Flexural behavior of reinforced concrete beams externally strengthened with Hardwire Steel-Fiber sheets

Fiber Reinforced Polymers (FRP) has been used predominantly as externally-bonded strengthening materials using epoxy adhesives. Recently emerged Hardwire Steel-Fiber (HSF) sheets have desirable characteristics that made them attractive candidates as strengthening materials. The literature lacks information on the flexural performance of RC beams when externally strengthened with HSF composite sheets. This paper presents an experimental investigation consists of seven reinforced concrete (RC) beams strengthened in flexure with externally-bonded HSF sheets using epoxy adhesives. Two types of HSF sheets with medium and high-cord densities of 4.72 and 7.87 cords/cm were investigated. Four-point bending tests were conducted and the load-deflection and strain response data at the beams' mid-span section were recoded until failure of the beam specimens. The test results were compared with a control unstrengtherned beam specimen. Experimental results showed an increase in the load-carrying capacity of the strengthened specimens ranging from 29% to 62% over the control unstrengthened specimen. However, the ductility of the strengthened specimens was less than that of the control specimen and all strengthened specimens failed in flexure by delamination of the concrete cover. The ultimate load-carrying capacity of the tested specimens was predicted using the guidelines of ACI 318-11 and ACI 440.2R-08, while mid-span deflection response curves were predicted using ACI 318-11 guidelines. The predicted results were in close agreement with the experimentally measured ones. It has been concluded that HSF sheets, externally-bonded with epoxy adhesives to the soffit of concrete beams, can serve as effective flexural strengthening composite material.