Abstract
This study investigated the flexural behavior of reinforcement concrete beam strengthened with different techniques. The purpose of this research to study the various techniques of strengthening and knowing the effect of each technique on the beam behavior .Ten simply supported beams tested in this study. The total length of the beams and clear span were 1800mm and 1650mm, respectively. The cross section was (180×250) mm. Tested beams were divided into two categories’ the first category consist of one beams and considered as reference, while the second category consist of nine beams divided into Two groups according to the Strengthening techniques such as near surface mounted (NSM) and external bonded reinforcement (EBR).The experimental results showed improvement in ultimate load capacity for strengthened beams ranging from (6 to 89%) for NSM and (31 to 96%) for EBR and reduction in deflection for strengthened beams ranging from (6 to 43%) as compared with reference beam. When the number and length of CFRP bars are increased, the number of cracks increase while the width of the cracks and the spacing decrease, and the same observation is made when the width of the CFRP sheet is increased. The experimental load capacities of strengthened beams were compared with the design provisions given by ACI440.2R-17 guideline for NSM and EBR technique and EC2 guideline for EBR technique, the average ratio (1.2 and 0.97) respectively ,which showed that reasonable and a good agreement for all strengthened beams.
Highlights
El-Gamal, et al [11] studied the behavior of RC beams strengthened in flexure with near surface mounted (NSM) technique using glass and carbon fiber, ten RC beams (300*200 mm, 2760 mm total length) was classified into two groups depended on the ratio of tension steel bar, the first group had two steel bars with a diameter of 12 mm on the bottom side and the second group had four steel bars with a diameter of 12 mm on the bottom side
The result show that they concluded that the use of a twin -layer of CFRP sheets to strengthen Glass-fiberreinforced polymer (GFRP)-RC beams is very efficient, the max. (Ɛ cu) was ranging between (0.42 %) to (0.55 %) respectively, these findings are higher than the standard values described by the ACIs which consider that for the specified concrete grades (Ɛ cu) is between (0.3%) and (0.35%)
The first group consist of six beams strengthened by NSMCFRP bar inserted into grooves, three of them (N1-6-165, N2-6-165 and N3-6-165) had different number (1,2 and 3) of CFRP bar φ6 mm with the same length 1650 mm inserted into grooves (10*10mm) according to the number of CFRP bar and the others three beams of the first group (N1-10-60,N1-10-90 and N1-10-165) had one CFRP bar φ10 mm with different length of CFRP bar (600,900 and 1650mm) inserted into one groove (15*15 mm) for example, code (N2- 6-165) indicates that the beam is strengthened by near surface mounted technique by using two CFRP bars of nominal diameter 6 mm inserted in two grooves in tension side and 1650 mm length of each bar
Summary
Traditional techniques have generally been used for the flexural strengthening of RC elements, such as overlaying, jacketing, external pre-stress and external bonding of steel plates. El-Gamal, et al [11] studied the behavior of RC beams strengthened in flexure with NSM technique using glass and carbon fiber, ten RC beams (300*200 mm, 2760 mm total length) was classified into two groups depended on the ratio of tension steel bar, the first group (seven beams) had two steel bars with a diameter of 12 mm on the bottom side and the second group (three beams) had four steel bars with a diameter of 12 mm on the bottom side. El-shafiey, et al.[13] studied the behavior of RC beams strengthened in flexure using different techniques (two NSM CFRP strips (BF), externally bonded steel plate (BS) and layer of ultra-high performance strain hardening cementitious composite (BU)). The result show that they concluded that the use of a twin -layer of CFRP sheets to strengthen GFRP-RC beams is very efficient, the max. (Ɛ cu) was ranging between (0.42 %) to (0.55 %) respectively, these findings are higher than the standard values described by the ACIs which consider that for the specified concrete grades (Ɛ cu) is between (0.3%) and (0.35%)
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