Shear Behavior of Reinforced Concrete Columns Strengthened with Ferro-Engineered Cementitious Composite Jackets

This study investigated the shear behavior of large-scale reinforced concrete (RC) columns strengthened with either Engineered Cementitious Composite (ECC) or Ferro-Engineered Cementitious Composite (Ferro-ECC) jackets, with the latter incorporating expanded steel wire mesh (ESWM), thereby distinguishing the contribution of the ECC jacket from the additional contribution of ESWM. Ten large-scale specimens were tested without axial compression under monotonic four-point loading to evaluate the effects of mesh type, number of mesh layers, and transverse reinforcement under two deficiency scenarios: excessive stirrup spacing (250 mm) and complete absence of stirrups. Structural performance was assessed in terms of load–deflection response, cracking behavior, failure mode, stiffness, deformability, energy absorption, and shear capacity. The experimental cracking moments and ultimate shear capacities were evaluated against widely used design codes, and modified prediction models were proposed to account for the contributions of ECC and ESWM strengthening. The results showed that ECC strengthening alone significantly enhanced the shear performance of both stirruped and unstirruped RC columns, increasing the ultimate load by approximately 92–118% relative to the corresponding control specimens. The use of hybrid ECC–ferrocement jackets further increased the ultimate load by 106–123% with a single mesh layer, while two mesh layers resulted in increases of up to 164% and 244% for the stirruped and unstirruped columns, respectively. Strengthening delayed the initiation of flexural and diagonal cracking, increased crack distribution, and maintained service-load crack widths within acceptable limits (≈0.10–0.30 mm). Initial stiffness increased by up to 136%, deformation capacity improved by 25–60%, and energy absorption increased by 121–240% for ECC alone and up to 6.21 times with ECC–mesh systems. Coarse mesh was more effective in single-layer configurations, whereas fine mesh provided superior performance in double-layer systems through enhanced crack control. The proposed cracking and shear prediction models showed good agreement with the experimental results.