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

Abstract

The strength and behavior of fiber reinforced concrete (FRC) members subjected to torsion has received little attention in the literature. The primary objective of including fibers in concrete is to bridge cracks once they form, and in doing so, provide some post‐cracking resistance to the otherwise brittle concrete. This and the accompanying paper that follows present the results of a comprehensive experimental and analytical study aimed at describing the behavior and strength of FRC members subjected to torsion. In this paper, results are presented on large scale pure torsion tests which have been conducted on eighteen 2.7 m long by 0.3 m wide by 0.3 m high beams with varying transverse and longitudinal reinforcement ratios along with varying steel fiber types and dosages. The results of this study demonstrates that the addition of steel fibers significantly increases the stiffness, rigidity and the maximum resisting torque and maximum twist when compared to the same specimen without fibers. The addition of fibers substantially reduced crack widths and crack spacings induced by torsion. The complementary behavior of specimens containing fibers and stirrups is explored along with a critical discussion on members containing low amounts of conventional longitudinal and/or transverse reinforcement.

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

“…The average width of the crack at the mid‐height of the section, w , is related to the longitudinal strain parameter, ε x . The SMCFT 18 predicts this relationship for shear critical specimens as Similarly, Facconi et al 10,19 found this expression to significantly overpredict the width of the localized crack at peak load. To fit in line with the results of the experiments of this research program, the following modified expression for w has been calibrated for specimens subjected to torsion: We note that for softening FRC, as is typically adopted in practice, the limiting term of Equation () provides a conservative, minimum crack width, for which the fibers are effective.…”

“…Early studies on torsion in plain RC assumed the compression field angle θ v at failure to be 45° 17 . The Simplified Modified Compression Field Theory (MCFT) 18 for shear critical members, hereafter referred to as SMCFT, predicts θ v as a function of the longitudinal strain at cross section mid‐height ε x : Facconi et al 10,19 found that is underestimated for large‐scale SFRC beams with little or no transverse reinforcement failing in pure torsion. Such an underestimation of θ v may lead to unsafe solutions.…”

“…In these instances, the critical crack would inherently be assumed to pass through multiple stirrups/links, which may not be the case in reality. To this end, based on the experimental results summarized and discussed in the accompanying paper, 19 a modified expression for θ v has been calibrated for beams subjected to torsion: Comparing Equations () and (), it is noted that for loading and geometrical configurations where torsional moments govern, Equation () yields strut angles close to 45°, which is more representative than those obtained through Equation ().…”

“…Moreover, the results using these methods should be carefully checked against predictions using the LoA II model and critically interpreted. In this article, the commercially available package ATENA 26 is deployed to investigate the response of a number of the beams tested in the accompanying paper 19 …”

“…The proposed LoA I and II models developed here are first compared to the 14 SFRC specimens tested in the accompanying paper 19 as well as the two SFRC torsion specimens tested by Amin and Bentz 9 . These specimens have been chosen as both datasets are complimented with a complete suite of material property tests, which quantify the post‐cracking residual tensile strength offered by the fibers.…”