NSM GFRP Strengthening of Reinforced Concrete Beams after Exposure to Fire: Experiments and Theoretical Model
Publication: Journal of Composites for Construction
Volume 27, Issue 1
Abstract
The effectiveness of near-surface mounted glass fiber–reinforced polymer (NSM GFRP) retrofitting of reinforced concrete (RC) beams after exposure to fire is investigated in this study both experimentally and analytically. Experiments were performed on nine RC beams: one beam was not exposed to fire (control specimen) and eight beams were divided into two groups exposed to fire for 30 and 60 min. In each group, one beam was not retrofitted, whereas the other three beams were retrofitted using NSM GFRP. After retrofitting, all beams were loaded until failure. The experimental results confirmed that the retrofitting technique effectively recovered the strengths of postfire RC beams. The failure mode of the GFRP retrofitted beams was the peeling-off of concrete cover, whereas that of the control and unretrofitted postfire beams was flexural failure via the yielding of tension steel. The NSM GFRP retrofitting fully recovered or significantly increased the yield and ultimate strengths of postfire RC beams by up to 39%. The yield deflection capacity of the NSM GFRP retrofitted postfire beams was much higher than that of the control beam; however, the ultimate deflection capacity of these beams significantly decreased. Consequently, the GFRP retrofitted postfire beams were of low ductility because of the peeling-off of the concrete cover. NSM GFRP retrofitting slightly improved but did not completely recover the yield stiffness reduced by fire, whereas it increased the plastic stiffness significantly by up to threefold. An analytical model for estimating the yield moment of postfire RC beams without/with NSM GFRP retrofitting was proposed, considering the very limited information, for example, fire duration obtained from actual fire events. The practicality and reasonable accuracy of the proposed model render it beneficial for structural engineers.
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Acknowledgments
This research was funded by Vietnam National University HoChiMinh City (VNU-HCM) under grant number B2021-20-07.
Notation
The following symbols are used in this paper:
- a
- depth of the equivalent stress block;
- ab
- distance from the bottom surface to the centroid of the bottom NSM GFRP bars;
- as
- distance from the bottom surface to the centroid of the side NSM GFRP bars;
- a0
- concrete cover measured to the center of tensile steel;
- area of the bottom NSM FRP bars;
- area of the side NSM FRP bars;
- area of the bottom resin;
- area of the side resin;
- As
- area of tensile steel;
- area of compressive steel;
- b′
- width of the cross section between the 500°C isotherm curves;
- Cc
- internal force of compressive concrete;
- compressive force of the compressive steel;
- c
- depth of the neutral axis measured from the top fiber;
- d
- effective depth measured from the top fiber to the centroid of tensile steel;
- Efrp
- elastic modulus of FRP;
- Er
- elastic modulus of resin;
- Fy
- yield load;
- compressive cylinder strength of concrete;
- stress of bottom NSM FRP;
- stress of side NSM FRP;
- stress of the bottom resin;
- stress of the side resin;
- fy
- yield strength of steel;
- fs
- stress of tensile steel;
- stress of compressive steel;
- h
- height of the beam;
- jd
- lever arm of the tensile force Ts;
- khb
- lever arm of the tensile force ;
- khs
- lever arm of the tensile force ;
- L
- span length;
- My
- yield moment;
- nw
- ratio of surface temperature to the concrete temperature;
- T
- furnace temperature;
- tensile force of GFRP bars and resin at the bottom surface;
- tensile force of GFRP and resin at the side surface;
- Ts
- force of tensile steel bars;
- t
- duration of fire;
- x500
- depth from the surface to the point of 500°C;
- αr
- thermal diffusivity;
- strain of the bottom GFRP bars;
- strains of the side GFRP bars;
- ɛm
- concrete strain at the extreme fiber;
- strain of the bottom resin;
- strains of the side resin;
- strain of steel;
- Δu
- ultimate deflection;
- Δy
- yield deflection; and
- μ
- ductility.
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Information & Authors
Information
Published In
Journal of Composites for Construction
Volume 27 • Issue 1 • February 2023
Copyright
© 2022 American Society of Civil Engineers.
History
Received: Feb 15, 2022
Accepted: Sep 1, 2022
Published online: Oct 26, 2022
Published in print: Feb 1, 2023
Discussion open until: Mar 26, 2023
ASCE Technical Topics:
- Beams
- Concrete
- Concrete beams
- Construction engineering
- Construction methods
- Disaster risk management
- Disasters and hazards
- Engineering materials (by type)
- Failure modes
- Fiber reinforced polymer
- Fibers
- Fires
- Forensic engineering
- Glass fibers
- Man-made disasters
- Materials engineering
- Polymer
- Rehabilitation
- Reinforced concrete
- Structural behavior
- Structural engineering
- Structural members
- Structural strength
- Structural systems
- Synthetic materials
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