Eccentrically Loaded Square Concrete-Filled Steel Tubes Strengthened with CFRP Grid-Reinforced Engineered Cementitious Composite
Publication: Journal of Composites for Construction
Volume 28, Issue 3
Abstract
The use of carbon fiber–reinforced polymer (CFRP) grid-reinforced engineered cementitious composite (CFGRE) systems to strengthen concrete-filled steel tubes (CFSTs) offers potential to improve the structural response as well as the resistance to high temperatures and corrosion. This study consists of an experimental investigation on the behavior of eccentrically loaded square CFSTs strengthened with CFGRE systems. Nineteen specimens were tested using a compression-testing machine with loads, deformations, and recorded test observations. The investigated parameters included the number of CFRP grid layers, width-to-thickness ratio of a steel tube, concrete strength grade, and eccentric ratio. The strengthened columns exhibited ductile failure. Due to stress concentrations, the CFGRE systems ruptured at the corners on the compression side. After strengthening, the yielding and ultimate loads of the CFST columns increased from 21.8% to 53.5% and 21.1% to 34.9%, respectively. Although an increase in the number of CFRP grid layers did not significantly affect the bearing capacities of the square specimens, it significantly enhanced the ductility of the columns. An increase in the eccentric ratio weakened the confining effect. An average decrease of 9.7%, 27.6%, and 41.4% was observed in the ultimate loads of the strengthened columns when the eccentric ratio increased from 0 to 0.1, 0.25, and 0.4, respectively. A five-point N–M interaction model was developed based on the principles of force equilibrium and deformation compatibility to predict the eccentric bearing capacities of strengthened columns. The prediction results exhibited high accuracy.
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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 work was supported by the National Nature Science Foundation of China (Grant No. 52238006), the China Postdoctoral Science Foundation (Grant No. 2022M722480), and the Fundamental Research Funds for the Central Universities (Grant No. 2042023kf1047).
Notation
The following symbols are used in this paper:
- Ac
- cross-sectional area of concrete core;
- AECC
- cross-sectional area of ECC;
- Ae
- effective confining area;
- Ae,s
- effective confining area of concrete confined by steel tube;
- Ae,GRE
- effective confining area of concrete confined by CFGRE;
- Ane,GRE
- ineffective confining area of concrete confined by CFGRE;
- Ane,s
- ineffective confining area of concrete confined by steel tube;
- As
- cross-sectional area of steel tube;
- B
- side length of CFST columns strengthened with CFGRE;
- Bc
- side length of the square concrete core;
- Bs
- side length of CFST columns;
- B0
- straight-line length within the side length of CFRP grid;
- Deq
- equivalent diameter;
- DI
- ductility index;
- dc
- height of concrete compression zone;
- d0
- distance from CFGRE layer center to concrete core edge;
- Ec
- Young's modulus of concrete;
- Ed
- energy dissipation capacity;
- Ef
- Young's modulus of CFRP;
- Em
- Young's modulus of ECC;
- Es
- Young's modulus of steel tube;
- Et1
- slope of first portion of ECC tensile stress–strain curve;
- Et2
- slope of second portion of ECC tensile stress–strain curve;
- E1
- slope of first portion of CFGRE tensile stress–strain curve;
- E2
- tangent slope at endpoint of second portion of CFGRE tensile stress–strain curve;
- E3
- slope of third portion of CFGRE tensile stress–strain curve;
- e0
- load eccentricity;
- cylinder compressive strength of concrete;
- confined concrete strength;
- fcecc
- compressive strength of ECC;
- fcu
- cubic compressive strength of concrete;
- fGRE
- tensile strength of CFGRE;
- fl
- total confining pressure;
- fl,GRE
- confining pressures provided by CFGRE;
- fl,s
- confining pressures provided by steel tube;
- fs
- transverse stress of steel tube at ultimate load;
- fy
- yield strength of steel tube;
- f0
- stress at the intercept of E2 with stress axis;
- k
- strength enhancement coefficient;
- kc
- effective confining coefficient;
- kc,GRE
- effective confining coefficients of concrete confined by CFGRE;
- kc,s
- effective confining coefficients of concrete confined by steel tube;
- ke
- strain efficiency factor of CFRP;
- L
- length of columns;
- Lse
- straight-line distance between the start and endpoints of the parabola;
- M
- bending moment;
- N
- axial load;
- nc
- curve-shape parameter;
- nf
- number of CFRP grid layers;
- Pf
- failure load of specimens;
- Pu
- ultimate load of specimens;
- Py
- yield load of specimens;
- R0
- chamfer radius of CFRP grid;
- tGRE
- thickness of CFGRE;
- ts
- thickness of steel tube;
- yi
- ordinate of an element;
- yp
- parabolic equation;
- β
- empirical coefficient;
- Δf
- failure deformation of specimens;
- Δu
- ultimate deformation of specimens;
- Δy
- yield deformation of specimens;
- ɛc
- ultimate strain of unconfined concrete;
- ɛcc
- ultimate strain of confined concrete;
- ɛe
- strain at endpoint of first portion of CFGRE tensile stress–strain curve;
- ɛfu
- ultimate strain of CFRP;
- ɛi
- strain of an element;
- ɛss
- strain at endpoint of stiffness-softening portion on CFGRE tensile stress–strain curve;
- ɛtu
- ultimate strain of CFGRE;
- ɛt1
- first cracking strain of ECC;
- ɛt2
- ultimate tensile strain of ECC;
- ɛy
- yield strain of steel tube;
- θ
- tangency angle of confinement edge;
- νe
- Poisson's ratio of a steel tube with filled-in concrete at the maximum strength point;
- νs
- Poisson's ratio of a steel tube without filled-in concrete at the maximum strength point;
- ρf
- volume fraction of CFRP grid;
- ρm
- volume fraction of ECC;
- σss
- stress at the endpoint of the stiffness-softening portion on CFGRE tensile stress–strain curve; and
- σt1
- first cracking strength of ECC.
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Journal of Composites for Construction
Volume 28 • Issue 3 • June 2024
Copyright
© 2024 American Society of Civil Engineers.
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Received: Jun 16, 2023
Accepted: Jan 5, 2024
Published online: Mar 28, 2024
Published in print: Jun 1, 2024
Discussion open until: Aug 28, 2024
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