Integration of structural requirements and conservation criteria in masonry wall interventions: A pilot study considering five in-plane strengthening methods

Abstract

Unreinforced masonry (URM) structures constitute a large portion of existing buildings and exhibit high seismic vulnerability due to their limited lateral resistance. Although several strengthening techniques have been proposed to enhance their shear capacity and ductility, comparative assessments that also consider conservationrelated constraints remain limited. This study addresses this gap by applying the Intervention Quality Index (IQI) to provide an integrated evaluation of structural effectiveness and conservation compatibility of five commonly used strengthening techniques: reinforced plaster (RPL), fibre-reinforced polymers (FRP), fibrereinforced cementitious matrices (FRCM), steel strips (SST), and near-surface mounted (NSM) strips. The IQI framework combines a Normalized Structural Index (SInm) and a Conservation Factor (CF). The structural index is derived from a systematic review of 709 experimental tests on strengthened URM specimens subjected to diagonal compression and in-plane cyclic loading under constant axial load, with consideration of gains in load capacity and ductility. Conservation aspects are quantified through expert-based evaluation using a structured questionnaire. The results show that FRCM provides the most balanced performance between structural performance and conservation requirements, achieving high structural efficiency (SInm= 0.92 for low-quality masonry under inplane loading) and the highest CF value (0.71), resulting in an IQI of 0.65. NSM shows high conservation compatibility but limited structural contribution, likely influenced by the scarcity of available experimental data. SST exhibits significant strength enhancement with moderate conservation compliance, whereas RPL and FRP, despite structural improvements, present low CF values and consequently low IQI scores. The proposed framework supports an evidence-based comparison of strengthening techniques and can assist in selecting seismic retrofit solutions for masonry structures.