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Effect of Intermediate Crack Debonding on the Flexural Strength of CFRP-Strengthened RC Beams

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Mechanics of Composite Materials Aims and scope

The flexural strength of reinforced concrete (RC) beams strengthened with a carbon-fiber-reinforced polymer plate, which fails by intermediate crack debonding, is evaluated. To consider the effect of debonding at the interface between the concrete and the CFRP plate, due to a flexural crack at the midspan, on the flexural strength of the beams, a strength reduction factor is proposed. This factor is derived from the results of flexural tests by using the model of effective strains and is defined as the ratio of the debonding strain to the ultimate strain of the CFRP plate. The validity, accuracy, and efficiency of the factor is verified by comparing analytical results with experimental data. The results of this study revealed that the strength reduction factor proposed can be used to efficiently assess the flexural strength of CFRP-strengthened RC beams with intermediate crack debonding.

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Abbreviations

A s :

= area of the tension steel reinforcement

A s ′ :

= area of the compression steel reinforcement

A f :

= area of CFRP reinforcement

A f,b :

= area of CFRP reinforcement in balanced conditions

a :

= depth of the equivalent rectangular stress block or the unbonded length reckoned from the span end to the FRP plate

b :

= width of beam cross section

B :

= distance from the span end to the loading point

b f :

= width of CFRP plate

C c :

= resultant compressive force of concrete

C s ´ :

= resultant compressive force of compression steel

CFRP:

= carbon-fiber-reinforced polymer

COV:

= coefficient of variation

CSG:

= concrete strain gage

c b :

= depth of neutral axis in balanced conditions

d s :

= depth of the tension steel reinforcemen; t

d ´ s :

= depth of the compression steel reinforcement

d f :

= depth of CFRP reinforcement

E c :

= elastic modulus of concrete

E f :

= elastic modulus of CFRP reinforcement

E s :

= elastic modulus of the tension steel reinforcement

E ´ s :

= elastic modulus of the compression steel reinforcement

ED:

= end debonding

FSG:

= FRP strain gage

f ´ c :

= compressive strength of concrete

f db :

= debonding stress of CFRP plate

f fu :

= ultimate stress of CFRP plate

f y :

= yield stress of the tension steel reinforcement

f ´ y :

= yield stress of the compression steel reinforcement

h :

= height of beam cross section

ICD:

= intermediate crack debonding

L :

= beam span

LVDT:

= linear variable differential transformer

M f,b :

= flexural strength in balanced conditions

M n :

= nominal flexural strength

N.A. :

= neutral axis

RC:

= reinforced concrete

SD:

= standard deviation

SSG:

= steel strain gage

T f :

= resultant tensile force of CFRP reinforcement

T s :

= resultant tensile force of the tension steel reinforcement

t f :

= thickness of CFRP plate

α :

= mean stress factor of concrete

γ :

= stress centroid factor of concrete

ε bi , :

= initial concrete bottom strain (prior to the installation of CFRP)

ε c :

= compressive strain of concrete

ε cu :

= concrete top fiber strain at the ultimate section

ε db :

= debonding strain of CFRP plate

ε fu :

= ultimate strain of CFRP plate

ε s :

= strain of the tension steel reinforcement

ε ´ s :

= strain of the compression steel reinforcement

φ frp :

= strength reduction factor of CFRP reinforcement.

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Acknowledgment

This investigation was supported by the Basic Research Program throught the National Foundation of Korea (NRF), funded by the Ministry of Education (2013R1A1A2059122).

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Authors and Affiliations

  1. College of Engineering, Sungkyunkwan University, 300, Cheongcheong-dong, Jangan-gu, Suwon, 440-746, Republic of Korea

    Sungnam Hong

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  1. Sungnam Hong
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Correspondence to Sungnam Hong.

Additional information

Russian translation published in Mekhanika Kompozitnykh Materialov, Vol. 50, No. 4, pp. 724-744, July-August, 2014.

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Hong, S. Effect of Intermediate Crack Debonding on the Flexural Strength of CFRP-Strengthened RC Beams. Mech Compos Mater 50, 523–536 (2014). https://doi.org/10.1007/s11029-014-9439-6

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  • DOI: https://doi.org/10.1007/s11029-014-9439-6

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