Shear Strengthening of RC Deep Beams with Circular Openings by Means FRP Composites

Abstract

The high depth created favorable space for placing the openings which are to provide some capabilities such as mechanical and electrical installations, but these openings reduced load bearing capacity of the beams. One solution to the mentioned shortcoming is to use FRP-Composite sheets; the effect of FRP-Composites in improving load bearing and ductility of concrete members such as columns and beams is approved in previous investigations. This study utilizes the CFRP sheets to compensate for weakness arisen from the created openings. To this end, 5 deep beams with 10x50x120 cm dimensions, each having two circular openings with 20 cm diameter placed in symmetrical order, are constructed and undergone a three-point monotonic bending. The Externally Bounded Reinforcement (EBR) and Externally Bounded Reinforcement on Grooves (EBROG) methods have been utilized to install the FRP sheets in two configurations being wrapped around and inclined. The results have shown the superiority of EBROG method as well as the efficiency of the inclined orientation of strengthening sheets in increasing the load bearing-capacity. Also, Shear failure was the type of failure in beams and it has been observed that generally, diagonal cracks, which lead to the strut formation, tend to be formed in the beams. The cracks started from the support plates and propagated towards the loading plate. In addition to the extended cracking, the strengthened specimens have experienced debonding and failure in their composite strips. The strengthening strips have experienced failure in the wrapped specimen as a result of providing suitable confinement and leaving no chance for strip debonding as well as in the specimen with inclined strengthening strips as a result of the high efficiency of tensile stresses on the strips. Compared to the related non- strengthened specimens, the load bearing capacity increase arising from inclined orientation is 40% to 43%. In addition, this amount compared to the wrapped around specimen is about 16%.

Keywords

• reinforced concrete deep beams
• opening
• cfrp composites
• ebr method
• ebrog method