Confinement Characteristics of GFRP-RC Circular Columns under Simulated Earthquake Loading: A Numerical Study
Publication: Journal of Composites for Construction
Volume 26, Issue 2
Abstract
The seismic behavior of fiber-reinforced polymer-reinforced concrete (FRP-RC) columns is far from being fully explored. Therefore, numerical and analytical studies were performed to address the effects of different parameters and evaluate the current design provisions for confinement reinforcement under seismic loading. Using a commercially available software package, a three-dimensional nonlinear finite-element model (FEM) was constructed and validated against the experimental results of full-scale glass FRP (GFRP)-RC circular columns previously tested by the authors. The validated FEM was, then, used to conduct an extensive parametric study investigating the effect of concrete compressive strength, spiral pitch, axial load level, and column aspect ratio (i.e., shear span-to-depth ratio). It was found that increasing the concrete strength caused an increase in lateral load capacity and initial stiffness, whereas the drift capacity decreased. The latter property was also significantly affected by the variation of spiral pitch and axial load level. On the other hand, the aspect ratio had a marginal effect on moment or drift capacities. Using the results of the FEMs, two new design models were proposed. The proposed models showed remarkably better predictions than the equation adopted by the Canadian standard for the design of FRP-RC structures.
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Acknowledgments
The authors express their sincere appreciation to the Natural Sciences and Engineering Research Council of Canada (NSERC) and the Manitoba Graduate Scholarship (MGS) for financial support.
Notation
The following symbols are used in this paper:
- Ac
- cross-sectional area of column core;
- Ag
- gross cross-sectional area of the column;
- Ash
- required area of confinement reinforcement;
- cts
- tension stiffening factor;
- D
- column diameter;
- ds
- nominal cross-sectional diameter of the hoop;
- Ec
- elastic modulus of concrete in compression;
- EEXP
- experimental total energy dissipation;
- EFEM
- total energy dissipation estimated by FEM;
- Ef
- elastic modulus of FRP reinforcement in tension;
- fc′
- specified concrete compressive strength;
- fFh
- design stress level in FRP confinement reinforcement;
- fFu
- ultimate strength of the GFRP reinforcement;
- ft-cr
- tensile stress at the crack location;
- ft′
- tensile strength of concrete;
- GF
- specific fracture energy of concrete;
- hc
- cross-sectional dimension of column core;
- KEXP
- experimental initial stiffness;
- KFEM
- initial stiffness estimated by FEM;
- KP
- proposed coefficient that denotes the synergistic effect of axial load level and the concrete strength;
- Kn
- normal shear crack stiffness of cracked concrete;
- Ks
- proposed coefficient combining the effects of spiral pitch and concrete compressive strength;
- Kt
- tangential shear crack stiffness of cracked concrete;
- kc
- confinement efficiency coefficient;
- L
- column shear span;
- P
- axial load applied to the column;
- Po
- nominal unconfined axial capacity of the column;
- reduction factor of compressive strength;
- SF
- shear factor coefficient of concrete;
- s
- spiral pitch;
- wd
- critical compressive displacement of concrete;
- VEXP
- experimental lateral load capacity in pushing direction;
- VFEM
- lateral load capacity in pushing direction as estimated by FEM;
- V′EXP
- experimental lateral load capacity in pulling direction;
- V′FEM
- lateral load capacity in pulling direction as estimated by FEM;
- wcr
- crack width;
- β
- multiplier for the specific flow direction;
- Δ
- lateral displacement at the column tip;
- δ
- design drift ratio;
- δCSA
- failure drift estimated as per CSA S806-12 (CSA 2017);
- δEXP
- experimental failure drift;
- δFEM
- failure drift estimated by FEM;
- δI
- failure drift estimated using Model I [Eq. (6)];
- δII
- failure drift estimated using Model II [Eqs. (9) or (10), as appropriate];
- ɛcp
- plastic strain at compressive strength;
- ɛzz
- plastic strain of concrete in the longitudinal direction of the column;
- µ
- Poisson's ratio;
- ρ
- specific material weight;
- ρf
- GFRP longitudinal reinforcement ratio; and
- ϕf
- material resistance factor for FRP reinforcement, taken equal to unity.
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Received: Aug 11, 2021
Accepted: Dec 2, 2021
Published online: Feb 2, 2022
Published in print: Apr 1, 2022
Discussion open until: Jul 2, 2022
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