Experimental Study on the Confinement of Concrete Cylinders with Large Rupture-Strain FRP Composites
Publication: Journal of Composites for Construction
Volume 25, Issue 4
Abstract
Large rupture strain (LRS) fiber-reinforced polymer (FRP) composites, typically formed from polyethylene naphthalate (PEN) and polyethylene terephthalate (PET) fibers, generally exhibit ultimate rupture strains >5%. Such fibers are particularly suited to the confinement of concrete columns on account of their LRS and sufficient elastic modulus. There are currently a limited number of studies on LRS FRP-confined concrete, particularly with high- and ultrahigh-strength concrete, so their behavior across a range of variables is still unknown. To improve this understanding, this paper systematically investigates the influence of fiber type, fiber thickness, and concrete strength on the behavior of FRP-confined concrete. To achieve this objective, the current investigation presents the results of 66 circular FRP-confined cylinders that are loaded concentrically. Three main parameters are investigated, namely, fiber type (i.e., PEN, PET, carbon, glass, and aramid), concrete strength (i.e., normal, high, and ultrahigh strength), and fiber thickness. The results show that regardless of fiber type, the stress–strain response is bilinear when the concrete is sufficiently confined. However, when there is insufficient confinement provided to the concrete core, the stress–strain response becomes trilinear. This trilinear response is more pronounced for LRS FRP-confined specimens because the confinement stiffness of the LRS FRP jacket is lower than that of a traditional FRP-confined specimen with an equivalent confinement ratio. Increasing the confining hoop stiffness (i.e., increasing FRP layers) reduces the magnitude of strength reduction after initial concrete cracking. It is also evident that as the unconfined concrete strength increases, the minimum confinement stiffness ratio necessary to prevent strength reduction after initial concrete cracking increases.
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Acknowledgments
The authors gratefully acknowledge the financial support provided by the Australian Research Council via a Discovery grant (DP170102992). The authors also thank Messrs Zi Sheng Tang and Connor Johnston for their valuable contribution to the experimental testing.
Notation
The following symbols are used in this paper:
- Cf,0
- constant strength value where the extrapolation of the second linear branch intersects the stress axis;
- D
- diameter of the concrete core;
- Ef
- elastic modulus of the FRP jacket;
- E1
- first elastic modulus of the bilinear FRP jacket;
- E2
- second elastic modulus of the bilinear FRP jacket;
- ff
- ultimate tensile stress of FRP;
- fl
- ultimate confining pressure (based on ɛf);
- nominal confinement ratio;
- fl,a
- actual confining pressure (based on ɛh,rup);
- actual confinement ratio;
- maximum axial stress;
- unconfined concrete strength;
- ultimate axial stress;
- strength enhancement ratio;
- initial peak stress;
- postpeak ravine stress;
- stress retention ratio;
- tf
- total nominal thickness of the FRP jacket;
- ɛf
- tensile strain capacity of FRP obtained from coupon tests;
- ɛf,0
- strain value where two linear branches of bilinear response intersect;
- ɛh,rup
- hoop rupture strain in the FRP jacket at specimen failure;
- ɛh,rup/ɛf
- strain efficiency factor;
- axial strain at unconfined concrete strength;
- ultimate axial strain;
- axial strain at initial peak stress;
- axial strain at postpeak ravine stress;
- ρK
- confinement stiffness ratio;
- σc
- stress applied to the FRP-confined specimen; and
- σf
- stress applied to the FRP tension coupon.
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Published In
Journal of Composites for Construction
Volume 25 • Issue 4 • August 2021
Copyright
© 2021 American Society of Civil Engineers.
History
Received: Nov 4, 2020
Accepted: Mar 13, 2021
Published online: May 5, 2021
Published in print: Aug 1, 2021
Discussion open until: Oct 5, 2021
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