Seismic upgrading of masonry churches

The paper is proposed for the topic Conceptual Design, in particular as regards existing buildings. The masonry churches are usually highly vulnerably to the horizontal transverse seismic action, since the bearing vertical structures (masonry columns along with the supported wall and the arch systems), which are isolated and slender, have to carry the seismic action only by mass. The seismic upgrading can be obtained only by transforming the transverse load-carrying capacity of the vertical bearing structures from mass strength to material strength. To this objective, the basis of the columns can be fixed at the soil, but this options is usually to onerous. Moreover, to this objective, external reinforcement can be epoxy bonded onto the masonry surfaces, but this option is usually prevented by evident aesthetic reasons. An alternative solution is obtainable by fixing the top of the vertical bearing structures to the edges of the horizontal structures that form the covering of the churches, and by inserting the reinforcement in the vertical masonry structures. The top joint transforms the isolated vertical structure in framed structure, hinged at the basis. The internal reinforcement provides the vertical bearing structures with the capacity of transmit high bending moment. Nevertheless, a special device has to be adopted to transfer longitudinally the top moment, otherwise the pillar and the beam of the ideal frame do not lay on the same vertical plane. Such system may upgrade the ultimate seismic capacity (severe damage). Conversely, such system does not upgrade the service limit state (limited damage), since does not enhance the stiffness. In order to upgrade also the stiffness of the structures, the reinforcement has to be pre-tensioned. In so doing, the seismic upgrading can be reached for a masonry church. The proposed conceptual approach to seismic upgrading has been applied to the case of the parish complex of San Giuliano di Puglia (in Molise; Italy). This building — compounded by church, parish house, parish school, belfry and civic tower — was severely damaged by the notorious earthquakes of October, 31, 2002 (when the elementary school collapsed, causing the death of 26 pupils and 3 teachers, and the hurting of many others people). Since the church, along with the major part of the building complex, were about to collapse, first-aiders decided to support arches and vaults with wood centrings, to wrap the columns by post-tensioned wood centrings, and to constrain the walls by external steel tendons. Although the extended and deep state of damage seemed to suggest the demolition of the building, the city administration and the historical overseers expected its restoration, because of its cultural and social value. The Italian Ministry of “Infrastrutture and Trasporti” bestowed the amount for recuperating the parish complex (3.7 million of euro) and the author was entrusted of the structural design of the repair, rehabilitation, and seismic upgrading of the whole building. The seismic upgrading was obtained by the above mentioned conceptual approach.