Behaviour of continuous concrete deep beams reinforced with GFRP bars

This research aims to investigate the behaviour of glass fibre reinforced 
\npolymer bars (GFRP) reinforced continuous concrete deep beams. For this 
\npurpose, experimental, analytical and numerical studies were conducted.
\nNine continuous concrete deep beams reinforced with GFRP bars and one 
\nspecimen reinforced with steel bars were experimentally tested to failure. The 
\ninvestigated parameters included shear span-to-overall depth ratio (𝑎/ℎ), size 
\neffect and web reinforcement ratio. Two 𝑎/ℎ ratios of 1.0 and 1.7 and three 
\nsection heights of 300 mm, 600 mm and 800 mm as well as two web 
\nreinforcement ratios of 0% and 0.4% were used. The longitudinal 
\nreinforcement, compressive strength and beam width were kept constant at 
\n1.2%, ≈55 MPa and 175 mm, respectively. The web reinforcement ratio 
\nachieved the minimum requirements of the CSA S806-12. The experimental 
\nresults highlighted that the web reinforcement ratio improved the load 
\ncapacities by about 10% and 18% for specimens having 𝑎/ℎ ratios of 1.0 and 
\n1.7, respectively. For specimens with web reinforcement, the increase of 𝑎/ℎ
\nratio from 1.0 to 1.7 led to reductions in the load carrying capacity by about 
\n33% and 29% for beams with overall depths of 300 mm and 600 mm, 
\nrespectively. Additionally, a considerable reduction occurred in the shear 
\nstrength due to the increase of the section depth from 300 mm to 600 mm. The 
\nexperimental results confirmed the impacts of web reinforcement and size 
\neffect that were not considered by the strut-and-tie method (STM) of the only 
\ncode provision, the Canadian S806-12, that addressed such elements. 
\nIn this study, the STM was illustrated and simplified to be adopted for GFRP 
\nRC continuous deep beams, and then, the experimental results obtained from 
\nthis study were employed to assess the performance of the effectiveness 
\nfactors suggested by the STMs of the American (ACI 318-2014), European 
\n(EC2-04) and Canadian (S806-12) codes as well as those factors 
\nrecommended by the previous studies to predict the load capacities. It was 
\nfound that these methods were unable to reflect the influences of member size
\nand/or web reinforcement reasonably, the impact of which has been confirmed 
\nby the current experimental investigation. Therefore, a new effectiveness 
\nfactor was recommended to be used with the STM. Additionally, an upper bound analysis was developed to predict the load capacities of the tested specimens considering a reduced bond strength of GFRP bars after assessing 
\nthe old version recommended for steel RC continuous deep beams. A good 
\nagreement between the predicted results and the measured ones was 
\nobtained with the mean and coefficient of variation values for 
\nexperimental/calculated results of 1.02 and 5.9%, respectively, for the STM 
\nand 1.03 and 8.6%, respectively, for the upper-bound analysis.
\nA 2D finite element analysis using ABAQUS/Explicit approach was carried out 
\nto introduce a model able to estimate the response of GFRP RC continuous 
\ndeep beams. Based on the experimental results extracted from the pullout 
\ntests, the interface between the longitudinal reinforcement and concrete 
\nsurface was modelled using a cohesive element (COH2D4) tool available in 
\nABAQUS. Furthermore, a perfect bond between the longitudinal reinforcement 
\nand surrounding concrete was also modelled to evaluate the validity of this 
\nassumption introduced by many previous FE studies. To achieve a reasonable 
\nagreement with the test results, a sensitivity analysis was implemented to 
\nselect the proper mesh size and concrete model variables. The suitability and 
\ncapability of the developed FE model were demonstrated by comparing its 
\npredictions with the test results of beams tested experimentally. Model 
\nvalidation showed a reasonable agreement with the experiments in terms of 
\nthe failure mode, total failure load and the load-deflection responses. The 
\nperfect bond model has overestimated the predicted results in terms of 
\nstiffness behaviour and failure load, while the cohesive element model was 
\nmore suitable to reflect the behaviour of those specimens. The validated FE 
\nmodel was then employed to implement a parametric study for the key 
\nparameters that govern the behaviour of beams tested and to achieve an in depth understanding of such elements. The parametric study showed that the 
\nhigher the 𝑎/ℎ ratio the more pronounced the effect of web and the longitudinal 
\nreinforcements and the lower the effect of concrete compressive strength; and 
\nvice versa when 𝑎/ℎ ratio reduces.

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