unified approach for determining the strength of FRC beams subjected to torsion–Part II: Analytical modeling

Abstract

The addition of fibers to structural concrete is an accepted means in academia and practice to traverse tension across cracks. Several international codes of practice contain provisions, which allow a designer to rely on the fibers to resist flexure and shear. However, despite the wider community appreciating that the presence of fibers can significantly increase the capacity of reinforced concrete in resisting torsion, design guidelines are currently unavailable to the practicing engineer. As a result of minimum reinforcement requirements prescribed by codes to prevent excessive torsional cracking in reinforced concrete, a significant underutilization of the fibers is often encountered and this can lead to costly and exorbitant designs. In the accompanying paper, benchmark experimental data were presented on 18 large‐scale fiber‐reinforced concrete (FRC) members subjected to torsion, which clearly identified the beneficial effects of the fibers at all stages of loading. In this study, simplified and advanced mechanically consistent analytical models are developed within the so‐called level of approximation approach (within the framework of current Model Code) to describe the strength of FRC beams loaded in torsion.

A unified approach for determining the strength of Frc members subjected to torsion—Part I: Experimental investigation

“…The tests were complemented with a full suite of material characterization tests to fully quantify the post cracking behavior of the FRC. The results presented in this paper provide experimental background to inform the theoretical models developed in the accompanying paper 36 …”

“…Within the same twist range, the specimens containing both stirrups and fibers presented similar normalized rigidities. After initial cracking, specimens containing both fibers and stirrups were stiffer than the corresponding beams containing only stirrups. In fact, the normalized rigidity of the former was about two times higher than the latter one. The inclination of the cracks ranged between 40° and 46° and did not appear to be significantly influenced by the FRC toughness, or with the quantity of transverse reinforcement. The presence of fibers significantly mitigated the detrimental effects that can be induced through the spalling of concrete and prevented the total detachment of the concrete cover from the core of the beam, even at very large rotations. These conclusions will be used to inform the model presented in the accompanying paper 36 …”

“…The results presented in this paper provide experimental background to inform the theoretical models developed in the accompanying paper. 36…”

“…To that end, this and the accompanying paper 36 present the results of a comprehensive experimental and analytical study aimed at describing the behavior and strength of SFRC members subjected to torsion. This paper specifically describes and reports on an experimental study where eighteen large‐scale fiber reinforced concrete beams were tested in pure torsion.…”

Destructive and Non-Destructive Evaluation of Fibre-Reinforced Concrete: A Comprehensive Study of Mechanical Properties

“…The equations for estimating the elasticity modulus and Poisson's ratio of FRC are not included in modern building codes, despite wider applications of steel FRC [8]. An in-depth understanding of FRC's measurement methods is necessary because the elastic parameters data are essential for structural design [2].…”