Experimental-numerical study of high-performance fiber-reinforced cementitious composite layer based strengthening of damaged beams

Strengthening reinforced concrete (RC) beams using high-performance fiber-reinforced cementitious composite (HPFRCC) layer has emerged as an effective technique for structural retrofitting. This study investigates the flexural behavior of damaged RC beams strengthened with prefabricated HPFRCC layers through a combined experimental and three-dimensional finite element approach. Four-point bending tests were conducted on control and HPFRCC-strengthened beams to validate the numerical model. The validated model was then employed to assess the effects of pre-damage level (0-0.9Fu), HPFRCC layer thickness, and longitudinal reinforcement ratio (0.5-2.0%) on strength, stiffness, ductility, and energy absorption. The results indicate that HPFRCC strengthening can increase the yielding load by up to 36% and the ultimate flexural capacity by up to 25% for beams with moderate pre-damage levels, while improvements reduce to below 10% for severely damaged beams. The numerical results indicate that strengthening damaged reinforced concrete beams with prefabricated HPFRCC composites increased the ultimate flexural load by 28-42%, depending on the composite thickness and strengthening length. The initial flexural stiffness improved by up to 35%, while the mid-span deflection at ultimate load decreased by 18-25% compared to the unstrengthened damaged beams. In addition, the strengthened beams exhibited an increase in the ductility index from 2.1 to 3.4, accompanied by a 30% reduction in tensile damage concentration at the critical cracking zone.