Shear Behavior of RC Beams Strengthened with Side-Bonded BFRP Grids
Publication: Journal of Composites for Construction
Volume 24, Issue 5
Abstract
This study examined the shear behavior of reinforced concrete (RC) beams that were strengthened with externally bonded composite reinforced mortar (CRM) layers consisting of basalt fiber-reinforced polymer (BFRP) grids and polymer cement mortar (PCM). The variable parameters included the shear span ratios (1.6, 2.0, and 2.4), strengthening materials (BFRP grids and BFRP sheets), bonding materials (PCM and epoxy resin), and angles between the longitudinal bars of the BFRP grid and the beam axis (0° and 45°). A total of 10 RC beams were cast and tested in the four-point flexural experiments. Three beams served as control specimens, four beams were strengthened with the 0° BFRP grids (one beam and three beams using epoxy resin and PCM as bonding materials, respectively), and one beam was strengthened with the 45° BFRP grids using PCM as the bonding material. The remaining two beams were strengthened with the BFRP sheets and PCM, respectively. The experimental results demonstrated that the BFRP grids effectively improved the ultimate load of the strengthened beams, and the contribution of the BFRP grids to the ultimate load was not sensitive to the shear span ratio. The RC beam strengthened with the 45° BFRP grids displayed an improved ability to restrict the development of diagonal cracks and restrain the degradation of the flexural stiffness compared to the beam strengthened with the 0° BFRP grids. Moreover, owing to the reliable interface performance between the BFRP grids and the concrete substrate, all of the BFRP grid-strengthened beams failed in shear, while the BFRP sheet-strengthened beam experienced local debonding with insufficient ductility. In conclusion, the BFRP grid was considered an effective strengthening material for RC members.
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Acknowledgments
The authors gratefully acknowledge the financial support provided by the National Natural Science Foundation of China (51678139). The authors also acknowledge Jiangsu GMV Co., Ltd. for providing the BFRP grids.
Notation
The following symbols are used in this paper:
- Ag
- total area of the BFRP grids;
- Agt
- the area of the BFRP grids by unit width;
- a
- distance from support to the external load position;
- b
- width of the beam;
- dg
- effective depth of the BFRP grids;
- Eg
- elastic tensile modulus of the BFRP grids;
- fc
- compressive strength of the concrete cylinder;
- Gf
- interfacial fracture energy;
- h0
- effective depth of the tension reinforcement;
- i
- direction of the BFRP grids;
- k1
- modification factor applied to κv to account for concrete strength;
- k2
- modification factor applied to κv to account for wrapping scheme;
- Le
- effective bond length of the BFRP grids;
- n
- number of plies of the BFRP grids;
- Pcr
- flexural cracking load;
- Pu
- ultimate load;
- Puc
- ultimate load of the control beam;
- Ru
- increased load of the strengthened beam over the corresponding control beam;
- sg
- distance between two bars of the BFRP grids;
- tg
- thickness of one ply of the BFRP grids;
- tm
- equivalent thickness of the BFRP grids;
- V
- nominal shear capacity of the BFRP grid-strengthened beams;
- Vc
- shear capacity contribution from the concrete;
- Vcr
- diagonal cracking load;
- Vg
- shear capacity contribution from the BFRP grids strengthening system;
- Vg,ACI440
- shear capacity contribution of the BFRP grids based on the ACI 440.2R guidelines;
- Vg,ACI549
- shear capacity contribution of the BFRP grids based on the ACI 549.4R guidelines;
- Vg,CSAS6
- shear capacity contribution of the BFRP grids based on the CAN/CSA S6 standards;
- Vg,exp
- experimental contribution of the BFRP grids to the shear capacity;
- Vg,Tri
- shear capacity contribution of the BFRP grids based on the model of Triantafillou et al.;
- Vs
- shear capacity contribution from the existing steel shear reinforcement;
- w
- width of the BFRP grid bar;
- α
- angle between the beam axis and the orientation of the BFRP grids;
- Δ
- midspan displacement at the ultimate load;
- ɛge
- effective strain of the BFRP grids;
- ɛgu
- ultimate strain of the BFRP grids;
- θ
- angle between the main diagonal crack and the longitudinal axis of the beam;
- κv
- reduction coefficient; and
- ρg
- reinforcement ratio of the BFRP grids.
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Published In
Journal of Composites for Construction
Volume 24 • Issue 5 • October 2020
Copyright
© 2020 American Society of Civil Engineers.
History
Received: Jun 16, 2019
Accepted: May 28, 2020
Published online: Jul 20, 2020
Published in print: Oct 1, 2020
Discussion open until: Dec 20, 2020
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