Effect of transversal steel connectors on the behaviour of rubble stone-masonry walls: two case studies in Italy

Multi-leaf masonry walls are very common in historical constructions and have been primarily designed to resist vertical static loads. Recent earthquakes have shown their high vulnerability against dynam-ic horizontal and static compression loads which can easily produce the detachment of the different leaves and determine important damage and catastrophic consequences. An increasing interest in the conservation of his-toric masonry constructions has produced a need for new consolidation and retrofitting methods. With the aim of increasing the mechanical characteristics, the overall structural behaviour and ultimately the safety of mul-ti-leaf masonry wall panels against out-of-plane collapse mechanisms, several reinforced techniques have been investigated. In this paper, a new strengthening system which consists in the application of a pre-loaded steel bar enclosed into a fabric protective bag-case, is investigated. The steel-bar connector is inserted into a pre-drilled hole made in the masonry in order to bond the masonry leaves and to prevent the detachment dur-ing seismic events; finally cement-based grout is injected at high pressure inside the fabric bag-case. The aim is to increase the collaboration between masonry leaves and increase the wall-capacity. The paper initially de-scribes the reinforcement technique and its fields of application and expected benefits. In the second part, the paper addresses two case studies where this reinforcing method has been recently applied: the medieval castle of Laurenzana, located in the southern Italian region of Basilicata and a coeval 18th-century annex building nearby the Royal Palace of Capodimonte (Naples).