Stress-strain relationship of FRP repaired concrete

Jacketing with fiber reinforced polymer (FRP) is highly effective in restoring and increasing the strength and ductility of reinforced concrete (RC) columns damaged by earthquakes, blasts, vehicle impact, etc. It has been well recognized in the literature that the behavior of FRP repaired (with pre-damage before jacketing) RC columns is significantly different from that of FRP retrofitted (without pre-damage) RC columns. A stress-strain model for FRP repaired concrete columns is not available so far. Through experimental and analytical investigations, the behavior of FRP repaired concrete columns is extensively studied. A total of 102 short columns were tested, involving the variations of damage level, concrete strength and confinement. The effects of pre-damage on the strength, strain capacity, rigidity of FRP repaired concrete are identified in terms of a damage index that is defined as the loss of concrete strength caused by damage. A design-oriented stress-strain relationship is developed for design and evaluation of FRP repair works. It is concluded from the work that the classic internal friction theory is applicable for estimating the strength of repaired concrete if the pre-damaged concrete is considered as sound concrete with a reduced strength. Also, the Hoek-Brown failure criterion is un-conservative for evaluating the strength of highly damaged concrete.