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Frontiers of Structural and Civil Engineering

ISSN 2095-2430

ISSN 2095-2449(Online)

CN 10-1023/X

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2018 Impact Factor: 1.272

Front. Struct. Civ. Eng.    2019, Vol. 13 Issue (5) : 1271-1287    https://doi.org/10.1007/s11709-019-0556-0
RESEARCH ARTICLE
Experimental study on flexural behavior of ECC/RC composite beams with U-shaped ECC permanent formwork
Zhi QIAO1, Zuanfeng PAN1,2(), Weichen XUE2, Shaoping MENG3
1. Key Laboratory of Concrete & Prestressed Concrete Structures of the Ministry of Education, Southeast University, Nanjing 210096, China
2. College of Civil Engineering, Tongji University, Shanghai 200092, China
3. School of Civil Engineering, Southeast University, Nanjing 210096, China
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Abstract

To enhance the durability of a reinforced concrete structure, engineered cementitious composite (ECC), which exhibits high tensile ductility and good crack control ability, is considered a promising alternative to conventional concrete. However, broad application of ECC is hindered by its high cost. This paper presents a new means to address this issue by introducing a composite beam with a U-shaped ECC permanent formwork and infill concrete. The flexural performance of the ECC/RC composite beam has been investigated experimentally with eight specimens. According to the test results, the failure of a composite beam with a U-shaped ECC formwork is initiated by the crushing of compressive concrete rather than debonding, even if the surface between the ECC and the concrete is smooth as-finished. Under the same reinforcement configurations, ECC/RC composite beams exhibit increases in flexural performance in terms of ductility, load-carrying capacity, and damage tolerance compared with the counterpart ordinary RC beam. Furthermore, a theoretical model based on the strip method is proposed to predict the moment-curvature responses of ECC/RC composite beams, and a simplified method based on the equivalent rectangular stress distribution approach has also evolved. The theoretical results are found to be in good agreement with the test data.

Keywords engineered cementitious composite (ECC)      durability      ECC/RC composite beam      permanent formwork      flexural performance      theoretical method     
Corresponding Author(s): Zuanfeng PAN   
Just Accepted Date: 17 June 2019   Online First Date: 19 July 2019    Issue Date: 11 September 2019
 Cite this article:   
Zhi QIAO,Zuanfeng PAN,Weichen XUE, et al. Experimental study on flexural behavior of ECC/RC composite beams with U-shaped ECC permanent formwork[J]. Front. Struct. Civ. Eng., 2019, 13(5): 1271-1287.
 URL:  
https://academic.hep.com.cn/fsce/EN/10.1007/s11709-019-0556-0
https://academic.hep.com.cn/fsce/EN/Y2019/V13/I5/1271
type diameter (μm) length (mm) elongation (%) density (g/cm3) elastic modulus (MPa) nominal strength (MPa)
unoiled 26 12 7 1.3 36.3 1560
oiled 39 12 7 1.3 42.8 1620
Tab.1  Comparison of parameters of mechanical properties of PVA fiber
Fig.1  Experimental load versus midspan-deflection curves of hybrid PVA- ECC.
Fig.2  Experimental compressive stress-strain curves of hybrid PVA-ECC.
material cement fly ash fumed silica slag sand coarse aggregates water fibre water reducer
unoiled oiled
concrete 1 0.1 0.3 2.8 4.2 0.6 0.0075
ECC 0.92 3.2 0.08 1.5 1.2 0.6% 1.0% 0.0028
Tab.2  Mixture proportions of concrete and ECC
Fig.3  Fabrication of the ECC permanent formwork.
Fig.4  Beam cross section details.
specimen shear span-depth ratio longitudinal reinforcement ratio (%) shear reinforcement (mm) matrix type surface treatment
N-1 2.67 1.5 stirrups φ6@80 ECC/concrete none
N-2 2.67 1.5 stirrups φ6@80 ECC/concrete none
S-1 2.67 1.5 stirrups φ6@80 ECC/concrete sand particles
S-2 2.67 1.5 stirrups φ6@80 ECC/concrete sand particles
T-1 2.67 1.5 stirrups φ6@80 ECC/concrete transverse grooves
T-2 2.67 1.5 stirrups φ6@80 ECC/concrete transverse grooves
RC-1 2.67 1.5 stirrups φ6@80 ECC/concrete
RC-2 2.67 1.5 stirrups φ6@80 concrete
Tab.3  Summary of specimen information
Fig.5  Schematic of test setup.
Fig.6  Typical failure mode of the ECC/RC beam.
Fig.7  Comparison of compressive strain of ECC and concrete at the top of the beams.
Fig.8  Load versus midspan-displacement curve of all tested members. (a) Specimens N-1 and N-2; (b) specimens S-1 and S-2; (c) specimens T-1 and T-2; (d) specimens RC-1 and RC-2.
specimen Vcr
(kN)
μcr
(mm)
Vyeild
(kN)
μyeild
(mm)
Vpeak
(kN)
Vsim
(kN)
μpeak
(mm)
μult
(mm)
μΔ
(mm)
N-1 9.5 0.58 65.5 9.1 83.6 78.9 16.8 26.5 2.91
N-2 10.4 0.43 70.1 7.2 84.6 11.5 19.7 2.74
S-1 9.8 0.28 72.8 9.7 85.3 16.2 28.1 2.89
S-2 9.3 0.46 68.8 7.5 87.1 12.1 25.7 3.43
T-1 11.1 0.56 70.8 8.4 87.2 15.5 28.2 3.36
T-2 8.4 0.51 73.1 7.1 82.9 14.0 30.6 4.31
strip method 10.2 0.34 74.5 6.5 82.5 22.4 22.4 3.45
RC-1 11.2 0.31 62.4 6.7 75.7 15.6 18.7 2.79
RC-2 9.9 0.39 58.4 7.1 73.8 15.2 20.8 2.93
Tab.4  Experimental results of tested beams
Fig.9  Crack pattern in tested beams after ultimate failure. (a) Specimen N-1; (b) specimen N-2; (c) specimen S-1; (d) specimen S-2; (e) specimen T-1; (f) specimen T-2; (g) specimen RC-1; (h) specimen RC-2.
Fig.10  Crack width versus normalized applied load curve.
Fig.11  Stress-strain relationship of ECC. (a) Under uniaxial tension; (b) under uniaxial compression.
Fig.12  The stress-strain relationship of concrete. (a) Under uniaxial tension; (b) under uniaxial compression.
Fig.13  Comparison between calculated and experimental load-deflection responses.
Fig.14  The calculated load-deflection relationship of the examples.
Fig.15  Simplified stress-strain relationship of ECC. (a) Under uniaxial tension; (b) under uniaxial compression.
Fig.16  Simplified model and moment distribution of U-shaped ECC formwork.
Fig.17  The distribution of stress and strain along the depth of the composite beam.
εc εe0
0.0045 0.005 0.0055 0.006 0.0065
αe βe αe βe αe βe αe βe αe βe
0.001 0.21 0.67 0.19 0.67 0.18 0.67 0.16 0.67 0.15 0.67
0.003 0.58 0.69 0.53 0.69 0.49 0.68 0.45 0.68 0.42 0.68
εe0 0.8 0.7 0.8 0.7 0.8 0.7 0.8 0.7 0.8 0.7
εecu 0.88 0.72 0.88 0.72 0.88 0.72 0.88 0.72 0.88 0.72
Tab.5  The value of αe and βe at different εc
Fig.18  Comparison between the predicted flexural strengths calculated by simplified method (Msim) and strip method (Mstr).
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