Flexural Behavior of Reinforced Concrete Beams Strengthened by Localized Unsymmetrical CFRP Sheets

Abstract

Rehabilitation of the reinforced1concrete1beams using fiber reinforced polymers (FRP) to deal with increased service loads on the building is widely adequate. In this study, reinforced concrete beams were reinforced by un-symmetrical sheets of Carbon fibers (CFRP) which were glued directly on beams’ surfaces at different positions depending on failure mode. Flexural spans were reinforced at the mid-span by using one and two layers of (CFRP) sheets. In order to study the effect of the increase of shear strength by using CFRP sheets, a group of tested beams was reinforced at the shear span on both sides by using one and two layers. fifteen beams of L-beams Shape with a dimension of the web (100 * 160 *1220 mm). also, the flange thick is 60 mm. The beam specimens were cast and tested under four points loading and divided into three groups according to the percentage of the preloaded. The group one teams consist of five beams one as a reference and other strengthened with different configuration without preloading. The percentage of the preloaded was limited from the test of the reference beam from group one. On the other hand, the group two preloading to the limit of the first cracks of the reference beam of the first group that is consists of five beams. Also, group three preloading to the limit of the yielding longitudinal steel bar. One beam considered as a reference (un-strengthened) beam reference beams for each group. For each group, two beams were strengthened in flexural span by one and two layers of CFRP sheets. Also, two beams were strengthened in shear span by one and two layers of the CFRP sheets. The results indicated that all strengthened beams show higher stiffness than that of the reference beams by about 20%. Also, deflection at a load of failure for the reference beams were greater than the deflection at the III failure for strengthened beams this advantage from using CFRP sheets. Although, the failure of the strengthened beam at ultimate load litter more than reference beam due to the de-bonding failure of anchorage under point load where the anchorage length equal to 100 mm. The de-bonding cause sudden reduce in the stiffness which gives rise to final failure. On the other hand, the result found that an increase in flexural ductility of beams with strengthening in one and two layers of CFRP sheets without preload as compared with reference beams. The increasing in flexural ductility for strengthened beams in flexural span without preloading as a compared with reference beam were 24.1% and 5.124%, for one and two layers respectively. Also, the increase in flexural ductility for strengthened beams in shear span without preloading as a compared with reference beam were 22.23% and 2.22%, for one and two layers respectively. The strengthened beams in flexural span by two layers of CFRP sheets with different preload level led to a reduction of the flexural ductility as compared with the strengthened beams by one layer. The beams preloaded have extensive cracks "post-cracks" these cracks reduced the overall strength of beams and reduce the stiffness and the flexural ductility. Furthermore, the deflection at failure for the reference beams with preload have a high deflection at failure and lower in load carrying capacity as compared to beams without preloaded.