FLEXURAL PERFORMANCE OF RC CONTINUOUS BEAMS STRENGTHENING BY CFRP WITH GROOVES
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Date
2024-09-22
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Abstract
Abstract Externally Bonded Reinforcement (EBR) is the most common technique that is used to strengthen the RC members with Carbon Fiber Reinforced Polymer (CFRP) sheets. Recently, a new proposed technique named; Externally Bonded Reinforcement on Grooves (EBROG) has been presented as an alternative method to avoid or eliminate the undesirable debonding failure mode that is accompanying to EBR method. This research
is devoted to investigate the effect of the strengthening techniques on the flexural behavior of reinforced concrete continuous beams externally strengthening with CFRP sheets in both hogging and sagging zones.
An experimental and analytical study is presented in the current work
on twelve beam specimens. All beams have a rectangular cross-section of
(130 ×200) mm with two equal spans, each span with length of 1050 mm. The beam specimens are designed to have a longitudinal reinforcement of (2φ8 mm) steel bars at each compression and tension zones with a (φ8@60
mm) diameter bars as a shear reinforcement. The parameters of this study include strengthening methods (EBR and EBROG), length and layers number of CFRP sheets and number, length and direction of grooves, in addition to the effect of presence steel fiber in the hogging zone. The results showed that the EBROG strengthening method has highly effective in improving the load carry capacity of strengthened beams. The beams strengthened by one of CFRP using EBROG with three longitudinal grooves has an increasing in the load capacity by about (24.4%) than that of the same beam strengthened by EBR. The positive effect of adopting the EBROG as the strengthening technique on the ultimate load is more observing with increasing the formed grooves number. Using double layers of CFRP sheets results in an improvement in
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the ultimate load, which be more significant in case of beams strengthening using EBROG method where the increasing ratio reached (87.2%) over the
control beam. Decreasing in the length of grooves and CFRP layer leads to reducing in the ultimate load of strengthened beams. Changing the grooves direction from diagonal grooves to inclined grooved with 30o angle had a
slight effect on the load carrying capacity. In addition, providing the tested beams with steel fiber in beam hogging zone in addition to CFRP sheet contributed with small increasing in the beams ultimate load.
The mode of failure was changed from CFRP de-bonding in case of EBR beams to CFRP rupture, or to concrete cover separation in EBROG beams. The strengthened beams with CFRP sheets presented a more brittle behavior at failure than the non-strengthened specimen, but the beams strengthening by EBROG show more ductile behavior than that reinforced by EBR method.
And also, this research introduces a comparison study to check the validity of ten existing different models to predict the ultimate load of beams strengthening with CFRP sheets in this study. It was found that the models introduced by the ACI 440.2R-17 and other checked models are appropriating to estimate the ultimate load of the beams externally strengthening using EBR method, but most of these significantly underestimate the load carry capacity of beams strengthening using
grooving method. Both Toutanji et. al., and Li and Wu models are preferred to use in estimating the ultimate load of these types of beams because it shows close predicted load to the experimental ones