PhD Oral Exam - Hamed Shabani Attar, Civil Engineering

When studying for a doctoral degree (PhD), candidates submit a thesis that provides a critical review of the current state of knowledge of the thesis subject as well as the student’s own contributions to the subject. The distinguishing criterion of doctoral graduate research is a significant and original contribution to knowledge.

Once accepted, the candidate presents the thesis orally. This oral exam is open to the public.

Abstract

Due to the lower elastic modulus and higher tensile strength of glass fibre-reinforced polymer (GFRP) bars compared to steel, the design of GFRP-reinforced concrete (RC) flexural members is primarily governed by serviceability limit states, including deflection and crack width. This study enhances the understanding of the flexural and shear behaviour of concrete beams reinforced with GFRP bars through experimental and analytical work. The main objective is to provide advanced knowledge about the effect of using GFRP bars as an internal reinforcement and fibre reinforced concrete (FRC) on the flexural and shear response of concrete beams. Furthermore, this investigation evaluates the existing design equations in North American standards, offering design recommendations to enhance the design of GFRP-FRC beams.

Accordingly, this research is divided into two main phases. Phase I, titled “Flexural and Serviceability Behaviour of GFRP-FRC Beams”, involves investigating the impact of macro-synthetic fibres on the behaviour of 11 GFRP-RC beams. The study investigates the existing deflection equations outlined in the CSA S806-12 standard and ACI 440.11-22 code, alongside assessing the ultimate flexural capacity in accordance with ACI 544.4R-18. Furthermore, digital image correlation (DIC) was utilized to capture the crack propagation, crack width, and deflection up to failure, demonstrating its effectiveness over conventional contact instrumentations such as linear variable differential transducers (LVDTs) and potentiometers.

Phase II, titled “Shear Behaviour of GFRP-RC Beams”, utilizing 15 full-scale beams, explores parameters including reinforcement ratio, stirrup type, stirrup reinforcement ratio, shear span to depth ratio, and fibre content. The study aims to establish the influence of these parameters on shear capacity, failure mode, and strain variation of stirrup and longitudinal rebar. The results indicated that the strain limits of ACI 440.11-22 and CSA S806-12 for GFRP stirrups are conservative, and a modified equation is proposed. Current GFRP design codes such as ACI 440.11-22, CSA S806-12 and CSA S6-19 do not consider the effect of fibres on the shear capacity of GFRP-RC beams. Moreover, the design standard ACI 544.4R-18 for fibre-reinforced concrete, developed for members with steel reinforcement, tends to overestimate the shear capacity of FRP-FRC beams. An experimental database was utilized to assess the accuracy of GFRP design code provisions in determining the shear capacity of GFRP-RC beams. A modified equation is proposed to incorporate the effect of macro-synthetic fibres, validated through literature and current tested specimens.