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Optimization and a new constitutive equation for RC beam strengthened by FRP

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Abstract

The use of FRP has been developed for flexural strengthening of reinforced concrete (RC) beams in recent years due to its advantages, such as ease of implementation, a slight change in cross-sectional dimensions, corrosion resistance, and increase in bearing capacity of the beam. Therefore, paying attention to technical considerations in applying FRP is crucial. This study intends to address two specific concerns. The first one is to determine the effect of the number of FRP layers on the improvement of mechanical and seismic properties in the flexural strengthening of RC beam and to specify the necessary numbers of FRP layers. The other consideration is to propose a new equation for FRP debonding stress and explain the behavior of FRP in tension after the occurrence of debonding failure. In this regard, reinforced concrete samples were prepared with zero, one, three, and five layers of GFRP, and then, four-point tests were performed on the samples. The results indicated an optimal number of GFRP layers that led to maximum mechanical and seismic properties in the flexural strengthening of beams. This study showed that the proposed model could not only estimate the debonding stress but also describe the behavior of GFRP after the debonding.

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Data availability

The datasets generated during and/or analysed during the current study are available from the corresponding author on reasonable request.

Abbreviations

be :

Effective width of FRP in contact with concrete surface (mm)

C:

Debonding constant value (N/mm)

Ef :

Tensile modulus of elasticity of FRP (MPa)

Fd :

Debonding force in FRP while debonding occurs (N)

f’c :

Specified compressive strength of concrete (MPa)

n:

Number of FRP layers

tf :

Nominal thickness of one ply of FRP reinforcement (mm)

\(\upvarepsilon\) :

Strain in FRP before debonding

ɛfd :

Debonding strain in FRP reinforcements (%)

ɛfu :

Fracture strain in FRP reinforcement (%)

\(\sigma\) :

Stress in FRP before debonding

σd :

Debonding stress in FRP while debonding occurs (MPa)

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Acknowledgements

The authors would like to sincerely thank the contribution of Mr. Borjali Darvishvand for his collaboration in editing the article and Mr. Yavari for arranging the mechanical testing facilities at the laboratory of Building and Concrete Industry Research Center in Qazvin Azad University, Iran.

Funding

The authors have not disclosed any funding.

Author information

Authors and Affiliations

  1. Department of Civil and Environmental Engineering, University of Hawaii at Manoa, Honolulu, USA

    Seiyed Ali Haj Seiyed Taghia

  2. Department of Civil Engineering, Qazvin Branch, Islamic Azad University, Qazvin, Iran

    Hamid Reza Darvishvand & Mostafa Maleki

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  1. Seiyed Ali Haj Seiyed Taghia
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  2. Hamid Reza Darvishvand
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Contributions

Seiyed Ali Haj Seiyed Taghia: Supervision, Approval of the manuscript, Analysis and/or interpretation of data, Reviewing and Editing Hamid Reza Darvishvand: Data curation, Analysis and/or interpretation of data, Software, Original draft preparation, Reviewing and Editing Mostafa Maleki: Conception and methodology of study, Investigation, Resources, Analysis and/or interpretation of data

Corresponding author

Correspondence to Seiyed Ali Haj Seiyed Taghia.

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The author would like to declare on behalf of all the co-authors that the work described is original research that has not been published previously, and not under consideration for publication elsewhere, in whole or in part. All the authors listed have approved the manuscript that is enclosed.

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Appendices

Appendix A

Moment–curvature procedure in Excel program

First step: Geometry and properties

figure a

This information is tabulated in Tables

Table 6 Geometry
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6,

Table 7 Concrete specifications
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7,

Table 8 FRP specifications
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8,

Table 9 Bar specifications
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9.

Second step: Analysis

figure b

Figure 

Fig. 13
figure 13

Procedure to generate moment–curvature relation

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13 illustrates the analysis procedure to generate a moment–curvature curve.

Appendix B

Table

Table 10 Material properties and technical specification of concrete and GFRP
Full size table

10 represents the material properties and technical specification of concrete and GFRP used to calculate debonding strain for proposed model and other references (Table 

Table 11 The equations of debonding strain for other references
Full size table

11).

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Taghia, S.A.H.S., Darvishvand, H.R. & Maleki, M. Optimization and a new constitutive equation for RC beam strengthened by FRP. Asian J Civ Eng (2024). https://doi.org/10.1007/s42107-024-01042-8

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