EFFECT OF VARIOUS STRENGTHENINGS OF VERTICAL CIRCULAR OPENINGS ON FLEXURAL STRENGTH OF REINFORCED CONCRETE BEAMS

Abstract

Effect of various strengthenings of vertical circular openings on the flexural strength of reinforced concrete beam is presented. Eighteen specimens of reinforced concrete beams of sizes 200mm x 230mm x 700mm with openings at a quarter and an eighth of the total length from the support with three types of strengthening materials located at the boundaries of the openings, were cast, cured and evaluated. The three strengthening methods used were steel plate, steel pipe and strut and tie method. The flexural strength of all the hardened beams specimens were determined. The results show that strengthening circular openings at quarter and eighth point distance along its length gives an average decrease in ultimate load of 18 and 20% with strength of 13 and 12N/mm2 respectively. With steel plate strengthening of 4mm gauge, the ultimate load capacity of the beam increases by 15 and 17% with flexural strength of 15N/mm2 each at a distance of L/4 and L/8 respectively as compared to beams with unstrengthened openings. Using galvanized steel pipe of 2mm thickness increases the ultimate load by 9 and 11% with flexural strength of 14N/mm2 at a distance L/4 and L/8 respectively. While the use of strut and tie method increases ultimate load by 3 and 5% with strength of 13N/mm2 at a distance of quarter and eighth point along its length respectively. It is therefore recommended to incorporate steel plate strengthening method when vertical circular openings are to be created in reinforced concrete beams.