Design Strategies for Seismic Retrofit of an Ancient Masonry Church With a Dissipative Timber System

Recent earthquakes in Italy have shown the strong seismic vulnerability of several historical and monumental buildings belonging to the national architectural heritage, such as churches. Without proper retrofitting measures, their structural integrity could be strongly compromised even with low seismic input, often because of lack of connections among structural elements and presence of flexible timber roof structures. However, at the same time, the need for preservation and conservation of historical architectures makes the design and realization of these interventions particularly challenging. In the recent years, several wood-based techniques for seismic retrofit have been analysed and started to find increasing application, such as the superposition of a layer of plywood panels, fastened to the planks of the existing timber roof. This type of intervention ensures an adequate reversibility and is compatible with the needs and requirements of architectural restoration. In this context, the present work examines the church of San Rocco in Collio (Brescia, Italy), an ancient masonry structure from the 15th century with timber roof. This church constitutes one of the few examples of gothic-roman architecture in the province of Brescia, and is particularly vulnerable to seismic events, due to its slender configuration, typical of the gothic style. A parametric study was conducted, considering different configurations of plywood panels overlays fastened to the existing timber roof structure. The improvement in the seismic response of the church was evaluated, including a cost-benefit analysis. The applied technique allows to activate large energy dissipation in the fasteners connecting planks and panels, thus dampening the seismic action, and contemporarily ensures a proper box behaviour and preventing local out-of-plane collapses of the masonry. In this way, the building can retrieve all its strength resources, without the need of invasive retrofitting measures on the masonry walls. Furthermore, it is proved that the examined technique is particularly cost-effective compared to other solutions. Based on the analysis of a valuable and relevant case-study building, this work confirms the enormous potential of plywood-based retrofitting technologies. These, besides ensuring an excellent resistance, also allow to include in the structure new dissipative resources, that can be implemented with simple, affordable, and ordinary construction and installation techniques.