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Experimental Investigation of the Flexural Strengthening of Fixed-Supported RC Beams

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Abstract

The performances of seven full-scale, fixed-supported reinforced concrete (RC) beams were investigated with the four-point bending test in this study. One of the RC beams was a reference beam (Ref) and six were strengthened beams. The strengthening of the RC beams was performed with near surface mounted (NSM), external bonded reinforcement (EBR), friction hybrid bonding (FHB), and hybrid techniques. Steel bars, CFRP bars, CFRP sheets, and mechanical fastener systems were used in the strengthening processes, according to the requirements of the applied techniques. The experimental results were evaluated for the effects of strengthening techniques and materials on the load–deflection response, ultimate load-carrying capacity, ductility, dissipated energy, failure modes, strain, and crack pattern. Strengthening applications using the NSM technique, with conventional steel, increased the load-carrying capacity of the RC beams by 22–24.9% while increasing their total energy dissipation by 40.7–68.9%. The load-carrying capacity was increased by 3.7–11.9% in RC beams strengthened by CFRP sheet and CFRP bar. However, except for the FHB technique, CFRP-applied RC beams could not perform the inelastic behavior. The FHB strengthening technique increased the load-carrying capacity and total energy dissipation of the beam by 11.6% and 21.2%, respectively. The results showed that NSM-Steel, NSM-Steel/90, and FHB-CFRP techniques quite improved the performance of the RC beams for both the elastic and plastic regions, while both of EBR-CFRP and Hybrid-CFRP techniques improved the elastic behavior of the RC beams to a great degree.

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Abbreviations

a :

Concentrated load distance from the face of the support or shear span

A f :

Cross-section area of FRP sheet

A s :

Tension rebar area at the cross section

A s,min :

Minimum reinforcement area at the cross section

A sp :

Cross-section area of the plate

b w :

Beam width dimension

c :

Neutral axis depth

C E :

Environmental reduction factor

CFRP:

Carbon fiber reinforced polymer

d :

Effective depth of the beam

d b :

Diameter of the strengthening bar

d f :

Effective depth of FRP reinforcement

d p :

Effective depth of steel plate

EBR:

External Bonded Reinforcement

E c :

Elasticity modulus of concrete

E f :

Modulus of elasticity of FRP laminates

E s :

Elasticity modulus of steel rebar

E sp :

Elasticity modulus of steel plate

f c ’ :

Characteristic compressive strength of concrete

f fe :

Effective stress on FRP

f fu :

Ultimate tensile strength of FRP

f fu * :

Ultimate tensile strength of FRP

FHB:

Friction Hybrid Bond

f s :

Effective stress on tension rebar

f sp :

Effective stress on steel plate

f y :

Characteristic tensile strength of steel rebar

f yp :

Characteristic tensile strength of steel plate

h :

Overall beam depth

k m :

Bond-dependent coefficient for flexure

l n :

Clearspan of the beam

M :

Moment

M nf :

FRP contribution to bending moment

M np :

Steel plate contribution to bending moment

M ns :

Steel contribution to bending moment

M p :

Plastic moment

M total :

Total bending moment capacity

n :

Number of ply

NSM:

Near surface mounted

P :

Applied load

t f :

Thickness per ply

W E :

External work

w f :

Width of FRP sheet

W i :

Internal work

α 1 :

Concrete stress block factor

β 1 :

Concrete stress block factor

Δu :

Ultimate deflection

Δy :

Yield deflection

ε bi :

Initial substrate strain

ε c :

Concrete strain at failure

ε c ’ :

Strain corresponding to fc’

ε fd :

The design strain of FRP accounting for debonding failure

ε fe :

Effective strain level

ε fu :

Design rupture strain

ε fu * :

Rupture strain

ε s :

The strain in the steel rebar

ε sp :

The strain in the steel plate

θ :

The rotation angle of the beam for the plastic mechanism

μ :

Ductility

ρ min :

Minimum reinforcement ratio

Ψ f :

Additional reduction factor for FRP

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Acknowledgements

This study was supported by Erciyes University Scientific Research Projects Unit under grant number FYL-2018-7960.

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Authors and Affiliations

  1. Department of Civil Engineering, Erciyes University, 38280, Talas, Kayseri, Turkey

    Yaser Alhamdan & Tamer Dirikgil

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  1. Yaser Alhamdan
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  2. Tamer Dirikgil
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Correspondence to Tamer Dirikgil.

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Alhamdan, Y., Dirikgil, T. Experimental Investigation of the Flexural Strengthening of Fixed-Supported RC Beams. Int J Civ Eng 18, 1229–1246 (2020). https://doi.org/10.1007/s40999-020-00531-6

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