Experimental and numerical assessment of optimized hybrid strengthening techniques for unreinforced masonry columns under axial compression

This study presents a comprehensive experimental and numerical investigation into the axial performance of unreinforced masonry (URM) columns strengthened with various hybrid retrofitting techniques. Thirteen full-scale brick masonry columns were tested under monotonic axial compression to evaluate the effects of strain-hardening cementitious composites (SHCC) jacketing, near-surface mounted (NSM) steel bars, and embedded steel/glass fiber reinforced polymer (GFRP) mesh. The experimental program examined load–displacement behavior, failure modes, ultimate capacity, ductility, and energy absorption. Results demonstrated that hybrid strengthening combining NSM bars and mesh-reinforced SHCC jacketing achieved up to 70 % increase in load capacity and double the energy absorption compared to the unstrengthened reference. A validated finite element model, developed in ABAQUS using cohesive damage and embedded interaction approaches, accurately replicated the experimental response, with an average experimental-to-numerical load ratio of 0.95 and displacement ratio of 0.90. Parametric studies showed that increasing longitudinal reinforcement ratio in hybrid systems enhanced axial capacity by up to 39 %, while increasing transverse mesh ratio improved strength by 25 % before plateauing. These findings highlight the synergistic role of axial and transverse reinforcement in improving strength and ductility and offer a reliable modeling framework for optimizing retrofit designs of URM columns in seismic and structural upgrade applications.