Ductility of CFRP strengthened concrete flexural members

Ductility of reinforced concrete flexural members depends on the amount and detailing of ordinary reinforcing steel bars. The addition of carbon Fiber Reinforced Polymer (CFRP) composites, which is another form of tension reinforcement, will affect the ductility of concrete flexural members strengthened with CFRP sheets. Several researchers in Japan, Europe, and the United States have investigated the use of CFRP for increasing the flexural strength of concrete flexural members. However, the flexural ductility with respect to the amount of existing ordinary steel bars has not been investigated in depth. In addition, delamination of CFRP sheets dominates the ultimate mode of failure of flexural members strengthened with CFRP sheets, which limits the ductility of strengthened members. End anchors could be used to prevent the debonding of CFRP sheets and enhancing the flexural ductility. This paper presents the results of an experimental investigation of seven full-scale reinforced concrete beams strengthened with CFRP composite sheets. The main variables are the amount of the existing reinforcing steel bars in the beams, and the use of CFRP anchorage. The amount (size and type) of the longitudinal CFRP sheets was maintained constant. Test results have shown that strengthened beams with lower amount of existing ordinary steel bars have lower flexural ductility. Test results have also shown that CFRP anchorage could significantly increase the flexural ductility of CFRP strengthened beams. Such important findings should be reflected on the design equations of CFRP sheets required for strengthening existing reinforced concrete beams to ensure an acceptable level of flexural ductility.