Analytical Studies on Debonding Behaviour of RC Beams Strengthened with UHPFRC Overlay

  • Ramachandra Murthy AvadhanamEmail author
  • Aravindan Muralidharan
  • Ganesh Prakasam
Original Contribution


The debonding characteristics of ultra-high-performance fibre-reinforced concrete (UHPFRC)-strengthened structures under certain loading conditions have been investigated in this paper. Debonding of UHPFRC-strengthened structures seldom occurs owing to the fact that the tensile strength and the stiffness of UHPFRC are similar to that of the concrete substrate. This work concentrates mainly on the strengthening scheme where UHPFRC is provided in the form of strips at the tension zone of concrete. The studies on the effect of normal and shear stresses at the interface of the beam and UHPFRC strip with load increments are essential to determine the scheme of strengthening. The effect of interfacial shear and normal stresses near the strip end was studied by using the Tounsi model which is a modification of Teng model. A comparative study on the variation of the interfacial shear and normal stresses for the beams retrofitted with UHPFRC strip and other repair materials has been carried out. In the present study, the variation of stresses is investigated at two load levels with one load close to the pre-damage load given to the beam and the other load close to the ultimate load. Analytical studies are carried out to study the debonding behaviour of damaged RC beams strengthened with UHPFRC strips under static and fatigue loading. Parametric studies have also been carried out to determine the optimum configuration of the strips to be bonded to the beams.


RC beam Static loading Debonding Ultra-high-performance fibre-reinforced concrete Retrofitting Fatigue loading 

List of Symbols

ε1, ε2

Strains at the top and bottom faces of the adhesive

u1(x), u2(x)

Longitudinal displacements at the base of concrete and top of UHPFRC layer

\( \varepsilon_{1}^{M} \), \( \varepsilon_{2}^{M} \)

Strain due to bending moments at the concrete and the UHPFRC layer

\( \varepsilon_{1}^{N} \), \( \varepsilon_{2}^{N} \)

Strain due to the longitudinal forces at the concrete and the UHPFRC layer

M1, M2

Bending moments at the concrete and the UHPFRC layer

N1, N2

Longitudinal forces at the concrete and the UHPFRC layer

E1, E2

Modulus of elasticity of the concrete and the UHPFRC layer

I1, I2

Moment of inertia of the concrete and the UHPFRC layer

y1, y2

Distances from the bottom of the concrete layer and the top of UHPFRC layer to their respective centroids

\( u_{1}^{N} , u_{2}^{N} \)

Displacement induced by longitudinal force of the respective adherends

\( \sigma_{p} \)

Axial stress in the plate

\( \sigma_{c} \)

Axial stress in the concrete prism

\( \tau\)

Shear stress in the adhesive layer


Thickness of the plate

\( t_{c} \)

Thickness of the concrete prism

\( \tau_{f} \)

Local bond strength


Interfacial slip, relative displacement between the two adherends

bp, bc

Width of the plate and the concrete prism


Interfacial fracture energy

\( \sigma_{1} \)

Normal stress at the strip


Interfacial fracture energy

\( \tau_{f0} ,\tau_{ft} \)

Cycle-dependent bond strengths at time zero and time \( t \) in min


Cycle-dependent slip


Frequency-dependent factor




Length of the softening zone

\( m \), \( n \)

Material constants


Fatigue debonding growth coefficient



The authors thank the staff of the Fatigue and Fracture Laboratory and Theoretical and Computational Mechanics Laboratory of CSIR-SERC for the cooperation and suggestions provided during the investigations. This paper is being published with the kind permission of the Director, CSIR-SERC.


Authors acknowledge the funding provided by UGC-UKERI collaborative project between CSIR-Structural Engineering Research Centre and Cardiff University, UK.


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Copyright information

© The Institution of Engineers (India) 2019

Authors and Affiliations

  • Ramachandra Murthy Avadhanam
    • 1
    Email author
  • Aravindan Muralidharan
    • 2
  • Ganesh Prakasam
    • 2
  1. 1.CSIR-Structural Engineering Research CentreChennaiIndia
  2. 2.AcSIR, CSIR-Structural Engineering Research CentreChennaiIndia

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