Residual Flexural Behavior of PBO FRCM-Strengthened Reinforced Concrete Beams after Exposure to Elevated Temperatures
Publication: Journal of Composites for Construction
Volume 28, Issue 1
Abstract
The residual flexural behavior of reinforced concrete (RC) beams strengthened with a fabric-reinforced cementitious matrix (FRCM) composite system after exposure to elevated temperatures was analyzed and discussed in the paper. Ten RC beams, two unstrengthened and eight strengthened with a polypara-phenylene-benzo-bisthiazole (PBO) FRCM system, were tested at ambient temperature (20°C) under three-point bending after being exposed to temperatures of 100°C, 200°C, and 300°C. Test results were analyzed in terms of failure modes, failure loads, load–deflection curves, strain, stress distributions, and ductility. The obtained results evidenced that the load-bearing capacity of the strengthened beams remained roughly constant for temperatures ranging from 20°C to 200°C (from 13% to 23% higher than that of the unstrengthened beams). On the other hand, the collapse of PBO FRCM-strengthened beams exposed to a temperature of 300°C occurred for load values that were, on average, 12% lower than those of strengthened beams at room temperature. The effects of exposure to elevated temperatures on the PBO FRCM-to-concrete debonding were also discussed. A semiempirical model based on the experimental results was defined to estimate the residual debonding strain of the composite system as a function of temperature. The accuracy of the proposed model as well as those of some different analytical procedures available in the literature was assessed through a comparison with experimental results.
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Data Availability Statement
All data, models, or code that support the findings in this study are available from the corresponding author upon reasonable request.
Acknowledgments
The authors would like to express their appreciation to Ruregold s.r.l., Italy, for providing the composite materials in this study.
Notation
The following symbols are used in this paper:
- Af
- textile area;
- b
- beam width;
- bf
- textile width;
- E1
- PBO FRCM uncracked modulus;
- E3
- PBO FRCM cracked modulus;
- Ef
- PBO elastic modulus;
- concrete compressive strength;
- fcfm
- mortar flexural strength;
- fcm
- mortar compressive strength;
- ffbm
- debonding stress;
- fu
- steel ultimate tensile strength;
- fy
- steel yielding tensile strength;
- h
- beam height;
- ist
- stirrup spacing;
- k
- debonding coefficient;
- kb
- slope factor;
- kc
- intermediate flexural crack factor;
- kin
- beam initial stiffness;
- km
- matrix factor;
- l
- beam span;
- Mdeb
- bending moment at debonding;
- Pcr
- cracking load;
- Pdeb
- debonding load;
- Pmax
- peak load;
- Pu
- failure load;
- Py
- yielding load;
- s
- slip;
- T
- temperature;
- teq
- textile equivalent thickness;
- β
- length factor;
- δcr
- deflection at cracking;
- δu
- deflection at failure;
- δy
- deflection at yielding;
- δ
- deflection;
- ɛ*
- peak strain;
- ɛcu
- concrete ultimate compression strain;
- ɛfmax
- debonding strain;
- ɛfu
- textile ultimate strain;
- ɛu
- PBO FRCM failure strain;
- ζ
- debonding strain reduction factor;
- η
- exploitation ratio;
- ρf
- reinforcement ratio;
- σcr
- PBO FRCM cracking strength;
- σf
- peak normal stress;
- σfmax
- PBO tensile strength;
- σu
- PBO FRCM tensile strength; and
- ξ
- ductility index.
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Journal of Composites for Construction
Volume 28 • Issue 1 • February 2024
Copyright
© 2023 American Society of Civil Engineers.
History
Received: Mar 16, 2023
Accepted: Sep 1, 2023
Published online: Oct 17, 2023
Published in print: Feb 1, 2024
Discussion open until: Mar 17, 2024
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