Effect of residual strains in damaged RC beam after unloading on the flexural and shear behaviours of SSS-ECC repaired beams

Abstract

This study investigated the effect of residual strains in damaged reinforced concrete (RC) beam after unloading on the flexural and shear behaviours of these beams repaired using stainless-steel strand reinforced engineered cementitious composites (SSS-ECC). Seventeen RC beams, including three controls and fourteen repaired beams, were pre-damaged, repaired using SSS-ECC, and underwent secondary loading. The test variables included the damage levels, reinforcement ratios of SSS, shear span-to-effective depth ratios, and repair methods. The test results demonstrated that SSS-ECC exhibited multiple cracking behaviour, thereby enhancing energy dissipation and delaying failure of the repaired beams. Compared to the control beams, the ultimate loads of the flexural-repaired and shear-repaired beams increased by 43 %-68 % and 23 %-48 %, and the ultimate deflections increased by 8 %-43 % and 25 %-83 %, respectively. The residual strains in RC beams after unloading increased exponentially with the damage levels, and the presence of residual strains resulted the performance degradation of the repaired beams. Increasing the reinforcement ratio of SSS enhanced improvements of strength and deformation. Increasing the shear span-to-effective depth ratio reduced the strength improvement but had a minimal effect on the deformation improvement. The U-wrapped method was less efficient than the fully-wrapped and both-sided bonding methods. Furthermore, a residual strain calculation model and a novel method for predicting flexural and shear strengths considering residual strains were proposed. Compared to existing models, the proposed model showed good accuracy and applicability, providing a new strategy for understanding the effect of residual strains and repair design.