Experimental and Analytical Study on Shear Performance of Embedded Through-Section GFRP-Strengthened RC Beams
Publication: Journal of Composites for Construction
Volume 26, Issue 5
Abstract
The structural performance of reinforced concrete (RC) beams strengthened in shear with embedded through-section (ETS) glass fiber-reinforced polymer (GFRP) bars is experimentally and analytically investigated. Three-point bending tests are performed. The investigated parameters include the number of existing steel stirrups (ρsw = 0.28%), concrete compressive strength ( = 27 and 43 MPa), shear span-to-effective depth ratio (a/d = 2.4, 3.6, and 4.8), anchorage presence (with and without anchorage), and anchorage properties (steel and GFRP anchorage systems, as well as the anchorage length). The results indicate that the shear capacity and stiffness of the beams are enhanced by applying ETS-GFRP, increasing concrete strength, and decreasing shear span-to-effective depth ratio. The ETS-GFRP-strengthened beams exhibit a more ductile failure mode than the unstrengthened beam owing to concrete crushing in loading areas. The beam stiffness depends significantly on the anchorage presence and properties, and the beam shear capacities differ considerably for different anchorage systems. Anchorage with four steel nuts or two GFRP nuts at the ETS bar ends provides the highest shear resistance and stiffness for the ETS-strengthened beams. The results of this study suggest that the details and configuration of the anchorage system should be carefully considered for the development of unanimous specifications. Additionally, previously proposed shear models can be used to conservatively analyze test results with sufficient accuracy. The newly developed model for estimation of the shear strengths of ETS-GFRP-strengthened beams and the effective strains in ETS-GFRP bars agrees well with the test data.
Practical Applications
The experimental results obtained from the present study demonstrate the potential of the embedded through-section (ETS) method for practical applications in the shear strengthening of the reinforced concrete (RC) beams. The predrilled holes through the beam height are made at the marked positions, which could be determined by a rebar detector. Next, the adhesive resin is fully injected into the holes prior embedding the fiber-reinforced polymer (FRP) bars. In the present study, the glass fiber-reinforced polymer (GFRP) bars are used. Then, the ends of each FRP bar are anchored with screwed nuts. Comparing with the unstrengthened beam, the ETS-strengthened beam offers a larger capacity, more ductility, and safer failure. The shear performance of the ETS-strengthened beams is proportional to the concrete compressive strength. The decrease of the shear span-to-effective depth ratio increases the shear resistance of the ETS-strengthened beams. The anchorage at two bar ends with two GFRP or four steel nuts is deemed to be most effective. Additionally, the proposed shear strength model can be used for the design of the beam with an ETS strengthening system.
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Acknowledgments
This research was supported by the Research Fellowship, Ratchadapisek Somphot Fund, Chulalongkorn University. This research project was also supported by the Ratchadapiseksompotch Fund Chulalongkorn University, Thailand (Grant No. RCU_D_64_005_21). The first author (L. V. H. Bui) acknowledges the support of Ton Duc Thang University. The second author (C. Klippathum) acknowledges the Second Century Fund (C2F), Chulalongkorn University. The authors acknowledge Sika (Thailand), Ltd. for supplying the adhesive material and Panjawattana Plastic Public Co., Ltd. for supplying GFRP bars. The authors also thank Songklod Wongjaroen, Thaweewat Kongpattanakit, and Yossapon Chaithong for their assistance with the laboratory testing.
Notation
The following symbols are used in this paper:
- a
- shear span length for investigation zone (mm);
- Af
- area of FRP bars used as shear reinforcement (mm2);
- Ag
- gross area of concrete section (mm2);
- As
- area of tension reinforcement (mm2);
- Av
- area of shear reinforcement within spacing s (mm2);
- bw
- web width or diameter of circular section (mm);
- d
- effective depth measured from extreme compression fiber to centroid of longitudinal tension reinforcement (mm);
- db
- ETS bar diameter (mm);
- Ef
- elastic modulus of ETS reinforcement (GPa);
- Es
- Young’s modulus of tension reinforcement (GPa);
- Esw
- Young’s modulus of stirrups (GPa);
- Fmax
- peak load in beam (kN);
- compressive strength of concrete (MPa);
- ff
- tensile strength based on FRP system (MPa);
- fy
- yield strength of transverse reinforcement (MPa);
- h
- height of beam (mm);
- L
- length of beam (support to support) (mm);
- Nu
- axial force, taken as positive for compression and negative for tension (N);
- p
- bond parameter;
- s
- center-to-center of reinforcements measured parallel to longitudinal bars (mm);
- sm
- slip at maximum bond stress between FRP bars and concrete (mm);
- umax
- deflection at peak load (mm);
- Vc
- shear force carried by concrete (kN);
- Vf
- shear force carried by ETS bars (kN);
- Vf
- Vmax(Bx) − Vmax(R1) = shear force carried by ETS bars (kN); for Beams B1, B3, and B4, Vmax (corresponding reference beam) is calculated using the JSCE model (JSCE 2007);
- Vmax
- maximum shear strength of beam measured in tests (kN);
- Vn
- total shear strength (kN);
- Vs
- shear resistance carried by existing stirrups (kN);
- α
- inclination of stirrups (°);
- ρf
- percentage of ETS bars (%);
- ρs
- As/(bwd) = ratio of tensile or longitudinal reinforcement (%);
- ρsw
- Aw/(bws) = ratio of transverse steel (%);
- λ
- modification factor for lightweight concrete;
- λs
- modification factor for size effect;
- θ
- crack angle (°); and
- τm
- maximum bond stress between FRP bars and concrete (MPa).
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Journal of Composites for Construction
Volume 26 • Issue 5 • October 2022
Copyright
© 2022 American Society of Civil Engineers.
History
Received: Aug 30, 2021
Accepted: Apr 24, 2022
Published online: Jun 23, 2022
Published in print: Oct 1, 2022
Discussion open until: Nov 23, 2022
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