Unloading and reloading process for the earthquake damage repair of ancient masonry columns: the case of the Basilica di Collemaggio

The repair of historical masonry columns damaged by earthquakes is a complex engineering procedure. In most cases, these elements support important vertical loads, and, for this reason, the repairing interventions (such as block replacement) could generate critical modifications of the stress pattern and eventually lead to local failures of the masonry material. In order to prevent critical situations, the repair work should account a complete unloading-reloading process of the column. However, at this time, no specific indications are provided by technical codes and guidelines. In the present paper, the unloading-reloading process developed for the stone masonry columns of the Basilica di Collemaggio in L’Aquila (Italy) is presented. Particularly, two specific unloading systems were designed and verified with advanced finite element analyses. A three-dimensional finite element model of the colonnade and supported nave wall was implemented to check if the unloading-reloading process would significantly change the state of stress in the masonry, causing local failures. The geometry of the structure was reconstructed from a complete laser scanner survey of the church, by considering all the intrinsic irregularities of heritage constructions. Finally, a comparison between the numerical results and the corresponding values measured during the worksite intervention was carried out.