PhD Oral Exam - Omar Mohamed, Civil Engineering
Effect of GFRP-Concrete Bond Characteristics on the Flexural and Serviceability Behaviour of GFRP-RC Beams
This event is free
School of Graduate Studies
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.
Nowadays, glass fibre-reinforced polymer (GFRP) bars have been utilized in reinforcing concrete structures as an alternative to steel reinforcement. The GFRP bars are characterized by their lower elastic modulus and higher tensile strength compared to steel; hence, the design of the GFRP reinforced concrete (RC) flexural members is controlled by the serviceability limit states, including deflection and crack width. Several research studies have experimentally investigated the flexural and serviceability behaviour of GFRP-RC flexural members. This research contributes to understanding the flexural and serviceability performance of concrete beams reinforced with GFRP bars through analytical, experimental, and numerical work. The main objective is to provide advanced knowledge about the effect of using GFRP bars as an internal reinforcement on the flexural and serviceability response of concrete beams. In addition, this research assesses the current design equations in the North American standards and guidelines; and provides design recommendations to improve the design of GFRP-RC beams.
The study started with a theoretical investigation that included a review of the different factors affecting the bond behaviour of the GFRP-RC beams. The study assessed the different parameters affecting the development length equation in the CSA S806 (2012) standard. This study was performed by analyzing 431 beam-bond tests compiled from the literature. Based on a linear regression analysis, two development length equations were proposed to represent a modified form of the current CSA S806 (2012) equation. The proposed equations were compared to other equations in different design standards and guidelines to determine the efficacy of the proposed equations. The results showed that the proposed development length equation showed better prediction than the other equations in the design standards and guidelines.
The study then experimentally investigated the different parameters influencing the GFRP bar-concrete bond interaction by testing 24 GFRP-RC beams. Previous studies showed that the GFRP bars' bond performance in concrete affects the crack width of the RC beams. The crack width equations in the different standards and guidelines account for the bond interaction between the GFRP bar and the surrounding concrete through the bond-dependent coefficient, kb. The kb values of the GFRP bars were computed by performing a well-defined test recommended by the CSA S806 (2012) standards. The experimental study focused on studying the effect of different parameters on the kb coefficient and calculating the kb values of the ribbed and sand-coated GFRP bars by conducting experimental tests on 24 concrete beams. The studied parameters were the clear concrete cover to GFRP bars, concrete compressive strength, reinforcement ratio, bar diameter, number of GFRP reinforcement layers, confinement effect due to closely spaced stirrups, bar surface profile, and spacing between the reinforcing rebars. The kb coefficient was quantified by measuring the maximum crack width in the middle flexural zone and obtaining the kb values from the CSA S806 (2012) crack width equation. The study also assessed the current deflection equations in the CSA S806 (2012) standard and ACI 440.1R (2015) guideline. Moreover, the flexural design equations in the different design provisions, including the prediction of the ultimate capacity, cracking moments, and moments at different serviceability limit states, were evaluated. The experimental study evaluated the available approaches in the literature used to quantify the deformability of the GFRP-RC beams to determine the optimal method of the deformability calculation and to check the proposed limits by the CSA S6 (2014) standard. The experimental results showed that the spacing between GFRP bars (at the same reinforcement ratio) and the confinement effect due to closely spaced stirrups influence the cracking and deflection behaviour. Moreover, it was found that the proposed effective moment of inertia equation provided more conservative results than the ACI 440.1R (2015) equation.
Finally, a numerical investigation was conducted using ATENA software. The study validated the numerical model to check the effectiveness of the conducted models in simulating the real beam behaviour. After that, a parametric study was performed to investigate the sensitivity of the nominal moment capacity and deflection values at different service loading levels of the GFRP-RC beams to the different material and cross-sectional parameters. The numerical results showed that the moment capacity and deflection values at the service stage are highly sensitive to the change in the concrete compressive strengths and GFRP bars' elastic modulus. The design of GFRP-RC can be improved through a prudent choice of the different design parameters.