Influence of damage on the stability of masonry arches

Masonry arches are a defining feature of historical infrastructure, commonly found in viaducts, aqueducts and monumental architecture. Built according to traditional techniques and empirical knowledge, these structures often show signs of deterioration due to age, limited maintenance and exposure to natural or anthropogenic actions such as seismic activity, soil settlement and material decay. These factors can compromise their structural integrity and complicate safety assessments. This study investigates the stability of masonry arches subjected to horizontal loading, which typically triggers a four-hinge collapse mechanism. A parametric analysis is carried out to explore the effect of localised damage, modelled as a reduction in thickness along the intrados, on the collapse behaviour of arches with varying geometries, ranging from elliptical to full-centred profiles. To reflect realistic construction conditions, the study incorporates arches with variable thickness. The collapse multiplier is calculated for both undamaged and damaged configurations, the latter involving different positions of the reduced-thickness zone. The results highlight the most critical damage locations and reveal how geometric parameters influence structural sensitivity. The proposed approach offers a streamlined yet informative method for assessing the vulnerability of historic masonry arches and can assist in prioritising conservation and strengthening strategies.