Axial Behavior of PET FRP-Confined Reinforced Concrete
Publication: Journal of Composites for Construction
Volume 25, Issue 1
Abstract
In reinforced concrete (RC) columns, the efficiency of confinement that is provided by fiber–reinforced polymer (FRP) composites is usually limited by the buckling of longitudinal steel bars. This situation is even more critical in noncircular columns in which the FRP ruptures due to a combination of buckling of the steel bars and FRP stress concentrations at the corners. The main objective of this study is to observe the effect of internal steel bars on the axial compressive response of noncircular RC column specimens confined with polyethylene terephthalate (PET) FRP, which possesses a large rupture strain (LRS) capacity. In total, 32 specimens were tested under monotonic axial compression. The parameters considered are the number of PET FRP layers, the stirrup spacing, and the cross-sectional aspect ratio. The test results indicate that the strength and deformation capacities of the confined specimens were significantly influenced by the parameters that were considered. Of interest, with an increase in PET FRP confinement, the effect of buckling length became less significant. In addition, the test results indicate that the PET FRP confinement provided a weak but prolonged constraint on the buckling of longitudinal bars. Moreover, PET FRP efficiently sustained the stress concentrations of bar buckling at corners that led to a considerable ductile response before failure.
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Acknowledgments
The authors would like to thank Maeda Kosen Co. LTD.-Japan and Mr. Nakai Hiroshi for providing the PET FRP and related mechanical information.
Notation
The following symbols are used in this paper:
- D
- steel bar diameter;
- E1
- initial elastic modulus for the first linear portion of PET FRP;
- E2
- second-stage elastic modulus for the second linear portion of PET FRP;
- Es
- elastic modulus of steel reinforcement;
- Fcc
- peak strength of PET FRP-confined RC specimens at the end of transition zone;
- Fco
- peak strength of control RC specimens;
- Fcu
- ultimate strength of PET FRP-confined RC specimens;
- ff
- tensile strength of PET FRP;
- fu
- ultimate strength of steel reinforcement;
- fy
- yield strength of steel reinforcement;
- kɛ
- strain efficiency factor;
- kɛ,avg
- average strain efficiency factor for a series or a shape of specimens;
- kɛc
- strain efficiency factor for corner location;
- kɛc,avg
- average strain efficiency factor for corner location;
- kɛl
- strain efficiency factor for long side;
- kɛl,avg
- average strain efficiency factor for long side;
- kɛs
- strain efficiency factor for short side;
- kɛs,avg
- average strain efficiency factor for short side;
- L
- length of steel bar between stirrups;
- ɛc
- axial strain of unconfined concrete cylinder;
- ɛco
- axial strain of control RC specimen;
- ɛcu
- ultimate axial strain of PET FRP-confined RC specimen;
- ɛfu
- ultimate strain of PET FRP;
- ɛh
- FRP hoop rupture strain;
- ɛh,avg
- average of all hoop rupture strains around the perimeter;
- ɛhc
- FRP hoop rupture strain at corner;
- ɛhl
- FRP hoop rupture strain at the middle of long side;
- ɛh,max
- maximum recorded hoop rupture strain around the perimeter;
- ɛh,min
- minimum recorded hoop rupture strain around the perimeter;
- ɛhs
- FRP hoop rupture strain at the middle of short side;
- ɛo
- strain at which the slopes of two linear portions of PET FRP curve intersect;
- ɛu
- ultimate strain of steel reinforcement;
- ɛy
- yield strain of steel reinforcement;
- ρl
- reinforcement ratio of longitudinal steel bar; and
- ρs
- volumetric ratio of transverse steel reinforcement.
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Published In
Journal of Composites for Construction
Volume 25 • Issue 1 • February 2021
Copyright
© 2020 American Society of Civil Engineers.
History
Received: Apr 18, 2020
Accepted: Aug 25, 2020
Published online: Nov 11, 2020
Published in print: Feb 1, 2021
Discussion open until: Apr 11, 2021
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