Experimental Investigation of Short and Slender Rectangular Concrete Columns Reinforced with GFRP Bars under Eccentric Axial Loads
Publication: Journal of Composites for Construction
Volume 24, Issue 6
Abstract
In this paper, the experimental behavior of short and slender concrete columns reinforced with glass fiber-reinforced polymer (GFRP) bars under eccentric compression loading is presented. A total of 10 large-scale concrete column specimens with a rectangular cross section (205 × 306 mm) were tested under a single curvature condition with equal load eccentricities at both ends of the column. Four slenderness ratios of 16.6, 21.5, 39.7, and 59.5 and two reinforcement ratios of 2.78% and 4.80% were considered. The results showed that no crushing of GFRP bars occurred prior to concrete spalling. The columns were able to sustain load, moment, and deformation after the concrete spalling up to the crushing of GFRP bars in compression. The latter was attributed to the contribution of GFRP bars in compression. An analytical model was also adopted to predict the behavior of the test specimens and to evaluate the effect of load eccentricities beyond the one considered in the experimental program. Also, the flexural stiffness and moment magnification factor obtained from the experimental program were compared with those calculated using equations from the literature. The results showed that most of the equations underestimated the flexural stiffness and the magnified moment.
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Acknowledgments
The authors would like to thank Jordan Maerz, Blair Nickerson, Brian Kennedy, Jesse Keane, and Brian Liekens for their assistance in the lab. The authors would also like to acknowledge and thank Natural Sciences and Engineering Research Council of Canada and Dalhousie University for their financial support as well as Owens Corning (Toledo, Ohio) for providing GFRP bars.
Notation
The following symbols are used in this paper:
- Af
- cross-sectional area of longitudinal FRP reinforcement;
- Afc
- area of GFRP bars in the compression side;
- Aft
- area of GFRP bars in the tensile side;
- Ag
- gross cross-sectional area of concrete;
- Ast
- cross-sectional area of longitudinal steel reinforcement;
- d1
- centroid of bars in the compression side;
- d2
- centroid of bars in the tensile side;
- dC
- distance between the neutral axis and the resultant of the internal compressive forces of concrete;
- dfc
- distance between the neutral axis and the centroid of the compressive GFRP bars;
- dft
- distance between the neutral axis and the centroid of the tensile GFRP bars;
- e0
- initial eccentricity;
- Ec
- modulus of elasticity of concrete;
- Ef
- modulus of elasticity of FRP bars;
- Efc
- modulus of elasticity of GFRP bars in compression;
- Eft
- modulus of elasticity of GFRP bars in tension;
- Es
- modulus of elasticity of steel rebars;
- EI
- effective stiffness;
- EID
- experimental flexural stiffness corresponding to design strength (when the concrete reaches the design strain of 0.003 mm/mm per ACI 318-19);
- EIGC
- experimental flexural stiffness corresponding to crushing of GFRP bars in compression;
- EIi
- calculated stiffness based on the ith equation provided in Table 6 (i 1–10);
- EIpeak
- experimental flexural stiffness corresponding to the peak load;
- EISP
- experimental flexural stiffness corresponding to concrete spalling;
- FC
- resultant of internal forces of concrete in compression;
- Ffc
- internal force of GFRP bars in compression;
- Fft
- internal force of GFRP bars in tension;
- compressive strength of concrete;
- ultimate crushing strength of GFRP bars in compression;
- ultimate rupture strength of GFRP bars in tension;
- yield strength of steel rebars;
- h
- width of column cross section;
- If
- moment of inertia of all GFRP bars in the concrete column;
- Ig
- moment of inertia of gross cross section of concrete (chamfers are excluded);
- Is
- moment of inertia of all steel bars in the concrete column;
- k
- effective length factor (unbraced length) of the concrete columns;
- l
- length of the column;
- M
- bending moment (M P × (e0 + Δ));
- MC
- internal moment resistance due to compressive concrete;
- MCC
- bending moment corresponding to concrete crushing;
- MD
- experimental moment at the design load (when the concrete reaches the design strain of 0.003 mm/mm at the furthest concrete fiber in compression);
- MD_1st
- experimental first-order moment calculated at the design load;
- Mfc
- internal moment resistance due to compressive GFRP bars;
- Mft
- internal moment resistance due to tensile GFRP bars;
- MGC
- bending moment corresponding to crushing of GFRP bars in compression;
- Mu
- moment capacity of the specimens at their peak load;
- Mult
- ultimate factored moment;
- Mu_1st
- experimental first-order moment calculated at the peak load;
- n
- modular ratio (the ratio of modulus of elasticity of GFRP bars to concrete);
- P
- axial load;
- PCC
- axial load corresponding to concrete crushing;
- Pcr
- critical buckling load;
- PD
- design load (when the concrete reaches the design strain of 0.003 mm/mm at the furthest concrete fiber in compression);
- PGC
- axial load corresponding to crushing of GFRP bars in compression;
- Po
- nominal axial strength at zero eccentricity;
- Pu
- axial capacity of the specimens at their peak load;
- Pult
- ultimate factored load;
- r
- radius of gyration;
- Δ
- lateral displacement at midspan;
- δ
- moment magnification factor;
- Δaxial
- axial displacement of the specimens at their peak load;
- ΔCC
- lateral displacement corresponding to concrete crushing;
- ΔGC
- lateral displacement corresponding to crushing of GFRP bars in compression;
- Δlateral
- lateral displacement of the specimens at their peak load;
- δcalc
- calculated moment magnification factor;
- δtest
- experimental moment magnification factor;
- ɛCC,c
- compressive strain of GFRP bar in compression side corresponding to crushing of concrete;
- ɛfc
- strain of GFRP bars in compression;
- ɛfcu
- ultimate crushing strain of GFRP bars in compression;
- ɛft
- strain of GFRP bars in tension;
- ɛftu
- ultimate rupture strain of GFRP bars in tension;
- ɛGC,c
- compressive strain of GFRP bars in the compression side corresponding to crushing of GFRP bars in compression;
- ɛpeak,c
- compressive strain of GFRP bars in the compression side corresponding to the peak load;
- ɛy
- yield strain of steel rebars;
- λ
- slenderness ratio;
- ρ
- reinforcement ratio; and
- ψ
- curvature of the column at the midsection.
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© 2020 American Society of Civil Engineers.
History
Received: Aug 30, 2019
Accepted: Aug 5, 2020
Published online: Sep 29, 2020
Published in print: Dec 1, 2020
Discussion open until: Mar 1, 2021
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