Stress–Strain Model for FRP-Confined Circular Concrete Columns Developing Structural Softening Behavior
Publication: Journal of Composites for Construction
Volume 28, Issue 1
Abstract
Even though several stress–strain models have been proposed for fiber-reinforced polymer (FRP)-confined concrete columns subjected to axial compressive loading, very few models can predict an axial response featuring postpeak strain-softening behavior. Furthermore, the reliability of most of these models is limited to only a certain concrete strength class (either normal-, high-, or ultrahigh-strength concrete). This study aimed to develop an analytical model for determining the axial response of FRP-confined concrete applicable to cases with different levels of confinement stiffness and concrete strength. For this purpose, this research proposed a new confinement stiffness threshold dependent on the coupled concrete strength and column dimension size effects to classify quantitatively FRP-confined concrete’s behavior in two distinguished subcategories: strain-hardening behavior and postpeak strain-softening behavior. For FRP-confined concrete with strain-hardening response, a parabolic–linear stress–strain relation was developed, where a new formulation was derived for the slope of the linear second portion, calibrated by 583 test data. To simulate FRP-confined concrete with postpeak strain-softening behavior, a new methodology was proposed whose key components were calibrated by using 121 test data. With these features, the proposed model can objectively account for the integrated influence of concrete strength and confinement stiffness on stress–strain response. The predictive performance of the developed stress–strain model was evaluated by comparing the predictions of a wide range of relevant experimental test data, which confirms the model’s reliability and accuracy. Compared to the other existing stress–strain models, the proposed model performed better.
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Data Availability Statement
All data, models, and codes generated or used during the study appear in the published article.
Acknowledgments
This study is a part of the project “Sticker –Innovative technique for the structural strengthening based on using CFRP laminates with multifunctional attributes and applied with advanced cement adhesives,” with reference POCI-01-0247-FEDER-039755. The first author also acknowledges the support provided by the FCT PhD individual fellowship 2019 with reference “SFRH/BD/148002/2019.” This work was partly financed by FCT/MCTES through national funds (PIDDAC) under the R&D Unit Institute for Sustainability and Innovation in Structural Engineering (ISISE) with reference UIDB/04029/2020 and under the Associate Laboratory Advanced Production and Intelligent Systems ARISE with reference LA/P/0112/2020.
Notation
The following symbols are used in this paper:
- B1
- regression coefficient;
- B2
- regression coefficient;
- B3
- regression coefficient;
- B4
- regression coefficient;
- B5
- regression coefficient;
- B6
- regression coefficient;
- B7
- regression coefficient;
- b
- column’s cross-sectional dimension;
- Ef
- FRP modulus elasticity;
- E2
- slope of the linear second portion;
- E2,0
- slope of the softening branch of unconfined concrete;
- fc
- axial stress corresponding to ɛc;
- fc0
- compressive strength of unconfined concrete;
- fctr
- stress at the transition zone;
- fcu
- ultimate axial stress;
- fc,res
- residual stress;
- axial stress at the second stage;
- axial stress at the third stage;
- compressive strength of the standard cylinder;
- fl,tr
- FRP confinement pressure at the transition stage;
- fl,rup
- confinement pressure at FRP rupture;
- H
- longer side of the section;
- KL
- FRP confinement stiffness;
- FRP confinement rigidity threshold;
- L
- column height;
- nf
- number of FRP layers;
- nd1f
- degree of the polynomial function;
- Rb
- corner radius ratio as 2r/b;
- Rλ
- cross-sectional aspect ratio as h/b;
- r
- corner radius;
- tf
- nominal thickness of an FRP layer;
- Xɛt
- strain ratio;
- α1
- polynomial coefficients;
- α2
- polynomial coefficients;
- α3
- polynomial coefficients;
- ɛc
- axial strain corresponding to fc;
- ɛc0
- axial strain corresponding to fc0;
- ɛci
- axial strain at the inflection point;
- ɛctr
- strain at the transition zone;
- ɛcu
- ultimate axial strain;
- ɛh,rup
- rupture strain of an FRP jacket;
- ηɛ
- calibration factor;
- η1
- calibration factor;
- η2
- calibration factor;
- ρK
- FRP confinement stiffness index;
- confinement stiffness threshold;
- νs,tr
- secant Poisson’s ratio;
- ψf
- reduction factor; and
- ψK
- reduction factor.
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Published In
Journal of Composites for Construction
Volume 28 • Issue 1 • February 2024
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© 2023 American Society of Civil Engineers.
History
Received: Apr 27, 2023
Accepted: Sep 28, 2023
Published online: Oct 30, 2023
Published in print: Feb 1, 2024
Discussion open until: Mar 30, 2024
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