Reducing seismic out of plane vulnerability of masonry church façades through optimization of capacity spectrum by tie rods

The analyses of the structural damages detected on the Italian churches after the recent earthquakes (Emilia 2012, Umbria-Marche 2016) highlighted the high vulnerability to the overturning of the façades. The façades collapse mechanisms are strongly dependent on the connection details between orthogonal masonry walls, the windows, the construction techniques and the possible restraining horizontal elements, such as tie-beams, bi-lateral connected roof, etc. Several studies focus on the evaluation of vulnerability of the church façades using different approaches, from global analyses (FEM and /or Discrete Element Methods) of the entire building, to local analyses (linear and non-linear kinematic approaches). The aims of the present paper is to use the method based on capacity spectra to evaluate the vulnerability of the church facades and the optimization of specific devices as tie-rods to improve their seismic behavior. The non-linear approach is now accepted by several standards regarding the evaluation of risks of collapse mechanisms for masonry walls of the facades. Appropriate devices have been considered in order to calibrate the capacity curve and to optimize the interventions. The out of plane rotation of blocks can be modified with various elasto-perfect-plastic tendons with appropriate retentions (while composite materials could be used to preserve integrity of blocks). The tendons can be allocated in proper location and the length of each calibrated to best determine their stiffness. This procedure have been here applied to the façade of Aula Magna S. Lucia of the Bologna University, considering also the problem of the interaction with the structure of the roof.