Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)


Civil Engineering

Committee Chair

Houssam A. Toutanji

Committee Member

John Gilbert

Committee Member

Ken Zuo

Committee Member

Hongyu Zhou

Committee Member

Nasim Uddin


Concrete construction., Fibrous composites., Fracture mechanics., Structural analysis (Engineering)


As an alternative to the overwhelming costs of rebuilding structures, rehabilitation of existing structures has become the focus of many researchers in the past few decades. To strengthen a reinforced concrete beam for flexure, fiber reinforced polymer (FRP) composites are usually bonded externally to the tension side of the structural element. Although, the usage of FRP has progressed and has been implemented in a number of projects worldwide, the behavior of FRP rehabilitated structures has yet to be appropriately considered for design purposes. For design, current design guidelines address conventional failure modes like concrete crushing, steel yielding and FRP rupture. However, the delamination failure modes like plate-end debonding and intermediate crack debonding are addressed by limiting the strain in FRP. Although a significant increase in strength can be achieved through externally bonded FRP, the limitation of strain imposed by design guidelines restricts the calculated degree of gain in strength. In this work, the strength is assessed by examining the stress state of concrete small element near FRP-concrete interface. A failure criterion is proposed based on 144 existing experimental data points. Failure criterion for plate-end debonding is proposed by limiting the maximum principal stress to the modified tensile strength of the concrete. With the application of theory of elasticity, the interfacial shear stress and interfacial normal stress at the FRP-concrete interface established by different researchers were investigated to derive the critical shear stress and critical normal stress. Critical shear stress and critical normal stress are derived by considering the critical stress state of a concrete small element in the vicinity of the bond interface. Considering the biaxial stress state of the concrete small element, maximum principal stress is calculated using proposed critical shear stress and critical normal stress along with flexural stress. The concrete tensile strength with a modification factor for FRP plate-end debonding is suggested by considering 144 four point bending test data failed in plate-end debonding. Finally, a design method based on developed failure criterion is proposed for FRP strengthened RC structures.



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