Design against cracking at openings in reinforced concrete beams strengthened with composite sheets

Web openings in beams and girders occur quite often in practice to provide a convenient passage for utility ducts. Accommodating the environmental services in such a manner eliminates a significant amount of dead space and results in a more compact and, often, more economical design. However, introducing an opening into the web of a reinforced concrete beam causes local cracking around the opening leading to reduction in stiffness and capacity of the beam. In this paper the use of fibre reinforced polymer (FRP) sheets to strengthen the opening region is presented. Several design parameters are varied including opening width and depth, and amount and configuration of the FRP sheets in the vicinity of the opening. The experimental program included testing of 10 reinforced concrete beams, five of which were strengthened with FRP sheets around the opening, four were tested without strengthening, and the remaining beam was solid without opening considered as a control beam. The effect of this strengthening technique on deflection, strain, cracking, and ultimate load is investigated.