عنوان مقاله [English]
In this paper, shear strengthening of RC beams with insufficient shear reinforcement by a new proposed technique, Prestressed Embedded Through-Section Bars (PETSB), was studied experimentally. This technique consist of boring holes through beam web and embedding steel bolt and tightening the bolt to the pre-determined prestressing force. In order to investigate the influence of the proposed strengthening method, a test program including 10 RC Beams with dimensions of $1700\times200\times200mm$ was planned. The beams were tested by two points loading at the midspan and a shear span of 600 mm on each side. The beams were fully shear reinforced at one side and poorly shear reinforced at the shear span on the other side ( no shear reinforcement in 5 beams, 0S Beams, and only one middle stirrup in 5 beams, 1S Beams). The strengthening bolts were one No.10 steel bolt or two No.6 steel bolts, prestressed or non-prestressed. To simulate the actual load conditions, an initial load was applied before strengthening to make initial shear cracks. Strengthening was performed in two loading status, under constant load or after load removal. After strengthening, each specimen was loaded to failure and the load vs deflection at midspan was recorded and drawn. Failure mode for most of specimens was shear failure but it changed in two of specimens strengthened by prestressed steel bolts to bending failure. These two specimens also had the maximum ductility and energy dissipation.Based on the results, embedding steel bolts effectively increased shear strength of beams in all test conditions, prestressed or non-prestressed bolts and constant load or load removal before strengthening, but better results were gained in prestressed bolts especially under constant load strengthening. Ductility and energy dissipation were also investigated. Prestressed bolts were
considerably more effective in ductility and energy dissipation improvement.